Distinguishing Sepsis From Blood Culture Contamination in Young Infants With Blood Cultures Growing Coagulase-Negative Staphylococci

Abstract

Coagulase-negative staphylococci represent the most common cause of serious nosocomial infection in many intensive care nurseries. However, these organisms are also common blood culture contaminants. To determine the value of quantitative blood cultures in distinguishing sepsis from culture contamination, we reviewed records of all infants in our nurseries who had peripheral blood isolates of coagulase-negative staphylococci during a 3-year period. Twenty-three episodes of sepsis were identified in 21 infants, and 10 infants had blood culture contamination. Colony counts from the initial peripheral blood culture were significantly different for the two study groups (P < .001). In 9 of 23 episodes of sepsis, the initial peripheral blood culture grew >100 colony-forming units (cfu) per mL. In the other 14 episodes, the initial culture yielded ≤50 cfu/mL. All 10 infants with culture contamination had colony counts of <50 cfu/mL, and in 9 the initial peripheral blood culture grew <20 cfu/mL. Infants with sepsis, including those with colony counts of ≤50 cfu/mL, were significantly more likely to have a central catheter or an abnormal hematologic value or both (P < .05). Infants who lacked these clinical features were more likely to have contamination. We conclude that quantitative blood cultures in conjunction with specific clinical information may distinguish sepsis from culture contamination with coagluase-negative staphylococci in young infants. In addition, low colony-count growth should not be ignored as contamination in this high-risk population.