The aim of the study was to evaluate three serological methods for their ability to identify CF patients in different infection status especially those at risk of developing chronic Pseudomonas aeruginosa (Pa) infection.
Methods: Two ELISA methods: exotoxin A (ExoA) and CF-IgG-ELISA (CF-IgG) and Crossed Immunoelectrophoresis (CIE) were used for measurement of Pa-antibodies in sera from 791 Scandinavian CF patients.
Results: 381 patients were cultured negative for Pa in the year before study start, 129 patients were intermittently colonized and 281 patients were chronically infected. The sensitivity of the investigated assays was 96%, 93% and 97%, specificity 89%, 89% and 83% for CIE, ExoA and CF-IgG respectively. The negative predictive value was for CIE 97%, for ExoA 95% and for CF-IgG 98% and positive predictive values 87%, 86% and 80%. Out of the 381 patients cultured negative for Pa, 11 changed status to chronically infected. Twenty-four out of the 129 patients intermittently colonized became chronically infected. The antibody levels in this latter group of patients were significantly higher already at the study start and increased significantly during the study period (p<0.05). Elevated levels of specific anti-Pseudomonal antibodies showed to be the risk factor for developing chronic P. aeruginosa infection (OR 4.9 and OR 2.7, p<0.05 for CF-IgG and ExoA).
Conclusion: All three serological assays were equally informative. The very high sensitivity of the assays made it possible to characterize patients with different infection status. Elevated levels of specific anti-Pseudomonas antibodies showed to be the risk factor for developing chronic Pa infection. Due to the specificity of the tests, antibiotic treatment based on serology might be considered in selected cases. There is a window of opportunity for suppression and eradication of initial P. aeruginosa infection making measurement of specific anti-Pseudomonas antibodies helpful.