Chronic infection with P. aeruginosa is expected in patients with cystic fibrosis (CF), but the ability to delay, prevent, or better manage infection with multiply-resistant P. aeruginosa (MRPA) can potentially increase quality of life and extend survival. The Texas Children's Hospital CF Care Center has identified an endemic MRPA strain (dominant clone), and this study aimed to identify risk factors for acquisition of the clone as well as determine differences in patient outcome associated with subsequent infection with the clone.

The study included 71 patients with CF with documented MRPA infection. Designation of patients as members of the dominant clone or a non-dominant clone group was based on molecular typing by rep-PCR of MRPA isolates from respiratory cultures. Patient data was collected from Port CF, the national patient registry of the CF Foundation. Patient demographic information and clinical parameters prior to MRPA infection were analyzed by logistic regression as potential risk factors. Differences in patient outcome including change in BMI, change in FEV1, and hospitalization rate were evaluated by MANOVA.

Recent hospitalization (≤ 90 days) was a statistically significant (p = 0.035) risk factor for acquisition of the dominant clone. Patients hospitalized ≤ 90 days prior to MRPA diagnosis were four times more likely to be infected with the dominant clone, and patients hospitalized 91-180 days prior were almost three times more likely. Increased hospitalization rates were seen in the dominant clone group both pre- (11 more days/year) and post-infection (14 more days/year) as compared to the non-dominant clone group. Patients infected with the endemic strain exhibited poorer outcomes in terms of nutritional status (3.73% decrease/year in BMI %ile) and lung function (3.7% decrease/year in FEV₁ %ile). Significant overlap in hospitalization episodes of patients known to be infected with the dominant clone and patients subsequently infected with the dominant clone was observed.

Recent hospitalization was a significant risk factor for infection with the dominant MRPA clone, and following infection, patients infected with the endemic strain exhibited declines in nutritional status and lung function and increased hospitalization rates. The results suggest potentially increased virulence and transmissibility of the endemic MRPA strain.