Sero-Epidemiological Results in the Human Population Exposed to Highly Pathogenic Avian Influenza H5N1 Outbreak in a Large Poultry Farm in the East of England

Abstract

In February 2007, the presence of highly pathogenic avian influenza H5N1 of Eurasian lineage (Clade 2.2) was confirmed in turkeys at one of 22 sheds of a large poultry farm located in the east of England. A multi-agency Incident Management Team assessed the risk to human health and instituted appropriate control measures. This is a summary of results of investigation into associations between risk-factors and outcomes as described below. A total of 482 individuals received chemoprophylaxis with Oseltamivir, of which 187 (39%) consented to blood testing for evidence of infection with H5N1 at 8—10 weeks following exposure. A supervised questionnaire was administered at the same time to investigate associations between exposure, occupational and demographic variables, and outcome. After excluding people with no exposure, 162 were available for analysis. 29 (18%) reported one or more symptoms of influenza like illness (ILI) experienced only after exposure, of whom 21 had received Oseltamivir before possible exposure to H5N1. 157/162 (97%) reported 90—100% compliance with taking prescribed Oseltamivir, while 73% reported total compliance with personal protective equipment (PPE). 141 (87%) individuals received seasonal influenza vaccination, of whom 16 (10%) had received the vaccination prior to the incident. There was no evidence of sero-conversion to H5. Multivariable logistic regression modeling failed to find any statistically significant associations between abovementioned variables and ILI symptoms at 5% significance level. However, there was a suggestion that ‘workers with no specific occupational activity’ may be at elevated risk (OR = 3.93; 95%CI: 1.00—15.54; p = 0.059). Interestingly, amongst others, there was no statistically significant association between ‘always wear complete PPE’ nor ‘always wear FFP2 or FFP3 respirator’ (both binary variables), and symptom development (p = 0.95, 0.9 respectively). The public health response included the largest ever mass provision of Oseltamivir for ‘at-risk’ individuals in the UK, the assessment framework for which needs review.