Outbreak detection and secondary prevention of Legionnaires' disease: a national approach.

BACKGROUND To stop a possible outbreak of Legionnaires' disease (LD) at an early stage an outbreak detection programme was installed in The Netherlands. METHODS The programme consisted of sampling and controlling of potential sources to which LD patients had been exposed during their incubation period. Potential sources were considered to be true sources of infection if two or more LD patients (cluster) had visited them, or if available patients' isolates and environmental Legionella spp. were indistinguishable by amplified fragment length polymorphism genotyping. RESULTS Rapid sampling and genotyping as well as cluster recognition helped to target control measures. Despite these measures, two small outbreaks were only stopped after renewal of the water system. The combination of genotyping and cluster recognition lead to 29 of 190 (15%) patient-source associations. CONCLUSION Systematic sampling and cluster recognition can contribute to outbreak detection and lead to cost-effective secondary prevention of Legionnaires' disease.