Roentgenographic Manifestations of Pulmonary Tularemia

Tularemia is an acute infectious disease of the Northern Hemisphere caused by a gram-negative, nonmotile, pleomorphic bacterium, Pasteurella tularensis. The disease is epizootic in numerous rodents and small mammals, with insects acting as both reservoirs and vectors. In North America the cotton-tail rabbit is the most important host so far as transmission to man is concerned. Man is infected by handling animal carcasses, by ingestion of infected animals or contaminated water, by insect bites, and by inhalation. The disease has been reported in all age groups, the incidence being related only to degree of opportunity for exposure. In this country, approximately 90 per cent of the cases are of the well known cutaneous variety, with an untreated case fatality rate of less than 5 per cent. A small ulcer develops at the site of contamination of the broken skin surface with infectious material or at the location of the arthropod bite. There are associated local lymphadenopathy, fever, and general malaise. Variations on this form result when the initial site is conjunctival or nasopharyngeal. Pneumonia occurs in some instances, usually appearing after the first week or ten days of illness. There may be single or multiple focal consolidations, often with pleural effusion and hilar adenopathy. This secondary pulmonary involvement has been adequately described by several authors (1). In contrast, if the route of infection is by inhalation of air-borne organisms, the early lesions appear as a primary pneumonic process. In untreated naturally occurring disease of this type, the estimated case fatality rate in North America is 30 per cent. Clinical Material It is the purpose of this discussion to emphasize the serial roentgen findings in 34 laboratory workers who became overtly ill following accidental respiratory exposure (2). Standard 6-foot postero-anterior and lateral chest films were obtained at least twice weekly during the illness and therapy; thereafter at least every other week until normal. The availability of recent pre-illness chest films permitted a critical evaluation. In 20 of the 34 patients the roentgen findings were positive. Most of these workers had received one or many inoculations with a killed P. tularensis vaccine. Their appearance in this series as patients is clear evidence that such a vaccination procedure falls short of its aim. After exposure, illness usually appeared within two to six days. The resultant disease was a grippal syndrome, with a sense of substernal tightness, a dry to slightly productive cough, and occasionally mild nasal stuffiness and sore throat. Pleuritic chest pain and productive cough were more frequent in the patients with radiographic evidence of pulmonary involvement. During the first few days of the disease the physical findings were usually minimal. Occasionally mild pharyngeal injection was noted.