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We used US population-based surveillance data to characterize clinical risk factors for Legionnaires' disease (LD). The LD incidence increased by age and the risk was elevated for 12 clinical conditions, when compared to healthy adults. This information can be used to guide testing, treatment, and public health prevention efforts., (Published by Oxford University Press for the Infectious Diseases Society of America 2019.)

Over the past decade, the reported incidence of Legionnaires' disease (LD) in the northeastern United States has increased, reaching 1-3 cases per 100,000 population. There is reason to suspect that this is an underestimate of the true burden, since LD cases may be underdiagnosed. In this analysis of pneumonia and influenza (P&I) hospitalizations, we estimated the percentages of cases due to Legionella, influenza, and respiratory syncytial virus (RSV) by age group. We fitted mixed-effects models to estimate attributable percents using weekly time series data on P&I hospitalizations in Connecticut from 2000 to 2014. Model-fitted values were used to calculate estimates of numbers of P&I hospitalizations attributable to Legionella (and influenza and RSV) by age group, season, and year. Our models estimated that 1.9%, 8.8%, and 5.1% of total (all-ages) inpatient P&I hospitalizations could be attributed to Legionella, influenza, and RSV, respectively. Only 10.6% of total predicted LD cases had been clinically diagnosed as LD during the study period. The observed incidence rate of 1.2 cases per 100,000 population was substantially lower than our estimated rate of 11.6 cases per 100,000 population. Our estimates of numbers of P&I hospitalizations attributable to Legionella are comparable to those provided by etiological studies of community-acquired pneumonia and emphasize the potential for underdiagnosis of LD in clinical settings., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Legionnaires' disease is an important cause of hospital-acquired pneumonia and is caused by infection with the bacterium Legionella. Because current typing methods often fail to resolve the infection source in possible nosocomial cases, we aimed to determine whether whole-genome sequencing (WGS) could be used to support or refute suspected links between cases and hospitals. We focused on cases involving a major nosocomial-associated strain, L. pneumophila sequence type (ST) 1., Methods: WGS data from 229 L. pneumophila ST1 isolates were analyzed, including 99 isolates from the water systems of 17 hospitals and 42 clinical isolates from patients with confirmed or suspected hospital-acquired infections, as well as isolates obtained from or associated with community-acquired sources of Legionnaires' disease., Results: Phylogenetic analysis demonstrated that all hospitals from which multiple isolates were obtained have been colonized by 1 or more distinct ST1 populations. However, deep sampling of 1 hospital also revealed the existence of substantial diversity and ward-specific microevolution within the population. Across all hospitals, suspected links with cases were supported with WGS, although the degree of support was dependent on the depth of environmental sampling and available contextual information. Finally, phylogeographic analysis revealed that hospitals have been seeded with L. pneumophila via both local and international spread of ST1., Conclusions: WGS can be used to support or refute suspected links between hospitals and Legionnaires' disease cases. However, deep hospital sampling is frequently required due to the potential coexistence of multiple populations, existence of substantial diversity, and similarity of hospital isolates to local populations., (© The Author 2017. Published by Oxford University Press for the Infectious Diseases Society of America.)

Background: Two proven nosocomial cases of Legionella pneumonia occurred at the Wesley Hospital (Brisbane, Australia) in May 2013. To trace the epidemiology of these cases, whole genome sequence analysis was performed on Legionella pneumophila isolates from the infected patients, prospective isolates collected from the hospital water distribution system (WDS), and retrospective patient isolates available from the Wesley Hospital and other local hospitals., Methods: Legionella pneumophila serogroup 1 isolates were cultured from patient sputum (n = 3), endobronchial washings (n = 3), pleural fluid (n = 1), and the Wesley Hospital WDS (n = 39). Whole genome sequencing and de novo assembly allowed comparison with the L. pneumophila Paris reference strain to infer phylogenetic and epidemiological relationships. Rapid disinfection of the hospital WDS with a chlorinated, alkaline detergent and subsequent superchlorination followed by maintenance of residual free chlorine, combined with removal of redundant plumbing, was instituted., Results: The 2011 and 2013 L. pneumophila patient isolates were serogroup 1 and closely related to all 2013 hospital water isolates based on single nucleotide polymorphisms and mobile genetic element profiles, suggesting a single L. pneumophila population as the source of nosocomial infection. The L. pneumophila population has evolved to comprise 3 clonal variants, each associated with different parts of the hospital WDS., Conclusions: This study provides an exemplar for the use of clinical and genomic epidemiological methods together with a program of rapid, effective remedial biofilm, plumbing and water treatment to characterize and eliminate a L. pneumophila population responsible for nosocomial infections., (© The Author 2015. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.)

