Background
The clinical consequences of chronic Stenotrophomonas maltophilia infection in cystic fibrosis (CF) patient are still unclear.

Method
All patients treated in the Copenhagen CF centre (N=278) from 1 January 2008 to 31 December 2009 were included. Each patient chronically infected with S. maltophilia for at least 2years without any other chronic Gram-negative infection were matched to two non-infected CF controls.

Results
Twenty-one patients were chronically infected with S. maltophilia during the 2-year study period. Fifteen were infected for at least 2years.

The patients in the S. maltophilia group had a steeper decline (-3.2%/year vs. -0.3%/year) in FEV1 compared to the non-infected CF controls (P=0.03). The rate of decline was the same as observed 3years before the patients became chronically infected.

Discussions
Chronic infection with S. maltophilia does not lead to a steeper decline in lung function when compared to the period before chronic infection.