title: Influenza A viral loads in respiratory samples collected from patients infected with pandemic H1N1, seasonal H1N1 and H3N2 viruses.
abstract: BACKGROUND
  Nasopharyngeal aspirate (NPA), nasal swab (NS), and throat swab (TS) are common specimens used for diagnosis of respiratory virus infections based on the detection of viral genomes, viral antigens and viral isolation. However, there is no documented data regarding the type of specimen that yields the best result of viral detection. In this study, quantitative real time RT-PCR specific for M gene was used to determine influenza A viral loads present in NS, NPA and TS samples collected from patients infected with the 2009 pandemic H1N1, seasonal H1N1 and H3N2 viruses. Various copy numbers of RNA transcripts derived from recombinant plasmids containing complete M gene insert of each virus strain were assayed by RT-PCR. A standard curve for viral RNA quantification was constructed by plotting each Ct value against the log quantity of each standard RNA copy number.
  
  
  RESULTS
  Copy numbers of M gene were obtained through the extrapolation of Ct values of the test samples against the corresponding standard curve. Among a total of 29 patients with severe influenza enrolled in this study (12 cases of the 2009 pandemic influenza, 5 cases of seasonal H1N1 and 12 cases of seasonal H3N2 virus), NPA was found to contain significantly highest amount of viral loads and followed in order by NS and TS specimen. Viral loads among patients infected with those viruses were comparable regarding type of specimen analyzed.
  
  
  CONCLUSIONS
  Based on M gene copy numbers, we conclude that NPA is the best specimen for detection of influenza A viruses, and followed in order by NS and TS.
authors.affiliation: Department of Microbiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Nathamon
authors.initials: N
authors.lastname: Ngaosuwankul
authors.forename: Pirom
authors.initials: P
authors.lastname: Noisumdaeng
authors.forename: Pisut
authors.initials: P
authors.lastname: Komolsiri
authors.forename: Phisanu
authors.initials: P
authors.lastname: Pooruk
authors.forename: Kulkanya
authors.initials: K
authors.lastname: Chokephaibulkit
authors.forename: Tawee
authors.initials: T
authors.lastname: Chotpitayasunondh
authors.forename: Chariya
authors.initials: C
authors.lastname: Sangsajja
authors.forename: Charoen
authors.initials: C
authors.lastname: Chuchottaworn
authors.forename: Jeremy
authors.initials: J
authors.lastname: Farrar
authors.forename: Pilaipan
authors.initials: P
authors.lastname: Puthavathana
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000821:virology*; D008875:Middle Aged; D009297:Nasal Mucosa / Q000821:virology*; D009305:Nasopharynx / Q000821:virology*; D010614:Pharynx / Q000821:virology*; D012367:RNA, Viral / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019562:Viral Load; D014763:Viral Matrix Proteins / Q000235:genetics; D055815:Young Adult
chemical_list: C031540:M-protein, influenza virus; D012367:RNA, Viral; D014763:Viral Matrix Proteins
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