Association between biosecurity and zoonotic transmission of LA-MRSA CC398 from industrial pig farms to farm workers and their household members.

Abstract

Background: Zoonotic transmission of livestock-associated methicillin-resistant Staphylococcus aureus clonal complex 398 (LA-MRSA CC398) from industrial pig farms to farm workers and their household members and secondary transmission to elderly and immunocompromised persons has led to a growing number of serious infections and even death.

Objective: We tested the hypothesis that conventional pig farms confer a higher risk for LA-MRSA CC398 carriage among farm workers and their household members than specific pathogen-free (SPF) farms, which follow a set of stringent rules concerning biosecurity, health control and transportation of pigs between herds.

Methods: We conducted a cross-sectional study of farm workers and their household members from 25 Danish pig farms positive for LA-MRSA CC398. Questionnaires were designed to obtain information about each farm and participant. Nasal samples from pigs and human volunteers were screened for LA-MRSA CC398. Multivariate logistic regression analyses were used to calculate adjusted ORs (aORs) and 95% CIs.

Results: The study included 25 pig farms, 154 farm workers screened at the farm (93 of whom were also screened at home) and 173 household members. The risk of LA-MRSA CC398 carriage among farm workers at the farm (aOR=5.40, 95% CI 1.05 to 27.80) and household members (aOR=8.32; 95% CI 2.81 to 24.63) was significantly higher in conventional pig farms than in SPF farms.

Conclusions: This study shows that strict biosecurity measures reduce the risk of LA-MRSA CC398 carriage among farm workers and their household members and thereby the disease burden in the general population.