AN OUTBREAK OF PRIMARY PNEUMONIC TULAREMIA ON MARTHA’S VINEYARD
[Feldman KA et al. NEJM 2001;345:1601]:
During June and July 2000, there were nine cases of pneumonic tularemia detected at Martha’s Vineyard. The authors, from the Massachusetts Department of Public Health and the CDC, report a case-controlled study of this outbreak to determine risk factors. A confirmed case required symptoms suggesting tularemia (acute illness with fever, adenopathy, skin ulcer or cough) and laboratory evidence of tularemia (antibody titer of ≥ 1:128, positive DFA or positive culture). There were 15 patients who satisfied the case definition, including 11 with primary pneumonic tularemia. There was one patient who had positive blood and lung cultures who died of this infection possibly due to a delay in seeking medical care. The major risk factor was use of a lawn mower or brush cutter during the two weeks before the onset of illness (odds ratio 9.2) during the summer. There was only one patient who reported exposure to a rabbit.
During most years in the United States, there are 100–200 reported cases of tularemia, most from Missouri, Arkansas, Oklahoma and Kansas where rabbits are the primary reservoir. Tick bites may also be a mechanism of transmission. As pointed out in the editorial by Richard Hornick (NEJM 2001;345:1637), Massachusetts has relatively few cases. There were 20 reported cases during the period 1953–1977, and then an epidemic similar in size to the one reported here occurred in 1978 (NEJM 1979;301:826). In the 2000 epidemic, the mechanism appeared to be mowing lawns and cutting brush presumably due to aerosols. This is a diagnostic consideration in patients with typical findings combined with contact with rabbits, insect bites or travel/residents in areas of endemic disease. The diagnosis is usually established with serology, but diagnostic titers require a week from the onset of symptoms to become positive. Cultures may yield the organism, but the laboratory must be warned because special media are required and there is a risk to microbiologists requiring protective hoods. It should be mentioned that tularemia is a category A microbe for bioterrorism, so that this becomes another consideration with such cases.