sábado, agosto 05, 2006

Multiple Cases of Familial Transmission of Community-Acquired

JOURNAL OF CLINICAL MICROBIOLOGY, Aug. 2006, p. 2994–2996 Vol. 44, No. 8
0095-1137/06/$08.00_0 doi:10.1128/JCM.00846-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Multiple Cases of Familial Transmission of Community-Acquired
Methicillin-Resistant Staphylococcus aureus
X. W. Huijsdens,* M. G. van Santen-Verheuvel, E. Spalburg, M. E. O. C. Heck,
G. N. Pluister, B. A. Eijkelkamp, A. J. de Neeling, and W. J. B. Wannet
National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands
Received 21 April 2006/Accepted 4 June 2006

The worldwide emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA)
can have severe public health implications. Familial transmissions of CA-MRSA in The Netherlands were
investigated. Among the families studied, two clusters of CA-MRSA could be identified. This report demonstrates
that family members can serve as reservoirs of CA-MRSA which may become a serious problem in
containing the spread of MRSA.


Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen causing nosocomial infections worldwide. MRSA strains have largely been confined to hospitals and long-term
care facilities but are also emerging in the community (22).
The differentiation between community-acquired MRSA (CAMRSA) and hospital-associated MRSA is becoming difficult since CA-MRSA could spread into hospitals (25). CA-MRSA
causes primary skin infections, mainly furunculosis and abscesses, but can also cause necrotizing tissue infections and fulminant pneumonia in young and previously healthy individuals (4, 11, 18, 23). Most CA-MRSA isolates contain the virulence factor Panton-Valentine leucocidin (PVL) and carry
staphylococcal cassette chromosome mec (SCCmec) type IV or V. The combination of the PVL loci, the mecA gene, and the spread of CA-MRSA makes this MRSA a well-adapted pathogen.
It is of interest to see to what extent PVL-MRSA transmission within families occurs, especially in families with young children. Transmission of MRSA between patients receiving health care and family members (1, 6, 24) and case reports of
intrafamilial spread of CA-MRSA have been described (3, 9,16, 19).
However, typing data from these familial MRSA transmissions is limited or even unknown.
The aim of this study was to determine the intrafamilial transmission of CA-MRSA in The Netherlands during a 2-year period (2003 and 2004). Approximately 10% of all Dutch MRSA isolates carry the genes for PVL (25). The MRSA
strains associated with familial transmission were characterized by pulsed-field gel electrophoresis (PFGE) (13), protein A (spa) typing (5), multilocus sequence typing (2), SCCmec multiplex PCR (7, 15), and accessory gene regulator (AGR) typing
(10). A toxin profile PCR was also determined (12). For the detection of exfoliative toxin D, oligonucleotides were developed on the basis of the nucleotide sequence deposited in the GenBank database under accession no. AB057421. The sequences of the exfoliative toxin D forward and reverse primers were 5_-CTATCATGTATCA
AGGATGGC-3_ and 5_-CAAATCAGT
TCCTTGTCCAT-3_, respectively. Both primers
were used at a concentration of 0.8 _M. Family transmissionwas defined as two or more members within a family, living atthe same postal address, who were colonized with an MRSA strain having the same PFGE type. In 2003 and 2004, 10 PVLMRSA familial transmissions were found. In 7 out of the 10 families, skin infections were reported, and in 6 families a link with a foreign country was noted. The transmissions involved
at least two family members, up to four members within a family of six. A total of 27 MRSA isolates were studied. The results (Table 1) showed that all MRSA strains within a family had the same typing characteristics, indicating the transmission
of CA-MRSA within families. In 7 of the 10 families, it involved transmission from parent to child or vice versa. In two cases of parent-child transmission, it involved two affected siblings (families 3 and 6), and in one case three siblings were affected (family 10). In two cases (families 6 and 10), some family members were colonized with a PVL-negative MRSA (data not shown). Interestingly, in family 10 the PVL-negative
MRSA of the mother (age 36) and one sibling (male, age 3) had the same PFGE type as the PVL-positive strains of the father and three siblings. No further typing of the PVL-negative strains was performed. Presumably, the MRSA strains of
the father and siblings obtained VLbacteriophages (14). This hypothesis was strengthened by the fact
that the upper band in the PFGE pattern of the PVL-negative MRSA strains was about 41 kb smaller, approximately the size of a PVL phage
genome.
Remarkably, twice the MRSA strains of two families (families 1 and 6 and families 4 and 8) had identical typing characteristics.
MRSA strains with PFGE type 50A (according to
the Dutch PFGE nomenclature classification) are rare in our national MRSA database. Further investigation revealed that families 1 and 6 lived in the same neighborhood. This indicates
a possible spread of an MRSA strain not only within a family but also between families. Whether there is any relationship between the two families is unknown. Families 4 and 8 lived in different areas of The Netherlands.
Seven out of the 10 families could be grouped into two clusters: the well-known ST8 (USA300) clone and the ST59 CA-MRSA clone. Remarkably, all MRSA strains with ST8 were spa type t008, SCCmec type IV, AGR type 1, and LukED
positive (families 2, 4, 5, and 8). The PFGE types of the ST8 MRSA strains were 46, 206, and 218. These PFGE types are closely related (_80%), indicating a clonal relatedness. This PFGE cluster is identical to the well-known PFGE USA300
CA-MRSA clone, which has been found in several outbreaks in the United States. Our findings confirm the recently described transatlantic spread of the USA300 clone (20, 26). A second MRSA cluster was also detected; the MRSA strains of
families 1, 3, and 6 seemed to be related to each other as well.
The MRSA strains in this cluster were ST59, either spa type t437 or spa type t441 (two closely related spa types), SCCmec type V or nontypeable, AGR type 1, and SEB positive. MRSA ST59 is also a well-known CA-MRSA which has been found in different parts of the world (8, 17, 25). MRSA ST80 was only
found in one family. The ST80-IV clone is a well-known CAMRSA in Europe (25, 27) and was also found in familial transmissions in Denmark (21).
In conclusion, transmission of community-acquired MRSA outside the healthcare setting poses a threat to public health and may be a serious problem in containing the spread of MRSA. This report demonstrates that family members can
serve as reservoirs of PVL-positive MRSA and that transmission can occur among family members. The prevalence of family transmission is probably much higher than that described in this study because family members of a patient are
not routinely tested for MRSA colonization. In 7 of the 10 families, young children no more than 8 years old were involved.
When a child gets pneumonia, possibly preceded by flu-like symptoms, it is important to consider MRSA infection especially when one of the family members is known to be MRSA positive

