Epidemiology of the avian influenza A (H7N9) outbreak in Zhejiang Province, China

Abstract

BackgroundA novel influenza A virus infection was identified on March 31, 2013 in China and a total of 134 cases were identified in 12 provinces of China between March 25 and September 31, 2013. Of these, 46 cases occurred in Zhejiang Province and the number of patients is the largest in China.MethodsField investigations were conducted for each confirmed H7N9 case. A standardized questionnaire was used to collect information about demographics, exposure history, clinical signs and symptoms, timelines of medical visits and care after onset of illness, and close contacts. Descriptive statistics were used to analyze the epidemiological and clinical characteristics. Samples from the patients were collected and tested by real time reverse transcriptase-polymerase chain reaction and viral culture.ResultsA total of 46 laboratory confirmed cases of H7N9 influenza infection were identified in the Zhejiang province between March 31 and September 31, 2013 of which 29 were male and 17 were female. The median age of patients was 61.5 years and 76.09% of cases occurred in persons aged ≥50 years old. Unlike other province, 34.78% of cases in Zhejiang Province were rural residents. Among 11 deaths, 9 were male, 10 were older than 60 years old, and 10 had underlying diseases. 30 of 38 cases with available data had a recent history of poultry exposures and 8 cases had multi-exposure history. The estimated median incubation period was two days which was shorter than corresponding data in other provinces. All cases were hospitalized and the median time from illness onset to hospitalization was 5 days. Symptoms at the onset of the illness included fever, cough, expectoration, shivering, fatigue, muscular aches, nausea, vomiting. Only 4.91% contacts developed respiratory symptoms, but their samples were tested negative for H7N9 virus designating lack of human-to-human transmission of the virus.ConclusionsAll cases were sporadic and there was no evidence of an epidemiologic link between them. Control measures including closing affected poultry and slaughtering backyard poultry are needed not only in urban areas but also in rural areas to reduce human H7N9 infection risk.

Biosecurity Strategies for Backyard Poultry: A Controlled Way for Safe Food Production

“…In China, a total of 46 H7N9 infections were identified in the Zhejiang province in humans during 2013. All the live poultry markets were closed and backyard poultry were slaughtered to control the outbreak in the locality (Gong et al, 2014). In Beijing (China), farmers who reared ducks in their backyards possessed antibody against Avian influenza, but they never vaccinated, indicating the means for possible transmission .…”

An extract from Taxodium distichum targets hemagglutinin- and neuraminidase-related activities of influenza virus in vitro

“…In 1997, the avian A/H5N1 virus was found in Hong Kong; this avian influenza virus showed direct bird-to-human transmission and resulted in serious mortality3. In 2013, a novel avian influenza virus H7N9 was identified in 12 provinces of China and caused a high mortality rate in humans45.…”

The Third Wave: H7N9 Endemic Reassortant Viruses and Patient Clusters

“…Patients typically presented with fever and cough, and while the majority developed pneumonia, a number of patients further developed acute respiratory distress syndrome (ARDS) which often led to refractory hypoxemia and death [4]. The simultaneous H7N9 circulation among market birds in outbreak regions [5,6] and frequent history of previous poultry contact among hospitalized H7N9 patients [4,7] suggested zoonotic transmission of the H7N9 virus. In response to the link between poultry contact and zoonotic transmission, Chinese authorities enforced widespread poultry market closures.…”