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

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 seroconverted a year later (annual incidence = 1.7%). The cumulative frequency of seropositivity for Lyme disease in the study population was > or = 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.

Effectiveness of Personal Protective Measures to Prevent Lyme Disease

“…Smith et al evaluated outdoor workers by using questionnaires and serologic tests for antibody to Borrelia burgdorferi and found that workers with a history of outdoor employment were twice as likely to be seropositive as those without such a history; however, this difference was not statistically signifi cant (9). A study conducted in California by Lane et al found that outdoor occupations such as woodcutting were associated with an increased risk for LD (10).…”

Lyme borreliosis

“…65 Outdoor recreational activities in similar vegetated areas can also increase chance of infection. 66 Persons whose occupation places them in wooded areas (eg, forestry or wildlife workers) may occasionally be exposed to infected ticks. 67 Dogs and horses that have ongoing access to densely vegetated areas near their home (peridomestic exposure) or occasional recreational access to these same areas are at equal or greater risk of becoming infected, compared with humans.…”

Anti-arthropod saliva antibodies among residents of a community at high risk for Lyme disease in California.

“…Ninety-three of these subjects completed a detailed questionnaire at the time of entry. 20 In the present study, sera from 104 of the original subjects, 85 of whom completed the entry questionnaire, were evaluated for AASA. Some of the serum specimens used in the initial 20 and subsequent serosurveys had been used up and therefore were unavailable for further testing.…”

“…[16][17][18][19] In northern California, bites by bloodsucking flies and seropositivity for B. burgdorferi were associated significantly in residents of a rural community at high risk (CHR). 20 The investigators cautioned that this association probably represented either an indirect measure of outdoor exposure or it may have been due to chance alone. So far, only 3 species of arthropods (2 fleas and 1 mosquito) other than ticks have been examined for the presence of spirochetes in California, 12,21,22 and none was found to contain spirochetes.…”

“…The present study was undertaken to determine the prevalence of anti-arthropod saliva antibodies (AASA) among members of the CHR. 20 In particular, we evaluated the degree of association between seropositivity for B. burgdorferi and arthropodal salivary proteins by I. pacificus and 3 other bloodsucking arthropods, i.e., the Pacific Coast tick (D. occidentalis), the western cone-nose bug (Triatoma protracta), and the western tree hole mosquito (Aedes sierrensis), that bite people in the same community.…”