sábado, abril 29, 2006

Score de candidemia

A bedside scoring system (“Candida score”) for early antifungal
treatment in nonneutropenic critically ill patients with Candida
colonization*
Cristóbal León, MD; Sergio Ruiz-Santana, MD, PhD; Pedro Saavedra, PhD; Benito Almirante, MD, PhD;
Juan Nolla-Salas, MD, PhD; Francisco Álvarez-Lerma, MD, PhD; José Garnacho-Montero, MD;
María Ángeles León, MD, PhD; EPCAN Study Group
The incidence of infections
caused by Candida species in
the critical care setting has
substantially increased in recent
years (1–3). Invasive candidiasis has
been associated with severe sepsis, septic
shock, and multiorgan failure with clinical
characteristics resembling those
caused by bacterial pathogens (4 –7).
Signs of invasive candidiasis might be
apparent early, but the disease is usually
diagnosed late in the course of intensive
care unit (ICU) stay, representing a diagnosis
challenge with an estimated mortality
rate of 40% despite the development
of new antifungal drugs (8).
Different risk factors for invasive candidiasis,
including prior Candida species
colonization, could allow recognition of
patients at highest risk. Such patients
may be potential candidates for preemptive
antifungal therapy. An important
proportion of patients are admitted or
become colonized in the ICU, but only
few subsequently develop systemic candidal
infection (9). Candida species colonization
assessment based on multiplebody-
site screening is now performed
routinely in many ICUs. The value of positive
surveillance cultures and of several
*See also p. 913.
See Appendix for list of EPCAN Study Group participants.
From the Intensive Care Unit (CL), Hospital Universitario
de Valme, Universidad de Sevilla, Sevilla; Intensive
Care Unit, Hospital Universitario Dr. Negrín (SRS),
and Mathematics Department (PS), Universidad de Las
Palmas de Gran Canaria, Las Palmas de Gran Canaria;
Infectious Diseases Unit (BA), Hospital Universitari Vall
d’Hebron, Universitat Autònoma, Barcelona; Intensive
Care Unit (JN, FAL), Hospital Universitari del Mar,
Universitat Autònoma, Barcelona; Intensive Care Unit
(JGM), Hospital Universitario Virgen del Rocío, Universidad
de Sevilla, Sevilla; and Intensive Care Unit (MAL),
Hospital General de Catalunya, Barcelona, Spain.
Supported in part by a grant from Gilead Sciences,
S.L., Madrid, Spain.
The authors declare that they have no competing
interests.
This study was presented in part at the 34th
Critical Care Congress of the Society of Critical Care
Medicine, Phoenix, Arizona, January 15–19, 2005.
Address requests for reprints to: Cristóbal León,
MD, Intensive Care Unit, Hospital Universitario de
Valme, Universidad de Sevilla, Carretera de Cádiz s/n,
E-41014, Sevilla, Spain. E-mail: cleong@telefonica.net
Copyright © 2006 by the Society of Critical Care
Medicine and Lippincott Williams & Wilkins
DOI: 10.1097/01.CCM.0000202208.37364.7D
Objective: To obtain a score for deciding early antifungal
treatment when candidal infection is suspected in nonneutropenic
critically ill patients.
Design: Analysis of data collected from the database of the
EPCAN project, an ongoing prospective, cohort, observational,
multicenter surveillance study of fungal infection and colonization
in intensive care unit (ICU) patients.
Setting: Seventy-three medical-surgical ICUs of 70 teaching
hospitals in Spain.
Patients: A total of 1,699 ICU patients aged 18 yrs and older
admitted for at least 7 days between May 1998 and January 1999
were studied.
Interventions: Surveillance cultures of urine, tracheal, and
gastric samples were obtained weekly. Patients were grouped as
follows: neither colonized nor infected (n  719), unifocal or
multifocal Candida colonization (n  883), and proven candidal
infection (n  97). The odds ratio (OR) for each risk factor
associated with colonization vs. proven candidal infection was
estimated. A logistic regression model was performed to adjust
for possible confounders. The “Candida score” was obtained
according to the logit method. The discriminatory power was
evaluated by the area under the receiver operating characteristics
curve.
Measurements and main results: In the logit model, surgery
(OR  2.71, 95% confidence interval [CI], 1.45–5.06); multifocal
colonization (OR  3.04, 95% CI, 1.45– 6.39); total parenteral
nutrition (OR  2.48, 95% CI, 1.16 –5.31); and severe sepsis (OR 
7.68, 95% CI, 4.14 –14.22) were predictors of proven candidal
infection. The “Candida score” for a cut-off value of 2.5 (sensitivity
81%, specificity 74%) was as follows: parenteral nutrition,
0.908; surgery, 0.997; multifocal colonization, 1.112; and
severe sepsis, 2.038. Central venous catheters were not a
significant risk factor for proven candidal infection (p  .292).
Conclusions: In a large cohort of nonneutropenic critically ill
patients in whom Candida colonization was prospectively assessed,
a “Candida score” >2.5 accurately selected patients who
would benefit from early antifungal treatment. (Crit Care Med
2006; 34:730–737)
KEY WORDS: Candida colonization; intensive care unit; critically
ill patients; Candida score; preemptive antifungal therapy; invasive
candidiasis

