Lyme Disease 2003
*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2003
Lyme disease is caused by the bacterium Borrelia burgdorferi and is the most commonly diagnosed tick-borne disease in Indiana. It is transmitted by the deer tick (Ixodes scapularis) by using small wild rodents as its reservoir. Transmission can occur after the tick has been attached and feeding for approximately 36 hours. Signs and symptoms can appear 3 to 30 days postexposure but generally occur 7 to 14 days postexposure.
In 2003, 25 cases of Lyme disease were reported in Indiana, for a rate of 0.4 cases per 100,000 population (Table 1). This is approximately the same rate reported in previous years. Figure 1 shows the number of reported cases per year for 1999-2003. Incidence of disease was greatest during the summer months (Figure 2). Over 75 percent of reported cases occur from May through September when ticks are active. The disease has been reported in all months of the year, as some infections do not result in an erythema migrans and may not be suspected until secondary symptoms occur. As shown in Figure 3, age-specific rates were highest among adults aged 30-39 years. Lyme disease cases were reported more in the northwestern part of the state. Twenty counties reported Lyme disease cases; however, no county reported five or more cases.