Risk of pneumonia among patients with splenectomy: a retrospective population-based cohort study

BACKGROUND: People without a spleen are particularly susceptible to various overwhelming infections including pneumonia. Although the association between splenectomy and pneumonia has been previously studied, there has been no study using the national claims data. OBJECTIVES: The aim of the study was to investigate the association between splenectomy and pneumonia. DESIGN: A retrospective population-based cohort analysis. SETTINGS: Database of the Taiwan National Health Insurance Program. PATIENTS: Persons newly diagnosed with splenectomy from 2000 to 2010 were compared with randomly selected subjects without splenectomy. The groups were matched by sex, age, comorbidities, and the year of index date and analyzed by multivariate methods. MAIN OUTCOME MEASURE: The difference in incidence of pneumonia at the end of 2011. RESULTS: In 12 757 individuals aged 20–84 years with splenectomy, the overall incidence of pneumonia was 1.86-fold higher than in the 51 019 individuals without splenectomy (25.0 vs. 13.4 per 1000 person-years, 95% CI 1.78, 1.95). After multivariate analysis, the adjusted hazard ratio for pneumonia was 2.2 for subjects with splenectomy (95%CI 2.07, 2.34). In further analysis, in the absence of any comorbidity, the adjusted HR for pneumonia was 3.03 for those with splenectomy alone (95% CI 2.76, 3.33) and 5.28 (95% CI 4.82, 5.78) for splenectomy and any comorbidity. CONCLUSIONS: Although not a novel finding, we confirmed that splenectomy increases the relative risk for developing pneumonia in a large study population. Even in the absence of any comorbidity, the risk remains high. Patients with splenectomy should receive preventive interventions for pneumonia, such as vaccination. LIMITATIONS: ICD-9 codes do not differentiate if pneumonia is caused by a viral, a bacterial or unspecified organisms, and some behavioral factors like smoking could not be ascertained directly.