RSV subtype B appears less harmful than subtype A

M. Douglas Baker, MD

Jafri and colleagues report data from a multicenter surveillance study conducted in EDs during two RSV seasons (September through May), which associate clinical consequences in infants aged younger than 1 year with infections by different RSV subtypes. The data were collected from 31 sites in 23 states, representing most geographical regions of the country. In their data set, infections by RSV subtype A were twice as common as those by subtype B. Subtype A-infected patients were more likely than subtype B-infected patients to be admitted to in-patient units (47.7% vs. 35.8%, respectively). The incidence of apnea or lower respiratory tract infections also seemed greater in subtype A infections. Other morbidities, such as requirement of supplemental oxygen, bronchodilator use, need for mechanical ventilation, and durations of in-patient admissions were fairly equivalent for each subtype.

This study is significant in that it likely represents the largest analysis of health care use trends in infants infected with different RSV subtypes. The initial indications that subtype A infections might result in more severe illness in infants might prove to be true.

However, it is important to recognize the limitations of the study at hand. Inclusion criteria included only infants who presented during non-summer months and were assigned a clinical diagnosis of bronchiolitis, pneumonia or apnea. It is likely that many infants with less severe presentations of RSV were excluded. In addition, severity of illness was not prospectively assessed. Rather, utilization of resources was used as a surrogate indicator of severity of illness. Nevertheless, the observations of Jafri and co-investigators warrant our attention, and serve as a foundation and stimulus for future study.