Outbreak of Acinetobacter Baumannii in a Neonatal Icu: Only a Case-Control Study Was Able to Identify the “Nest”

Infection with carbapenem-resistant Acinetobacter baumannii (CRAB) in the Neonatal Intensive Care Unit (NICU) is a serious threat. Between April and August 2024, six CRAB bloodstream infections prompted aggressive outbreak control measures: hand hygiene, colonization screening, intensified cleaning/disinfection, review of the antibiotic protocol, and revision of the central venous catheter (CVC) care bundle (including PICC). Even after these measures, CRAB cases still increased to 14 in September 2024. Here, we present the results of the case-control study conducted to investigate the CRAB outbreak. For each CRAB case, three controls were selected — neonates without any infection or colonization — matched by week of admission and birth weight. A total of 27 variables were collected, including birth conditions, comorbidities, presence of invasive procedures, surgery, and antibiotic use. Data were recorded in a Google spreadsheet and analyzed using Epi Info. A total of 14 cases and 38 controls were analyzed. Due to the matching method, neither gestational age nor birth weight differed significantly between cases and controls. Univariate analysis of categorical variables identified that meropenem use, surgery, and ventilator use were significantly associated with the CRAB outbreak. An aggressive investigation of these three factors was immediately initiated. Initially, no specific findings were identified. Surgical procedures were evaluated by the infection control team. A thorough microbiological investigation was conducted in the ventilation system and its components, including cleaning and disinfection procedures. Subsequently, the probable source, or “nest,” was identified: Acinetobacter baumannii was found in the ventilator filters. The rigorous application of hand hygiene, colonization screening, intensified cleaning/disinfection, review of the empirical antibiotic protocol, and revision of the CVC care bundle were insufficient to identify the source of the CRAB outbreak. Only a qualitative-quantitative analysis, associating the results of a case-control study with qualitative investigation, was able to identify the CRAB reservoir and contain the outbreak. After correction of the ventilator filter disinfection procedures, no new CRAB cases occurred.