Which risk factor in an 8-month-old infant is most concerning for RSV?

In infants, respiratory syncytial virus (RSV) is a significant cause of respiratory illness, particularly in younger children. One of the most concerning risk factors for severe RSV infection is prematurity. An infant born at 33 weeks gestation is classified as preterm, and this increases their susceptibility to respiratory viruses due to underdeveloped lungs and immune systems.

Premature infants may not have developed enough lung capacity or sufficient maternal antibodies that are important for combating viral infections. As a result, they are at a higher risk for severe manifestations of RSV, which can lead to hospitalization and complications.

The other aspects mentioned, such as a mother testing positive for group B Streptococcus (GBS) during pregnancy, the infant receiving a combination of breast milk and formula, or being born by C-section, do not carry the same level of risk for RSV specifically. While these factors may have their own implications for an infant's health, prematurity stands out as the most concerning risk factor linked to severe RSV outcomes in an 8-month-old infant.