DPP4 and susceptibility to pneumonia measurement: In a sub-group analysis, DPP4 inhibitors were not associated with an increased risk of an upper respiratory tract infection (adjusted HR = 0.94; 95% CI 0.84–1.05); however, when examining pneumonia and influenza specifically, DPP4 inhibitors were found to have a protective effect over sulfonylureas (adjusted HR = 0.63; 95% CI 0.44–0.90).