Livestock associated MRSA (LA-MRSA) and its relevance for humans in Germany

Livestock-associated Staphylococcus aureus (LA-MRSA) are mainly associated with the clonal complex (CC) 398. Although having its main reservoir as MRSA in livestock such as pigs, poultry or cattle LA-MRSA CC398 has no pronounced host specificity and can colonize or infect other animals such as horses and dogs and also humans. In German conventional farming systems nasal colonization of the animals and of humans occupationally exposed to them (up to 86%) are frequent. Further human-to-human dissemination in households occurs more rarely in general (∼4% of humans living on farms but without occupational exposition). Nasal colonization with LA-MRSA of humans at hospital admission is found in 0.08-0.2% for Germany in general. However, this proportion is higher in areas with a high density of livestock production such as in northwestern North Rhine-Westphalia or Lower Saxony. LA-MRSA CC398 is not less pathogenic for humans than S. aureus in general. Hence, LA-MRSA accounts for ∼15% of all MRSA isolates from deep-seated skin and soft-tissue infections in the community and for about 0.8-2% of all MRSA isolated from clinical specimens obtained in hospital settings. When introduced into the hospital it can cause postoperative wound infections and even septicemia. Differently from hospital-associated MRSA clones, LA-MRSA CC398 has obviously limited capacity to spread in the nosocomial setting so far (proportion of ∼1.8% among MRSA from nosocomial infections, the proportion among MRSA from blood cultures is ∼1%).