Comparison of the performance of direct fluorescent antibody staining, a point-of-care rapid antigen test and virus isolation with that of RT-PCR for the detection of novel 2009 influenza A (H1N1) virus in respiratory specimens

Although infections with the novel pandemic 2009 influenza A (H1N1) virus (A/H1N1/2009) appeared to be relatively mild during the first summer of circulation ('off season'), there has been significant morbidity and hospitalization and several fatal cases. Thus, rapid detection of A/H1N1/2009 is crucial for efficient treatment and infection control measures In contrast to seasonal influenza, where point-of-care (POC) rapid antigen tests and direct fluorescent antibody (DFA) staining ensure rapid detection, diagnosis of A/H1N1/2009 has so far been based on RT-PCR This study retrospectively compared the performance of the Quidel QuickVue POC test, DFA staining and virus isolation with that of RT-PCR for A/H1N1/2009 detection in 526 respiratory specimens collected during the first wave of the outbreak from May to September 2009. A/H1N1/2009 was detected in 9 1% (48/526) of samples One hundred and thirty-seven of the A/H1N1/2009 PCR-negative samples were additionally tested using a RealAccurate Respiratory RT-PCR panel, revealing other respiratory viruses (mainly entero/rhino- and adenoviruses) in 42 3% (58/137) All methods analysed detected A/H1N1/2009 with excellent specificity but different sensitivities (POC test 18 2%, DFA staining 38 7%, virus isolation. 45 7%). Therefore, the POC test was not suitable for diagnosis, detecting A/H1N1/2009 only if present in high concentrations (corresponding median C, value=19 0, range=16 5-21 4) DFA staining was also able to detect A/H1N1/2009 in specimens with a lower virus concentration (median C(1) value=24 0, range=16 5-29 8) Virus isolation, which was positive after a median time of 7 5 days, was too time-consuming In summary, DFA staining is superior to POC testing and may be appropriate for patients expected to have a rather high level of virus replication Nevertheless, in DFA-negative specimens, A/H1N1/2009 should be excluded by RT-PCR