Evaluation of a new definition for chronic Pseudomonas aeruginosa infection in cystic fibrosis patients.

Background: Patients were defined each successive month as either 'chronic' when more than 50% of the preceding 12 months were PA culture positive, 'intermittent' when < or =50% of the preceding 12 months were PA culture positive, 'free of PA', with no growth of PA for the previous 12 months, having previously been PA culture positive, or 'never infected', when PA had never been cultured.

Methods: Cross-sectional analysis of 146 children attending the Leeds Regional Cystic Fibrosis Centre was performed to assess relationship between the new definition and clinical scores and investigations. The response variable was regressed on age and sex and the residuals analysed using the Kruskal-Wallis test.

Results: The 'chronic' group (18% of patients) had significantly worse Shwachman-Kulczycki (SK) and Northern chest X-ray scores, and % predicted FEV(1) values than the 'free' (28%) or 'never' (20%) categories (P<0.004). The 'intermittent' group (34%) had a significantly higher SK score than the 'chronic' group (P<0.0001), and a significantly lower % predicted FEV(1) value than the 'free' or 'never' groups (P<0.0003). 'Chronic' patients were significantly associated with a positive, and 'never' patients with a negative, PA antibody result (P<0.001).

Conclusions: The validity and importance of identifying these four subgroups is demonstrated. Previous definitions may over-estimate the prevalence of chronic infection.