Frequency-risk and duration-risk relations between occupational livestock contact and methicillin-resistant Staphylococcus aureus carriage among workers in Guangdong, China

Increasing evidence indicates a strong association between occupational livestock contact and methicillin-resistant Staphylococcus aureus (MRSA) carriage. However, it remains unclear whether there are frequency-risk and duration-risk relations between occupational livestock contact and human MRSA carriage.

A cross-sectional survey was conducted in Guangdong, China, using a multistage sampling method. Participants were interviewed and provided a nasal swab for S aureus analysis. All MRSA isolates were genotyped by multilocus sequence typing. The dose-response relation was examined using logistic regression models.

Among the 1,860 participants, 1.4% of controls tested positive for MRSA (characterized as sequence type [ST] 59 and ST7), and 7% of workers with livestock contact tested positive for MRSA (characterized as ST9, ST59, and ST7). There was a 5.31 times increased risk of MRSA carriage corresponding to occupational livestock contact (odds ratio = 6.31; 95% confidence interval, 3.44-11.57) using no contact as reference. We found frequency and short-term duration of occupational livestock contact were associated with increased risk of MRSA carriage in a dose-response manner. These significant trends were observed consistently among workers with occupational pig contact. However, no long-term duration-risk increasing trend was observed for occupational livestock or pig contact.

Our findings suggest that there may be dose-response relations between occupational livestock contact and human MRSA carriage. Nasal MRSA clonal complex 9 is not found in controls, but it is found in workers with livestock contact.