Mixed infections with influenza A and B viruses.

In the course of an influenza A and B epidemic, influenza virus was isolated from 46 patients. Seven of these patients showed seroconversion against influenza virus plus another respiratory virus. In 9 patients, simultaneous antibody increase against both influenza A and B viruses was demonstrated, but only a single virus type was isolated. In one case the isolated virus population could be separated into type A and B viruses.