In this 5-year project, we will compare the rates of self-reported clinical illnesses likely to be related to three zoonotic agents (S. aureus/MRSA; influenza A virus, Hepatitis E virus) in cohorts of swine veterinarians and companion animal veterinarians. Rates of exposure will be compared based on quarterly submission of nasal swabs (S. aureus and influenza), or by collecting three blood samples from the swine vets over the course of the study (Hepatitis E virus). Sampling and survey data collection are conducted quarterly in March, June, September and December each year. None of the 117 participants has withdrawn from the study, and the group has maintained high compliance in sample collection (~ 98%) and survey completion (~95%). Data obtained over the last year are consistent with the earlier years and confirm that the swine veterinarians test positive for S. aureus much more often than the companion animal veterinarians do, and that they are predominantly carrying S. aureus variants of swine origin. For the most recent completed sampling in June 2019, prevalence of S. aureus (72%) and MRSA (12%) in swine veterinarians were again much higher than in the companion animal control group (37% and 2% respectively). The prevalences of S. aureus and MRSA in the companion animal are similar to historic data for the general US population. Although prevalence is higher in the swine veterinarians than the control group, there appears to be no indication of increasing MRSA prevalence in swine veterinarians to date in the course of this study, or compared to our earlier study in 2013/2014.

Based on spa typing of all isolates, about 80% of the swine vet isolates are ‘livestock associated’ variants commonly found in pigs (Figure 1). With one exception, putative livestock variants have not been detected in companion animal vets. One companion animal veterinarian continues to be consistently positive for the ST398/t034 spa type that is most common in pigs and swine veterinarians. We have ascertained that this participant has daily contact with the six horses they own. As ST398 S. aureus (including t034) are known to be relatively common in horses, this is the likely origin of exposure. Serum samples continue to be collected from swine veterinarians for Hepatitis E serology. To date, 114 samples have been obtained, including from 57 of the 69 subjects, and the target of three samples per subject has been attained for 21 veterinarians. Because three more collection events are planned, we anticipate obtaining over 200 samples, including multiple samples from at least 50 participants (currently 36), which should enable reasonable estimation of seroprevalence and incidence of seroconversion to Hepatitis E virus.

We have not confirmed the presence of influenza virus in quarterly nasal swabs submitted for S. aureus culture. Targeted sampling of participants with influenza like symptoms during the winter of 2018/2019 yielded 46 samples for influenza testing, of which four were influenza virus positive. The positive samples are undergoing RNA sequencing for further characterization. This approach will be replicated in the winters of 2019/2020 and 2020/2021. Survey compliance for health events has been excellent (>95%), but interim analysis has not been conducted.

Figure 1: Distributions of S. aureus spa types in June 2019 nasal swab samples of swine veterinarians and companion animal veterinarians (spa types in bold consistent with livestock origin)