developed colonization indexes to predict
the risk for invasive candidiasis and to
indicate preemptive antifungal therapy is
currently a matter of active investigation
(10). Therefore, the objective of this study
was to obtain a simple scoring system
(named “Candida score”) that may assist
clinicians in differentiating between Candida
species colonization and proven candidal
infection when they are considering
preemptive antifungal treatment for nonneutropenic
critically ill patients.
METHODS
Study Population
This study was performed in the context of
the EPCAN project (Estudio de Prevalencia de
CANdidiasis, Candidiasis Prevalence Study), a
surveillance study of fungal infection and colonization
in critically ill patients (11, 12). A
total of 1,765 patients over the age of 18 yrs
who were admitted for at least 7 days to 73
medical-surgical ICUs in 70 tertiary care hospitals
in Spain between May 1998 and January
1999 were included. The study was approved
by the institutional review board of the participating
centers.
Design
This was a prospective, cohort, observational,
multicenter study. For all patients,
screening cultures for Candida species were
performed on ICU admission and once a week
thereafter until discharge from the ICU or
death. Samples were obtained from tracheal
aspirates, pharyngeal exudates, gastric aspirates,
and urine, as part of the EPCAN surveillance
study. Other samples, taken from peripheral
blood, intravascular lines, feces,
wound exudates, surgical drains, or other infectious
foci, were obtained at the discretion of
the attending physician. Samples were processed
by the different reference clinical microbiology
laboratories of the participating
hospitals according to standard procedures,
including seeding of the samples in Sabouraud
dextrose agar culture medium and Sabouraud
agar with cicloheximide and chloramphenicol
(mycobiotic agar) and incubation at 35°C for 7
days. Blood cultures were processed with an
automated system (BACTEC, Becton Dickinson
Diagnostic Instrument Systems, Paramus,
NJ). Identification of yeasts at the species level
was made with the API 20C, API 32C, or the
YST card of the Vitek system (bioMérieux España,
Madrid, Spain) whenever possible (13).
A case report form was completed for each
patient and data were prospectively included
in the EPCAN database. For the purpose of this
study—that is, to develop the “Candida score”
system for deciding the use of early antifungal
treatment when Candida colonization is diagnosed
in nonneutropenic critically ill patients
—the following data were collected from
the database: age, gender, underlying disease,
reason for ICU admission, concomitant infections,
presence and duration of risk factors for
Candida species colonization and infection,
antifungal treatment, and vital status at discharge
(survival vs. death). Neutropenia was
an exclusion criterion. Severity of illness on
ICU admission was calculated with the Acute
Physiology and Chronic Health Evaluation II
(APACHE II) system (14). According to diagnoses
at the time of ICU admission, patients
were classified as surgical, trauma, or medical.
Surgical patients were those for whom the
reason of ICU admission was the postoperative
control of an elective or urgent procedure,
trauma patients were those admitted for trauma-
related acute lesions, and medical patients
were those admitted for any other reason.
Only insulin-treated patients were considered
to have diabetes mellitus. Chronic bronchitis
was defined as the presence of a productive
cough or expectoration for 90 days a
year (although on separate days) and for 2
(consecutive) yrs, provided that a specific disorder
responsible for these symptoms was not
present. Chronic liver disease was confirmed
by liver biopsy or signs of portal hypertension,
such as esophageal varices or ascites. Chronic
renal failure was considered in patients requiring
hemodialysis or peritoneal dialysis at the
time of admission to the hospital. Severe heart
failure was defined as grades III and IV of the
New York Heart Association (NYHA) classifi-
cation (15). Other risk factors included the
following: arterial catheter, central venous
catheter, total parenteral nutrition, enteral
nutrition, urinary catheter, antibiotic treatment
(when given within 10 days before ICU
admission), extrarenal depuration procedures
(hemodialysis or continuous hemofiltration),
and use of steroids (a daily dose equivalent to
20 mg prednisone for at least 2 wks or 30 mg
for at least 1 wk before isolation of Candida in
cultures). The development of organ failure,
sepsis, and septic shock was also recorded
(16).
Definitions of Colonization and
Infection
Colonization was defined as the presence of
Candida species in nonsignificant samples obtained
from the oropharynx, stomach, urine,
or tracheal aspirates. Colonization was considered
unifocal when Candida species were isolated
from one focus and multifocal when
Candida species were simultaneously isolated
from various noncontiguous foci, even if two
different Candida species were isolated. Oropharynx
and stomach were considered one site
(digestive focus). Unifocal and multifocal colonization
persistence was defined by at least
two weekly consecutive sets of Candidapositive
cultures. Proven candidal infection
required one of the following criteria: presence
of candidemia, that is, documentation of
one blood culture that yielded a Candida species;
ophthalmic examination consistent with
candidal endophthalmitis in a patient with
clinical sepsis; isolation of Candida species in
significant samples (e.g., pleural fluid, pericardial
fluid) or candidal peritonitis; or histologically
documented candidiasis. Ophthalmic examination
was done routinely for every patient
with sepsis. Candidal peritonitis was defined
by the isolation of Candida species in a peritoneal
sample obtained by laparotomy or percutaneous
puncture in patients with associated
clinical findings, including perforation of
an abdominal organ, dehiscence of an intestinal
suture with peritonitis, severe acute pancreatitis,
or presence of a peritoneal catheter
for dialysis. Catheter-related candidemia was
considered in those patients who had an intravascular
device and one or more positive
cultures of blood samples obtained from the
peripheral vein, clinical manifestations of infection
(e.g., fever, chills, and/or hypotension),
and no apparent source for bloodstream infection
(with the exception of the catheter), as
well as a positive catheter culture, either semiquantitative
(15 colony-forming units [cfu]
per catheter segment) or quantitative (102
cfu per catheter segment), whereby the same
organism (species and susceptibility) was isolated
from a catheter segment and a peripheral
blood sample (17).
Patients were classified into three groups
as follows: neither colonized nor infected, unifocal
or multifocal Candida species colonization
without proven infection, and proven
candidal infection.
Statistical Analysis
To estimate the predictive model that will
allow us to differentiate between Candida species
and proven candidal infection, the crude
odds ratio (OR) for each risk factor associated
with colonization vs. proven candidal infection
was estimated. In order to estimate the
multivariate model, the dataset was subdivided
into two groups: a training set to fit the
model, composed of 65% of the sample, and a
validation set to validate the model, made up
of 35% of the sample (18). Based on the cases
of the training set, a logistic regression (logit)
model was performed to adjust for possible
confounders. Statistically significant variables
in the univariate analysis were included in the
model, and through a stepwise elimination
process, the so-called “Candida score” was obtained.
The discriminatory power of this score
was evaluated by the area under the receiver
operating characteristics (ROC) curve and the
95% confidence interval (CI). Then, a cut-off
value to estimate the diagnostic sensitivity and
specificity in the validation set was selected.
Statistical significance was set at p  .05. Data
were analyzed with the SPSS statistical program
(11.5, SPSS, Chicago, IL) for Windows.
RESULTS
Of the initial 1,765 patients included
in the study, 96 (5.4%) were excluded
because of inadequate data collection.
The study population consisted of 1,669
patients, 66.5% men, with a mean (SD)
age of 57.8 (17.2) yrs.
There were 719 (43.1%) patients in
the neither-colonized-nor-infected
group, 67.9% men, with a mean age of
57.5 (17.0) yrs. The median (5th to 95th
percentile) APACHE II score on ICU admission
was 18 (6.6 –33). A total of 239
died, for a mortality rate of 33.2%.
Colonization solely by Candida species
was diagnosed in 883 patients. There
were 577 men and 306 women in this
group, with a mean age of 58.9 (17.0) yrs
and a median APACHE II score of 18
(8 –32.4). Unifocal Candida species colonization
was diagnosed in 388 patients
(43.9%) and multifocal Candida species
colonization in the remaining 495 patients
(56.0%). The overall mortality rate
was 40.2%. There were 103 deaths (mortality
