BACKGROUND: This study reports on the prevalence of coagulase-negative staphylococci (CNS) on the hands of nurses, specifically large numbers of Staphylococcus warneri, and the clinical relevance of this organism among neonates in two neonatal intensive care units (NICUs).

METHODS: A total of 119 full-time nurses were recruited from two high-risk NICUs in New York City. Hand cultures from nurses were obtained at baseline and on a quarterly basis from March 2001 to January 2003. Data regarding healthcare-associated infections (HAIs) were collected prospectively on all neonates admitted during the same study period. All samples were analyzed to identify bacterial growth and antimicrobial susceptibilities. Vancomycin minimum inhibitory concentrations (MICs) of S. warneri from nurse hand cultures were determined by E-test. Pulsed-field gel electrophoresis (PFGE) was used to compare S. warneri isolates of neonates and staff.

RESULTS: A total of 834 hand cultures were obtained from the nurses; 1195/1442 (83%) isolates were CNS. The majority of nurse CNS isolates were S. epidermidis (n=524, 44%) and S. warneri (n=520, 44%). As detected by E-test, decreased susceptibilities to vancomycin (MIC >2) were demonstrated by 117 (23%) of S. warneri isolates recovered from nurse hands. A total of 647 clinical isolates were recovered from neonates, 221 (34%) were CNS species, with 202 (91.4%) available for analysis. Seventeen neonates (8%) had HAIs caused by S. warneri, including 15 bloodstream infections, one skin infection, and one eye infection. Thirteen of 15 (87%) neonatal blood isolates were available for molecular typing; four (31%) were indistinguishable from each other (PFGE designated clone A) and eight (61%) were related (clone A1-A2a). Eighteen isolates from nurses who provided direct patient care to six of the neonates were typed; 5/6 (83%) of neonates had a strain (clone A-A2a) indistinguishable or related to the nurse caregiver.

CONCLUSIONS: S. warneri is commonly carried on the hands of healthcare workers but is an uncommon cause of neonatal infection, despite clonal spread within a NICU. Our finding of decreased vancomycin susceptibilities among S. warneri strains, underscores the need for continued surveillance for vancomycin resistance. Further research is warranted to determine if S. warneri is emerging as a pathogen associated with HAI and whether the decreased susceptibilities of vancomycin were causally related to our findings.