Livestock associated MRSA - Tiger or Pussycat?

A novel lineage (ST398) of MRSA was first recognized in Holland in 2003. The high prevalence of colonization seen in animals, initially pigs and later other species, raised concerns about a new reservoir of community acquired MRSA infections, and possibly foodborne exposure. The ST398 lineage of organisms has subsequently been identified in livestock and people in many countries, including cases of clinical infection some of which have been severe and fatal. An extensive review was conducted of published reports of ST398 clinical infections, recording when available details of clinical severity, methicillin resistance and previous exposure to animals. As of January 2012, 396 clinical cases were identified of which 75 were deemed invasive including 5 fatal cases. Four of the 5 fatal cases were associated with methicillin sensitive spa type t571 isolates, and had no history of livestock exposure. This spa type is relatively uncommon in animal isolates. The sole fatal case of ST398 MRSA involved an elderly medically compromised individual. Apart from infected bite wounds, reports of severe infections in otherwise healthy livestock workers are remarkably few given the high frequency of exposure reported. The data suggest that ST398 MRSA have had minor impact as an occupational disease in farm workers, and that livestock are not the sole reservoir of these organisms.