ObjectiveTo evaluate the effect of carbapenem exposure on isolation rate of multidrugresistant organisms(MDROs) and prognosis of elderly patients with severe pneumonia. MethodsElderly patients with severe pneumonia and admitted to the intensive care unit in a hospital between February 2014 and February 2016 were investigated retrospectively. According to whether there was carbapenem exposure, patients were divided into group A(carbapenem exposure group) and group B(carbapenem nonexposure group). Patients in group A were subdivided into two subgroups according to exposure time of carbapenems, group A1 received carbapenems for>7 days, group A2 received carbapenems for ≤7 days. The isolation rates of MDROs, mechanical ventilation days, length of stay in ICU, and 28day mortality among groups were compared and analyzed. ResultsA total of 86 patients were enrolled in the investigation, 57 were males and 29 were females; the average age was(80.12+10.45) years (range: 65-92 years). There were 40 cases in group A, 46 in group B; 24 cases in group A1, and 16 in group A2. The isolation rates of MDROs in group A and group B were 65.00% and 36.96% respectively, difference was statistically significant（P＜0.05）；Comparison between two groups of patients revealed that mechanical ventilation days, length of stay in ICU, and 28day mortality in group A were all higher than group B, difference was statistically significant（all P＜0.05）；the isolation rates of MDROs in group A1 was higher than group A2 (75.00% vs 43.75%, P＜0.05）; mechanical ventilation days of group A1 was higher than group A2 （［7.69±2.22］d vs ［6.34±1.56］d, P＜0.05）；28day mortality and length of stay in ICU between group A1 and A2 were not significantly different（both P＞0.05）. ConclusionCarbapenem exposure can increase the occurrence of MDRO infection, especially the nonfermentative bacterial colonization or infection, and prolong the mechanical ventilation days and length of stay in ICU, thus affect the prognosis of patients.