Researchers at Massachusetts General Hospital (MGH) have unveiled four distinct molecular subtypes of bronchiolitis caused by the respiratory syncytial virus (RSV). They have linked one subtype to a high risk of asthma in children.

Bronchiolitis is a common lung infection in young children and infants, which is characterized by inflammation and congestion of the small airways called bronchioles in the lung. It typically peaks during the winter months.

In the United States, bronchiolitis is one of the leading causes of hospitalizations in infants. More than 30% of those with severe bronchiolitis later develop asthma.

The researchers published their findings in the journal Nature Communications.

Lead author Dr. Yoshihiko Raita said, “While bronchiolitis has been considered a single disease with similar mechanisms, emerging evidence has suggested that bronchiolitis consists of multiple disease subgroups.”

Dr. Raita is a researcher in the MGH Department of Emergency Medicine.

“But our limited understanding of RSV bronchiolitis, and how it varies, has held up efforts to develop RSV bronchiolitis treatment and asthma prevention strategies,” he added.

Dr. Raita and his team analyzed genetic and molecular data from more than 220 infants hospitalized with RSV bronchiolitis who were followed until five years of age, according to Science Daily.

The researchers then gathered information on the viruses that had infected the children. They also collected information on the microbes, metabolites, and immune response-related molecules present in the children’s nasal passages.

The team found that there are four biological and clinical subtypes (endotypes) of RSV bronchiolitis. And of these, one endotype had a 40% risk of developing asthma by age five.

This particular endotype is characterized by co-infection by rhinovirus, dominance by specific bacteria, and high interferon (antiviral) response, per Science Daily.

Dr. Raita explained, “Our data add significant support to the emerging concept that bronchiolitis represents several diseases with unique biological mechanisms.”

“For clinicians, our findings give an evidence base for the early identification of high-risk children during an important period of airway development: early infancy,” he added.

“For researchers, our data offer new avenues for the development of subgroup-specific strategies — such as fine-tuning the airway immune response and microbiome — for treating bronchiolitis and preventing asthma,” explained Dr. Raita. The article was published in Science Daily.