Risk Factors for Highly Pathogenic Avian Influenza Incursion into Commercial Poultry Farms in Lagos State: A Case-Control Study

This study identifies farm-level risk factors for incursion of highly pathogenic avian influenza (HPAI) H5N1 into commercial poultry farms in Lagos State, located in Nigeria's South West geopolitical zone. HPAI H5N1 has caused recurrent devastating outbreaks in Nigerian poultry since 2006, and understanding farm-level risk factors is essential for targeted biosecurity investment and outbreak prevention. Using a matched case-control study design, 40 farms that experienced confirmed HPAI H5N1 outbreaks between 2021 and 2023 were matched to 80 control farms without confirmed HPAI history during the same period, matched by farm type, location, and flock size. Structured questionnaires administered to farm managers collected data on biosecurity practices, proximity to live bird markets, wild bird exposure, worker practices, and vaccination histories. Conditional logistic regression was used to calculate matched odds ratios for candidate risk factors. The study addresses the gap in quantitative risk factor data for HPAI at farm level in South West Nigeria. Findings revealed that proximity within two kilometres of a live bird market (OR 8.4), absence of a vehicle decontamination point (OR 5.2), and purchase of replacement birds from multiple sources (OR 4.1) were the strongest independent risk factors. Regular wild bird entry into poultry houses (OR 3.7) and non-use of dedicated protective clothing (OR 2.9) were also significant. The study recommends HPAI risk-stratified biosecurity mandates for farms near live bird markets and stricter sourcing regulations. Keywords: avian influenza, HPAI, risk factors, case-control, Lagos State.