Background Antibiotic-associated diarrhea (AAD) is a condition characterized by diarrhea that occurs following the use of antibiotics and cannot be attributed to other causes. There are numerous types of antibiotics administered to elderly patients with severe illnesses, leading to a significant increase in the risk of AAD. However, there are limited reports analyzing the factors associated with AAD in elderly patients with severe illnesses.

Objective To analyze the factors associated with antibiotic-related diarrhea in elderly ICU patients with severe illness who have received antibiotics.

Methods Clinical data of patients admitted to the Department of Intensive Care Medicine at the First Medical Center of PLA General Hospital from January 1, 2020, to June 30, 2022, were retrospectively analyzed to identify the factors associated with antibiotic-associated diarrhea in elderly patients with severe illness.

Results The clinical data of 815 patients were collected, including 125 patients with AAD and 690 patients without AAD. Compared to the non-diarrhea group, the age-adjusted Charlson Comorbidity Index (aCCI) and SOFA scores were higher in the diarrhea group. Additionally, the usage rates of third-generation cephalosporin antibiotics, fluoroquinolones, carbapenems, glycopeptides, piperacillin-tazobactam sodium, and antifungal drugs were higher (P < 0.05). The AAD group had a higher mortality rate than the non-AAD group (P < 0.05). Multivariate Logistic regression analysis suggested that tracheotomy (OR=7.227, 95% CI: 2.147-24.326, P=0.001), CRRT (OR=4.529, 95% CI: 1.344-15.258, P=0.015), high C-reactive protein (OR=1.125, 95% CI: 1.019-1.241, P=0.019), high lipase (OR=1.005, 95% CI: 1.001-1.005, P=0.015), high aCCI (OR=1.706, 95% CI: 1.373-2.121, P<0.001), piperacillin tazobactam (OR=4.040, 95% CI: 1.405-11.622, P=0.010), third-generation cephalosporins (OR=6.787, 95% CI: 2.791-16.506, P<0.001), carbapenems (OR=5.714, 95% CI: 1.874-17.425, P=0.002), and diuretics (OR=9.098, 95% CI: 5.131-16.131, P<0.001) in critically ill elderly patients were associated with a higher risk of developing AAD. Conclusions: Tracheotomy, continuous renal replacement therapy (CRRT), C-reactive protein, lipase, aCCI, piperacillin tazobactam sodium, third-generation cephalosporin antibiotics, carbapenems antibiotics, and diuretic use were independently associated factors for the occurrence of AAD in elderly patients with severe disease.