Objectives: Community-associated Staphylococcus aureus (CA-MRSA), especially Panton-Valentine leukocidin (PVL) producing strains, raises concern world wide. We estimated the proportion of CA-MRSA in Finland, and incidence and type of clinical CA-MRSA infections were studied. In addition, the strain types of MRSA isolates obtained in persons with and without hospital contact were compared.
Methods: We analyzed previous hospitalizations for all MRSA-positive persons during 2004-2006 (n=4030) by using data from the National Hospital Discharge Register. MRSA isolate was defined as community-associated if MRSA specimen was obtained outside hospital settings or within two days of hospital admission from a person who had not been hospitalized within two years before a positive MRSA culture. For persons without hospitalizations, additional background information was obtained by a questionnaire survey. The isolates were characterized for genotype, and presence of PVL genes.
Results: A total of 298 (7%) persons had CA-MRSA; 192 (64%) had clinical infection (average annualized incidence 1.2/100.000), 81% of which were skin and soft tissue infections. No bacteriemias or deaths were reported. Two old and 5 new strain types and 25 sporadic strains were associated with community acquisition. Of all CA-MRSA isolates, 89 (30%) were PVL positive, including 11/25 sporadic strains and 3 of the new strain types. Infections caused by PVL positive isolates were more often associated with abscesses, need for surgery and systemic antimicrobial treatment than infections caused by PVL-negative isolates.
Conclusions: CA-MRSA strain types were divergent. Although majority of CA-MRSA infections were mild, PVL positivity among news strain types and sporadic strains may pose emerging threat.