Risk Factors for Lyme Disease in a Small Rural Community in Northern California

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Abstract
A 1-year prospective study of risk factors for seropositivity to and contraction of Lyme disease among members of a small rural community (population, approximately 150) was conducted in northwestern California in 1988–1989.The initial rate of seropositivity for Borrelia burgdorferi for 119 current or former residents ranged from 15 to 20% among three laboratories, with statistically significant interlaboratory agreement. Questionnaires were completed by 93 current residents at entry and 80 residents a year later to evaluate the association of serologic status with 20 categorical and 47 continuous variables, seropositive subjects had resided in the study area about 2 years longer, were bitten by unspecified biting flies more often, and were less likely to have engaged in hiking than seronegative subjects.One of 59 seronegative subjects sero-converted a year later (annual incidence = 1.7%).The cumulative frequency of seropositivity for Lyme disease in the study population was ≥24%.Of 83 subjects examined physically, 13 were diagnosed as having definite and 18 as having probable Lyme disease.The seropositivity rate was significantly higher (38.7%) among individuals with definite/probable Lyme disease than in asymptomatic subjects (13.5%). Subjects who were seronegative or free of Lyme disease reported nearly as many tick bites as subjects who were seropositive or had a diagnosis of the disease. Age, time spent outdoors in the fall multiplied by a clothing index, and woodcutting were significantly associated with Lyme disease in logistic regression analyses. Am J Epidemiol 1992; 136: 1358–68.

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