Influenza virus detection in clinical specimens

The authors compared the results of influenza A (H1N1) and influenza A (H3N2) virus detection in nasopharyngeal swabs from flu patients by molecular hybridization (MH), ELISA, virus isolation and seroconversion. Using the immunofluorescence (IF) technique influenza virus was detected in cell suspensions from the first chick embryo passage. Altogether 63 swabs from various epidemic seasons were separated into 3 groups according to specimen sampling and storage. It was shown that influenza virus RNA could be found in 16 out of 22 swab specimens (72%) stored at -70 degrees C without thawing and that ELISA revealed the influenza virus antigen in 19 cases (86%); in contrast, IF was positive in 6 (27%) and virus isolation in 5 (22%) cases only. However, the positive rate of MH decreased to 9% in 21 swab specimens repeatedly thawed and stored at -20 degrees C and was completely negative after prolonged storage of repeatedly thawed samples. Despite these conditions, ELISA was still successful in both latter sample groups (71-80%). For specificity control, 29 samples coming from patients with influenza B virus and other respiratory virus diseases (adeno- and respiratory syncytial virus) were used.