Bronchiolitis—the most common lung infection in young children, and which is most often caused by respiratory syncytial virus, or RSV—is the leading cause of hospitalizations in U.S. infants, and about 30% of those with severe bronchiolitis later develop asthma. A team led by investigators at Massachusetts General Hospital (MGH) has uncovered four distinct molecular subtypes of RSV bronchiolitis and has linked a certain subtype to a higher asthma risk. The findings are published in Nature Communications.