Epidemiological investigation on the first local clustering of human infection with H7N9 avian influenza in Beijing

Abstract

Objective Through an epidemiological survey on the clustering of human infection with H7N9 avian influenza, the source of infection, route of transmission and prevention and control measures were analyzed. Methods Epidemiological investigation, sample collection and laboratory testing was carried out on the cases who were from clustering of human infection with H7N9 in 2017. The investigation of the source of infection, sampling and testing for environment samples were also applied. Results Two brothers were identified as cases in the clustering. Both cases had contact with chickens from itinerant traders before the onset of the disease and these chickens have died of illness. Nucleic acid of H7N9 avian influenza virus was found in the chickens and environmental samples from the chicken house of case 2. In the intensive surveillance of medical institutions, patient Zhou who lived in a different town of the first two cases were found. The patient had contact with the chickens from itinerant vendors before the onset of the disease. Gene sequencing for the 3 cases and environment samples indicated that case 1 and 2 gene had completely consistent sequences while case 2 and the 3 related environmental samples showed 99.80%-100.00% of nucleotide sequence similarity in all 8 fragments of the genome. Conclusions Two human cases have been exposed to chicken infected by the virus or to contaminated environment. Enhanced surveillance is an important measure in the discovery of human cases of H7N9 avian influenza. Strengthening the supervision of living poultry traders is one of the key measures for the prevention and control of H7N9 avian influenza. Key words: Influenza in birds; Epidemiologic studies; Human infection with avian influenza A (H7N9); Clustering; Gene sequencing