Outbreak of Legionnaires' disease in Glasgow Royal Infirmary: microbiological aspects

Population analysis of Legionella pneumophila reveals a basis for resistance to complement-mediated killing

Legionella pneumophila is the most common cause of the severe respiratory infection known as Legionnaires' disease. However, the microorganism is typically a symbiont of free-living amoeba, and our understanding of the bacterial factors that determine human pathogenicity is limited. Here we carried out a population genomic study of 902 L. pneumophila isolates from human clinical and environmental samples to examine their genetic diversity, global distribution and the basis for human pathogenicity. We find that the capacity for human disease is representative of the breadth of species diversity although some clones are more commonly associated with clinical infections. We identified a single gene (lag-1) to be most strongly associated with clinical isolates. lag-1, which encodes an O-acetyltransferase for lipopolysaccharide modification, has been distributed horizontally across all major phylogenetic clades of L. pneumophila by frequent recent recombination events. The gene confers resistance to complement-mediated killing in human serum by inhibiting deposition of classical pathway molecules on the bacterial surface. Furthermore, acquisition of lag-1 inhibits complement-dependent phagocytosis by human neutrophils, and promoted survival in a mouse model of pulmonary legionellosis. Thus, our results reveal L. pneumophila genetic traits linked to disease and provide a molecular basis for resistance to complement-mediated killing.

Current and emerging Legionella diagnostics for laboratory and outbreak investigations

Legionnaires' disease (LD) is an often severe and potentially fatal form of bacterial pneumonia caused by an extensive list of Legionella species. These ubiquitous freshwater and soil inhabitants cause human respiratory disease when amplified in man-made water or cooling systems and their aerosols expose a susceptible population. Treatment of sporadic cases and rapid control of LD outbreaks benefit from swift diagnosis in concert with discriminatory bacterial typing for immediate epidemiological responses. Traditional culture and serology were instrumental in describing disease incidence early in its history; currently, diagnosis of LD relies almost solely on the urinary antigen test, which captures only the dominant species and serogroup, Legionella pneumophila serogroup 1 (Lp1). This has created a diagnostic "blind spot" for LD caused by non-Lp1 strains. This review focuses on historic, current, and emerging technologies that hold promise for increasing LD diagnostic efficiency and detection rates as part of a coherent testing regimen. The importance of cooperation between epidemiologists and laboratorians for a rapid outbreak response is also illustrated in field investigations conducted by the CDC with state and local authorities. Finally, challenges facing health care professionals, building managers, and the public health community in combating LD are highlighted, and potential solutions are discussed.

Assessing maintenance of evaporative cooling systems in legionellosis outbreaks

This study was designed to conduct systematic reviews of existing evaporative cooling system maintenance guidelines and of published Legionnaires' disease outbreaks to determine what, if any, maintenance practices were in place at the time of the disease outbreaks and then to contrast the reported practices with the published guidelines for evaporative cooling systems. For the first review, similarities in the reported recommendations were assessed; in the second review, any reported information about the state of the evaporative cooling system during the outbreak investigation was summarized. The systematic reviews yielded 38 current guidelines for evaporative cooling systems and 38 published outbreak investigations. The guidelines varied regarding the recommended type and dose of biocides, frequency of general inspections and total system maintenance, the preferred disinfection and cleaning procedures when testing a system for microbiological contamination, the type and frequency of testing procedures, and interpretation of test results. Overall, the maintenance guidelines did not contain sufficiently detailed procedures to prevent the problems that were observed in the outbreak investigations. These maintenance procedures included lack or improper use of a biocide; infrequent testing for microbiological contamination; improper use or maintenance of drift eliminators; and lack of a total system cleaning within 6 months of the outbreak for cooling systems that were either under continuous use, recently started up, or frequently switched on and off. This study suggests that more specific and standardized maintenance guidelines for the control of Legionella bacteria are needed and that these guidelines must be properly implemented to help reduce further Legionnaires' disease outbreaks associated with evaporative cooling systems.

Surveillance of hospital water and primary prevention of nosocomial legionellosis: what is the evidence?

