Management of influenza infections relies on rapid, accurate, and sensitive diagnostic techniques. Influenza A (IA) strain typing has become more important since the emergence of highly pathogenic avian and novel influenza strains and the high frequency of oseltamivir resistance in circulating H1N1 isolates.
To analyze the performance of indirect fluorescent antibody testing for subtyping a broad range of IA strains.
Ten indirect fluorescent antibody reagents were used to detect and type 100 archived IA respiratory specimens from 1986 through 1995 and 2006 through 2007 and a reassortant, nonpathogenic H5N1 sample. Both direct specimen and cultured isolates were tested. Reverse transcription-polymerase chain reaction was used to confirm indirect fluorescent antibody results. Three H1N1-, 2 H3N2-, and 1 H1-H2-H3-H5-specific antibodies (Chemicon Diagnostics), an IA pool reagent (Trinity Biotech), and H1, H3, and H1-H3-specific antibodies (Centers for Disease Control and Prevention) were used.
Reverse transcription-polymerase chain reaction confirmed all 100 isolates as IA and identified 71 as H1, 22 as H3, and 7 as non-H1-H3. Sensitivity of direct specimen testing ranged was 18.3% to 57.7% for the H1 reagents, 36.4% to 50.0% for the H3 reagents, and 40.0% to 53.8% for the pool reagents. Subtyping was more sensitive on cultured isolates than direct specimens. Specificity for all antibodies was 89.7% to 100%. The H5N1 sample was positive by direct testing and culture (reverse transcription-polymerase chain reaction, Centers for Disease Control and Prevention H5N1 pool, Chemicon H1-H2-H3-H5). No cross-reactivity was observed when the 10 antibodies were tested against other common respiratory viruses.
When positive, IA subtyping antibodies can serve as a useful diagnostic tool when multiple influenza virus subtypes are cocirculating with different susceptibility patterns.