Pneumonic tularemia on Martha's Vineyard: clinical, epidemiologic, and ecological characteristics.

Martha's Vineyard, Massachusetts, is the site of the only two recognized outbreaks of primary pneumonic tularemia in the United States. Beginning in 2000 and continuing through 2006, 59 presumed or confirmed tularemia cases have been reported from Martha's Vineyard, with more than 60% of these presumed to be due to inhalation of the agent. A joint CDC/Massachusetts Department of Public Health case-control study identified landscaping activities such as lawnmowing or brush cutting to be important risk factors. The fomites that serve as the basis for risk for landscapers, however, remain unidentified. Clinically, cases generally have a pneumonic component, but the development of pulmonary signs can be greatly delayed. The spectrum of illness ranges from relatively mild disease, in which cases may be treated on an outpatient basis, to severe illness requiring hospitalization. In each scenario, gentamicin therapy tends to rapidly induce defervescence, although exceptions have been noted. Even with heightened awareness during the current outbreak, physicians may easily miss a diagnosis of tularemia, usually by attributing illness to the more common Febrile illnesses. Dog ticks appear to maintain the agent on this island, with as many as 5% infected by the agent of tularemia. The main hosts for dog ticks, skunks and raccoons, are very frequently seroreactive, suggesting the possibility for their involvement in environmental contamination due to their peridomestic habits. Why tularemia is prevalent on Martha's Vineyard and why it commonly presents as a pneumonic disease there remain undescribed.