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Background: The source of infection for most sporadic cases of Legionnaires' disease remains unknown. This study aims quantify the relationship between cases and wet cooling systems (WCS), a potential source of aerosolised legionella bacteria., Methods: The study analysed data on 1163 sporadic, community-acquired cases of Legionnaires' disease in England and Wales with onset between 1996 and 2006, and 11630 postcode controls randomly sampled in proportion to population size and matched on region, age group and sex. The relationship between risk of Legionnaires' disease and distance from a WCS was analysed by conditional logistic regression., Results: Cases and controls had a mean age of 56.3 years; 79.3% were male. Cases lived appreciably closer to WCS than their controls (mean distance of cases=2.11 km, controls=2.58 km; mean difference 0.47 km (95% CI 0.28 to 0.65)). The OR for disease within 1 km of a WCS compared with over 6 km (a distance taken to reflect background rates of Legionnaires' disease) was 1.59 (95% CI 1.26 to 2.01) when adjusted for socio-economic deprivation, and 1.33 (95% CI 1.04 to 1.71) when additionally adjusted for population density. The results suggest that residential proximity to a WCS may account for 19.6% of sporadic community-acquired cases., Conclusions: WCS may be an important source of sporadic, community-acquired cases of Legionnaires' disease, an observation that has important implications for health protection, especially given the likely increase in such systems as a component of strategies to improve energy efficiency in buildings.

A statement released last week by the Health Protection Agency highlighted a recent increase in the incidence of Legionnaire's disease in England and Wales. Although an upsurge in cases is common at this time of year due to people returning from holidays abroad, only a small proportion of the recent cases can be attributed to foreign travel. Nurses need to be aware of the symptoms and what health measures they can take.

Two hundred and one cases of legionnaires' disease were reported to the PHLS Communicable Disease Surveillance Centre in 1996. Twenty-four cases (12%) were known to have died. One hundred and one cases were associated with travel, either abroad or in the United Kingdom. Two cases acquired infection in hospital, the smallest number ever reported, and the remaining 98 were presumed to have acquired infection in the community. Fifty-five (27%) of the 201 cases were linked to outbreaks or clusters and the remaining 146 (73%) were reported as single cases. Six outbreaks were associated with industrial premises. Twenty-two of the travel associated cases were part of three travel outbreaks and six clusters. The proportion of cases diagnosed by detection of urinary antigen has continued to increase and in 1996 this method of diagnosis was used for 43% of the cases.

Two hundred and eighteen nosocomial cases of Legionnaires' disease with 68 deaths were reported to the National Surveillance Scheme for Legionnaires Disease between 1980 and 1992, representing 15% of the reported infections acquired in England and Wales. Twenty-two nosocomial outbreaks accounted for 135 (62%) of these cases, the remainder occurring as single cases either in hospitals where other single cases or outbreaks had been reported in different years or as 'sporadic' cases in hospitals from which no other cases were reported. A clinical history prior to onset of Legionnaires' disease was available for 124 patients, 61 of whom had undergone recent transplant therapy or were immunosuppressed for other reasons. Sixty cases (27%) were diagnosed by culture of the organism and isolates from 56 patients were typed; 25 (42%) were non L. pneumophila serogroup 1 infections. Methods for prevention and control of nosocomial outbreaks are discussed, in particular the susceptibility to Legionnaires' disease of certain groups of hospital patients.

One hundred and eleven cases of legionnaires' disease were reported in England and Wales in 1991, a smaller total than in any year since reporting began in the late 1970s. Four cases were hospital acquired and a further nine may have been associated with a hospital stay. Nosocomial legionellosis remains a cause for concern. Fifty-two cases were associated with travel abroad.

National surveillance of legionnaires' disease in England and Wales identified 588 cases during the years 1979--1982. The majority of cases appeared to be sporadic but 32 clusters of two or more cases were recognised, 24 in association with hotels, seven with hospitals and one with a construction site. Reports (3 published and 3 unpublished) on the investigation and control of six outbreaks are reviewed. All six were found to be common source outbreaks; four hotel associated, one was nosocomial and one was associated with a construction site. Domestic water systems were implicated as sources in the four hotels and the hospital. The most effective control measure was found to be continuous chlorination of the water supply combined with raising the hot water temperature to 60 degrees C or more in the calorifier and at least 55 degrees C to a maximum of 60 degrees C at outlets. Raising hot water temperatures alone was not always completely successful as a control measure. Only in the construction site outbreak was a cooling water system shown to be the principal source of infection.

Tremendous progress has been made recently in characterization of Legionella pneumophila and infections caused by it. Certain areas that are particularly germane to immunosuppressed patients, who are affected more frequently than other patients, and areas that are controversial and merit particular consideration are considered herein. These include pathogenesis and correlation of experimental and clinical evidence, nosocomial outbreaks and almost ubiquitous distribution of L. pneumophila in water despite only a limited number of studies linking the two by aerosols, prevalence and possible reasons for the apparent spotty distribution, protean clinical manifestations, difficulties in diagnosis, certain aspects of therapy, and control by environmental changes.

Between December, 1979, and July, 1980, 12 cases of legionnaires' disease were recognised in a district general hospital. 11 of the patients probably acquired their infection within the hospital. Epidemiological and environmental studies indicated that the plumbing system and possibly also the air-conditioning cooling-tower exhaust in the new building of the hospital were the sources of infection. Chlorination of the cold-water supply and raising the hot-water temperature appeared to terminate the outbreak.

The installation of a valve to drain away water on the completion of showering was found to have no significant effect on the numbers of microorganisms in shower water and on the internal surfaces of shower fittings.