rate, 26.5%) among patients with
unifocal Candida colonization and 252
deaths (mortality rate, 50.9%) among patients
with multifocal colonization.
Proven candidal infection was diagnosed
in 97 patients (5.8%). There were
68 men and 29 women in this group, with
a mean age of 58.5 (16.9) yrs and a median
APACHE II score of 17 (10.6 –30.8).
Fifty-eight patients developed candidemia,
30 peritonitis, 6 endophthalmitis,
and 3 candidemia and peritonitis concomitantly.
Fifty-six patients died, for a
mortality rate of 57.7%. Eighty-five patients
(87.6%) received antifungal treatment.
The median (5th to 95th percentile)
time elapsed between the onset of
proven candidal infection and the beginning
of the antifungal therapy was 12
(0.3–37.8) days. The median (5th to 95th
percentile) APACHE II score at the start
of the antifungal treatment was 18 (4.9–
29.3). Eighteen patients (18.6%) had
catheter-related candidemia, and the
catheter was removed from all of them.
There were no statistically significant
differences in the APACHE II scores between
the groups who were noncolonized,
noninfected, colonized with Candida species,
and infected by Candida species
(Kruskal-Wallis test, p  .145). However,
when the risk for death was estimated (Table
1), there were statistically significant
differences between the variable indicating
patient group and the variable indicating
the mortality in the Mantel-Haenszel test
for linear association (p  .001).
As shown in Table 2, patients with
candidal infection compared with those
with Candida species colonization alone
showed statistically significant differences
in the following variables: length of
ICU stay, patient category, surgery on
ICU admission, total parenteral nutrition,
extrarenal depuration procedures, unifocal
or multifocal colonization, and severe
sepsis. Central venous catheters were not
found to be a significant risk factor for
proven candidal infection (p  .292).
In the logit model adjusted for possible
confounding variables, surgery on
ICU admission, total parenteral nutrition,
multifocal Candida species colonization,
and severe sepsis were independently associated
with a greater risk for proven
candidal infection (Table 3). Through a
stepwise elimination process, the Candida
score was obtained (Table 4). The
discriminatory power of this score, assessed
by the area under the ROC curve
and its main cut-off values, is shown in
Figure 1.
DISCUSSION
This study shows that the new Candida
score allows differentiating between
Candida species colonization and candidal
infection in nonneutropenic ICU patients.
Multifocal colonization, total parenteral
nutrition, surgery as the reason of
ICU admission, and clinical symptoms of
severe sepsis were found to be independent
predictors of systemic candidiasis in
this population. Accordingly, it is possible
to stratify the risk of proven candidal
infection in a large population of critically
ill patients and to select those patients
who will most benefit from starting
antifungal therapy (i.e., early antifungal
administration given to patients with evidence
of colonization in the presence of
multiple risk factors for candidal infection).
An important finding of the study is
that multifocal fungal colonization is really
an independent risk factor of proven
candidal infection in this large cohort of
both medical and surgical critically ill
patients at various centers. In the National
Epidemiology of Mycoses Survey
(NEMIS) study conducted in surgical
ICUs at six sites in the United States (19),
recovery of Candida species in rectal
and/or urine surveillance cultures was
not associated with an increased risk of
candidal bloodstream infections. The fact
that fungal colonization assessment was
based on multiple-site cultures performed
weekly in the present study could
account for the discrepant results, since
only two sites were cultured in the
NEMIS study.
Nosocomial fungal infections in nonneutropenic
critically ill patients are
caused by mainly Candida species. The
proposed definitions of “probable,” “possible,”
and “proven” opportunistic fungal
infections intended for immunocompromised
patients (20) may be unreliable for
nonneutropenic patients (21). The clinical
significance of Candida species colonization
as a determinant risk factor for
invasive candidiasis has been largely recognized,
and recent efforts have been directed
toward developing a predictor for
the diagnosis of systemic infection based
on colonization density. A colonization
index with a 0.5 threshold, defined as the
ratio of the number of culture-positive
Table 1. Risk for death in the study population, according to colonization and infection status (n 
1,669)
Patient group
Nonsurvivors
Odds Ratio (95% Confidence
Interval)a
No.
Mortality
Rateb Crude Adjustedc
Neither colonized nor infected, n  719 239 33.2% 1 1
Candida species colonization, n  883
Unifocal, n  388 103 26.5% 1.02 (0.8–1.4) 1.04 (0.8–1.4)
Multifocal, n  495 252 50.9% 1.55 (1.3–2) 1.54 (1.2–1.9)
Candidal infection, n  97 56 57.7% 2.74 (1.8–4.2) 3.2 (2.0–5.0)
aEstimated by logistic regression analysis; bp  .001, linear association test; cfor Acute Physiology
and Chronic Health Evaluation (APACHE II) score.
sites to the number of sites cultured, and its corrected version with a 0.4 threshold
(22) have been used as tools to start preemptive
antifungal treatment in ICU patients
(10). In a before/after intervention
study of 2-yr prospective and 2-yr historical-
control cohorts carried out by Piarroux
et al. (10), patients with a corrected
colonization index 0.4 received early
preemptive antifungal therapy, and only
18 cases (3.8%) of proven candidiasis
were diagnosed; all were imported infections.
The incidence of ICU-acquired
proven candidiasis significantly decreased
from 2.2% to 0% (p  .001, Fisher test).
The authors concluded that targeted preemptive
strategy may efficiently prevent
acquisition of proven candidiasis in patients
admitted to a surgical ICU. It
should be noted that the Candida score
takes in account other relevant risk factors
of candidiasis, in addition to colonization,
to improve the specificity of the
test.
For patients considered “heavily” colonized
by Candida species, there are no
biological markers that may assist clinicians
in deciding to prescribe or not prescribe
antifungal agents. According to the
results of a survey in medical-surgical
ICUs in France, most of the units showed
a homogeneous antifungal prescription
pattern. Furthermore, most intensivists
interviewed prescribed antifungal treatment
in the presence of multifocal Candida
colonization, clinical signs of sepsis,
and several other risk factors for invasive
candidiasis (23). In agreement with these
Table 3. Results of multivariate analysis: Risk factors for proven candidal infection in 1,669 adult
patients
Variable
Proven
Candidal
Infection
% p Value
Crude Odds
Ratio (95%
Confidence
Interval)
Adjusted Odds Ratio
(95% Confidence
Interval)
Surgery on ICU admission
No 6.9
Yes 16.5 .001 2.69 (1.76–4.10) 2.71 (1.45–5.06)
Total parenteral nutrition
No 2.8
Yes 15.5 .001 6.46 (3.48–11.98) 2.48 (1.16–5.31)
Severe sepsis
No 4.5
Yes 28.8 .001 8.63 (5.49–13.56) 7.68 (4.14–14.22)
Candida species colonization
No 4.2
Yes 12.3 .001 3.20 (1.85–5.53) 3.04 (1.45–6.39)
ICU, intensive care unit.
Table 2. Results of univariate analysis: Risk factors for invasive candidiasis according to colonization and infection status (n  1,669)
Variable
Unifocal or Multifocal Candida
Species Colonization n  883
Proven Candidal
Infection n  97 p Value
Age, yrs, mean (SD) 58.9 (17.0) 58.5 (16.9) .825
Male/female 577/306 68/29 .337
APACHE II score on admission, median (range) 19 (1–67) 17 (6–45) .203
Length of ICU stay, days, median (range) 20 (7–166) 28 (7–138) .001
APACHE II score, no. (%)
15 302 (34.2) 37 (38.5) .137
15–25 408 (46.3) 48 (50.5)
25 173 (19.5) 12 (11.0)
Diagnosis on ICU admission, no. (%)
Medical 449 (50.8) 34 (35.1) .001
Surgical 258 (29.2) 51 (52.6)
Trauma 176 (19.9) 12 (12.4)
Underlying disease, no. (%)
Chronic bronchitis 197 (22.3) 14 (14.4) .073
Diabetes mellitus 136 (15.4) 14 (14.4) .801
Chronic liver disease 40 (4.5) 2 (2.1) .255
Chronic renal failure 44 (5.5) 4 (4.1) .710
Heart failure 40 (4.5) 2 (2.1) .255
Risk factors, no (%)
Broad spectrum antibiotics 866 (98.0) 97 (100) .380
Central venous catheter 873 (98.9) 97 (100) .292
Urinary catheter 870 (98.5) 93 (95.9) .078
Mechanical ventilation 837 (94.8) 92 (94.8) .982
Enteral nutrition 695 (78.7) 68 (70.1) .053
Arterial catheter 666 (75.4) 68 (70.1) .251
Total parenteral nutrition 462 (52.3) 85 (87.6) .001
Corticosteroids 214 (24.2) 22 (22.7) .734
Hemodialysis or continuous hemofiltration 106 (12.0) 29 (29.9) .001
Severe sepsis, no. (%) 156 (17.7) 63 (64.9) .001
Candida species colonization, no. (%) .001
Unifocal 390 (44.1) 17 (17.5)a
Multifocal 493 (55.8) 69 (71.1)a
APACHE II, Acute Physiology and Chronic Health Evaluation II; ICU, intensive care unit.
aEleven patients in the proven candidal infection group did not have previous Candida colonization.
733 Crit Care Med 2006 Vol. 34, No. 3

