Residential history, family characteristics and non-Hodgkin lymphoma, a population-based case-control study in the San Francisco Bay Area.

A population-based, case-control study (N = 1,593 cases, N = 2,515 controls) was conducted in the San Francisco Bay Area, California, to determine risk factors for non-Hodgkin lymphoma (NHL). This report examines residential characteristics, number of siblings, childhood infections, and allergic rhinitis to evaluate the association between NHL and the hygiene hypothesis. Adjusted unconditional logistic regression analyses included HIV-negative participants (N = 1,304 cases, N = 2,402 controls) ages 21 to 74 years, who completed in-person interviews. At childhood ages, odds ratios (OR) for NHL decreased with increasing number of household rooms (age 8 years, P(trend) = 0.08; age 15 years, P(trend) < 0.0001) and increased with more crowded living conditions (quartiles of no. people/no. rooms; age 8 years, P(trend) < 0.0001; age 15 years, P(trend) = 0.0004), whereas at older ages a greater number of people in the household and greater number of household rooms were positively associated with NHL. ORs increased with increasing number of siblings (P(trend) = 0.0003) and increasing birth order (P(trend) = 0.01). Participants with five or more younger siblings had a 50% increased OR for NHL. ORs for NHL decreased with an increasing number of different infections during childhood (age 8 years, P(trend) < 0.0001; age 15 years, P(trend) = 0.0003) and with history of allergic rhinitis (P < 0.0001). Our results are somewhat consistent with the hygiene hypothesis that less crowding and better sanitation results in fewer infections early in life and an increased incidence of immune-related conditions later in life. The role of the complex relationship between residential history, family characteristics, childhood infections, and immune function in the development of NHL warrants further investigation in pooled analyses.