Human MRSA CC398, Finland, Table 1 | CDC EID

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Volume 16, Number 10–October 2010
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Human Cases of Methicillin-Resistant Staphylococcus aureus CC398, Finland

Saara Salmenlinna Comments to Author, Outi Lyytikäinen, Anni Vainio, Anna-Liisa Myllyniemi, Saara Raulo, Mari Kanerva, Merja Rantala, Katariina Thomson, Jaana Seppänen, and Jaana Vuopio
Author affiliations: National Institute for Health and Welfare, Helsinki, Finland (S. Salmenlinna, O. Lyytikäinen, A. Vainio, J. Vuopio); Finnish Food Safety Authority, Helsinki (A.-L. Myllyniemi, S. Raulo, J. Seppänen); Helsinki University Central Hospital, Helsinki (M. Kanerva); and University of Helsinki, Helsinki (M. Rantala, K. Thomson)

Suggested citation for this article

Abstract
Animals may serve as a reservoir for methicillin-resistant Staphylococcus aureus (MRSA). The MRSA lineage clonal complex (CC) 398 has been reported to be common among pigs (1–3) and has also been found among other animal species. Occupational exposure to animals has been recognized as a new risk factor for MRSA (4,5). In Finland, MRSA has occasionally been detected in pets and farm animals. MRSA CC398 was first recognized in Finland in 2007 and involved a veterinary hospital epidemic of 13 horses and 1 employee. Since then, MRSA CC398 has also appeared in other persons and has been found in pig samples. The objective of this study was to recognize possible connections of emerging MRSA CC398.

The Study

Nationwide surveillance of MRSA in Finland, including notification for human cases and isolate characterization, was started in 1995 (6). From 1995 through April 2009, a total of 10,615 nonduplicate human isolates of MRSA were typed by using pulsed-field gel electrophoresis (PFGE); 1 in 2007, 6 in 2008, and 3 in 2009 (n = 10, 0.09%) were nontypable, a typical feature of MRSA CC398 isolates (7). Samples of animal origin are usually investigated clinically and through official surveys. No systematic national MRSA surveillance for animals exists, but it is possible to send suspected isolates for confirmation. After the horse epidemic in 2007, some admission screening of animals started at the veterinary hospital where the epidemic occurred. From January 2007 through April 2009, a total of 35 animal MRSA isolates were typed by PFGE; 20 (57%) were nontypable.

For this study, all human and animal isolates of MRSA nontypable by SmaI PFGE were further analyzed by testing antimicrobial drug susceptibility against 14 different antimicrobial drug groups, typing the ccr and mec complex regions within the staphylococcal cassette chromosome mec (SCCmec) by PCR (8), detecting the presence of Panton-Valentine leukocidin (PVL) genes (9), spa typing, and PFGE by using ApaI as the restriction endonuclease. ApaI PFGE was performed as described (10), except that the restriction digestion was performed with ApaI at 30°C for 4 h, and initial and final switching times of 5 s and 15 s, respectively, were used for a 20-h PFGE run. Multilocus sequence typing (MLST) (11) was performed on representative isolates of each different combination of origin (human vs. animal species), spa type, and SCCmec.

For persons whose MRSA isolate was nontypable by SmaI PFGE, a structured questionnaire was used to inquire about the presence of commonly known healthcare-related risk factors for MRSA (online Technical Appendix, www.cdc.gov/EID/content/16/10/1626-Techapp.pdf). These data were collected from infection control nurses at relevant healthcare districts or directly from patients by telephone interview.

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Human MRSA CC398, Finland, Table 1 | CDC EID

Suggested Citation for this Article

Lyytikäinen O, Vainio A, Myllyniemi A-L, Raulo S, Kanerva M, et al. Human cases of methicillin-resistant Staphylococcus aureus CC398 infection, Finland. Emerg Infect Dis [serial on the Internet]. 2010 Oct [date cited]. http://www.cdc.gov/EID/content/16/10/1626.htm

DOI: 10.3201/eid1610.091571