Rocky Mountain spotted fever epidemiology and demographics

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Epidemiology

Rocky Mountain spotted fever has been a reportable disease in the United States since the 1920s. In the last 50 years, approximately 250-1200 cases of Rocky Mountain spotted fever have been reported annually, although it is likely that many more cases go unreported. CDC compiles the number of cases reported by the state health departments. To ensure standardization of reporting across the country, CDC advises that a consistent case definition be used by all states.

Epidemiology Graph 1 - Reported cases of Rocky Mountain spotted fever in the United States, 1942-1996

Epidemiology Graph 2 - Number of Rocky Mountain spotted fever cases in the United States, 1997-2002, as determined by the number of cases reported to the Centers for Disease Control and Prevention by the states via the National Electronic Telecommunications System for Surveillance (NETSS).

Epidemiology Graph 3 - Comparison between RMSF cases and their fatality.

Epidemiology Graph 4 - Showing the number of annual cases of Rocky Mountain Spotted Fever.

Seasonal Distribution of Rocky Mountain Spotted Fever

Over 90% of patients with Rocky Mountain spotted fever are infected during April through September. This period is the season for increased numbers of adult and nymphal Dermacentor ticks. A history of tick bite or exposure to tick-infested habitats is reported in approximately 60% of all cases of Rocky Mountain spotted fever.

Geography of Rocky Mountain Spotted Fever

Over half of Rocky Mountain spotted fever infections are reported from the south-Atlantic region of the United States (Delaware, Maryland, Washington D.C., Virginia, West Virginia, North Carolina, South Carolina, Georgia, and Florida). Infection also occurs in other parts of the United States, namely the Pacific region (Washington, Oregon, and California) and west south-central (Arkansas, Louisiana, Oklahoma, and Texas) region.

The states with the highest incidences of Rocky Mountain spotted fever are North Carolina and Oklahoma; these two states combined accounted for 35% of the total number of U.S. cases reported to CDC during 1993 through 1996. Although Rocky Mountain spotted fever was first identified in the Rocky Mountain states, less than 3% of the U.S. cases were reported from that area during the same interval (1993-1996).

Epidemiology Image 4 - Annual incidence per million population for Rocky Mountain spotted fever by state in the United States for 2002, as determined on the basis of cases reported to the National Electronic Telecommunications System for Surveillance.

Worldwide Infection

Infection with Rickettsia rickettsii has also been documented in Argentina, Brazil, Colombia, Costa Rica, Mexico, and Panama. Some synonyms for Rocky Mountain spotted fever in other countries include tick typhus, Tobia fever (Colombia), São Paulo fever and fiebre maculosa (Brazil), and fiebre manchada (Mexico). Closely related organisms cause other types of spotted fevers in other parts of the world.

Table of Human Disease Around the World Caused by Spotted Fever Group Rickettsiae

Demographics

The frequency of reported cases of Rocky Mountain spotted fever is highest among males, Caucasians, and children. Two-thirds of the Rocky Mountain spotted fever cases occur in children under the age of 15 years, with the peak age being 5 to 9 years old. Individuals with frequent exposure to dogs and who reside near wooded areas or areas with high grass may also be at increased risk of infection.

Infection with Rickettsia rickettsii has also been documented in Argentina, Brazil, Colombia, Costa Rica, Mexico, and Panama. Closely related organisms cause other types of spotted fevers in other parts of the world.