Serologic survey of swine workers for exposure to H2N3 swine influenza A

Of the 16 influenza A hemagglutinin (H) subtypes, only H1, H2 and H3 viruses have been shown to cause sustained human infection. Whereas H1 and H3 viruses currently circulate seasonally in humans, H2 viruses have not been identified in humans since 1968. In 2006, an H2N3 influenza virus was isolated from ill swine in the United States. Objective: To assess the potential for zoonotic influenza transmission, the current study looked for serologic evidence of H2 influenza infection among workers at two swine facilities, some exposed and some unexposed to H2N3-positive pigs. Methods: The sera were assessed for antibodies to swine H2 influenza and currently circulating seasonal human influenza A subtypes H1N1 and H3N2. Workers were interviewed to obtain details such as age, influenza vaccination history, experiences of influenza-like-illness, and use of personal protective equipment and hygiene when working with pigs. Exposure and risk factors for positive antibody titers were compared for exposed and unexposed individuals as well as for H2 antibody-positive and H2 antibody-negative individuals. Results: Blood was taken from 27 swine workers, of whom four had positive H2 antibody titers (≥1:40). Three of the positive employees were born before 1968 and one had an unknown birth date. Only one of these workers had been exposed to H2N3-positive pigs, and he was born in 1949. Conclusions: These data do not support the hypothesis that swine workers were infected with the emergent swine H2N3 influenza A virus.