Nationwide study of invasive Pseudomonas aeruginosa infection in Norway: importance of underlying disease.

Objective: Pseudomonas aeruginosa is an opportunistic pathogen that may cause invasive disease. We describe the epidemiology of invasive P. aeruginosa infection in Norway and identify associated clinical factors.

Methods: All patients with invasive P. aeruginosa and Pseudomonas not identified at the species level (Pseudomonas spp.) in Norway 1992-2002 were included. Detailed information was collected for all cases during 1999-2002. Population and health institution statistics were obtained from national databases.

Results: In 1999-2002 the incidence rate was 3.16 per 100 000 person-years at risk or 0.20 per 1000 hospital stays. For hospital-acquired infection the rate was 671 per 100 000 person-years as compared with 1.13 for community-acquired infection, and 37 in nursing homes. The highest risk for invasive Pseudomonas disease was found in patients with malignant neoplasms of lymphoid and haematopoietic tissue (risk per 1000 hospital stays 1.9; 95% CI 1.5-2.3) and other diseases of blood and blood-forming organs (2.2; 95% CI 1.2-3.7). The case fatality rate was 35%.

Conclusions: The incidence of invasive P. aeruginosa infection in this population-based study was much lower than in most single-hospital studies. The nationwide study design and prudent antibiotic use may explain some of the difference. Infection risk is strongly associated with certain underlying diseases.