Trends in the occurrence of MRSA strains in Upper Austria in a 4year time period

Abstract number: P1065

Krziwanek K., Metz-Gercek S., Mittermayer H.

Objectives: The project "MRSA-Registry Upper Austria" exists since 2006 and aims to systematically collect and analyse data of all human MRSA-isolates which are detected in Upper Austria. All 9 Upper Austrian laboratories and 22 Upper Austrian hospitals take part in this project. In this study we investigated the trends in the occurrence of MRSA types and subtypes in Upper Austria within a time period of 4 years.

Methods: From January 2006 until October 2009 we received all consecutively collected primary clinical MRSA-isolates. All isolates were cultured and investigated for the presence of mecA/femA as well as for the PVL genes lukS-lukF via PCR. All isolates were typed using PFGE, the bigger part of the isolates were additionally investigated by spa-typing and MLST (multi locus sequence typing).

Results: We received 1,436 human primary MRSA isolates. The isolate number was slightly decreasing over the years (2006 n = 461, 2007 n = 374, 2008 n = 385, Jan-Oct 2009 n = 216). 29 different MRSA types were detected using PFGE as well as MLST. Both techniques showed that the 4 most frequent strains comprised 83% of all isolates: ST8 34%, ST5 32%, ST22 11% and ST228 6%. Within these MRSA types we recognised predominant PFGE-subtypes. Interestingly, these PFGE- and MLST-types as well as the predominant subtypes remained similar frequent throughout the 4 years. Investigating about 17% of all isolates by spa typing, we detected 61 different spa-types. Also, the main spa-types – t008, t190 (mostly CC8/ST8), t002, t003 (mostly CC5/ST5), t001, t041 (mostly CC5/ST228) – remained the dominant types throughout the described time period. The proportion of PVL-positive isolates, especially those belonging to ST8, increased since 2007 (2006 8.0%, 2007 5.6%, 2008 6.2%, 2009 11.1%). Most of the PVL-positive isolates belonged to ST8 (n = 21, 15 isolates thereof were USA300), ST152 (n = 21), ST5 (n = 18), ST777 (n = 11) and ST88 (n = 10).

Conclusions: The MRSA population in Upper Austria is not as dynamic as probably expected. No matter which typing method was used, the predominant MRSA strains as well as subtypes remained to be the most frequent ones throughout the last 4 years and were not replaced by minor clones. The increase of PVL-positive isolates since 2007 is partly a consequence of the occurrence of USA300 in Austria. Our data suggest to continue MRSA surveillance with an additional focus on community associated MRSA.