Evaluation of direct immunofluorescent assay (DFA) and rapid antigen test (RAT) for diagnosis of new pandemic influenza A H1N1 2009 (FLU AH1N1) during first wave in Santiago, Chile
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Date
2010
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ELSEVIER SCI LTD
Abstract
Background: Since May 17th 2009 (epidemiological week 20th), the new strain of influenza A H1N1 was detected in respiratory samples of symptomatic patients in Santiago, Chile. The circulation of the virus lasted 11 weeks, with a peak between weeks 25-27th. The objective of our study was to evaluate the performance of influenza tests for diagnosis of FLU AH1N1.
Methods: Nasopharyngeal swabs were taken from in and outpatients with influenza like illness (ILI), between June 1st and July 19th of 2009 (weeks 23-29th) and the results of DFA and RAT were compared using RT-PCR FLU AH1N1 (Light mix Kit Influenza A virus M2 and Light Mix Kit FLU A swine H1Ò of TIB MOLBIOL) as gold standard. We analyzed sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of DFA (D3 Ultra 8 DFA Respiratory & Identification Kit ä de Diagnostic Hybrid) and RAT (QuickVeuÒ of Biomerieux). Results were compared by age group and over three different periods of the outbreak: increasing, peak and decreasing.
Results: 510 patients had RT-PCR for FLU AH1N1 with simultaneous DFA, 385 with RAT and 48 with both tests. Average age with DFA was 25,8 years (1 month-108 years, 53% females) and with RAT 32,9 years (2 months-108 years, 51% females), (p <0,0001). Comparing periods of the outbreak, DFA sensitivity was 58%, 77% and 81% in ascending, peak and descending period, respectively (p <0,001) and specificity was 90%, 83% and 91% respectively (p>0,05). Evaluating RAT, sensitivity was 41%, 61% and 67% (p<0,001) and specificity was 87%, 96% y 92% (p> 0,05) in different periods.