Serological Response in RT-PCR Confirmed H1N1-2009 Influenza A by Hemagglutination Inhibition and Virus Neutralization Assays: An Observational Study

• Published in: PloS one Vol. 5; no. 8; p. e12474
• Main Authors: Chen, Mark I., Barr, Ian G., Koh, Gerald C. H., Lee, Vernon J., Lee, Caroline P. S., Shaw, Robert, Lin, Cui, Yap, Jonathan, Cook, Alex R., Tan, Boon Huan, Loh, Jin Phang, Barkham, Timothy, Chow, Vincent T. K., Lin, Raymond T. P., Leo, Yee-Sin
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 30.08.2010; Public Library of Science (PLoS)
• Subjects: Adult; Analysis; Antibodies; Antibodies, Viral - analysis; Antibodies, Viral - immunology; Blood; Blood circulation; Cohort Studies; Confidence intervals; Cross Reactions; Epidemiology; Family medical history; Female; Health aspects; Health services; Health surveillance; Hemagglutination inhibition; Hemagglutination Inhibition Tests - methods; Hospitals; Humans; Immunization; Immunoglobulins; Immunology/Immunity to Infections; Infections; Infectious diseases; Infectious Diseases/Viral Infections; Influenza; Influenza A; Influenza A virus; Influenza A Virus, H1N1 Subtype - physiology; Influenza viruses; Influenza, Human - diagnosis; Influenza, Human - immunology; Male; Medical laboratories; Medical research; Middle Aged; Neutralization; Neutralization Tests - methods; Observational studies; Outbreaks; Pandemics; Polymerase chain reaction; Public health; Reverse Transcriptase Polymerase Chain Reaction; Seroconversion; Serology; Swine flu; Vaccines; Virology/Diagnosis; Virology/Emerging Viral Diseases; Viruses; Young Adult; Singapore
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0012474

We describe the serological response following H1N1-2009 influenza A infections confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR). The study included patients admitted to hospital, subjects of a seroepidemiologic cohort study, and participants identified from outbreak studies in Singapore. Baseline (first available blood sample) and follow-up blood samples were analyzed for antibody titers to H1N1-2009 and recently circulating seasonal influenza A virus strains by hemagglutination inhibition (HI) and virus micro-neutralization (VM) assays. 267 samples from 118 cases of H1N1-2009 were analyzed. Geometric mean titers by HI peaked at 123 (95% confidence interval, CI 43-356) between days 30 to 39. The chance of observing seroconversion (four-fold or greater increase of antibodies) was maximized when restricting analysis to 45 participants with baseline sera collected within 5 days of onset and follow-up sera collected 15 or more days after onset; for these participants, 82% and 89% seroconverted to A/California/7/2009 H1N1 by HI and VM respectively. A four-fold or greater increase in cross-reactive antibody titers to seasonal A/Brisbane/59/2007 H1N1, A/Brisbane/10/2007 H3N2 and A/Wisconsin/15/2009 H3N2 occurred in 20%, 18% and 16% of participants respectively. Appropriately timed paired serology detects 80-90% RT-PCR confirmed H1N1-2009; Antibodies from infection with H1N1-2009 cross-reacted with seasonal influenza viruses.