Tick-Borne Disease Surveillance in California, 2005

Vector-Borne Diseases in California, Annual Report 2005, California Department of Health Services, Vector-Borne Disease Section

Human disease surveillance

Lyme disease

A total of 94 cases of Lyme disease were reported to the California Department of Health Services (CDHS) in 2005. Case-patients were residents of 26 counties. Humboldt County reported the most cases (11). Reported incidence was highest in Trinity County at 23 cases per 100,000 residents. Of 44 cases for whom county of likely exposure was reported, 32 had exposure outside their county of residence; 28 of these reported exposure outside California. The most frequently reported location of exposure was Massachusetts (eight cases).

The median age of reported Lyme disease cases was 43 years (range, 3 to 78 years) and 51 (54%) were female. Of 79 cases for which race was reported, 74 (94%) were white, 3 were Native American, and 1 each was Asian and Black. Erythema migrans (EM) was identified in 59 (63%) cases. Of 51 cases with EM for which date of illness onset was reported, 36 (71%) occurred between May and August.

Tick-borne relapsing fever

Five cases of tick-borne relapsing fever (RF) were reported to CDHS in 2005. Case-patients were residents of three counties (El Dorado, Humboldt, Santa Cruz) and ranged from 6 to 58 years old. Four case-patients were likely infected in the greater Lake Tahoe area; one case-patient was likely infected while visiting a private cabin in Lassen County. One case had onset of illness in April, while the remaining four had onset in late July and August.

CDHS collaborated with the El Dorado County Departments of Health and Environmental Management, the Nevada State Health Division, and the Division of Vector-Borne Infectious Diseases (DVBID), U.S. Centers for Disease Control and Prevention (CDC), to investigate two cases of RF with unusually severe clinical courses. A 46-year-old woman from Nevada and a 43-year-old woman from El Dorado County both developed RF between February and April that progressed to severe respiratory distress and extended hospitalizations. Both patients eventually recovered. Both case-patients had a history of travel to or residence in the Lake Tahoe area. Preliminary investigation of the California case’s residence revealed live and dead mice in the garage, as well as live chipmunks in and around the house. One engorged Ornithodoros sp. tick was discovered in the bedroom. Several Ornithodoros ticks were also recovered from rodent and bird nests removed from underneath the building’s exterior siding.