Type 2 diabetes mellitus and risk of community-acquired pneumonia: a systematic review and meta-analysis of observational studies

BACKGROUND: People with type 2 diabetes are at greater risk for infections than those without type 2 diabetes. Our objective was to examine the association between type 2 diabetes and the risk of community-acquired pneumonia (CAP). METHODS: In this systematic review and meta-analysis, we searched MEDLINE, Embase, CINAHL, ProQuest theses and dissertations, Global Health, the Global Index Medicus of the World Health Organization, and Google Scholar. We included observational studies published in English or French between Jan. 1, 1946 (start of MEDLINE) and July 18, 2020. Two independent reviewers extracted data and assessed quality using the ROBINS-I tool. DerSimonian–Laird random-effects models were used to pool estimates of the association between type 2 diabetes and CAP. RESULTS: Our systematic review included 15 articles, reporting on 13 cohort studies and 4 case–control studies (14 538 968 patients). All studies reported an increased risk of pneumonia among patients with type 2 diabetes, and all were at serious risk of bias. When estimates were pooled across studies, the pooled relative risk was 1.64 (95% confidence interval [CI] 1.55–1.73); although there was a substantial amount of relative heterogeneity (I(2) 94.2), the amount of absolute heterogeneity was more modest (T(2) 0.008). The relative risk was 1.70 (95% CI 1.63–1.77, I(2) 85.2%, T(2) 0.002) among cohort studies (n = 13), and the odds ratio was 1.54 (95% CI 1.14–2.09, I(2) 92.7%, T(2) 0.07) among case–control studies (n = 4). INTERPRETATION: Type 2 diabetes may be associated with an increased risk of CAP; however, the available evidence is from studies at serious risk of bias, and additional, high-quality studies are needed to confirm these findings. PROSPERO REGISTRATION: CRD42018116409