China is thought to be a hotspot for zoonotic influenza virus emergence, yet there have been few prospective studies examining the occupational risk of such infections.
We present the first two years of data collected from a five-year, prospective cohort study of swine-exposed and unexposed participants, pigs, and six swine farms in China. We conducted serological and virological surveillance to examine evidence for swine influenza A virus infection in humans.
Two hundred and seven (31.5%) of the 658 participants (521 swine-exposed and 137 unexposed), enrolled at any time period, seroconverted against at least one SIV subtype (swine H1N1 or H3N2). Swine-exposed participants´ microneutralization titers, especially those enrolled at confined animal feeding operations (CAFOs), were higher against the swine H1N1 virus than were other participants at 12 and 24 months. Despite elevated titers, among the 187 study subjects for whom we had complete follow-up, participants working at swine CAFOs had significantly greater odds of seroconverting against both swine H1N1 (OR 19.16; 95% CI 3.55, 358.65) and swine H3N2 (OR 2.97; 95% CI 1.16, 8.01) viruses compared to unexposed and non-CAFO swine workers with less intense swine exposure.
While some of the observed increased risk against swine viruses may have been explained by exposure to human influenza strains, study data suggest that even with elevated preexisting antibodies, swine-exposed workers are at high risk of infection with enzootic swine influenza A viruses.