Surge in U.S. Cases of Rocky Mountain Spotted Fever

THURSDAY, Oct. 4, 2007 (HealthDay News) -- Reports of tick-transmitted Rocky Mountain spotted fever in the United States almost tripled from 695 in 2001 to 1,936 in 2005, researchers say.

The potentially fatal disease is caused by Rickettsia rickettsii bacteria, which is transmitted to humans through the bite of the dog tick or Rocky Mountain wood tick. Within 14 days after being bitten by an infected tick, a person typically develops a fever, headache, body aches upset stomach and rash. If not treated with antibiotics, organ failure may develop. About two percent of people with the disease die.

"This disease is becoming more common in cities and suburbs, likely because people are going to rural areas and coming home to the cities, and possibly also because suburbia is encroaching on rural, tick-infested areas," study author Dr. David Swerdlow noted in a prepared statement.

At the time of the study, Swerdlow was team leader for the Rickettsial Zoonoses Branch of the U.S. Centers for Disease Control and Prevention in Atlanta. The researchers analyzed 6,598 Rocky Mountain spotted fever cases reported in 45 states from 2001 to 2005. There were 22 deaths reported, but Swerdlow said the actual number was likely higher.

Nationwide, 53 counties had a fivefold increase in infections, and 51 percent of counties were newly affected by the disease between 2001 and 2005. The largest increases were seen in South Atlantic states. Suburban areas had a greater incidence of the disease than rural areas. Only five states did not report any cases: Alaska, California, Hawaii, Maine and Washington.

The findings were to be presented Thursday at the annual meeting of the Infectious Diseases Society of North America, in San Diego.

More information

The U.S. National Institute of Allergy and Infectious Diseases has more about Rocky Mountain spotted fever.