CASE-CONTROL STUDY OF RISK-FACTORS FOR INCIDENT LYME-DISEASE IN CALIFORNIA

To identify risk factors for incident Lyme disease in California durin g the period June 1, 1991 to December 31, 1992, the authors compared t he activities of 101 cases of physician-diagnosed erythema migrans asc ertained via both active and passive surveillance with those of 107 co ntrols matched on sex, age, and neighborhood. Questions asked by telep hone pertained to location of home, presence of wildlife around the ho use, hours of outdoor work and outdoor leisure activities, pet ownersh ip, precautionary measures to avoid tick bites, tick removal methods, and knowledge about Lyme disease. For cases, activities pertained to t he month prior to the onset of erythema migrans; controls were intervi ewed about the same activities during the same one-month period. The o bservation of deer and lizards around the home and a history of exposu re to ticks were associated with Lyme disease (deer, odds ration (OR) = 2.53, 95% confidence interval (CI) 1.25-5.15; lizards, OR = 2.14, 95 % CI 1.14-4.04). However, the only activity associated with Lyme disea se was the use for more than 5 hours per week of wide maintained trail s (OR = 11.33, 95% CI 1.33-123.5); this association occurred only in p ersons with other outdoor leisure activities. No other behaviors or ac tivities were identified as risk factors for acquisition of Lyme disea se in California.