A network-based surveillance approach to assess MRSA epidemiology in NICU, Palermo, Italy

Background Methicillin resistant Staphylococcus aureus (MRSA) is a major causal agent of infection in neonatal intensive care units (NICUs). Colonized neonates generally act as a reservoir fuelling cross transmission within/between NICUs. Methods Since February 2014 a network surveillance study is performed in five NICUs in Palermo, Italy, including the NICU of the teaching University hospital (NICU1) where a five-year long surveillance program is in place. The aim of our study was to assess MRSA colonization frequency and to describe local epidemiology. Nasal swabs were collected at four week-intervals and cultured on selective media. MRSA were typed by Multi Locus Variable Number Tandem Repeat Fingerprinting (MLVF), PCR for tst-1 and pvl genes, SCCmec characterization, MultiLocus Sequence Typing (MLST). Prevalences was compared by statistical methods. Results Mean yearly MRSA colonization prevalences were as follow: NICU1, 6.0 %, NICU2, 11.7%, NICU3, 3.1%, NICU4, 25.1%, NICU5, 26.0%. Prevalences significantly differed between NICUs. A tst1- positive ST22-MRSA-IVa strain was predominant in all NICUs, accounting for 68% (NICU4) to 95% (NICU1) of MRSA isolates. Of interest, ST217-MRSA-IVh, ST1-MRSA IVa, ST5-MRSA-IVg and pvl positive ST80-MRSA-IVa were also detected. Most MRSA strains were shared between at least two NICUs. Conclusions Prevalences of MRSA colonization in the five NICUs under study were high, but significantly different. UK-EMRSA-15/ ‘‘Middle Eastern Variant’’ confirmed to be endemic in our NICUs. Moreover, transfer of neonates was epidemiologically linked to spread of some MRSA isolates within NICUs, supporting the need of a network-based surveillance approach. Main Messages A network-based surveillance approach can be a helpful tool to understand local epidemiology of MRSA. Further investigations will clarify the cross transmission routes within NICUs.