Viral and rickettsial etiology of an outbreak of acute respiratory tract infection.

An outbreak of 111 cases of acute respiratory tract infection was recorded in a community of the town "T" in April-May 1984. The clinical picture was severer than usual; 28% of the cases had to be hospitalized, average absenteeism being as high as 26 days per case. Serological investigations demonstrated the previous circulation of influenza virus B/Singapore/222/79 and the simultaneous circulation during the outbreak of influenza virus A/England/333/80 (H1N1) and of Rickettsia burneti (as also ascertained by isolation in the chick embryo of the former and by visualization by immunofluorescence in exfoliated cells of the latter pathogen). The association of the two etiological agents appears to account for the severe and protracted course of the disease.