Hospital-acquired Legionnaires' disease may be sporadic or may occur as part of an outbreak. As Legionella spp. are ubiquitous in many water systems, it is not surprising that hospital water may be colonized with Legionella pneumophila and other species. However, there is some controversy about the relationship between the presence of legionella in hospital water systems and nosocomial legionellosis. Primary prevention, i.e. measures to prevent legionella in a hospital or healthcare facility with no previous documented cases of nosocomial legionellosis, includes heightened awareness of hospital-acquired Legionnaires' disease with appropriate laboratory diagnostic facilities, and ensuring that the water system is well designed and maintained in accordance with national standards, e.g. the circulating hot water is maintained above 55 degrees C. Secondary prevention, i.e. preventing further cases occurring when a case has been confirmed, should include an investigation to exclude the hospital water system as a source. However, the necessity to sample hospital water routinely to detect legionella outside of outbreaks, i.e. as a component of primary prevention, is unclear. Some studies demonstrate a clear link but others do not. Differences between the patient populations studied, the methods of laboratory diagnosis of clinical cases, the analysis of hospital water and differences in the design of hospital water systems may partly explain this. Whilst further research, probably in the form of multi-centred prospective trials, is needed to confirm the relationship between environmental legionella and hospital-acquired legionellosis, including establishing the relative importance of L. pneumophila group 1 vs. non-group 1 and other Legionella spp., each hospital should consider the spectrum of patients at particular risk locally. Centres with transplant units or other patients with significant immunosuppression should, in the interim, consider routine sampling for legionella in hospital water in addition to other control measures. Therefore, infection control teams must work closely with hospital engineering and technical services departments and hospital management, as well as ensuring that physicians and others have a heightened awareness of hospital-acquired legionellosis.

Colonization of transplant unit water supplies with Legionella and protozoa: precautions required to reduce the risk of legionellosis

Organ transplant recipients and other immunosuppressed patients are known to be at increased risk of nosocomial Legionnaires' disease. Although the ecology of Legionella in hospital water storage and distribution systems (including a protozoonotic relationship with free-living protozoa) has been well documented, little is known regarding the quality of water supplied to high-risk units. Hot- and cold-water samples (two first draw and one run to waste for 5 min) were taken from 69 (85%) of the 81 United Kingdom organ transplant units (31 renal, 24 bone marrow, nine cardiopulmonary and five liver transplant units) and cultured for Legionella and protozoa. Legionella spp. were isolated from the water supplies of 38 (55%) units and Legionella pneumophila from 31 (45%). The blue-white fluorescent group of Legionella (Legionella gormanii, Legionella bozemanii and others) was isolated from 18 (26%) units. Free-living protozoa were isolated from 47 units (68%) and genera of the protozoa known to permit the intracellular growth of Legionella (PGIGL), from 40 units (58%). Possible associations between Legionella and the variables Protozoa; PGIGL; water pH; and circulating water temperature (recorded after running to waste for 5 min) were examined by logistic regression analysis. In cold-water supplies, a significant association was found between the isolation of Legionella and PGIGL (P = 0.032; OR = 1.81; 95% CI 1.1-3.1). In hot-water supplies, an inverse association was found between the isolation of Legionella and circulating water temperature (P = 0.034; OR = 1.0719 per degree C; 95% CI 1.0052-1.1432). (We failed to isolate Legionella when the circulating hot water was > 58 degrees C. No other associations were significant. We recommend the active surveillance of water quality in high-risk patient areas, and that transplant units, either with a history of nosocomial Legionnaires' disease, or where active surveillance indicates a persistently high Legionella colony count, take remedial action. The quality of cold water may be improved by provision of a dedicated supply taken directly from the incoming mains; and of hot water by the use of a dedicated calorifier, able to maintain a minimum circulating hot water return temperature of 60 degrees C.

Legionellosis linked with a hotel car park--how many were infected?

