Table 2.

Effect of quality of nasal wash specimen on the ability to isolate viruses and detect influenza virus by rapid diagnosis or by culturea

GroupnCulture positive (any virus)Culture positive (influenza virus)NAbpositiveIFA positiveEIA positivec
1 (abundant cellsd)26150.2%28.4%29.5%21.5%26.3%
2 (sparse cellse)6031.7%21.7%18.3%5%14%
3 (inadequate cellsf)10226.5%21.6%12.7%0%19.5%
P values
 Between groups 1 and 2P = 0.01NSgNSP = 0.003P = 0.04
 Between groups 1 and 3P < 0.001NSP = 0.001P < 0.001NS
 Between groups 2 and 3NSNSNSP < 0.001NS
  • a Includes 423 specimens in which IFA was performed.

  • b NA, neuraminidase assay.

  • c EIA, enzyme immunoassay for influenza A virus. Includes only 395 specimens for which both EIA and IFA were performed.

  • d Abundant cells, >20 cells per well with >3 to 5 cells per high-power field.

  • e Sparse cells, >20 cells per well with <3 to 5 cells per high-power field.

  • f Inadequate cells, <20 cells per well.

  • g NS, difference not statistically significant.