Public Health considerations for influenza A (H7N9) infection

Abstract

INTRODUCTION: Human infections with novel avian-origin influenza A(H7N9) virus were first emerged in March 2013 in the eastern provinces of China. Clinical outcome of many cases remained poor despite the early initiation of treatment and provision of intensive care. We reported here our work on the public health aspect of the disease for informing the preparation of future waves of the epidemic. METHODS: We analyzed clinical and epidemiological information of laboratory-confirmed cases of avian influenza A(H7N9) virus infection reported in first wave (March-May, 2013) of the epidemic. We compared this with information from patients having H5N1 or pH1N1 infections and other severe respiratory infections captured by routine surveillance. RESULTS: The majority of hospitalized patients were having a severe disease, with an overall fatality risk of 36%. Comparing with H5N1 or pH1N1, H7N9 patients were hospitalized for a longer duration, and with longer median time from onset to death. The estimated mean incubation period was around 3 days. Overall 75% of patients had reported an exposure to poultry. The male-to-female ratio was 2•9:1 and 1•6:1 in urban and rural areas respectively, possibly explained by a sex-based differential exposure. Closure of live-poultry markets was estimated to have reduced the mean daily number of infections by 97-99% in different epidemic cities by a statistical model. Cases detected via the sentinel surveillance system for influenza-like illness were generally mild, and suggested the existence of a 'clinical iceberg' with substantial undetected cases. For patients presenting with an acute respiratory infection, male sex, poultry exposure history, hemoptysis, shortness of breath, fever, radiographic consolidation and leukopenia were all important risk factors for A(H7N9) infection in a score-based prediction rule. CONCLUSION: Characterizing the public health dimension of the influenza A(H7N9) infection is important for informing the proper preparation for future waves of the evolving epidemic.