The Diverse Etiology of Epidemic Influenza

Abstract

This paper presents evidence that cases of influenza in one epidemic, even in a single institution, may be due to infection by one or more of at least 3 distinct agents. Studies of sera and throat washings obtained from numerous cases of influenza which occurred during 3 epidemic periods in 1 yr. were carried out. In each epidemic period evidence was obtained that some cases were infected by influenza A virus and others by influenza B virus. In many cases no evidence of infection by either virus was demonstrable; these cases may have resulted from infection by an agent or agents as yet unknown but distinct from either influenza A virus or influenza B virus. Since cases of influenza A, influenza B, and influenza of unknown cause sometimes occurred simultaneously in a single institutional outbreak, epidemics of influenza may not infrequently be of diverse etiology. If influenza A virus and influenza B virus are present and both produce cases at the same time, as apparently is not infrequently true, the number of cases due to either virus should be a function of the number of persons susceptible to infection by it and their chances of contact with it. Similar considerations should also be applicable to the hypothetical agent or agents responsible for cases of influenza of unknown cause.