An outbreak of legionellosis associated with a hotel in Sydney, Australia, and the subsequent epidemiological and environmental investigations are described. Four cases of Legionnaires' disease were notified to the Public Health Unit. A cross-sectional study of 184 people who attended a seminar at the hotel was carried out. Serological and questionnaire data were obtained for 152 (83%) of these. Twenty-eight (18%) respondents reported symptoms compatible with legionellosis. Thirty-three subjects (22%) had indirect fluorescent antibody (IFA) titres to Legionella pneumophila serogroup 1 (Lp-1) of 128 or higher. The only site which those with symptoms of legionellosis and IFA titre > or = 128 were more likely to have visited than controls was the hotel car park (adjusted odds ratio [OR] 14.7, 95% confidence interval [CI]: 1.8-123.1). Those with symptoms compatible with legionellosis, but whose IFA titres were < 128 were also more likely to have visited the hotel car park (adjusted OR 4.4, 95% CI: 1.5-12.9). Seroprevalence of Lp-1 antibodies was higher in those who attended the seminar than in a population sample of similar age. Findings suggested that the 4 cases represented a small fraction of all those infected, and highlighted difficulties in defining illness caused by Lp-1 and in interpreting serology.

Fatal nosocomial Legionnaires' disease: relevance of contamination of hospital water supply by temperature-dependent buoyancy-driven flow from spur pipes

The investigation, epidemiology, and effectiveness of control procedures during an outbreak of Legionnaires' disease involving three immunosuppressed patients are described. The source of infection appeared to be a network of fire hydrant spurs connected directly to the incoming hospital mains water supply. Removal of these hydrants considerably reduced, but failed to eliminate, contamination of water storage facilities. As an emergency control procedure the incoming mains water was chlorinated continuously. Additional modifications to improve temperature regulation and reduce stagnation also failed to eliminate the legionellae. A perspex test-rig was constructed to model the pre-existing hospital water supply and storage system. This showed that through the hydraulic mechanism known as 'temperature buoyancy', contaminated water could be efficiently and quickly exchanged between a stagnant spur pipe and its mains supply. Contamination of hospital storage tanks from such sources has not previously been considered a risk factor for Legionnaires' disease. We recommend that hospital water storage tanks are supplied by a dedicated mains pipe without spurs.

Monitoring of hospital water supplies for Legionella

In order to determine the value of regular surveillance for Legionella in the prevention of hospital-acquired (nosocomial) legionellosis, water samples were obtained over a three-year period from 17 hospitals located in England and Scotland. Prior to the study, all of the hospitals had in operation defined protocols and maintenance schedules which followed national guidelines for the prevention of legionellosis in health care premises. Six samples, from key locations in the water system of each hospital, were taken at six-monthly intervals. Total viable bacterial count (TVC), coliform count and legionella cultures were performed on all the samples. No coliforms were detected in any of the samples, whereas the TVC was variable. Legionella pneumophila was isolated from both the hot and cold water supplies of two hospitals. The TVC was not related to the isolation of Legionella. Confirmation of the presence of Legionella was subsequently attributed to defects in the equipment and water maintenance programmes. It was concluded that the microbiological examination of water is an effective approach to the audit of the maintenance of hospital water systems in order to prevent legionellosis.

Outbreak of Legionnaires' disease at University Hospital, Nottingham. Epidemiology, microbiology and control

Twelve patients in a large teaching hospital contracted Legionnaires' disease over a period of 11 months. The source was a domestic hot water system in one of the hospital blocks, which was run at a temperature of 43 degrees C. Five different subtypes of Legionella pneumophila serogroup 1 have been isolated from water in different parts of the hospital, over a period of time. Only one subtype, Benidorm RFLP 14, was implicated in disease. Circumstantial evidence suggested that the outbreak may have been due to recent colonization of the hot water system with a virulent strain of Legionella pneumophila. The outbreak was controlled by raising the hot water temperature to 60 degrees C, but careful surveillance uncovered two further cases in the following 30 months. Persistent low numbers of Legionella pneumophila were isolated from the domestic hot water of wards where Legionnaires' disease had been contracted, until an electrolytic unit was installed releasing silver and copper ions into this supply.

