A prevalence study on carriage of methicillin-resistant Staphylococcus aureus in a Finnish nursing home

Abstract number: 1134_02_183

Kerttula A.-M., Lyytikäinen O., Virolainen-Julkunen A., Finne-Soveri H., Agthe N., Vuopio-Varkila J.

Objectives:

Due to the increasing problem of MRSA in Finnish long-term care facilities, we carried out a prevalence study in the largest nursing home in Helsinki metropolitan area. Of the residents, 76 % were females, the mean age was 83 years and 62% suffered from dementia. The objective was to study MRSA colonization rate in such setting. In addition, the role of screening sites, and use of broth enrichment culture on sensitivity to detect S. aureus was analysed.

Methods:

Of the 25 available wards, 9 such wards were chosen, where at least one of the residents had either indwelling catheter or open skin lesions but no previously known MRSA contacts. The patients volunteered had their nostrils, throats, perineums, skin lesions, and catheter exit sites swabbed, and catheter urines cultured. The specimens were cultured onto the non-selective (blood) and selective (ORSAB) agar, with or without enrichment in salt-containing trypticase soy broth (TSB). S. aureus was identified by routine methods and methicillin-resistance detected by oxacillin disk diffusion, and MIC E-tests, GenoType MRSA^® -test (Hain Lifescience, Germany) was used for MRSA confirmation. MRSA genotypes were characterized by pulsed-field gel electrophoresis (PFGE).

Results:

Total of 663 specimens (210 from nostrils, 197 throats, 207 perineums, 24 skin lesions, 9 catheter exit sites, and 16 from catheter urines) were obtained from 213 patients. 165 samples (25%) from 94 patients (44%) were positive for S. aureus, and three samples (0.4%) from two (0.9%) patients were positive for MRSA. Two different MRSA strains were found; a non-multiresistant MRSA strain from the perineum of one patient and a multidrug-resistant strain both from the nostrils and catheter exit site of another, respectively. Of 165 S. aureus isolates, 26 (16%) were found only from other sites than nostrils (25 MSSA, and 1 MRSA from a total of 25 patients). TSB enrichment detected an additional 29 (4 %) S. aureus isolates (28 MSSA, and 1 MRSA).

Conclusions:

Carriage of S. aureus was high but prevalence of MRSA low in this long term care facility setting. Omission of surveillance sampling sites other than nostrils would have missed 12% (24 MSSA and one MRSA case) of S. aureus carriers. Addition of the broth enrichment step resulted in finding 7 (3%) additional S. aureus-positive carriers.