data, 79% of 135 Spanish intensivists in
45 ICUs reported that they would start
antifungal treatment for nonneutropenic
critically ill patients if clinical signs of
infection and multifocal Candida isolates
were noted (24).
Recommendations for starting antifungal
treatment for nonneutropenic
critically ill patients have also recently
been reported in the literature (25–27). A
predictive rule based on known risk factors,
including colonization, that allow us
to differentiate between Candida species
colonization and proven candidal infection
would help clinicians more accurately
than colonization alone to select
those ICU patients who would benefit
from early antifungal treatment. Paphitou
and associates (28) and Ostrosky-
Zeichner and colleagues (29) have proposed
prediction rules for invasive
candidiasis following a retrospective multicenter
study in 12 ICUs at nine hospitals
in the United States and Brazil. The bestperforming
rule required a combination
of at least one “major” and at least two
“minor” risk factors among several
known for candidal infection in patients
staying in the ICU for at least 48 hrs and
who were expected to stay for 2 more
days. Their clinical prediction rule identified
ICU patients with a 10% risk of
invasive candidiasis, but validation of this
instrument is pending. Fungal coloniza-
Table 4. Calculation of the Candida score: Variables selected in the logistic regression model
Variable
Coefficient
()
Standard
Error Wald 2
p
Value
Multifocal Candida species colonization 1.112 .379 8.625 .003
Surgery on ICU admission .997 .319 9.761 .002
Severe sepsis 2.038 .314 42.014 .000
Total parenteral nutrition .908 .389 5.451 .020
Constant 4.916 .485 102.732 .000
ICU, intensive care unit.
Candida score  .908  (total parenteral nutrition)  .997  (surgery)  1.112 (multifocal
Candida species colonization)  2.038 (severe sepsis). Candida score (rounded)  1  (total
parenteral nutrition)  1  (surgery)  1 (multifocal Candida species colonization)  2  (severe
sepsis). All variables coded as follows: absent, 0; present, 1.
Figure 1. A, receiver operating characteristics (ROC) curve and area under the ROC curve (AUC) for assessing the discriminatory power of the Candida score.
B, cut-off values for the ROC curve.
734 Crit Care Med 2006 Vol. 34, No. 3
tion was not included in this prediction
rule proposed by Ostrosky-Zeichner et al.
(29) because it was derived from the
NEMIS study results (19). The Candida
score presented here could therefore be
considered to be more reliable, given the
weight of fungal colonization in the
pathogenesis of candidiasis.
DuPont and co-workers (30) carried
out a retrospective systematic review of
surgical intensive care patients, with a
prospective follow-up in France. A scoring
system was proposed with the following
risk factors: female gender, upper
gastrointestinal origin of peritonitis, cardiovascular
failure, and use of antibiotics.
A grade C score, defined as the presence
of three qualifiers, was associated with a
sensitivity of 84% and specificity of 50%
for the detection of yeasts in the peritoneal
fluid of patients with peritonitis. The
main drawbacks of this study included its
single-center setting and its potential application
restriction to surgical patients.
We used the EPCAN database, which is
a large cohort of nonneutropenic ICU patients
for whom, among other goals, Candida
colonization and invasive candidiasis
were studied prospectively. As previously
reported (21), the rate of proven candidal
infection found in the present study was
low, but the mortality rate was high. The
mortality rate increased significantly according
to the patient group, that is, with
unifocal colonization (26.5%), multifocal
colonization (50.9%), and candidal
proven infection (57.7%). Although colonization
does not define infection, these
data support the well-known role of Candida
colonization as a key factor in the
decision to start early antifungal treatment
for ICU patients.
The new Candida score was based on
the respective predictive value of previously
reported risk factors. In addition to
multifocal Candida species colonization,
three other risk factors were found to be
significant predictors of proven candidal
infection in the logistic regression model:
use of total parenteral nutrition, surgery
on ICU admission, and clinical manifestations
of severe sepsis. The respective
weight of colonization and these risk factors
as shown in the Candida score allowed
us to reliably differentiate between
Candida species colonization and proven
candidal infection. Although central venous
catheters are repeatedly described
as major risk factors for proven hematogenous
candidiasis (19, 31), in this large
dataset from a prospective multicenter
study, venous catheters were not signifi-
cant predictors of proven candidal infection.
The medical literature is flooded with
complicated prediction rules and scores
(32–37), and there is a need to have available
bedside easy-to-remember scores
that would make daily tasks easier for
clinicians. The simplified version of this
score, after rounding up to 1 the weight
for total parenteral nutrition, surgery, or
multifocal Candida species colonization
and up to 2 the weight for clinical severe
sepsis, is a quite simple ready-to-use prediction
rule. With a cut-off value of 2.5,
that it to say, with a sensitivity of 81%
and a specificity of 74%, we shall only
need the presence of sepsis and any one of
the three other remaining risk factors or
the presence of all of them together except
sepsis in order to consider starting
antifungal treatment for one particular
patient. Finally, the Candida score also
identifies critically ill patients with
proven candidiasis: patients with a score
2.5 are 7.75 times as likely to have
proven infection (risk ratio  7.75; 95%
CI, 4.74 –12.66) than patients with a Candida
score up to 2.5.
Therefore, the easy rule of thumb for
prescribing antifungals, according to a
Candida score 2.5, will allow more effi-
cient selection of patients who indeed will
benefit from the increasing number of
available antifungal drugs (38) and, at the
same time, more adequate prevention of
the development of new resistant species
due to an excess of inappropriate and
potentially detrimental antifungal treatments
(39). Assessment with the Candida
score should be performed at the time of
ICU admission and any time candidiasis is
suspected.
CONCLUSIONS
A new score, the Candida score, which
was calculated according to data collected
in the EPCAN database (in which all cases
of Candida species colonization and
proven candidal infection were prospectively
recorded), is an easy-to-remember
bedside prediction rule. A score 2.5 will
help intensivists select patients who will
benefit from early antifungal administration.
Finally, although the Candida score
contributes to predicting proven candidal
infection, the benefits of preemptive (prophylactic
or empirical) antifungal therapy
remain to be determined.
ACKNOWLEDGMENT
We thank Marta Pulido, MD, for editing
the manuscript.
REFERENCES
1. Vincent JL, Anaissie E, Bruining H, et al:
Epidemiology, diagnosis and treatment of
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8. Ostrosky-Zeichner, L: Prophylaxis or preemptive
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2552–2553
9. Álvarez-Lerma F, Palomar M, León C, et al:
Colonización y/o infección por hongos en
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10. Piarroux R, Grenouillet F, Balvay P, et al:
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viernes, marzo 31, 2006

