Sero‐epidemiologic study of influenza A(H7N9) infection among exposed populations, China 2013‐2014

Abstract

BackgroundThe first human infections of novel avian influenza A(H7N9) virus were identified in China in March 2013. Sentinel surveillance systems and contact tracing may not identify mild and asymptomatic human infections of influenza A(H7N9) virus.ObjectivesWe assessed the seroprevalence of antibodies to influenza A(H7N9) virus in three populations during the early stages of the epidemic.Patients/MethodsFrom March 2013 to May 2014, we collected sera from the general population, poultry workers, and contacts of confirmed infections in nine Chinese provinces reporting human A(H7N9) infections and, for contacts, second sera 2‐3 weeks later. We screened for A(H7N9) antibodies by advanced hemagglutination inhibition (HI) assay and tested sera with HI titers ≥20 by modified microneutralization (MN) assay. MN titers ≥20 or fourfold increases in paired sera were considered seropositive.ResultsAmong general population sera (n=1480), none were seropositive. Among poultry worker sera (n=1866), 28 had HI titers ≥20; two (0.11%, 95% CI: 0.02‐0.44) were positive by MN. Among 61 healthcare and 117 non‐healthcare contacts’ sera, five had HI titers ≥20, and all were negative by MN. There was no seroconversion among 131 paired sera.ConclusionsThere was no evidence of widespread transmission of influenza A(H7N9) virus during March 2013 to May 2014, although A(H7N9) may have caused rare, previously unrecognized infections among poultry workers. Although the findings suggest that there were few undetected cases of influenza A(H7N9) early in the epidemic, it is important to continue monitoring transmission as virus and epidemic evolve.

Avian Influenza A Virus Infection among Workers at Live Poultry Markets, China, 2013–2016

“…In our study, a much lower seroprevalence of anti-H7N9 virus ranged from 0% to 0.56% during the enrollment and follow-up times in poultry workers. Our findings are similar to the 0.11% seroprevalence of MN titers > 20 found in poultry workers in 6 provinces in China ( 18 ). In comparison with studies that did not perform MN testing, the proportion of elevated HI titers > 20 in our study was also much lower (0%–2.83% in poultry workers).…”

“…Serologic evidence of human infection with H7N9 has previously been reported ( 14 – 18 , 22 – 24 ). In those studies, the seroprevalence ranged from 0% to 17.1%.…”

“…Most human infections with AIVs (e.g., subtypes H7N9, H5N1, and H5N6) have been associated with exposure to poultry and resulted in severe illness ( 6 ). However, these severely ill patients could represent the tip of the iceberg because mild and asymptomatic infections with H7N9, H9N2, and H5N1 subtypes have been observed by surveillance ( 7 – 11 ) and serologic studies ( 12 – 18 ). Surveillance might miss persons with mild or asymptomatic infection who do not seek medical care.…”

Spatial characteristics and the epidemiology of human infections with avian influenza A(H7N9) virus in five waves from 2013 to 2017 in Zhejiang Province, China

“…There are likely to be many more cases than those reported due to there being an unknown number of mild and subclinical infections [ 11 ]. The objectives of this study are to identify the epidemiological characteristics and the distribution of H7N9 virus in human infection from 2013 to 2017.…”

C-C Motif Chemokine Ligand 2 (CCL2) Mediates Acute Lung Injury Induced by Lethal Influenza H7N9 Virus

“…H7N9 infection resulted in fever and cough, acute lung injury (ALI), and acute respiratory distress syndrome (ARDS), which frequently required admission to an intensive care unit (ICU); moreover, it was associated with considerable morbidity and mortality (Chen et al, 2013). As of July 19, 2016, a total of 793 cases had been reported, including 319 deaths (Xiang et al, 2017). …”