Outbreak report of investigation and control of an outbreak of Panton-Valentine Leukocidin-positive methicillin-sensitive Staphylococcus aureus (PVL-MSSA) infection in neonates and mothers

BACKGROUND: In January 2011, there was an outbreak of Panton-Valentine Leukocidin-positive methicillin-sensitive Staphylococcus aureus (PVL-MSSA) infection in a neonatal unit (NNU). We describe the investigation and control of an outbreak of PVL-MSSA infection in neonates. Setting: Neonatal unit in West London. METHODS: We performed descriptive and analytical (case-control study) epidemiological investigations. Microbiological investigations including screening of MSSA isolates by PCR for the presence of the luk-PV, mecA and mecC genes and comparison of isolate with Pulsed field gel electrophoresis (PFGE). Control measures were also introduced. RESULTS: Sixteen babies were infected/colonised with the outbreak strain. Of these, one baby developed blood stream infection, 12 developed skin pustules and four babies were colonised. Four mothers developed breast abscesses. Eighty-seven babies in the unit were screened and 16 were found to have same PVL-MSSA strain (spa type t005, belonging to MLST clonal complex 22). Multivariate analysis showed gestational age was significantly lower in cases compared to controls (mean gestational age: 31.7 weeks v 35.6 weeks; P = 0.006). Length of stay was significantly greater for cases, with a median of 25 days, compared to only 6 days for controls (P = 0.01). Most (88%) cases were born through caesarean section, compared to less than half of controls. (P = 0.002). No healthcare worker carriers and environmental source was identified. The outbreak was controlled by stopping new admissions to unit and reinforcing infection control precautions. The outbreak lasted for seven weeks. No further cases were reported in the following year. CONCLUSIONS: Infection control teams have to be vigilant for rising prevalence of particular S. aureus clones in their local community as they may cause outbreaks in vulnerable populations in healthcare settings such as NNUs.