Objective: To report the identification and control of a GR-MSSA outbreak that affected 19 babies on a 36-bed NNU.

Methods: The outbreak was recognised in November 2007. Control measures included admission and weekly screening for GR-MSSA, cohorting of affected babies, environmental and staff screening, hydrogen peroxide vapour (HPV) decontamination for terminal disinfection of cohort bays, and reinforcement of hand hygiene. The outbreak strain was characterised by automated antimicrobial susceptibility testing, spa typing, pulsed-field gel electrophoresis (PFGE) and PCR for a range of toxin genes.

Results: Nineteen babies were affected from August 2007 – April 2008; 32% were bacteraemic and 68% were asymptomatic carriers. New acquisitions were associated in space and time with known cases. The outbreak strain was gentamicin-resistant, variably penicillin-resistant, t084, Panton-Valentine Leukocidin negative and all isolates were indistinguishable by PFGE. None of the 113 staff members tested were colonised with GR-MSSA. GR-MSSA was cultured from 8.5% of 189 environmental surfaces including 7.1% of 28 communal surfaces and 4.1% of 74 surfaces after terminal cleaning; none of the 64 surfaces sampled after HPV yielded GR-MSSA. Nine MSSA bacteraemias occurred in 2007, five of which were due to GR-MSSA compared with a mean of 1.8 cases per annum from 1998-2006 (range 0-5, 3 in 2006).

Conclusions: This strain of GR-MSSA appeared to be more transmissible than other MSSA in the NNU and had a high rate of invasive infection. The molecular mechanisms underlying these characteristics warrant further investigation. In this outbreak occasional breakdown in hand-hygiene compliance and contaminated environmental surfaces probably contributed to transmission.