Effectiveness of on-the-ground locating in reducing loss to follow-up in the gulf long-term follow-up study (GuLF STUDY)

Background and Objective The GuLF STUDY is a prospective cohort study assessing potential health effects among 55,000 workers and volunteers who cleaned-up the 2010 Deepwater Horizon oil spill. A subgroup of 20,000 participants is being selected to complete a home visit within a month of the telephone-based enrollment interview to collect biological samples and clinical measurements. About 20% of participants initially agreeing to a home visit cannot be reached for scheduling. We conducted a pilot study to determine whether on-the-ground locating efforts could reduce loss to follow-up.

Methods Study personnel visited the last known addresses of a sample of 96 participants and attempted to re-establish contact and document reasons for loss to follow-up.

Results We verified that 48 (50%) of these presumably “lost” participants still resided at their last known address. Among those located, 60% agreed to schedule a home visit, 13% asked for more time to consider, and 8% refused the home visit. Unstable phone numbers were common among all those who were located. After multiple visits, the validity of the last known address was not determined for 30% of participants. Only 20% of addresses were invalidated.

Conclusion Our pilot study suggests that many of those initially lost to follow-up can be retained by on-the-ground locating efforts. We will continue this initiative and estimate that we will retain 30% of participants (N=1,200) who would otherwise have been lost to follow-up.