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Population-based Surveillance for Zoonotic Influenza A (abstract)

We plan to initiate a series of epidemiological studies of zoonotic influenza A with a long term goal of reducing cross-species influenza morbidity. Such cross-species influenza research has been recommended by numerous public health experts including a panel from the Institute of Medicine . In this proposed study of rural Midwestern agricultural workers, our objectives are to determine the prevalence of evidence of previous zoonotic influenza infection, to estimate the incidence of zoonotic influenza infection, and to determine risk factors for zoonotic influenza infection. It is our central hypothesis that zoonotic influenza infection will be relatively frequent among Iowa ’s swine and poultry workers and that we will be able to identify populations at high risk.

We will test our hypotheses by conducting a prospective study of 600 rural Iowans. We will use data from the 90,000-person Agricultural Health Study to identify 450 study subjects who are occupationally exposed to swine and/or poultry, and a gender and age-group matched group of 150 control subjects without such exposures. As influenza activity cannot be predicted, we will follow the subjects over two winter periods. Upon enrollment, and after 12 and 24 months of follow-up, participants will be asked to complete a questionnaire and to donate sera. During the 2 years of follow-up, if participants develop signs and symptoms of an influenza-like illness, they will additionally be asked to complete a questionnaire, provide gargle and nasal samples within 48 hours of symptom development, and ship the questionnaire and gargle sample to the investigators. We will use hemagglutination inhibition and microneutralization procedures to examine sera. Hypotheses testing will be performed for any swine (H1, H3) or avian (H3, H4, H5, H6, H7, H9) influenza hemagglutinin type and later stratified by each swine and avian type. Serologic results will be adjusted for antibodies to human influenza virus. To validate serological outcomes, culture and molecular studies will be performed on gargle specimens to identify influenza and specific hemagglutinin types. Prevalence and incidence rates will be adjusted using the direct adjustment method with the entire population as the standard population. Conditional logistic regression will be used to examine risk factors.