Whether it is a simple cold or a more severe disease, acute respiratory infections are very frequent in the first years of life. Lower airways infections (especially pneumonia and bronchiolitis) are the main cause of hospitalization in children under 5 years old. But while some children get one infection after the other (5 to 7 per year) or catch severe forms, other are able to elude microbes. Of course, known risk factors (prematurity, daycare, age) can explain this difference in sensitivity, but only partially. Could their nasal microbiota play a role?
5 microbiota profiles
A team of Finnish researchers analyzed the results from a large study that included 839 healthy newborns who were monitored from birth to age two. Based on the samples from the nasal microbiota that were collected at the age of two months, 5 different profiles were identified, according to the dominant bacterial group: Moraxella (30.4%), Streptococcus (22.4%), Dolosigranulum (22.4%), Staphylococcus (17.9%) and Corynebacteriaceae (6.9%). The researchers observed that the frequency of acute respiratory infections depended on each of these profiles.
More Moraxella, more infections
Microbiotas dominated by Moraxella bacteria were less abundant and less diversified than the others, and were associated to a higher incidence of acute respiratory infections, especially lower airways infections, and to longer-lasting symptoms. Affected children also shared other factors: they were more likely to have siblings and to have mild respiratory symptoms as soon as two months old. This was also observed in children whose microbiota was dominated by Staphylococcus bacteria; on the contrary, children with a profile dominated by Corynebacteriaceae bacteria were less often ill.
Identifying at-risk children
Despite some limits acknowledged by the authors, this study still substantiates a link between nasal microbiota and incidence/severity of acute respiratory infections. Further studies are needed to elucidate the complex interactions between this ecosystem, immunity and these diseases in order to identify the children at a greater risk.
