New nasal methicillin-resistant Staphylococcus aureus colonization during hospitalization in children: a prospective observational study from Iran

Abstract Background Nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) may increase the risk of subsequent infection and facilitate transmission in healthcare settings. However, data on MRSA acquisition during hospitalization among children in Iran are limited. We aimed to determine the frequency of new nasal MRSA colonization and identify associated clinical and healthcare-related factors. Methods In this prospective observational study, children aged ≤ 18 years admitted to five clinical units at Mofid Children’s Hospital, Tehran, Iran, were enrolled between December 2025 and January 2026. Nasal swabs were obtained within 48 hours of admission and repeated at discharge and every 10 days during prolonged hospitalization. New MRSA colonization was defined as a positive follow-up culture after a negative baseline culture. Demographic, clinical, antibiotic exposure, and healthcare-related factors were evaluated. Antimicrobial susceptibility and Panton–Valentine leukocidin (PVL) gene status were assessed in newly acquired MRSA isolates. Results Among 313 children screened at baseline, 164 met the criteria for the final analysis. New nasal MRSA colonization occurred in 10 children (6.1%), with a mean time to detection of 8.1 ± 5.1 days. Most children with new MRSA colonization had an underlying disease (80.0%), including malignancy in 50.0%. Female sex (90.0% vs 37.7%, p = 0.002), sulfonamide exposure (30.0% vs 5.8%, p = 0.027), corticosteroid use (70.0% vs 36.4%, p = 0.046), and clinical unit (p = 0.047) were associated with MRSA acquisition. Nasogastric tube insertion showed a borderline association (p = 0.054). All isolates were susceptible to linezolid and rifampin, while none carried the PVL gene. Conclusions New nasal MRSA colonization occurred in 6.1% of hospitalized children who completed follow-up, particularly among those with underlying diseases. Female sex, sulfonamide and corticosteroid exposure, and clinical unit were associated with acquisition. Given the small number of cases, these findings should be considered exploratory and confirmed in larger multicenter studies.