Blood Culture Contamination:

MINIREVIEW
Blood Culture Contamination: Persisting Problems and Partial Progress
Melvin P. Weinstein*

Departments of Medicine and Pathology, University of Medicine and Dentistry of New Jersey—Robert Wood Johnson Medical School, and Microbiology Laboratory, Robert Wood Johnson University Hospital, New Brunswick, New Jersey 08903-0019


INTRODUCTION
Top
Introduction
References

Although it has been widely appreciated for many years among physicians and microbiologists that blood cultures are among the most important laboratory tests performed in the diagnosis of serious infections (35), it has become equally apparent in more recent years that contaminated blood cultures are common (25, 42), enormously costly (3, 29), and frequently confusing for clinicians (1, 12, 14, 26). Clinical studies of bloodstream infections over 3 decades have provided guidelines for differentiating true pathogens from contaminants or organisms of unknown significance (14, 18, 41, 42); however, a true "gold standard" for differentiating pathogens from contaminants does not exist (4, 25). Moreover, the most common blood culture contaminants, coagulase-negative staphylococci (CoNS), which were almost always such several decades ago (18, 41), now are pathogens more frequently (19, 25, 26, 42), and judging the clinical significance of this group of microorganisms in blood has proven to be especially problematic (1, 11, 22, 24, 26, 42; S. J. Peacock, I. C. Bowler, and D. W. Crook., Letter, Lancet 346:191-192, 1995). This review focuses on how pathogen-contaminant decisions are made, the phenomenon of increasing contamination of blood cultures, potential methods for addressing high contamination rates, and practical laboratory approaches to the workup of likely contaminants.


TOOLS FOR INTERPRETING THE CLINICAL SIGNIFICANCE OF POSITIVE BLOOD CULTURES

A number of clinical and laboratory tools have been proposed to aid microbiologists and physicians in deciding whether a blood isolate is a pathogen or a contaminant. These include the identity of the microorganism itself; clinical features such as fever, leukocytosis, and results of imaging studies (available to the clinician but usually not to the microbiologist); the proportion of blood culture sets positive as a function of the number of sets obtained; the time it takes for growth to be detected once a blood culture is received in the laboratory; and the number of culture vials within a culture set that show growth. Some of these tools have proven to be quite useful, whereas others have not.

