The severity of bronchiolitis depends on babies’ nasal flora

The risk and severity of bronchiolitis may be associated with the bacterial composition of the respiratory microbiota that lines babies’ noses, according to an American study.

In the United States, bronchiolitis is the second leading cause of emergency room visits and the primary cause of hospitalizations for babies. The infection is primarily caused by respiratory syncytial virus (RSV, 2/3 of cases) and rhinovirus (1/4 of cases), two germs to which almost all children are exposed. So why do only some of them develop bronchiolitis? And why does the severity vary so much from one child to another?

Suspecting that the respiratory microbiota may be involved, American researchers compared the microbiota of babies hospitalized for severe bronchiolitis to that of healthy infants. The analysis shows that the babies’ nasal mucosa is dominated by three bacterial groups: Moraxella (32%), Corynebacterium (16%) and Staphylococcus (15%), followed by Dolosigranulum (8%) and Streptococcus (7%). Among hospitalized infants, those whose microbiota was dominated by Staphylococcus rather than than Moraxella or Corynebacterium/Dolosigranulum were far greater in number (57% compared to 14% and 17%, respectively). The authors also calculated that the risk of bronchiolitis associated with a nasal microbiota dominated by Staphylococcus was five times higher than that associated with a nasal microbiota dominated by Moraxella. Babies whose nasal flora contained equal parts of each of the three species also had elevated risk. The nature of the virus involved, however, made no difference.

According to the authors, these results should encourage therapeutic approaches to bronchiolitis centered on the respiratory microbiota, rather than the virus.

Sources:

Hasegawa K. et al. Nasal Airway Microbiota Profile and Severe Bronchiolitis in Infants A Case-control Study. Pediatr Infect Dis J 2017;36:1044–1051