Increased risk of zoonotic Salmonella and Campylobacter gastroenteritis in patients with haematological malignancies: a population-based study

We hypothesised that haematological malignancies increase the risk of acquiring zoonotic Salmonella or Campylobacter gastroenteritis. The population-based study comprised all first-time Salmonella/Campylobacter gastroenteritis cases in two Danish counties (1991–2003), with age- and gender-matched controls from the background population. We linked the study cohort to registries to obtain data on malignancies, chemotherapy (yes/no), and main comorbidities diagnosed before Salmonella/Campylobacter gastroenteritis. Based on this design, we determined incidence rate ratios (IRR) in conditional logistic regression analyses, and we used weighted mean regression curves to evaluate fluctuations in risk 0–5 years after the malignancy diagnosis. Sixty-eight of 13,324 cases (0.5%) and 29 of 26,648 controls (0.1%) had haematological malignancy before their Salmonella/Campylobacter gastroenteritis. Comorbidity-adjusted IRR for Salmonella/Campylobacter gastroenteritis in patients with haematological malignancy as compared to patients without malignancy were 4.46 [95% confidence intervals (CI), 2.88–6.90] for all individuals, 8.33 (95% CI, 4.31–16.1) for Salmonella, and 2.17 (95% CI, 1.15–4.08) for Campylobacter. Stratification on chemotherapy treatment did not change these estimates. In time-related analyses, IRR were 7–8 in the first 2 years after the haematological malignancy diagnosis and 4–5 in the following 3 years. Patients with haematological malignancy had increased long-term risk of enquiring Salmonella or Campylobacter gastroenteritis.