Value of serology in predicting Pseudomonas aeruginosa infection in young children with cystic fibrosis

Background Early detection of Pseudomonas aeruginosa is essential for successful eradication. The accuracy of serum antibodies against specific and multiple P aeruginosa antigens at predicting lower airway infection in young children with cystic fibrosis (CF) was investigated. Methods A commercial P aeruginosa multiple antigen (MAg) ELISA and an in-house exotoxin A (ExoA) ELISA were compared in two populations: a discovery population of 76 children (0.1-7.1 years) undergoing annual bronchoalveolar lavage (BAL)-based microbiological surveillance and a test population of 55 children (0.1-5.6 years) participating in the Australasian CF Bronchoalveolar Lavage Trial. Results In the discovery population, P aeruginosa was cultured from BAL fluid (>= 10(5) colony-forming units (cfu)/ml) in 15/76 (19.7%) children (median age 1.88 years). Positive MAg and ExoA serological results were found in 38 (50.0%) and 30 (39.5%) children, respectively. Positive (PPV) and negative (NPV) predictive values for serology at diagnosing P aeruginosa infection (>= 10(5) cfu/ml) were 0.14 and 0.99 respectively (MAg assay) and 0.11 and 0.98 (ExoA assay). In the test population, P aeruginosa was cultured from BAL fluid (>= 10(5) cfu/ml) in 16/55 (29.1%) children (median age 1.86 years) and from oropharyngeal swabs in 32/36 (88.9%). Positive MAg and ExoA serology was detected in 19 (34.5%) and 33 (60.0%) children, respectively. The PPV and NPV of serology were 0.26 and 0.94 respectively (MAg assay) and 0.19 and 0.98 (ExoA assay) and were marginally higher for oropharyngeal cultures. Conclusions Measuring serum antibody responses against P aeruginosa is of limited value for detecting early P aeruginosa infection in young children with CF.