Lessons learned from a structured and descriptive analysis of nosocomial outbreaks in hematology-oncology

Nosocomial outbreaks among immunocompromised patients are serious events. We conducted a descriptive analysis of nosocomial outbreaks in hematology and oncology, drawing on data from 196 outbreaks included in the Worldwide Outbreak Database. Our analysis includes patient characteristics, pathogens, outbreak sources, routes of transmission, and infection control measures. Furthermore, it determines risk factors for increased infection control effort by using the Weighted Cumulative Hygiene Score (WCHS). Bloodstream infections and lower respiratory tract infections were most often observed in the outbreak patient population. The primary infectious agents were Pseudomonas aeruginosa and other non-fermenting Gram-negative rods as well as enterococci. An index person (patient/staff) and the environment were the main reservoirs for transmission. Noteworthy, the exact source could not be identified in nearly half of the outbreak events. Infection control measures were usually implemented as bundles including but not limited to screening of patients, changes in the disinfection or sterilization regime and enforcement of proper hand hygiene. Multivariable regression analysis revealed the following factors being independently associated with a high infection control effort: causative agent fungi (other than molds) (OR=6.26; CI95:1.60-24.44), multi-drug resistant bacteria (OR=6.01; CI95:2.56-14.09), antibiotic therapy (OR=2.97; CI95:1.05-8.38), a high number (≥ 10) of patients involved in the outbreak (OR=2.54; CI95:1.11-5.81), and the transmission route being direct contact (OR=3.42; CI95:1.43-8.16). The occurrence of lower respiratory tract infections was strongly associated with mortality (OR=7.95; CI95:2.06-30.73). Staff working in hematology and oncology should be aware of these details in order to approach a nosocomial outbreak appropriately at a most early time point.