Evaluation of Routine Serological Diagnostic Methods for the 2009 Pandemic Influenza A (H1N1) Virus

Reda Tagajdid, Jean Sebastien Casalegno, Bruno Lina, Saâd Mrani, Yahia Mekki


Background: In April2009, a novel influenza A(H1N1) virus emerged in North America andMexico. In the face of a pandemic influenza, serology provides important public health data and is a valuable research tool. The labor intensiveness of the hemagglutination inhibition (HI) test is a major hindrance to its use on a large scale in routine. Recently, a commercial enzyme-linked immunosorbent assay (ELISA) (pandemic A(H1N1) IgG and IgA Genzyme Virotech®) has been developed. In addition, the need for surveillance led us to develop complement fixation test (CF) with2009 A(H1N1) viral lysate. The following study was conducted to assess the antibody detection accuracy of this two tests in comparison with the HI test as “gold standard”.

Patients and methods: Serum samples tested in this study were collected from 2 groups of subjects. The first group comprised 75 unvaccinated patients; the second group comprised 69 subjects receiving immunosuppressive therapy and vaccinated three weeks ago against2009 A(H1N1). All were tested by the three techniques.

Results and conclusion: Sero-prevalence was significantly higher in vaccinated than unvaccinated subjects (p = 0,032). In vaccinated group, the ELISA IgA gave a sensitivity of 61% and a specificity of 78%, ELISA IgG gave the same value for specificity but 75% for sensitivity; the CF titre cut-off (80) gave a sensitivity of 15% and a specificity of 87%. The CF titer cut-off value that provided the highest sensitivity (71%) and specificity (78%) was 10. In unvaccinated patients, the ELISA IgG gave a sensitivity of 57% and 87% for specificity; the CF titre cut-off (80) gave a sensitivity of 70% and a specificity of 100%.; strong positive correlation (r²=0.67, p<0.0001) was noted between CF and IH titers. CF results had good concordance with HI for general population screening. ELISA may be superior to CF for the detection of2009 A(H1N1) antibodies among vaccinated patients. 


ELISA, complement fixation, hemagglutination inhibition, pandemic A(H1N1) influenza

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