Coagulase-Negative Staphylococcal Bacteremia Among Very Low Birth Weight Infants: Relation to Admission Illness Severity, Resource Use, and Outcome

¹ Joint Program in Neonatology (Brigham and Women's Hospital, Children's Hospital, Beth Israel Hospital, and Harvard Medical School), Boston, MA
² Joint Program in Neonatology (Brigham and Women's Hospital, Children's Hospital, Beth Israel Hospital, and Harvard Medical School), Department of Maternal and Child Health, Harvard School of Public Health, Boston, MA
³ Hospital Epidemiology Program (Children's Hospital and Harvard Medical School), Boston, MA

Objective. To examine the impact of admission-day illness severity on nosocomial bacteremia risk after consideration of traditional risk determinants such as birth weight and length of stay.

Methods. The hospital courses for 302 consecutive very low birth weight (less than 1500 g) infants admitted to two neonatal intensive care units were examined for the occurrence of nosocomial coagulase-negative staphylococcal bacteremia. Using both cumulative incidence and incidence density as measures of bacteremia risk, we explored the relation between illness severity (as measured by the Score for Neonatal Acute Physiology [SNAP]) and bacteremia both before and after birth weight adjustment. In addition, the effect of bacteremia on hospital resource use was estimated.

Results. Coagulase-negative staphylococcus was the most common pathogen noted in blood cultures drawn at 48 hours after admission or later. It was isolated on at least one occasion in 53 patients (cumulative incidence of 17.5 first episodes per 100 patients). These episodes occurred during 7652 days at risk, giving an incidence density of 6.9 initial bacteremias per 1000 patient-days at risk. As expected, when compared with the nonbacteremic group, bacteremic patients were of lower birth weight (888 ± 231 vs 1127 ± 258 g; P < .01) and gestational age (26.4 ± 2.1 vs 28.9 ± 2.8 weeks; P < .01). In addition, these patients were more severely ill on admission (SNAP 17.3 ± 6.5 vs 12.2 ± 5.8; P < .01). Even after birth weight stratification, the risk of bacteremia by both measures increased with higher SNAP scores. For example, among infants with birth weights greater than 1 kg, 25% of the most severely ill patients (SNAP 20 and higher) experienced at least one bacteremic episode, whereas the rates seen in infants with intermediate (SNAP 10 to 19) and low illness severity (SNAP 0 to 9) were 8.6% and 3.0%, respectively (² for trend = 7.25; P < .01). Multivariate linear regression showed that bacteremia was associated with a prolongation of neonatal intensive care unit stay of 14.0 ± 4.0 days (P < .01) and an increase in hospital charges of $25 090 ± 12 051 (P < .05), even after adjustment for birth weight and admission-day SNAP.

Conclusions. Nosocomial coagulase-negative bacteremia is an important complication among very low birth weight infants. Assessment of illness severity with SNAP provides information regarding nosocomial infection risk beyond that available from birth weight alone.

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