As the result of intensive studies of 9ctte respiratory infection in military populations-from 1941 to 1946, an entity termed "acute respiratory disease" was described by the Commission on Acute Respiratory Diseases (1-4). This syndrome, for convenience, was termed "ARD," and this designation will be employed hereafter. ARD is an acute febrile respiratory infection of short duration with both constitutional symptoms and localized respiratory symptoms characterized predominately by cough and hoarseness (1, 2). In addition, irritated throat, nasal obstruction, and chest pain were frequent complaints. Epidemiological investigation (1) as well as human transmission experiments (3, 4) indicated that the incubation period of this infection was five to six days, and that during convalescence there developed an homologous immunity but not heterologous resistance to common cold or primary atypical pneumonia (4). It was postulated as a result of these investigations (1-4) that ARD was an entity distinguishable from other acute respiratory illnesses such as common cold, streptococcal pharyngitis and tonsillitis, and primary atypical pneumonia, and that it was caused by a single filterable agent, probably a virus, or a closely related group of agents. Attempts to isolate an agent in experimental animals and chick embryos were not successful.Although ARD has not been recognized in epidemic form in civilian populations, similar infections such as non-streptococcal pharyngitis and grippe-like illnesses not caused by influenza vi-I
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