Pinpointing clusters of apparently sporadic cases of Legionnaires' disease

OBJECTIVES

To test the hypothesis that many non-outbreak cases of legionnaires' disease are not sporadic and to attempt to pinpoint cases clustering in space and time.

DESIGN

Descriptive study of a case series, 1978-86.

SETTING

15 health boards in Scotland.

PATIENTS

203 probable cases of non-outbreak, non-travel, community acquired legionnaires' disease in patients resident in Scotland.

MAIN MEASURES

Date of onset of disease and postcode and health board of residence of cases.

RESULTS

Space-time clustering was present and numerous groups of cases were identified, all but two being newly recognised. Nine cases occurred during three months within two postcodes in Edinburgh, and an outbreak was probably missed. In several places cases occurred in one area over a prolonged period--for example, nine cases in postcode districts G11.5 and G12.8 in Glasgow during five years (estimated mean annual incidence of community acquired, non-outbreak, non-travel legionnaires' disease of 146 per million residents v 4.8 per million for Scotland). Statistical analysis showed that the space time clustering of cases in the Glasgow and Edinburgh areas was unusual (p = 0.036, p = 0.068 respectively).

CONCLUSION

Future surveillance requires greater awareness that clusters can be overlooked; case searching whenever a case is identified; collection of complete information particularly of date of onset of the disease and address or postcode; ongoing analysis for space-time clustering; and an accurate yet workable definition of sporadic cases. Other researchers should re-examine their data on apparently sporadic infection.

Decreased biocide susceptibility of adherent Legionella pneumophila

In a study of the in vitro effectiveness of biocides against Legionella pneumophila, some aspects of the cooling tower environment were replicated in the laboratory, paying particular attention to water hardness and pH. Pieces of Douglas fir and polyvinyl chloride were colonized in a recirculating system and the comparative efficacy of two biocides (Bronopol and Kathon) against the sessile and planktonic populations was examined. While the biocides were relatively effective against the planktonic L. pneumophila population over a short period of time (minimum 9-12 h), substantially longer periods of time (maximum greater than 48 h) were required to reduce the number of cultivable bacteria to below detectable levels in the adherent population. The results indicate that failure to monitor the sessile population of L. pneumophila in laboratory studies of biocides may result in the use of incorrect dosages and/or contact times in field trials with apparently reduced in situ efficacy.

An outbreak of Legionnaires' disease in Gloucester

Fourteen people living in or near the city of Gloucester fell ill with Legionnaires' disease caused by Legionella pneumophila serogroup (SG) 1 between 27 August and 27 October 1986. Another patient had fallen ill on 30 May. Nine of the 15 were diagnosed retrospectively during a case finding exercise. There were three deaths. Three cases of Pontiac fever were also diagnosed. The source was probably one or more wet cooling towers. Nineteen premises in the city with such towers were identified, and three just outside Gluocester. Samples from 11 of the 22 premises grew Legionella spp.; from nine of these L. pneumophila SG 1 (Pontiac) was isolated. The efficacy of regular addition of biocide in addition to hypochlorite added at the time of disinfection in inhibiting the growth of Legionella spp. was demonstrated. A survey of patients' movements during their likely incubation period showed that there was no single building that all patients had visited, but there were two areas of the city which nearly all had visited or passed through by car. A case-control study demonstrated an association with one of these areas. Cooling towers near both areas may have been sources but the evidence is insufficient to incriminate any single one. The unexpected finding of L. pneumophila SG 1 (Pontiac) in nine towers supports the hypothesis that there may have been multiple sources. Cooling towers may have been contaminated by mains water or by drift from other towers.

A prospective study of 100 gelatin-sealed aortic grafts

A gelatin-sealed knitted Dacron graft has been developed which has zero porosity at implantation and does not require preclotting. Its patency rate up to 57 months and effectiveness at saving blood loss have been studied. Gelatin-sealed aortic grafts were implanted into 100 consecutive patients--77 men, 23 women. Surgery was performed for aneurysm in 36 patients (including four with rupture), intermittent claudication in 44, rest pain in 17, and gangrene in three, over an 18 month period. The patients were followed up prospectively for 57 months. Perioperative mortality was 1%. Cumulative primary graft patency was 99%. There was no measurable blood loss at implantation. Forty-seven patients required blood transfusion: mean volume transfused was 430 ml. There were no problems related to the sealant.

