Epidemiology of Pseudomonas aeruginosa infection in patients treated at a cystic fibrosis centre.

484 isolates of P. aeruginosa were obtained from the respiratory tract of 45 out of 70 cystic fibrosis (CF) patients of monthly examinations during one year at the Danish CF Centre. All isolates were serogrouped (O-antigens) and phage typed, and in this way 99 per cent of the isolates could be grouped and/or typed. The isolates from CF patients belonged to many different sero-groups, but 55 per cent were polyagglutinable, and most of these belonged to the 0-3/9 complex. This was significantly different from the distribution into O-groups of isolates obtained from non-CF patients. The results of the combined phage typing and sero-grouping of the isolates revealed the occurrence of 13 clusters of distinct epidemiological types of P. aeruginosa among small groups (2-10 individuals) of CF patients. The predominating endemic strain, which was isolated from 10 (22 per cent) of the patients, belonged to the 0-3/9 complex and was lysed by phage 109, either alone or in combination with a few other phages. Furthermore, in a few cases the eradication of another strain of P. aeruginosa by chemotherapy was followed by colonization of the lungs with the above-mentioned predominating strain, and this strain was associated with high lethality. According to these results, measures should be undertaken to identify and eliminate routes of cross-infection in CF centres in order to diminishe the prevalence of P. aeruginosa infection and thereby reduce the lethality of CF patients.