Tularemia -- United States, 1990-2000

Morbidity and Mortality Weekly Report. 2002;51(9) 

In This Article

Editorial Note

The number of tularemia cases reported annually has decreased substantially since the first half of the 1900s. The incidence was highest in 1939, when 2,291 cases were reported (2) and remained high throughout the 1940s. The number of cases declined substantially in the 1950s and 1960s to the relatively constant number of cases reported since that time.

In the United States, most persons with tularemia acquire the infection from arthropod bites, particularly tick bites, or from contact with infected mammals, particularly rabbits. Historically, most cases of tularemia occurred in summer, related to arthropod bites, and in winter, related to hunters coming into contact with infected rabbit carcasses. In recent years, a seasonal increase in incidence has occurred only in the late spring and summer months, when arthropod bites are most common. Outbreaks of tularemia in the United States have been associated with muskrat handling [3], tick bites [4,5], deerfly bites [6], and lawn mowing or cutting brush [7]. Sporadic cases in the United States have been associated with contaminated drinking water [8] and various laboratory exposures [9]. Outbreaks of pneumonic tularemia, particularly in low-incidence areas, should prompt consideration of bioterrorism [10].

The high incidence of tularemia among males and among children aged <10 years might be associated with increased opportunity for exposure to infected ticks or animals, less use of personal protective measures against tick bites, or diagnostic or reporting bias. The high incidence among American Indians/Alaska Natives might be associated with their increased risk for exposure; outbreaks of tularemia have been reported on reservations in Montana and South Dakota, where a high prevalence of tularemia infection was found in ticks and dogs [4,5].

The findings in this report are subject to several limitations, including underreporting and the lack of documented laboratory confirmation for all cases. Surveillance for tularemia could be improved by documenting laboratory confirmation of diagnosis and by including additional data (e.g., clinical presentation, exposure history, and outcome).

Following a dramatic decline in the second half of the 20th century, the incidence of tularemia in the United States remains low. The epidemiologic characteristics described in this report provide a background against which unusual patterns of disease occurrence, including bioterrorism events, may be recognized more quickly.

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