A Comparison of Various Methods of Demonstrating Influenza Virus in Throat Washings. *

Abstract

Summary

During the epidemic of influenza A in 1943-44, throat washings from military personnel were tested in ferrets or hamsters, or in both species, and a smaller number of the same washings were inoculated into chick embryos.

None of the throat washings from 23 persons in whom response to serological tests for influenza A virus was negative produced antibodies to that virus after intranasal inoculation in ferrets.

Of 30 throat washings from persons showing positive response to serological tests for influenza A virus, 17 (56.7 ± 9.05%) produced in ferrets an increase in antibodies to the virus. With 2 exceptions all ferrets showing an increase in antibodies also developed fever 2 to 3 days after inoculation. Four of 41 ferrets showing no increase in antibodies had similar febrile reaction.

Thirty, or 56.6 ± 6.81% of 53 throat washings from persons with known cases of influenza A were positive in hamsters, a result identical with that obtained in ferrets. Twelve throat washings that were negative in ferrets produced no antibody response in hamsters.

Seventeen throat washings shown to contain influenza A virus by tests in ferrets or hamsters were inoculated into chick embryos by the amniotic route. Of these, 7 (41.2 ± 11.9%) infected the embryos. Virus was demonstrated in 4 throat washings in the first passage and in 3 in the second, but usually 1 or 2 additional amniotic or allantoic passages were necessary before the virus reached sufficient titer to be positively identified as influenza A.

In 2 of 13 unfiltered throat washings inoculated into the allantois of chick embryos, virus was demonstrated on first passage.