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Interspecies transmission of influenza A virus between pigs and people represents a threat to both animal and public health. To better understand the risks of influenza transmission at the human–animal interface, we evaluated 1) the rate of influenza A virus detection in swine farmworkers before and after work during two human influenza seasons, 2) assessed risk factors associated with influenza A virus detection in farmworkers and 3) characterized the genetic sequences of influenza A virus detected in both workers and pigs.
Of 58 workers providing nasal passage samples during 8-week periods during the 2017/18 and 2018/19 influenza seasons, 33 (57%) tested positive by rRT-PCR at least once. Sixteen (27%) workers tested positive before work and 24 (41%) after work. At the sample level, 58 of 1,785 nasal swabs (3.2%) tested rRT-PCR positive, of which 20 of 898 (2.2%) were collected prior to work and 38 of 887 (4.3%) after work. Although farmworkers were more likely to test positive at the end of the working day, there were no influenza-like illness symptoms, or other risk indicators, associated with influenza A virus detection before or after reporting to work. Direct whole-genome sequencing from samples obtained from worker nasal passages indicated evidence of infection of a worker with pandemic 2009 H1N1 of human-origin influenza A virus (H1-pdm 1A 3.3.2) when reporting to work, and exposure of several workers to a swine-origin influenza A virus (H1-alpha 1A 1.1) circulating in the pigs on the farm where they were employed.
Our study provides evidence of 1) risk of influenza A virus transmission between pigs and people, 2) pandemic H1N1 influenza A virus infected workers reporting to work and 3) workers exposed to swine harbouring swine-origin influenza A virus in their nasal passages temporarily. Overall, our results emphasize the need to implement surveillance and transmission preventive protocols at the pig/human interface.
Lopez-Moreno G, Davies P, Yang M, Culhane MR, Corzo CA, Li C, Rendahl A, Torremorell M. Evidence of influenza A infection and risk of transmission between pigs and farmworkers. Zoonoses and Public Health. 2022; 00: 1-12. https://doi.org/10.1111/zph.12948