An outbreak of meticillin-resistant Staphylococcus aureus colonization in a neonatal intensive care unit: use of a case-control study to investigate and control it and lessons learnt.

Aim: To describe the investigation and management of a meticillin-resistant Staphylococcus aureus (MRSA) outbreak on a neonatal intensive care unit (NICU) and the lessons learnt.

Methods: This was an outbreak report and case-control study conducted in a 40-cot NICU in a tertiary referral hospital and included all infants colonized/infected with gentamicin-resistant MRSA.

Intervention: Standard infection-control measures including segregation of infants, barrier precautions, enhanced cleaning, assessment of staff practice including hand hygiene, and increased MRSA screening of infants were implemented. Continued MRSA acquisitions led to screening of all NICU staff. A case-control study was performed to assess staff contact with colonized babies and inform the management of the outbreak.

Findings: Eight infants were colonized with MRSA (spa type t2068), one of whom subsequently developed an MRSA bacteraemia. MRSA colonization was significantly associated with lower gestational age; lower birthweight and with being a twin. Three nurses were MRSA colonized but only one nurse (45) was colonized with MRSA spa type t2068. Multivariable logistic regression analysis identified being cared for by nurse 45 as an independent risk factor for MRSA colonization.

Conclusions: Lack of accurate recording of which nurses looked after which infants (and when) made identification of the risk posed by being cared for by particular nurses difficult. If this had been clearer, it may have enabled earlier identification of the colonized nurse, avoiding subsequent cases. This study highlights the benefit of using a case-control study, which showed that most nurses had no association with colonized infants.