The identity of the microorganism that grows from a positive blood culture provides important interpretative information. MacGregor and Beaty (18) documented this observation in the early 1970s, and studies by my colleagues and I confirmed and updated the earlier findings (41, 42). A predictive model that assessed multiple variables also documented microorganism identity as an independent predictor (4). Microorganisms that always or nearly always (>90%) represent true bacteremia or fungemia include Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli and other members of the Enterobacteriaceae, Pseudomonas aeruginosa, and Candida albicans (42). Although published data from large studies with multiple isolates of the following organisms are lacking, it is my observation that Streptococcus pyogenes, Streptococcus agalactiae, Listeria monocytogenes, Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae, members of the Bacteroides fragilis group, Candida species other than C. albicans, and Cryptococcus neoformans always or virtually always represent true infection. In contrast, microorganisms such as Corynebacterium species, Bacillus species other than B. anthracis, and Propionibacterium acnes represent true bacteremia only rarely (42). Detection of CoNS, the most frequent of all blood culture isolates, can be especially vexing. These bacteria are most often contaminants, but they have taken on increased clinical importance as the etiologic agents of catheter-associated bacteremia and bacteremia in patients with vascular and other prostheses (19, 26, 42). Accordingly, one can no longer judge the clinical significance of a CoNS isolate solely on the basis of its identity. Similarly, the clinical significance of other microorganisms also cannot be judged based only their identity. For example, in a recent study, enterococci and viridans group streptococci were pathogens 78 and 38% of the time, respectively, and Clostridium perfringens most often (77%) was a contaminant, whereas other Clostridium species most often (80%) were pathogens (42).

The number of blood culture sets that grow microorganisms, especially when measured as a function of the total number obtained, has proved to be a useful aid in interpreting the clinical significance of positive blood cultures (18, 41, 42). In contrast to patients with endocarditis or other bloodstream infections, in whom all blood cultures or the majority thereof are positive, patients whose blood cultures grow contaminants usually have only a single blood culture (when two or more are obtained) that is positive (42). Although obvious, it bears emphasis that if only a single blood culture is obtained, the value of this tool ceases to exist; and this is but one reason (another being increased blood volume) that at least two blood culture specimens are recommended as standard practice (2, 23, 37). The value of obtaining more than a single blood culture is that it also assists in interpreting the clinical significance of positive results by virtue of the following calculation. If an institution has a baseline blood culture contamination rate of 3%, the probability of recovering the same organism in two culture sets from a patient, and of that organism being a contaminant, is less than 1 in 1,000 (0.03 x 0.03 = 0.0009)!

A laboratory tool that has been used as an aid to differentiating clinically significant isolates from contaminants is assessment of the time necessary for microbial growth to occur (4). The underlying premise is that growth of pathogens, which are likely to be present in larger inocula, will be detected earlier than that of contaminants, which are likely to be present in much smaller quantities (18). Whereas this concept likely has validity, the degree of overlap in the detection times of true pathogens versus contaminants is such that this variable cannot be relied upon as a predictor of a true-positive culture (8). Moreover, with the wide use of continuously monitoring blood culture systems and the concomitant decrease in the time to detection of growth, the time difference between the detection of true pathogens and contaminants has been narrowed even further.

Some microbiologists and clinicians have used the number of culture bottles positive within a blood culture set as a guide to determine whether isolates represent true pathogens or contaminants. However, there now are published data, at least for CoNS, that show that this technique is not clinically useful (22; Peacock et al., letter). Although clinically significant CoNS may grow more often in multiple bottles within a set as opposed to a single bottle, and contaminants may more often grow in only one bottle of a set, the degree of overlap is such that for a given culture this information cannot predict clinical significance reliably (22; Peacock et al., letter). Accordingly, this criterion should not be used.


THE PARADOX OF INCREASING NUMBERS OF CONTAMINANTS

Despite numerous advances in blood culture methodology and systems in recent decades, some hospitals and laboratories have noted that an increasing proportion of blood culture isolates represent contamination compared with those in years past (42). There are several possible explanations for this unexpected observation. The newer continuously monitoring blood culture systems have improved algorithms for detecting microbial growth and may be detecting microorganisms present in low numbers that previously were missed. Moreover, several broth medium formulations such as the BACTEC Plus Resin media (Becton Dickinson, Sparks, Md.) and BacT/ALERT FN media (bioMerieux, Durham, N.C.) have been shown to have improved detection of staphylococci, including CoNS which most often are contaminants (10, 20, 28, 38, 40, 43, 45). Thus, the ability of new systems and media to detect these organisms, even when present in small numbers, may be responsible in part for the observed increase in the proportion of blood cultures with contaminants.

The increased use of central venous access catheters and utilization of these devices for the purpose of obtaining blood specimens for culture may also be contributing to the increased numbers of contaminated blood cultures. Several studies have documented increased contamination when blood cultures are obtained in this fashion (5, 6, 7; R. B. Sivadas, B. Vazirani, S. Mirrett, and M. P. Weinstein, Abstr. 101st Gen. Meet. Am. Soc. Microbiol., abstr. C10, 2001), perhaps because it is more difficult to sterilize these devices than it is the skin before blood is obtained. Although physicians and nurses may believe they are saving patients the pain of an extra needle stick when blood cultures are obtained from catheters rather than by venipuncture, they may actually be doing their patients and the health care system a disservice if contaminants are grown from the culture resulting in the need for even more cultures, other diagnostic studies, unnecessary antibiotic therapy, and the associated incremental costs of care.

Prior to the human immunodeficiency virus (HIV) era, blood cultures traditionally were obtained by a two-needle technique, using a sterile needle and syringe to perform the venipuncture, then changing to a second sterile needle before inoculating the blood culture vial. The purpose of the two-needle technique was to reduce the chance that skin microorganisms that might be present on the needle used for the venipuncture would be inoculated into the blood culture vial, thereby resulting in a contaminated blood culture. As the knowledge of HIV as a bloodborne pathogen and the risks of needle stick transmission of HIV became evident, several studies were undertaken to determine whether contamination rates would be affected if only one needle was used for both venipuncture and inoculation of blood culture vials (9, 15, 16). The results of each of these studies showed no significant increase in contamination rates when the single-needle technique was used. Subsequently, however, a meta-analysis suggested that single-needle blood cultures were associated with contamination rates of 3.7% compared with 2.0% when a two-needle technique was used (30). Since the current standard of care continues to be the single-needle technique in order to reduce the risk of occupational needle stick injuries, slightly higher contamination rates may have to be tolerated.


REDUCING THE NUMBER OF CONTAMINATED BLOOD CULTURES

Although it is not possible to achieve contamination rates of zero or even close to zero (31), there are potential means by which contamination can be reduced. These include the use of collection methods that increase the chances for sterility, for example, obtaining blood via venipuncture rather than from an intravascular catheter or using a two-needle rather than a single-needle technique, as has already been mentioned. For the reasons already stated, the two-needle method is unlikely to return to widespread use; however, laboratories and institutions can and should actively promote blood cultures obtained from venipuncture rather than intravascular devices as a means of practicing evidence-based medicine.

