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J Occup Environ Hyg. 2016 Aug;13(8):577-87. doi: 10.1080/15459624.2016.1159688.

Modeling risk of occupational zoonotic influenza infection in swine workers.

Author information

1
a Occupational and Environmental Medicine Program , Yale University , New Haven , Connecticut.
2
b Division of Environmental and Occupational Health Sciences, School of Public Health , University of Illinois at Chicago , Chicago , Illinois.
3
c Department of Environmental Health , School of Public Health-Bloomington, Indiana University , Bloomington , Indiana.
4
d Department of Biostatistics , Yale School of Public Health, Yale University , New Haven , Connecticut.
5
e Veterinary Population Medicine Department , College of Veterinary Medicine, University of Minnesota , St. Paul , Minnesota.
6
f Department of Environmental and Occupational Health Sciences, Department of Global Health , University of Washington School of Public Health , Seattle , Washington.

Abstract

Zoonotic transmission of influenza A virus (IAV) between swine and workers in swine production facilities may play a role in the emergence of novel influenza strains with pandemic potential. Guidelines to prevent transmission of influenza to swine workers have been developed but there is a need for evidence-based decision-making about protective measures such as respiratory protection. A mathematical model was applied to estimate the risk of occupational IAV exposure to swine workers by contact and airborne transmission, and to evaluate the use of respirators to reduce transmission.  The Markov model was used to simulate the transport and exposure of workers to IAV in a swine facility. A dose-response function was used to estimate the risk of infection. This approach is similar to methods previously used to estimate the risk of infection in human health care settings. This study uses concentration of virus in air from field measurements collected during outbreaks of influenza in commercial swine facilities, and analyzed by polymerase chain reaction.  It was found that spending 25 min working in a barn during an influenza outbreak in a swine herd could be sufficient to cause zoonotic infection in a worker. However, this risk estimate was sensitive to estimates of viral infectivity to humans. Wearing an excellent fitting N95 respirator reduced this risk, but with high aerosol levels the predicted risk of infection remained high under certain assumptions.  The results of this analysis indicate that under the conditions studied, swine workers are at risk of zoonotic influenza infection. The use of an N95 respirator could reduce such risk. These findings have implications for risk assessment and preventive programs targeting swine workers. The exact level of risk remains uncertain, since our model may have overestimated the viability or infectivity of IAV. Additionally, the potential for partial immunity in swine workers associated with repeated low-dose exposures or from previous infection with other influenza strains was not considered. Further studies should explore these uncertainties.

KEYWORDS:

Infection risk model (influenza infection risk assessment); influenza A virus; mask protection; occupational exposure; personal protective equipment; swine

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