Legionnaires' disease: an atypical pneumonia.

Given the present state of the art, any case of apparent pneumonia that is not responding to optimum therapy, or of "viremia" which appears to be progressively deteriorating, should be considered Legionnaires' disease and treated accordingly until proven otherwise. Titers for antibody to the disease in serum obtained during the acute and convalescent stages should always be determined in such cases. This may initially prove to be a rather wasteful and expensive procedure. However, only by carefully studying these titers can the elusive course of the disease be better delineated and techniques perfected that may allow earlier diagnosis and thus reduction in mortality.