Geumhee Oh, Eunsang Go
The outbreak demonstrated a high attack rate among newborns, with approximately half of the confirmed cases remaining asymptomatic. In crowded neonatal care settings, timely detection and prompt intervention are essential for preventing further transmission during outbreaks.
OBJECTIVES: On March 4, 2026, a respiratory syncytial virus (RSV) outbreak affecting newborns was reported at postpartum care center A in Seoul, the Republic of Korea. An epidemiological investigation was initiated to characterize the outbreak, determine its patterns, and prevent further spread.
METHODS: A retrospective cohort study was conducted among the 18 exposed newborns at the postpartum care center to evaluate risk factors for RSV infection. In addition, epidemiological investigations were conducted among all 64 exposed individuals, including parents and staff members, to identify the source and transmission patterns. Cases were defined as individuals whose RSV infection was confirmed by real-time reverse transcription polymerase chain reaction (RT-PCR). Researchers assessed clinical characteristics and exposure factors using the Korea Disease Control and Prevention Agency epidemiological investigation form. Additionally, respiratory and environmental samples were collected for RT-PCR testing.
RESULTS: Of the 64 exposed individuals, 10 tested positive for RSV, yielding an overall attack rate of 15.6%. The attack rate among newborns was 50.0% (9 of 18), consisting of 5 symptomatic and 4 asymptomatic cases. The index case was admitted on February 21, 2026, became symptomatic with sneezing on February 28, and tested positive on March 3. Subsequent cases were identified through March 11. One asymptomatic staff member was also infected without symptoms, whereas all 28 environmental specimens tested negative. This retrospective cohort study identified no significant risk factors associated with RSV infection.
CONCLUSIONS: The outbreak demonstrated a high attack rate among newborns, with approximately half of the confirmed cases remaining asymptomatic. In crowded neonatal care settings, timely detection and prompt intervention are essential for preventing further transmission during outbreaks.