Erythrocyte Binding Preference of Human Pandemic Influenza Virus A and Its Effect on Antibody Response Detection

BACKGROUND: Validation of hemagglutination inhibition (HI) assays is important for evaluating antibody responses to influenza virus, and selection of erythrocytes for use in these assays is important. This study aimed to determine the correlation between receptor binding specificity and effectiveness of the HI assay for detecting antibody response to pandemic influenza H1N1 (pH1N1) virus. METHODS: Hemagglutination (HA) tests were performed using erythrocytes from 6 species. Subsequently, 8 hemagglutinating units of pH1N1 from each species were titrated by real-time reverse transcription-PCR. To investigate the effect of erythrocyte binding preference on HI antibody titers, comparisons of HI with microneutralization (MN) assays were performed. RESULTS: Goose erythrocytes showed most specific binding with pH1N1, while HA titers using human erythrocytes were comparable to those using turkey erythrocytes. The erythrocyte binding efficiency was shown to have an impact on antibody detection. Comparing MN titers, HI titers using turkey erythrocytes yielded the most accurate results, while those using goose erythrocytes produced the highest geometric mean titer. Human blood group O erythrocytes lacking a specific antibody yielded results most comparable to those obtained using turkey erythrocytes. Further, pre-existing antibody to pH1N1 and different erythrocyte species can distort HI assay results. CONCLUSIONS: HI assay, using turkey and human erythrocytes, yielded the most comparable and applicable results for pH1N1 than those by MN assay, and using goose erythrocytes may lead to overestimated titers. Selection of appropriate erythrocyte species for HI assay allows construction of a more reliable database, which is essential for further investigations and control of virus epidemics.

Novel H1N1 2009 influenza virus infection in Bangkok, Thailand:effects of school closures

Background: Influenza virus is the major cause of respiratory illness, especially in young and older age groups. Since 1918, many subtypes, defined by hemagglutinine (HA) and neuraminidase (NA), have caused global infections or pandemics. The recently isolated swine origin influenza virus (S-OIV) subtype H1N1 has been defined by the World Health Organization (WHO) as the cause of the present influenza pandemic. Objective: To describe and attempt to predict the epidemiology of the novel H1N1 2009 in Bangkok and to evaluate the effects of school closures during the outbreaks. Materials and methods: The first two human cases infected by this S-OIV subtype H1N1 or H1N1 2009 in Thailand have been reported in May 12, 2009 by the Ministry of Public Health. Between May 12 and July 30, 2009, 1212 nasopharyngeal (NP) swabs from four private hospitals and Chulalongkorn Hospital, Bangkok have been sent to a laboratory for Influenza virus diagnosis. The diagnosis was based on real time RT-PCR for seasonal influenza (H1, H3) and H1N1 2009. Results: One thousand two hundreds and twelve specimens of patients with influenza like illness were tested using real time RT-PCR detection. Between mid June and early July, the number of H1N1 2009 increased rapidly with a high prevalence among the 6- to 20-year olds. School closure policy, long public holiday, and additional preventive measures have led to a rapid reduction in the number of H1N1 2009 positive patients. Conclusion: Preventive measures including school closures are important to slow down the outbreak and thus enable health care centers to cope with the large number of patients. Everyone should play a role in delaying the spread of this pandemic.