BackgroundNosocomial infections are major public health problem which affects more than 100 million patients each year globally. This leads to prolonged hospital stays, a high mortality rate, and a vast financial burden to the healthcare system as well as the patients. This study aimed to find out the incidence of nosocomial infections and determinant factors among admitted adult chronic illness patients at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia.MethodsAn institutional-based retrospective follow-up study design was employed among 597 respondents. The secondary data was collected from April 15 to May 15, 2021. A computer-generated random sampling technique was used to select a total of 599 patients using Open-epi software. Structured checklists were used to collect data. For data entry and analysis Epi-Data version 4.6 and STATA 16 were used respectively. To identify statistically significant variables Cox-regressions (univariable and multivariable) were performed. To declare statistically significant variables based on p < 0.05 in the multivariable Cox-regression model, adjusted hazard ratio with 95% CI was used.ResultsA total of 597(99.6%) adult chronic illness patients were included in the study. Of these, 53 (8.88%) participants developed nosocomial infections and the incidence rate of nosocomial infection was 6.6 per 1,000 person-days observation. In this study, not taking antibiotics (AHR = 2.74, 95% CI: 1.49, 5.04), using mechanical ventilation (AHR = 2.67, 95% CI: 1.36, 5.26), being on urinary catheter (AHR = 4.62, 95% CI: 2.22, 9.65), being on intravenous catheter (AHR = 3.42, 95% CI: 1.22, 9.61) and length of hospital stay >20 days (AHR = 2.66, 95% CI: 1.43, 4.94) were significantly associated with nosocomial infections.ConclusionsThe findings have indicated that the incidence of nosocomial infection was low. No taking antibiotics, intravenous insertion, mechanical ventilation, length of hospital stay, and urinary catheterization were the predictors for the development of nosocomial infection. Therefore, we recommend that the healthcare providers need to give emphasis on infection prevention and control in the institution on these factors that have a significant effect on nosocomial infection.