Home and garden insecticide use and non-Hodgkin lymphoma (NHL) risk

Purpose NHL incidence has risen in past decades. Reasons for this increase are largely unexplained. In this population-based case-control study, we examined NHL risk and use of home and garden insecticides. Methods We identified NHL cases, uninfected with HIV, diagnosed between 1998 and 2000 among men and women aged 20–74 years in Iowa, Los Angeles County, and the Detroit and Seattle metropolitan areas. Controls were selected using random-digit-dialing or Medicare files. Computer-assisted personal interviews (1321 cases, 1057 controls) elicited data on insecticide use at each home occupied since 1970. Insecticide levels were measured in dust taken from used vacuum cleaner bags (682 cases, 513 controls). Multiple logistic regression models were used to obtain odds ratios (ORs) and 95% confidence intervals (CI), and trend tests were performed using natural log transformed continuous variables. Results People whose homes were treated for termites had elevated NHL risk (OR = 1.3, CI = 1.0–1.6). Risk was modestly elevated in all but one study center and in all sexes and races. The elevation in risk was restricted to people whose homes were treated before the 1988 chlordane ban. There was a significant trend of increasing risk with increasing levels of -chlordane residues in dust (Ptrend = 0.05) and a marginally significant trend for (-chlordane (Ptrend = 0.06). Compared to people with no termite treatment and no measurable chlordane in dust, those with more than two treatments and above-median levels of chlordane had a three- to four-fold risk of NHL. We did not find evidence of associations for treatment of insects overall, for specific types of insects other than termites, or for elevated residues of other insecticides that were widely used between 1970 and 2000. Conclusion Treatment of termites with chlordane may increase NHL risk. We are currently investigating the association between NHL risk and chlordane metabolites in blood, and the relationships between chlordane levels in dust, chlordane metabolites in blood, and termiticide use.