Nationwide study of invasive Pseudomonas aeruginosa infection in Norway: Importance of underlying disease Bjørn G. Iversen a, *, Arne B. Brantsæter a,b , Preben Aavitsland a a Norwegian Institute of Public Health, P.O. Box 4404 Nydalen, NO-0403 Oslo, Norway b Asker and Bærum Hospital, P.O. Box 83, NO-1309 Rud, Norway Accepted 28 May 2008 Available online 9 July 2008 KEYWORDS Pseudomonas aeruginosa; Bacteraemia; Nosocomial infection; Mortality; Epidemiology; Central nervous system infections; Pseudomonas infections; Gram-negative bacteria; Hospital-acquired infection; Community-acquired infection Summary 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 spe- cies level (Pseudomonas spp.) in Norway 1992e2002 were included. Detailed information was collected for all cases during 1999e2002. Population and health institution statistics were obtained from national databases. Results: In 1999e2002 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 lym- phoid and haematopoietic tissue (risk per 1000 hospital stays 1.9; 95% CI 1.5e2.3) and other dis- eases of blood and blood-forming organs (2.2; 95% CI 1.2e3.7). 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 cer- tain underlying diseases. ª 2008 The British Infection Society. Published by Elsevier Ltd. All rights reserved. Introduction Pseudomonas aeruginosa, a gram-negative aerobic bacte- rium with minimal nutritional requirements, is common in moist environments. 1,2 It rarely causes infection in healthy humans but may do so following disruption of physical bar- riers and in patients with certain underlying illnesses. 1e3 * Corresponding author. Tel.: þ47 21 07 65 16; þ47 93 46 03 75 (mobile); fax: þ47 21 07 65 13. E-mail address: bjorn.iversen@fhi.no (B.G. Iversen). 0163-4453/$34 ª 2008 The British Infection Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jinf.2008.05.010 www.elsevierhealth.com/journals/jinf Journal of Infection (2008) 57, 139e146