Cystic Fibrosis Exacerbations Linked to Chronic Infection With Stenotrophomonas maltophilia

Laurie Barclay, MD

October 01, 2010

October 1, 2010 — Cystic fibrosis (CF) exacerbations are linked to chronic infection with the bacterium Stenotrophomonas maltophilia, according to the results of a study reported online today in the American Journal of Respiratory and Critical Care Medicine.

"Our study showed that chronic infection with S. maltophilia, which was previously not regarded as prognostically significant, may have a real impact on the progression of CF in patients," lead author Valerie Waters, MD, assistant professor of infectious diseases at the Hospital for Sick Children in Toronto, Canada, said in a news release. "We hope that this study is a starting point for further research, which may point to therapeutic possibilities associated with controlling these infections."

The goal of this cross-sectional study was to assess the effect of chronic S maltophilia infection on lung disease in CF, using a serologic assay specific for S maltophilia that was developed by the investigators. To determine whether a definition of chronic S maltophilia isolation based on culture results predicted an immunologic response, the investigators measured serum antibodies to S maltophilia in patients with CF.

Using this validated definition and 1997 - 2008 data from the Toronto CF Database, the investigators then assessed the effect of chronic S maltophilia on the severity of lung disease in a retrospective cohort of 692 patients, with an average follow-up of 8.3 years.

Among 179 patients with CF and with serum antibody to S maltophilia, those with chronic S maltophilia had higher mean antibody levels to S maltophilia flagellin (P < .0001) and whole cells (P = .0004) than did patients with intermittent or no S maltophilia. Increased antibody levels were also associated with lower lung function, as measured by forced expiratory volume in 1 second (FEV1).

In the cohort study, patients with chronic S maltophilia infection had a greater risk for pulmonary exacerbation leading to hospitalization and antibiotic use than did patients who had never had S maltophilia (risk ratio, 1.63; P = .0002), based on an adjusted log linear model.

The increased antibody levels were also associated with lower lung function, as measured by FEV1.

"This is the first study to our knowledge that demonstrates CF patients with chronic S. maltophilia infection have a specific immune response, which is in turn associated with lower lung function," Dr. Waters said. "There have been few studies that investigate the effect of S. maltophilia infection on clinical outcomes; those that have been short-term and have not shown any significant clinical effects of the infection. This study, however, points to the possibility that chronic infection has a real and significant clinical impact on these patients."

Limitations of this study include its cross-sectional design and the possible failure to detect strain-specific immune responses.

"It is crucial that we look to determine whether chronic S. maltophilia infection directly results in the worsening of lung function," Dr. Waters concluded. "We plan to investigate the effects of chronic S. maltophilia during pulmonary exacerbations in future studies."

The Canadian Cystic Fibrosis Foundation supported this study.

Am J Respir Crit Care Med. Published online October 1, 2010.

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