Abstract
Human infection with avian influenza A H7N9 virus was first identified in March 2013 and represents an ongoing threat to public health. There is a need to optimize serological methods for this new influenza virus. Here, we compared the sensitivity and specificity of the hemagglutinin inhibition (HI), microneutralization (MN), and Western blot (WB) assays for the detection of human antibodies against avian influenza A (H7N9) virus. HI with horse erythrocytes (hRBCs) and a modified MN assay possessed greater sensitivity than turkey erythrocytes and the standard MN assay, respectively. Using these assays, 80% of tested sera from confirmed H7N9 cases developed detectable antibody to H7N9 after 21 days. To balance sensitivity and specificity, we found serum titers of ≥20 (MN) or 160 (HI) samples were most effective in determining seropositive to H7N9 virus. Single serum with HI titers of 20–80 or MN titer of 10 could be validated by each other or WB assay. Unlike serum collected from adult or elderly populations, the antibody response in children with mild disease was low or undetectable. These combinations of assays will be useful in case diagnosis and serologic investigation of human cases.
Highlights
In March 2013, the first documented infection of humans with a novel avian influenza A (H7N9) virus was identified in China [1]
A total of 258 control serum samples collected from 2010–11 were obtained from subjects for specificity testing as follows: 94 from the general population in Shanghai collected in January 2010, 100 from individuals in Mongolia collected in June 2010 that simultaneously contained hemagglutinin inhibition (HI) antibodies against five seasonal influenza viruses (H1N1 [40– 640], H3N2 [40–640], H1N12009 pandemic [40–2560], B Victoria [40–640], and B Yamagata [40–640]) (Table1); 15 sera obtained from poultry workers and patients in China with antibody titers (80–640) against H5N1 virus; and 49 from poultry workers in China with antibodies to H9N2 virus (80–160) collected in 2011
HI and MN Optimization Similar to lower antibody responses detected in previous H7 subtype infection in humans [9], the first two available convalescent sera from H7N9 infected individuals only achieved titers of 40 using turkey RBCs (tRBCs) HI and titers of 20 and 40 by MN
Summary
In March 2013, the first documented infection of humans with a novel avian influenza A (H7N9) virus was identified in China [1]. As of February 21st, 2014, 356 of H7N9 infection were have been reported in mainland China with 114 death and 5 cases in Hong Kong and 2 cases in Taiwan [2]. Similar to human infection with H5N1 viruses, most human cases typically present with severe pneumonia [5], and only few mild cases with fever have been reported [6]. Serological assays serve a critical role in the identification of mild and asymptomatic infections caused by H7N9 viruses in humans. There remains a need to comprehensively evaluate the sensitivity and specificity of different serological assays to detect human antibodies against H7 viruses in general, and H7N9 viruses in particular
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