In our NICU over 70% of all nosocomial infections are caused by CONS, with an incidence of 10% over the past 10 years. Risk factors are prematurity, low birth weight and central venous catheters (CVC's), with an incidence of 14 CONS septicemias/1000 CVC-days. During the last few years increasing methicillin-resistance among CONS blood isolates has been observed, which has led to increased usage of vancomycin. The sources of these CONS infections are unknown. Recently we have conducted a molecular epidemiologic study of CONS isolates from our NICU during a period of 10 weeks, including 9 blood isolates from 7 neonates with septicemia. Swabs from throat and skin of 53 neonates and swabs from nose and hand of 60 members of the medical and nursing staff and samples of the air of the unit were collected weekly. Molecular typing was performed by RAPD (random amplification of polymorphic DNA). Among 282 CONS isolates included in the study 41 different RAPD-types could be distinguished. The 9 blood isolates yielded 7 RAPD-types, which belonged to the most common RAPD-types found in the NICU. Determination of methicillin-resistance by detecting mec A gene carriage by targeted PCR among CONS isolates revealed that 26% of air isolates, 39% of the staff isolates and 76% of the neonatal isolates (blood isolates 78%) were mec A positive. This increasing mec A gene carriage can be explained by antibiotic dependent selection.
Conclusions: 1. No distinct source of coagulase-negative staphylococci was found. 2. Prevalence rate of certain CONS-types within the NICU environment seemed an important risk factor for CONS septicemia. 3. Increasing mec A gene carriage of CONS isolates was found from environment to bloodstream, possibly due to antibiotic dependent selection.
