Rapid detection of influenza virus infections in human fetal lung diploid cell cultures

Haemadsorbing foci were found in human fetal lung (HFL) diploid cell cultures 12 h after inoculation with influenza viruses A and B. The size and number of the foci were maximal after 48 h of incubation, being limited by production of an unidentified inhibitor. By contrast, inoculation with parainfluenza virus type 3 led to haemadsorption which increased during 10 days of incubation. For the detection of influenza viruses A and B maximum sensitivity was achieved by changing the medium, the day before use to one that was serum free. The number of foci at 15.5 h post-infection and infectivity for primary African green monkey kidney (AGMK) cultures were similar. Virus infectivity and production of haemagglutinin in HFL cells were entirely cell-associated; they were not affected by treatment with trypsin. Nevertheless, influenza viruses A and B antigens were identified in the infected cells by means of immunofluorescence at 15.5 h and virus was recovered by passage of frozen and thawed cells in AGMK cultures. For rapid routine diagnosis of viral infections, the early haemadsorption test was shown to have the same sensitivity as immunofluorescence tests on specimens and virus detection by the shell-vial technique but was cheaper and simpler to perform.