There is also evidence that some antiseptic preparations may be more efficacious than others in reducing contamination rates. Povidone iodine preparations require 1.5 to 2 min of contact time to produce their maximum antiseptic effect, whereas iodine tincture requires approximately 30 s (13). Health care workers who obtain blood cultures are often in a hurry, do not understand the importance of antiseptic preparation contact time, and are less likely to wait 1.5 to 2 min as opposed to half a minute before obtaining blood. At least two studies have documented a significantly lower contamination rate using iodine tincture compared with an iodophor (17, 31). Another report compared the use of 0.2% chlorine peroxide and 10% povidone iodine and demonstrated lower contamination rates when chlorine peroxide was used (29). Lastly, an alcoholic solution of 0.5% chlorhexidine gluconate used as an antiseptic prior to blood culture was associated with significantly lower contamination rates compared with a standard povidone-iodine preparation (21).

Several published studies have shown that trained phlebotomists or blood culture teams can reduce contamination rates in individual institutions (27, 32, 36), and this has been confirmed in my own institution (Sivadas et al., 101st Gen. Meet. Am. Soc. Microbiol.). At a New York City, N.Y., community teaching hospital, the contamination rate for blood cultures drawn by a blood culture team using a commercially available blood culture prep kit was approximately 1% compared with rates of 4.8% for blood cultures drawn by resident physicians using the same method (36). The contamination rate when residents did not use the commercial prep kit was even higher (8.4%) (36). In a large survey of over 600 hospitals sponsored by the College of American Pathologists, median contamination rates for institutions in which more than half of all blood cultures were collected by resident physicians was 3.9%, compared with 2.2% in the remaining institutions (27). In a pilot study at my institution, contamination of blood cultures obtained by phlebotomists trained and monitored monthly by microbiology laboratory staff was 3%, compared with nearly 11% for blood cultures obtained by resident physicians, nondegree nursing assistants, and nurses (M. P. Weinstein, unpublished observation). Subsequently, my colleagues and I assessed contamination in a larger study and again found that samples collected by phlebotomists had lower contamination rates than those collected by nondegree nursing assistants, nurses, and resident physicians (the last of whose samples had the highest contamination rates) (Sivadas et al., 101st Gen. Meet. Am. Soc. Microbiol.).

Whether or not commercially marketed blood culture prep kits are associated with reduced blood culture contamination rates remains controversial. Some studies have shown reduced contamination (27, 36) with commercial prep kits, whereas others have shown no difference (44). The manufacturer of at least one commercial prep kit has offered ongoing in-service education for personnel obtaining blood cultures (M. P. Weinstein, personal observation), which itself may be associated with reduced contamination rates.


LABORATORY WORKUP OF LIKELY BLOOD CULTURE CONTAMINANTS

In the real world of clinical microbiology laboratories, nearly half of all positive blood cultures represent contamination (42). Complete laboratory workup of contaminant isolates is associated with increased technologist workload and institutional cost. Therefore, some laboratories have developed algorithms for dealing with this problem based, at least in part, on many of the studies reviewed in this article.

At the University of Iowa, for example, Richter et al. (25) tested, validated, and implemented an algorithm to minimize the workup of blood culture contaminants. CoNS, aerobic and anaerobic diphtheroids, Micrococcus spp., Bacillus spp., and viridans group streptococci are considered contaminants if certain criteria are met. If two or more blood cultures are obtained and only one is positive, the isolate is reported as a probable contaminant and susceptibility testing is not done unless the physician calls the laboratory. If only a single blood culture is obtained and grows one of the likely contaminants, a pathology resident reviews the patient's chart and judges the clinical significance of the isolate based on published data (42). Susceptibility testing is not done if the isolate is judged to be a contaminant. If two or more blood cultures are obtained and two cultures are positive within a 48-h period, one of two actions is taken. If the isolates are viridans group streptococci, they are presumed to be clinically significant and a full workup is done. If one of the other likely contaminants is present, the pathology resident reviews the patient's chart, and the laboratory workup proceeds according to the resident's judgment regarding clinical significance.

In my laboratory, a similar protocol is followed, but it is modified somewhat based on the fact that pathology residents are not always assigned to microbiology. The same microorganisms are considered likely contaminants. If two or more blood cultures are submitted and only one is positive, neither species identification nor susceptibility testing is done; the isolate is reported as a probable contaminant. If only one blood culture is submitted and it grows a likely contaminant, the workup is the same; the isolate is reported to be of indeterminate significance and the physician is advised to call the laboratory director if additional workup is needed. If two or more blood cultures grow a likely contaminant other than CoNS (see below) within a 48-h period, a full workup is done. If the isolates are the same, the identification and susceptibility results are reported. If the isolates are different, they are reported as probable contaminants without susceptibility results.

When two or more blood cultures grow CoNS, my laboratory undertakes species identification and reports susceptibility results. I find that the additional information assists in determining whether the isolates are clinically significant (12, 39). If the strains isolated have the same biochemical profile and antibiogram, it is probable that they are identical (although only molecular typing provides proof). This information increases the likelihood that the isolates represent clinically significant bacteremia, and identification and susceptibility results are reported to the clinician. However, if the biochemical profiles and antibiograms are not the same (i.e., two or more differences in biochemical results and susceptibilities [susceptible versus resistant]), the isolates are much more likely to represent contamination. In this instance, the laboratory reports that two different CoNS strains were identified, and susceptibility results are not provided. Although this technique has proven clinically useful in most circumstances, the algorithm is not foolproof. Two studies from the same center in Belgium have described polyclonal CoNS bacteremia (33, 34). Thus, in patients who have multiple positive blood cultures growing CoNS that appear to be different strains, the laboratory may need to perform additional testing if clinicians believe clinically significant infection is present.

As is apparent from the foregoing discussion, the current state of the art remains suboptimal. Although progress has been made, the interpretation of the clinical significance of microorganisms that are common blood culture contaminants and the technical effort and institutional costs associated with working up probable contaminants remain problematic. Gold standards for solving these problems still are elusive.


FOOTNOTES

* Mailing address: Robert Wood Johnson Medical School, 1 Robert Wood Johnson Pl., New Brunswick, NJ 08903-0019. Phone: (732) 235-7713. Fax: (732) 235-7951. E-mail: weinstei@umdnj.edu. Back

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