"Type of stress ulcer prophylaxis and risk of nosocomial pneumonia in cardiac surgical patients: cohort study"
BMJ Sep 19
http://www.bmj.com/content/347/bmj.f5416 
"Conclusions Patients treated with proton pump inhibitors for stress ulcer had a small increase in the risk of postoperative pneumonia compared with patients treated with H2receptor antagonists; this risk remained after confounding was accounted for using multiple analytic approaches."