Epidemiology and significance of coagulase-negative staphylococci isolated in blood cultures from critically ill adult patients

Background: Little published data are available on the epidemiology and significance of coagulase-negative staphylococci (CoNS) in blood culture isolates among critically ill adult patients. Objectives: To describe the epidemiology and frequency of CoNS blood culture isolates in critically ill adults, and investigate the association between time to positivity (TTP) of blood cultures and number of culture-positive bottles with organ dysfunction and mortality. Design, setting and participants: A retrospective chart audit in the intensive care unit of a tertiary hospital comprising all patients who had positive blood cultures for CoNS in 2009. Main outcome measures: TTP, number of culture-positive bottles, Sequential Organ Failure Assessment (SOFA) scores, resolution of fever and white cell response and inotrope requirement, length of stay in ICU and mortality. Results: In 2009, there were 1514 and 109 positive blood culture sets for the hospital and ICU patients, respectively. Of these, 515 sets from patients outside the ICU (34% of all hospital positive blood cultures) and 54 from the ICU (49.5% of all ICU positive blood cultures) were positive for CoNS. Patients with TTP ≤ 24 hours had higher organ failure scores by 0.9 (95% CI, 0-3.4; P = 0.052). There was a trend towards an association between increased 28-day mortality and TTP ≤ 24 hours (7/22 v 3/32; P = 0.071). There was no significant correlation between number of bottles positive for culture and mortality, length of stay, SOFA score, resolution of fever, white cell response, and inotrope requirement. Conclusions: Early TTP of blood cultures with CoNS may be associated with poorer outcome and may be a marker of true infection. Given the relatively high frequency of this microbiological problem, larger prospective observational studies are required to more clearly define the significance of a CoNS blood culture isolates in critically ill adult patients.