The Role of Molecular Typing in the Epidemiologic Investigation and Control of Nosocomial Infections

Abstract

In September 2001 4 patients in the neonatal intensivecare unit (NICU) were culture-positive for methicillinresistant Staphylococcus aureus (MRSA) and this prompted an epidemiologic investigation. Initial screening of all 28 babies and 236 healthcare workers (HCWs) in the NICU demonstrated MRSA colonization of 11 additional infants and 6 HCWs. An enhanced infection control program was introduced. This included weekly nasal surveillance cultures of all NICU patients, cohorting and strict contact isolation of MRSA-positive babies, and introduction of a waterless hand hygiene gel. Designated HCWs cared for MRSA-positive babies. All staff underwent intensive reeducation. Molecular typing of the MRSA isolates revealed 3 MRSA clones (A, B, and G) in neonates and 6 MRSA clones (A-F) in HCWs. Transmission of the initial MRSA clone A was controlled 3 weeks after starting weekly surveillance cultures. Typing of subsequent MRSA isolates was suggestive of repeated reintroduction of different MRSA clones from the adjacent adult hospital. Further spread of these MRSA clones was controlled within 1 to 5 weeks. This experience demonstrates the benefit of active surveillance cultures and molecular typing as part of a comprehensive program to manage the spread of MRSA and limit infections from this important hospital pathogen.