Rapid typing, subtyping and RNA quantification of influenza virus type A strains in respiratory secretions.
During the winter-spring season 2006-2007, 38 influenza virus strains were identified in patients admitted to hospital with an acute respiratory tract infection. Infections were diagnosed in parallel by direct fluorescent antibody (DFA) staining using type-specific monoclonal antibodies and real-time reverse transcription (RT)-PCR targeting the gene M (nt 25-124). In addition, virus strains were isolated in MDCK cells. Overall, 37 influenza virus strains were type A, and one type B. Of these, 35 (80.4%) were detected and typed by real-time RT-PCR, 34 (80.1%) by DFA, and 27 (71.0%) by virus isolation. Subtyping of 37 influenza virus A strains by RT-PCR and DFA gave the following results: 4/6 H1 strains were correctly subtyped by both methods, while of the 29 H3 strains subtyped by RT-PCR 7 were missed by DFA. Thus, the overall concordance of the two subtyping methods was 28/37 (75.7%). Viral RNA quantification by real-time PCR showed that when respiratory secretion collection was done within 5 days after the onset of symptoms, viral load was greater than 1 x 10(6) RNA copies/ml. In conclusion, typing and subtyping of influenza virus type A strains may benefit from both MAbs and RT-PCR, while viral RNA quantification may provide an indication of symptom onset.
Servizio di Virologia, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy.
Elena
E
Percivalle
Francesca
F
Rovida
Antonio
A
Piralla
Vanina
V
Rognoni
Maurizio
M
Zavattoni
Fausto
F
Baldanti
Antonietta
A
Marchi
Giuseppe
G
Gerna
D000818:Animals; D002460:Cell Line; D004285:Dogs; D019085:Fluorescent Antibody Technique, Direct; D006801:Humans; D009980:Influenza A virus / Q000235:genetics / Q000302:isolation & purification*; D007251:Influenza, Human / Q000175:diagnosis* / Q000821:virology; D012367:RNA, Viral / Q000032:analysis; D012141:Respiratory Tract Infections / Q000821:virology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013183:Sputum / Q000821:virology*; D019562:Viral Load; D014776:Virus Cultivation / Q000379:methods
D012367:RNA, Viral