Silent geographical spread of the H7N9 virus by online knowledge analysis of the live bird trade with a distributed focused crawler

Chen, Chen; Lu, Shan; Du, Pengcheng; Wang, Haiyin; Yu, Weiwen; Song, Huawen; Xu, Jianguo

Approximately one month after confirmation of the first three cases of human infection with the new reassortant avian influenza virus (H7N9), the disease had extended to 42 cities in 12 provinces, infecting 134 people and killing 45 people in China as of September 10, 2013. 1 The viral isolates from patients were similar to the isolate from an epidemiologically linked market chicken. 2 Approximately 77% of patients had a history of exposure to live poultry. 3 The virus was clearly of avian origin, and the patients were infected in farmers' markets with live birds (FMLB) through an unknown mechanism. Suspending the FMLB can prevent new human infections in cities with a high population density. 4 The sporadic human infection patterns were distributed in 39 cities and occurred at various times, indicating that the virus is silently spreading in live birds over a far larger geographical area and at a far greater speed than originally thought. 2, 5, 6 The movement of live birds is a well-known risk factor for the geographic dissemination of the virus among poultry flocks. The daily incidence of H5N1 virus outbreaks in Vietnam peaks around the annual holiday festivities in February coinciding with poultry movement increases. 7, 8 Therefore, determining the location of live birds carrying the virus and the FMLB that is contaminated by the live-bird trade is critical in stopping the surge of human infection and the geographical dissemination of the disease. The traditional investigation of animals carrying the virus is based on the virological diagnosis of animals with a possible epidemiological link. 9, 10 This task can be difficult because China has approximately six billion domestic birds. Until the source of infection has been identified and controlled, more cases of human infection by the virus are expected. 6, 11 Crowd-powered expansion and the distrib-uted focused crawler are methods that use large-scale online data to reveal human behavior accessible to research. 12 The method as used in this study to reveal live-bird-trading information to predict the potential nationwide geographic spreading of H7N9 virus, which could not be identified by traditional epidemiological investigation methods.