Seasonal variation of Legionnaires' disease in Scotland

A summer and autumn peak in incidence is a characteristic epidemiological feature of Legionnaires' disease, a fact which may help in diagnosis. Previous reports from Scotland have reported a winter peak. This study examined the seasonal variation in Legionnaires' disease in Scotland in each year and by category of diagnosis. A characteristic summer/autumn peak was seen for travel-related infection. For non-travel infection, there was an autumnal peak between 1978 and 1982 but an early winter peak between 1983 and 1986. Overall, the pattern could be described as a summer/autumn plateau reaching a peak in early winter. This pattern, seen in men and women, was clearest in the Greater Glasgow area. Nosocomial cases were clustered in the months of October, November and December. In non-travel cases the classical seasonal pattern was not observed and clinicians cannot rely upon this epidemiological feature for diagnosis. However, the relative infrequency of the disease between January and May was a consistent and potentially useful feature. Most reports on seasonal variation are based on aggregated data on travel and non-travel cases. The present observations question the hypotheses developed to explain the seasonal pattern and call for further studies.

Proximity of the home to a cooling tower and risk of non-outbreak Legionnaires' disease

OBJECTIVE

To study the source of non-outbreak legionnaires' disease, particularly the role of cooling towers, by comparing the locations of patients' homes in relation to the location of cooling towers.

DESIGN

Retrospective, descriptive study of a case series of patients with legionnaires' disease ill between 1978 and 1986 and, for comparison, a case series of patients with lung cancer. A prospectively developed register and interview based survey provided data on the location of cooling towers.

SETTING

The city of Glasgow.

PATIENTS

134 patients aged 14-84 with legionnaires' disease during 1978-86 and 10,159 patients with lung cancer during the same period.

MAIN OUTCOME MEASURES

The locations of patients' homes and cooling towers as defined by postcodes, which provided map grid references accurate to 10 m; numbers of expected and observed cases of legionnaires' disease in census enumeration districts; and distance of enumeration districts from the nearest cooling tower as defined by five distance categories.

RESULTS

Most cooling towers were in or near the city centre or close to the River Clyde, as were the places of residence of patients with community acquired, non-travel, non-outbreak legionnaires' disease (n = 107). There was an inverse association between the distance of residence from any cooling tower and the risk of infection, the population living within 0.5 km of any tower having a relative risk of infection over three times that of people living more than 1 km away. There was no such association with respect to travel related legionnaires' disease, and for lung cancer the association was weak (relative risk less than or equal to 1.2 in any distance group).

CONCLUSION

In Glasgow cooling towers have been a source of infection in two outbreaks of legionnaires' disease and, apparently, a source of non-outbreak infection also. Better maintenance of cooling towers should help prevent non-outbreak cases. This method of inquiry should be applied elsewhere to study the source of this and other environmentally acquired disease.

Variation in time and space of non-outbreak Legionnaires' disease in Scotland

The main aim of this study was to measure and explain geographic variations in the incidence of Legionnaires' disease in Scotland, particularly to help understand the source of non-outbreak infection. Between 1978 and 1986 the overall mean annual incidence rate was 7.9 per million (range 3.1-20.2), and for non-outbreak, non-travel cases it was 5.6. There were geographical variations by health board, by city and within cities, e.g. the mean annual incidence rate per million for non-travel, non-outbreak disease was 1.2 in Tayside Health Board, 3.7 in Lanarkshire, 5.6 in Lothian and 14.4 in Greater Glasgow. In Greater Glasgow Health Board non-travel cases lived in and around the city centre and in some postcode sectors there, the mean annual incidence rate exceeded 100. Travel-related cases lived in peripheral areas. These variations could not be explained by differences in access to and use of diagnostic services, surveillance, or host susceptibility (as reflected by socioeconomic status and frequency of other respiratory disease). The explanation probably lay in environmental factors, though differences in agent virulence were not excluded. The two main conclusions are, that non-outbreak cases were not truly sporadic, and that the space-time variations in incidence support the hypothesis that cooling towers were an important source of infection for non-travel, non-outbreak cases. If so such infection is potentially preventable.

