P. aeruginosa, but Not Rhinovirus, Worsens Lung Function in Children
In children with cystic fibrosis (CF), evidence of the bacteria Pseudomonas aeruginosa was associated with poorer lung function — based on predicted forced expiration volume in one second, FEV1% — while those testing positive for rhinovirus, which frequently causes the common cold, were more likely to have better lung function, a Swiss study reported.
“To our best knowledge, this is the first report of an association between higher FEV1% and rhinovirus detection,” the scientists wrote.
The study, “Unexpected associations between respiratory viruses and bacteria with Pulmonary Function Testing in children suffering from Cystic Fibrosis (MUCOVIB study),” was published in the Journal of Cystic Fibrosis.
In CF, the lung microbiota, the community of microorganisms like bacteria and viruses found there, contributes to the progressive worsening in lung health.
Young children with CF have a rich lung microbiota, but antibiotic use ultimately favors the growth of harmful bacteria, such as P. aeruginosa. As a result, an imbalance in lung microbiota is seen in adults with CF and linked to declining lung function.
How individual microbes affect lung function in children with CF is still unknown. To address this, researchers in Switzerland conducted a multicenter study — called the Mucoviscidosis, Respiratory VIruses, Intracellular Bacteria and fastidious organisms (MUCOVIB) project — to investigate how viruses and bacteria affect the lungs of young patients.
A total of 61 children with CF were followed for two years, from April 2016 to May 2018, at the respiratory clinics of Lausanne and Geneva University hospitals. Lung function was assessed with FEV1% — the volume of air a person can forcibly exhale in one second— and the lung clearance index (LCI), a measure of how well the lungs can get new air in and old air out.
Their median age at study enrollment was 7.4, a majority (59%) were boys and most (90.2%) had one other health condition related to CF. Twenty children experienced at least one lung exacerbation during the study period.
Using a common technique called polymerase chain reaction (PCR), the researchers were able to detect and amplify specific segments of DNA from several bacteria and viruses. About 45% of samples, taken from 56 patients, tested positive for at least one respiratory virus. The most common were rhinovirus (26.5%), seasonal coronavirus (8.7%), and human metapneumovirus (5.7%).
Microbiology cultures revealed that S. aureus (44.6%), P. aeruginosa (6.8%), S. pyogenes (3.7%) and H. influenzae (3.4%) were the most common bacteria.
Statistical analysis showed that bacteria and rhinovirus were more likely to be detected in the spring relative to the winter. Additionally, the odds for rhinovirus detection were higher for younger children.
The presence of any bacteria or virus was associated with a reduced FEV1%. The detection of a lung virus had no impact on LCI values, whereas detecting bacteria correlated with an higher lung clearance index. Co-infection with a virus and a bacteria was associated with a higher FEV1% but had no effect on LCI values.
Poorer lung function, or low FEV1%, was more common in children with P. aeruginosa infection, while rhinovirus was associated with higher FEV1% values but also no effect on LCI, the scientists reported.
Next, the team compared the routine culture method with the culture-free assay 16S rRNA metagenomics, a technique used to evaluate microbial diversity. 16S rRNA metagenomics detected pathogens with more than twice the frequency of routine culture, but with less specificity, which refers to the ability to correctly identify samples without pathogens.
According to the researchers, differences seen between the two methods highlight the need for a better protocol to guide metagenomics and could partly be due to false positive results with this method.
“In conclusion, P. aeruginosa impacted negatively on FEV1% while rhinovirus was surprisingly associated with better FEV1%,” the investigators wrote. “Culture-free assays [identify] significantly more pathogens than standard culture, [but] with disputable clinical correlation.”