IgG antibodies in early Pseudomonas aeruginosa infection in cystic fibrosis

The relationship between IgG antibodies to Pseudomonas aeruginosa and its isolation from sputum was determined in 100 patients with cystic fibrosis observed at intervals of two months for a median period of one year. Only one patient had a raised antibody titre (greater than 22.9 ELISA units) before isolation of P aeruginosa. Initially 65 patients were antibody negative, of whom 48 were also culture negative. Of 24 patients with positive sputum culture and negative antibodies, seven became antibody positive at a median (range) 15 (6-25) months later. The remaining 17 patients continued antibody negative until the end of the study at a median range 15 (1-123) months after becoming culture positive. This latter group were younger and had more intermittently positive sputum cultures. In general positive IgG antibody titres do not predate isolation of P aeruginosa, but in some patients are present soon after acquisition of infection. A positive titre indicates significant exposure to P aeruginosa and could be used to detect infection in patients unable to produce sputum and possibly indicate the effect of early antipseudomonal treatment.