Abstract:
Transmission of Influenza A viruses between humans and pigs is associated with
occupational and environmental exposures. The main objective of the study was to
identify the influenza viruses circulating among humans, pigs and poultry and
determine factors associated with acute respiratory illness among pig workers at
household and slaughterhouse levels. The study was conducted in four repeated
cross-sectional studies among humans, pigs and poultry with the household
component conducted in Kiambu county while the slaughterhouse component was
done in Kiambu, Siaya and Kisumu counties. Three participants were randomly
selected in each selected household, while the pigs were sampled proportionate to
herd size. Nasopharyngeal (NP) and Oropharyngeal (OP) swabs were collected from
participants who reported acute respiratory illness (ARI) defined as cough
with/without history of fever within the previous seven days. Nasal swabs and blood
samples were collected from pigs and poultry. The human and animal swab samples
were tested for viral nucleic acid by RT-PCR and animal sera tested by ELISA for
antibodies. Data were collected using an interviewer administered questionnaire and
a logistic generalized linear mixed effect model was implemented to assess the
association between pig exposure and occurrence of ARI within 30 days of sampling.
All study participants gave informed consent and the study obtained ethical approval.
In the household component of the study, 1,267 including 384 (30.3%) pig workers
and 883 (69.7%) non-pig workers were enrolled. Of 130 human NP/OP swabs tested,
four (3.1%) were positive for Influenza A virus. Seroprevalence of animal sera was
6.2% (265/4273), including 11.6% (230/1990) in pigs and 1.5% (25/2283) in poultry.
In the slaughterhouse component of the study, a total of 288 participants were
sampled, 91.3% of them being male. Fifteen (5.2%) participants had ARI but the
nine swabs collected from them were negative for influenza A virus by PCR. Of the
1,128 pigs sampled, five (0.4%) nasal swabs tested positive for influenza
A/H1N1/pdm09 by PCR whereas seroprevalence was 19.8%. The adjusted odds ratio
for the association between pig workers and reporting ARI was 1.12 (95%CI [0.77 –
1.63]) at household level and 0.48 (95%CI [0.24, 0.96]) at slaughterhouse level.
Having a member of the household with an episode of ARI in the previous three
months (3.6 [95%CI 2.28 – 5.68]) and chronic disease (1.96 [95%CI [1.26-3.06])
were associated with reporting ARI on multivariable regression. The study reports
detection of influenza virus (A/H1N1/pdm09) among pigs, a virus associated with
human seasonal influenza. There is need to conduct influenza surveillance among pig
workers and pigs in slaughterhouses as an important early warning system for
influenza related zoonotic events.
