BACKGROUND

Pseudomonas aeruginosa is an opportunistic bacterium that can cause severe infection in susceptible patients. During the winter of 2001-2002, we investigated an outbreak of P. aeruginosa infection among patients in several hospitals across Norway.

METHODS

A nationwide outbreak investigation was performed with case finding, questionnaires, and product sampling. All available clinical and environmental P. aeruginosa strains were genotyped. Detailed information was collected from patients with the outbreak strain or with any P. aeruginosa in blood or cerebrospinal fluid samples. To identify risk factors, we conducted a case-control study among patients with P. aeruginosa isolated from blood or cerebrospinal fluid samples during October 2001-December 2002. Case patients were patients infected with the outbreak genotype, and control subjects were patients infected with other genotypes.

RESULTS

A total of 231 patients from 24 hospitals were identified as having the outbreak strain; 39 of these patients had positive blood culture results. Seventy-one patients (31%) died while hospitalized; all of the patients who died had severe underlying disease. Among 39 case patients and 159 control subjects, use of the moist mouth swab (adjusted odds ratio, 5.3; 95% confidence interval, 2.0-13.6) and receipt of mechanical ventilation (adjusted odds ratio, 6.4; 95% confidence interval, 2.3-17.2) were associated with infection due to the outbreak strain. Genotypically identical strains of P. aeruginosa were identified in 76 mouth swabs from 12 different batches and from the production line.

CONCLUSIONS

Contamination of mouth swabs during production caused the largest-ever outbreak of P. aeruginosa infection in Norway. Susceptible patient groups should use only documented quality-controlled, high-level-disinfected products and items in the oropharynx.