Prevalence and characteristics of community carriage of methicillin-resistant Staphylococcus aureus in Malta

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. Malta is one of the countries with the highest MRSA prevalence in Europe, as identified from hospital blood cultures (1). However, community preva- lenceofMRSAhasneverpreviouslybeeninvestigated.Thisstudyaimedatestablishing the prevalence of community MRSA nasal colonization in Maltese individuals and iden- tifying the clonal characteristics of the detected isolates. Nasal swabs were collected from 329 healthy individuals who were also asked to complete a brief questionnaire about risk factors commonly associated with MRSA carriage and infection. The swabs were transported and enriched in a nutrient broth supplemented with NaCl. The pres- ence of MRSA was then determined by culturing on MRSA Select chromogenic agar and then confirming by several assays, including catalase, coagulase and PBP2a agglutina- tiontests.Theisolateswereassayedforantibioticsusceptibilitiesandtypedbymicro- arrayanalysistodeterminetheclonalcharacteristicsofeachstrain.Theprevalenceof MRSA nasal colonization in the healthy Maltese population was found to be 8.81% (95% confidence interval (CI), 5.75-11.87%), much higher than that found in other studies carried out in several countries. No statistical association was found between MRSA carriage and demographics or risk factors; however, this was hindered by the small sample size. Almost all the isolates were fusidic-acid resistant. The majority were found to belong to a local endemic clone (CC5) which seems to be replacing the pre- viously prevalent European clone UK-EMRSA-15 in the country. A new clone (CC50- MRSA-V) was also characterized. The presence of such a significant community reser- voir of MRSA increases the burdens already faced by the local healthcare system to control the MRSA epidemic. Colonization of MRSA in otherwise healthy individuals may represent a risk for endogenous infection and transmission to hospitalized