A field study of the survival of Legionella pneumophila in a hospital hot-water system

The colonization, survival and control of Legionella pneumophila in a hospital hot-water system was examined. The organism was consistently isolated from calorifier drain-water samples at temperatures of 50 degrees C or below, despite previous chlorination of the system. When the temperature of one of two linked calorifiers was raised to 60 degrees C, by closing off the cold-water feed, the legionella count decreased from c. 10(4) c.f.u./l to an undetectable level. However, 10 min after turning on the cold-water feed which produced a fall in calorifier temperature, the count in the calorifier drain water returned to its original level. Investigations revealed that the cold-water supply was continually feeding the calorifiers with L. pneumophila. Simple modifications in the design of the system were made so that the cold-water feed no longer exceeds 20 degrees C; these measures have considerably reduced the number of L. pneumophila reaching the calorifiers.

The Stafford outbreak of Legionnaires' disease

A large outbreak of Legionnaires' disease was associated with Stafford District General Hospital. A total of 68 confirmed cases was treated in hospital and 22 of these patients died. A further 35 patients, 14 of whom were treated at home, were suspected cases of Legionnaires' disease. All these patients had visited the hospital during April 1985. Epidemiological investigations demonstrated that there had been a high risk of acquiring the disease in the out patient department (OPD), but no risk in other parts of the hospital. The epidemic strain of Legionella pneumophila, serogroup 1, subgroup Pontiac 1a was isolated from the cooling water system of one of the air conditioning plants. This plant served several departments of the hospital including the OPD. The water in the cooling tower and a chiller unit which cooled the air entering the OPD were contaminated with legionellae. Bacteriological and engineering investigations showed how the chiller unit could have been contaminated and how an aerosol containing legionellae could have been generated in the U-trap below the chiller unit. These results, together with the epidemiological evidence, suggest that the chiller unit was most likely to have been the major source of the outbreak. Nearly one third of hospital staff had legionella antibodies. These staff were likely to have worked in areas of the hospital ventilated by the contaminated air conditioning plant, but not necessarily the OPD. There was evidence that a small proportion of these staff had a mild legionellosis and that these 'influenza-like' illnesses had been spread over a 5-month period. A possible explanation of this finding is that small amounts of aerosol from cooling tower sources could have entered the air-intake and been distributed throughout the areas of the hospital served by this ventilation system. Legionellae, subsequently found to be of the epidemic strain, had been found in the cooling tower pond in November 1984 and thus it is possible that staff were exposed to low doses of contaminated aerosol over several months. Control measures are described, but it was later apparent that the outbreak had ended before these interventions were introduced. The investigations revealed faults in the design of the ventilation system.

Maintenance of cooling towers following two outbreaks of Legionnaires' disease in a city

This survey assessed the maintenance of evaporative cooling towers in Glasgow, following two Legionnaires' disease outbreaks. Information was obtained from 76 of 81 premises and a maintenance score was calculated for each of 174 towers. The quality of maintenance was extremely varied (range of maintenance scores, 8-30; mean, 22 (S.D., 5.0); median, 23; maximum possible, 33) and some towers were neglected. Breaches of maintenance principles were mainly structural and organizational, e.g. inadequate drift control, rather than failure to use chemicals. Low maintenance scores were associated with no log book, no guidelines, no change in procedures in last 5 years, solitary cooling towers, and towers on industrial premises. Despite intense publicity the standard of cooling tower maintenance in Glasgow remained a concern. Information campaigns directed at those responsible for cooling-tower maintenance are necessary.

