Staphylococcus aureus and MRSA colonization and antimicrobial susceptibility among neonates, mothers, and the NICU environment in Addis Ababa, Ethiopia

Staphylococcus aureus , particularly methicillin-resistant S. aureus (MRSA), is a major cause of healthcare-associated infections and contributes substantially to the global burden of antimicrobial resistance. Neonates admitted to neonatal intensive care units (NICUs) are especially vulnerable because of their immature immune systems, frequent invasive procedures, and prolonged exposure to healthcare environments. Colonization with MRSA may precede invasive infection and facilitate transmission within NICUs. However, data describing MRSA colonization among neonates, their mothers, and the NICU environment remain limited in Ethiopia. To determine the prevalence of S. aureus and MRSA colonization and describe antimicrobial susceptibility patterns among neonates, their mothers, and environmental surfaces in the neonatal intensive care unit of Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia. A hospital-based cross-sectional study was conducted from February 2021 to January 2022 among 116 mother–newborn pairs admitted to the neonatal intensive care unit of Tikur Anbessa Specialized Hospital. In addition, 230 environmental samples were collected from frequently touched NICU surfaces. Nasal swabs were obtained from mothers and neonates using systematic random sampling. Staphylococcus aureus was identified using standard microbiological techniques, including culture on mannitol salt agar, catalase testing, tube coagulase testing, and β-haemolysis on blood agar. Methicillin resistance was determined using the cefoxitin (30 µg) disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) 2020 guidelines. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disk diffusion method, while vancomycin minimum inhibitory concentrations (MICs) were determined using the E-test. Descriptive statistics were generated, and prevalence estimates were reported with 95% confidence intervals. Overall, 43/232 participants (18.5%; 95% CI 13.7–23.9) were colonized with S. aureus . Colonization was detected in 26/116 mothers (22.4%) and 17/116 neonates (14.7%). MRSA was detected in 6/232 participants (2.6%), including 4/116 mothers (3.4%) and 2/116 neonates (1.7%). Six mother-newborn pairs were colonized with S. aureus in both members of the pair, including one pair in which both mother and neonate were colonized with MRSA. Environmental contamination was low, with S. aureus isolated from 11/230 samples (4.8%) and MRSA from 1/230 samples (0.4%). All 54/54 (100%) S. aureus isolates were resistant to penicillin, whereas susceptibility remained high to clindamycin and erythromycin. All 7/7 (100%) MRSA isolates met the study definition of multidrug resistance, with resistance spanning at least three antimicrobial classes. Among all 54 S. aureus isolates, 47/54 (87.0%) had vancomycin MICs in the susceptible range, while 7/54 (13.0%) had MICs within the intermediate range. No isolates had vancomycin MICs in the resistant range. Although MRSA colonization was relatively uncommon, S. aureus colonization remained frequent among mothers and neonates admitted to the NICU. The observed maternal and neonatal colonization pattern highlights the importance of continued infection prevention and control measures, antimicrobial stewardship, and targeted surveillance of high-risk NICU populations to reduce the risk of subsequent neonatal infection and healthcare-associated spread.