Pet birds and risk of lung cancer in North-Western Germany.

In a case-control study on lung cancer and occupational exposures, a subgroup of 144 cases and 253 population-based controls interviewed in the last 16 months of the study, were additionally asked about their exposure to pet birds and other pets. We used the same questionnaire as a previous German study that found a positive association between pet bird keeping and lung cancer. Odds ratios were calculated for lifetime and adulthood exposure respectively. The adjusted odds ratio for ever keeping pet birds was 0.85 (95% CI: 0.53-1.35), and 0.87 (95% CI: 0.56-1.36) for adulthood exposure. There was no evidence of a trend for increasing lung cancer risk with duration of pet bird keeping. With decreasing age at diagnosis, an apparent risk emerged, yielding an odds ratio of 7.62 (95% CI: 2.15-26.95) for ever versus never in the youngest age group (< or =55 years). This odds ratio was reduced to 3.82 (95% CI: 0.98-14.92) after adjustment for smoking and was only 1.39 (95% CI: 0.49-3.95) for adulthood exposure. In general, our results indicate that pet bird keeping does not seem to increase the risk of lung cancer. The divergent findings at younger ages may be explained by age-related recall bias, but should be investigated in future studies.