Leukemia and lymphoma patients linked by prior social contact. Evaluation using a case-control approach

A case-control approach was used to evaluate whether patients with leukemia or lymphoma have a greater than expected tendency to have had prior close personal associations. Two census enumeration districts in different states with low population mobility were chosen, and each resident who had developed leukemia or lymphoma during a predetermined fixed interval was ascertained by review of tumor registry records. For each patient, a resident of the area was selected as a control matched for age, sex, race, and geographic location as of the time of diagnosis. Close personal associations between patients, controls, and both were determined by interviewing. In Area 1 the 8 patients had 11 social links (3 direct, 8 indirect) and the controls had 2 (both direct); P=0.0156, one-tailed significance test. In Area 2, the 21 patients had 21 close links (15 direct, 6 indirect) whereas the controls had 10 (direct 8, indirect 2; 0.25 greater than P greater than 0.20).