Livestock-associated Methicillin-Resistant Staphylococcus aureu s in Humans, Europe

Abstract

To estimate the proportion of methicillin-resistant Staphylococcus aureus (MRSA) isolates from humans that were sequence type (ST) 398, we surveyed 24 laboratories in 17 countries in Europe in 2007.Livestock-associated MRSA ST398 accounted for only a small proportion of MRSA isolates from humans; most were from the Netherlands, Belgium, Denmark, and Austria.L ivestock-associated methicillin-resistant Staphylo- coccus aureus (MRSA) was fi rst associated with human disease in 2003, when a MRSA clone associated with a reservoir in pigs and cattle was isolated from a human.This clone was not typable by pulsed-fi eld gel electrophoresis with SmaI macrorestriction digestion and belonged to multilocus sequence type (ST) 398 (1).Since then, rates of MRSA ST398 carriage have been high (25%-35%) for persons in the Netherlands who have frequent contact with pigs and veal calves, but associated illness is rare (2).However, in Europe, Asia, and the United States, invasive infections and a hospital outbreak of MRSA ST398 have been reported (3).We estimated the proportion of MRSA isolates from humans in Europe in 2007 that were ST398. The StudyQuestionnaires were mailed to 43 laboratories in 23 European countries, selected on the basis of expertise and publications about MRSA.Questions asked for level of laboratory and typing methods used, number of MRSA isolates identifi ed in 2007, number of these isolates that were typed, and number of typed isolates that were MRSA ST398.MRSA isolates were considered to be ST398 if they 1) belonged to multilocus ST398, 2) were spa types t011, t034, t108, t567, t571, t588, t753, t898, t899, t1184, t1254, t1255, t1451, t1456, t1457, t2123, t2330, t2383, t2582, or t3013 (4; National Institute for Public Health and the Environment, unpub.data); or 3) were not typable by pulsed-fi eld gel electrophoresis with SmaI macrorestriction digestion.Laboratories were asked to report data on clinical isolates only (as opposed to screening isolates) and to provide the distribution by body site.For each laboratory, the proportion of MRSA ST398 among all typed MRSA isolates from humans and the 95% Wilson confi dence interval (CI) were calculated.For laboratories that typed all MRSA isolates, χ 2 testing compared proportions of isolates from various body sites for MRSA ST398 isolates and for other MRSA isolates.For each country, we compared the proportions of MRSA ST398 among human MRSA isolates with number of pigs per km 2 , number of cattle <1 year of age (a surrogate for veal calves) per km 2 , and 2 indices multiplying these animal densities with human population densities.