Recruitment of population-based controls for ALS cases from the National ALS Registry

Objective: In 2010, the United States Agency for Toxic Substances and Disease Registry (ATSDR) created the National ALS Registry (Registry) to examine the epidemiology of ALS and potential risk factors. We are currently recruiting population-based controls for an epidemiologic case-control study to examine ALS environmental risk factors using this Registry. To date, we have recruited 181 non-diseased, population-based controls for comparison to Registry cases (n = 280). Here we report our recruitment methods for controls and the associated response rates and costs. Methods: Eligible ALS cases had complete risk factor survey data, DNA analysis, and blood concentrations of persistent organic pollutants (POPs). Age, sex, and county-matched controls were identified from commercial/consumer databases using a targeted landline phone sample. Eligible controls were consented, surveyed, and mailed the POPs' blood analysis consent form. Once consented, phlebotomy was scheduled. Results: We mailed 3760 recruitment letters for 181 potential case-matches across 42 states between 9/2018 and 3/2020. After making phone contact and determining eligibility, 146 controls agreed to participate (response rate = 11.4%, cooperation rate = 22.8%). To date, 127 controls completed the survey and bloodwork. Though controls were matched to cases on age, sex, and county, unmatched characteristics (e.g. smoking) did not differ statistically. Interviewing and incentive costs are estimated at $211.85 per complete participation. Conclusions: Recruiting matched population-based controls for comparison to cases from the Registry for a study involving completion of a detailed survey and blood specimen provision is relatively feasible and cost effective. This recruitment method could be useful for case-control studies of other rare disorders.