Nosocomial legionella pneumonia: demonstration of potable water as the source of infection

From January 1983 until December 1985, 35 cases of sporadic nosocomial legionella pneumonia, all caused by Legionella pneumophila, were diagnosed in a university hospital. L. pneumophila serogroup (SG) 1 was cultured from 12 of the 35 cases and compared to corresponding L. pneumophila SG 1 isolates from water outlets in the patients' immediate environment by subtyping with monoclonal antibodies. The corresponding environmental isolates were identical to 9 out of 12 (75%) of those from the cases. However, even in the remaining three cases identical subtypes were found distributed throughout the hospital water supply. From the hospital water supply four different subtypes of L. pneumophila SG 1 were isolated, three of which were implicated in legionella pneumonia. Of 453 water samples taken during the study 298 (65.8%) were positive for legionellae. Species of Legionella other than L. pneumophila have not been isolated. This may explain the exclusiveness of L. pneumophila as the legionella pneumonia-causing agent. Our results suggest that the water supply system was the source of infection.

Nosocomial Legionnaires' disease--advances in diagnosis and typing

The impact of new methodologies on the routine diagnosis of legionella pneumonia has been limited but the potential for advance is considerable. Antigen detection immunoassays have not yet reached the stage where they are used in routine practice. Monoclonal antibodies have been successfully used for direct fluorescence of bronchial aspirates. Nucleic acid hybridization techniques have yet to find a role in diagnosis. Serology remains the most commonly used method in the diagnosis of Legionnaires' disease. Methods of typing Legionella pneumophila include monoclonal antibodies and isoenzyme, plasmid and nucleic acid analysis. Biotyping methods have not been found to be of value. The use of monoclonal antibodies has permitted the comparison of clinical and environmental isolates and allowed the separation of serogroup 1 into subgroups of differing virulence. The subgroup of serogroup 1 called Pontiac is responsible for the majority of sporadic and epidemic legionella pneumonia in the UK. An internationally accepted panel of monoclonal antibodies is used to define these strains. The extent to which other subgroups of serogroup 1 and other serogroups of L. pneumophila cause disease appear to reflect their environmental prevalence.

Nosocomial Legionnaires' disease: a global perspective

Nosocomial Legionnaires' disease is a worldwide problem. The lack of prospective surveys using sensitive diagnostic means, such as culture, has resulted in ignorance about the exact magnitude of the problem except at a handful of individual hospitals. Contaminated hospital hot water systems, cooling towers, and non-sterile tap water used for respiratory therapy may all cause disease. Culture diagnosis is the preferred method of case ascertainment, and provides bacterial isolates which can be used to implicate specific environmental sites using molecular epidemiologic techniques. Environmental culture surveys, done in the absence of known disease, are probably not indicated, but there remains concern that wards housing very high risk patients should be legionella-free. Use of monoclonal antibody typing of environmental isolates of L. pneumophila serogroup 1 may be useful in this regard, as it can possibly detect strains most likely to cause disease. Control of nosocomial disease requires centralized management and consultation by expert engineers, epidemiologists, and microbiologists.

How to deal with a hospital outbreak of Legionnaires' disease

The outbreak of Legionnaires' disease in Glasgow Royal Infirmary is discussed together with the problems such an outbreak poses to the microbiologist. The importance of early diagnosis is stressed. The outbreak was managed by a team drawn up from various disciplines within the hospital. Frank daily reports to the press, together with regular staff meetings with staff representatives helped to allay public anxiety. The subsequent maintenance and monitoring of the wet cooling tower required for the hospital ventilation system have resulted in considerable additional work for the microbiology department but especially for the hospital engineers.

Rapid diagnosis of an outbreak of Legionnaires' disease at Glasgow Royal Infirmary

In the last three months of 1985 there was an outbreak of legionnaires' disease at Glasgow Royal Infirmary affecting 15 patients and one surgeon; five patients died. Legionnaires' disease was first suspected when a second case of severe nosocomial pneumonia occurred in a high dependency unit. The application of the direct fluorescent antibody test to specimens obtained at bronchoscopy was responsible for the rapid diagnosis of legionnaires' disease, which led to the prescription of appropriate antibiotic treatment and the shutting down of the contaminated cooling tower, thereby containing the outbreak. It also led to a search for further cases. It is suggested that these diagnostic techniques should be included in the investigation of affected patients in an outbreak of pneumonia.