S. maltophilia Infection Does Not Raise Risk of CF-related Diabetes, Study Says

Despite being commonly found in patients with cystic fibrosis-related diabetes, the bacteria Stenotrophomonas maltophilia cannot be considered as an independent risk factor for developing CFRD, study says.

The study, “Cystic fibrosis related diabetes is not independently associated with increased Stenotrophomonas maltophilia infection: Longitudinal data from the UK CF Registry,” was published in the Journal of Cystic Fibrosis.

In recent years, the spectrum of microbes causing pulmonary infections in patients with cystic fibrosis (CF) has shifted dramatically. S. maltophilia (previously known as Pseudomonas maltophilia and Xanthomonas maltophilia) is a Gram-negative qne multi-drug resistant bacteria — meaning one increasingly resistant to antibiotics — that is estimated to affect up to 31% of all CF patients.

“The clinical significance of S. maltophilia remains controversial as no clear evidence for more rapid pulmonary decline following S. maltophilia acquisition has been found. It is therefore of interest to understand which factors affect the acquisition of S. maltophilia, and recently CFRD has been implicated,” the researchers wrote.

With this in mind, investigators from the Liverpool Heart and Chest Hospital in the U.K. decided to study the relationship between S. maltophilia and CFRD in more detail.

They assessed patients’ clinical records from the UK Cystic Fibrosis Registry, filed between 2011 and 2015. All information, including demographics, CFRD diagnosis, lung function, and sputum (phlegm; mucus expelled by coughing) bacteria composition were analyzed.

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The study involved 8,047 CF patients, age 6 and older. Of these, 1,138 (14.1%) were infected with S. maltophilia, and 1,815 (22.6%) patients were diagnosed with CFRD — including 285 patients infected with S. maltophilia.

A correlation analysis showed that patients infected with S. maltophilia had a higher incidence of CFRD, 25.0% vs 22.2%.

In addition, these patients were more likely to be affected by severe forms of the disease, compared to those without the bacterial infection. This was reflected in a poorer lung function:  68.6% vs. 76.0% predicted forced expiratory volume (FEV1), more days requiring antibiotic treatment per year (10 vs. 0 days), and a higher prevalence of other species of harmful bacteria in the lungs, including Pseudomonas aeruginosa (48.2% vs. 44.7%), Staphylococcus aureus (45.0% vs. 34.9%), and Aspergillus spp. (32.9% vs. 9.3%).

However, further analysis that adjusted the results by taking into account other clinical parameters — like “markers of severe lung disease including poorer lung function and increased IV antibiotic exposure” — failed to identify a clear association between S. maltophilia infection and CFRD.

“[T]his is by far the largest study looking at the association between S. maltophilia and CFRD, where multiple datasets in many thousands of individuals were compared over a number of years,” the researchers wrote.

“We have shown that the previously documented association between S. maltophilia and CFRD is no longer apparent once adjustment for other clinical parameters has been made,” they added.

Based on the results, the team concluded that “although S. maltophilia is more common in people with CFRD, it is not an independent risk-factor for S. maltophilia acquisition.”