January 31, 2014
1 min read

Environmental, behavioral factors influence risk for Lyme disease

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Susceptibility to Lyme disease is related to environmental and behavioral factors, with protective clothing identified as the most effective means of reducing exposure, recent study data suggest.

In a longitudinal study, researchers conducted a concurrent analysis of the relationships between Lyme disease and both individual and environmental variables. The study took place on Block Island, R.I., from 2005 to 2011.

The researchers utilized high-resolution imagery to ascertain the arrangement and density of lawn-shrub edges on all residential properties, where most contact with ticks is thought to occur. This assessment of environmental risk was corroborated by collecting ticks along shrub edges on a subset of properties.

The study population consisted of Block Island residents who agreed to take part in annual serological surveys conducted there every spring and fall. These participants completed a questionnaire and provided blood samples for Borrelia burgdorferi and B. microti serological analyses. Patients were considered to have Lyme disease exposure if they tested positive for a B. burgdorferi antibody.

The questionnaire evaluated individual risk factors through questions about previous tick-borne illness, age, home or property factors possibly linked to tick exposure, protective behaviors and outdoor activities. The researchers also conducted extensive landscape metrics and used negative binomial regression to determine the association between landscape metrics and tick density.

They conducted univariate analyses for all variables and assessed multivariate models that included all combinations of variables found to be significant in the univariate analyses.

Factors found to be significantly correlated with positive Lyme disease blood tests included: prior self-reported Lyme disease episodes; the use of protective clothing while outside; the average number of hours each day spent in a tick habitat; age of participant; and the denseness of shrub edges on the participant’s property. Previous Lyme diagnosis and age comprised the best fit multivariate model. The second best multivariate model consisted of hours spent near a tick habitat, participant’s age, shrub edge thickness (increased risk) and the use of protective clothing (decreased risk).

“Consistent with previous studies, wearing protective clothing was a significantly protective behavior against Lyme disease,” the researchers wrote. “We did not identify a significant effect of tick checks, which was found to be effective in one previous study.”

Disclosure: Funding was provided by the Environmental Protection Agency, NIH grants and the Gordon and Llura Gund Foundation.