Background: Travel-associated Legionnaires' disease (LD) is a serious problem, and hundreds of cases are reported every year among travelers who stayed at hotels, despite the efforts of international and governmental authorities and hotel operators to prevent additional cases., Methods: A systematic review of travel-associated LD events (cases, clusters, outbreaks) and of environmental studies of Legionella contamination in accommodation sites was conducted. Two databases were searched (PubMed and EMBASE). Data were extracted from 50 peer-reviewed articles that provided microbiological and epidemiological evidence for linking the accommodation sites with LD. The strength of evidence was classified as strong, possible, and probable., Results: Three of the 21 hotel-associated events identified and four of nine ship-associated events occurred repeatedly on the same site. Of 197 hotel-associated cases, 158 (80.2%) were linked to hotel cooling towers and/or potable water systems. Ship-associated cases were most commonly linked to hot tubs (59/83, 71.1%). Common contributing factors included inadequate disinfection, maintenance, and monitoring; water stagnation; poor temperature control; and poor ventilation. Across all 30 events, Legionella concentrations in suspected water sources were >10,000 cfu/L, <10,000 cfu/L, and unknown in 11, 3, and 13 events, respectively. In five events, Legionella was not detected only after repeated disinfections. In environmental studies, Legionella was detected in 81.1% of ferries (23/28) and 48.9% of hotels (587/1,200), while all 12 cruise ships examined were negative., Conclusions: This review highlights the need for LD awareness strategies targeting operators of accommodation sites. Increased standardization of LD investigation and reporting, and more rigorous follow-up of LD events, would help generate stronger, more comparable evidence on LD sources, contributing factors, and control measure effectiveness., (© 2015 International Society of Travel Medicine.)

Background: Healthcare-associated Legionnaires' disease (LD) is a preventable pneumonia with a 30% case fatality rate. The Centers for Disease Control and Prevention guidelines recommend a high index of suspicion for the diagnosis of healthcare-associated LD. We characterized an outbreak and evaluated contributing factors in a hospital using copper-silver ionization for prevention of Legionella growth in water., Methods: Through medical records review at a large, urban tertiary care hospital in November 2012, we identified patients diagnosed with LD during 2011-2012. Laboratory-confirmed cases were categorized as definite, probable, and not healthcare associated based on time spent in the hospital during the incubation period. We performed an environmental assessment of the hospital, including collection of samples for Legionella culture. Clinical and environmental isolates were compared by genotyping. Copper and silver ion concentrations were measured in 11 water samples., Results: We identified 5 definite and 17 probable healthcare-associated LD cases; 6 case patients died. Of 25 locations (mostly potable water) where environmental samples were obtained for Legionella-specific culture, all but 2 showed Legionella growth; 11 isolates were identical to 3 clinical isolates by sequence-based typing. Mean copper and silver concentrations were at or above the manufacturer's recommended target for Legionella control. Despite this, all samples where copper and silver concentrations were tested showed Legionella growth., Conclusions: This outbreak was linked to the hospital's potable water system and highlights the importance of maintaining a high index of suspicion for healthcare-associated LD, even in the setting of a long-term disinfection program., (Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2015. This work is written by (a) US Government employee(s) and is in the public domain in the US.)

Background: To date, all descriptions of legionellosis in neonates have emerged from a small number of isolated case reports in newborns with unusually severe pneumonia. In December 2008, a large outbreak of Legionella infection occurred in term neonates in Cyprus, providing new information on the epidemiological and clinical features of Legionellosis in this age group., Methods: An environmental investigation was performed at a small private hospital where the infected neonates were delivered. The medical records of the infected neonates were retrospectively reviewed to obtain clinical data on presentation, complications, and course of disease., Results: Nine of the 32 (28%) newborns who were exposed to the contaminated source at the private nursery were infected with Legionella. Six subjects had pulmonary infiltrates, but in 3 cases there were no abnormal radiological findings and clinical presentation was mild. In 4 neonates, pulmonary infiltrates at presentation were bilateral and extensive and 3 died, conferring a mortality rate of 50% in subjects with pulmonary infiltrates and an overall mortality of 33.3%. Legionella pneumophila serogroup 3 was recovered in neonatal biological samples, although in some patients there was implication of a second strain, serogroup 1. It was determined that the neonates were infected while in the nursery at the private hospital by aerosol produced by a recently installed cold-mist humidifier that was filled with contaminated water., Conclusions: Use of humidifiers in nursery units must be avoided as the risk of disseminating Legionella in neonates is very high. In neonates legionellosis should be suspected when signs of infection first appear and take an unusual course, even when no pulmonary infiltrates appear.

Alerting providers to public health situations requires timeliness and context-relevance, both lacking in current systems. Incorporating decision support tools into electronic health records may provide a way to deploy public health alerts to clinicians at the point of care. A timely process for responding to Health Alert Network messages sent by the New York City Department of Health and Mental Hygiene was developed by a network of community health centers. Alerts with order sets and recommended actions were created to notify primary care providers of local disease outbreaks. The process, effect, and lessons learned from alerts for Legionella, toxogenic E coli, and measles outbreaks are described. Electronic alerts have the potential to improve management of diseases during an outbreak, including appropriate laboratory testing, management guidance, and diagnostic assistance as well as to enhance bi-directional data exchange between clinical and public health organizations.

Background: In France, Legionnaires disease is mainly caused by Legionella pneumophila. Here, we investigated possible host factors associated with susceptibility to community-acquired Legionnaires disease caused by the endemic Paris and Lorraine strains., Methods: We conducted a double-nested exploratory case-control study with use of data from the French national surveillance network of incident Legionnaires disease cases notified from 1998 through 2007. Patients with community-acquired Legionnaires disease and an L. pneumophila serogroup 1 isolate were eligible. Case patients were patients infected by the Paris or Lorraine strain, and control patients were those infected by sporadic strains. Epidemiological and clinical factors associated with infection with the Paris and Lorraine strains were assessed by calculating adjusted odds ratios (aOR) in multivariate logistic regression models., Results: We studied 1090 patients infected by sporadic strains (n = 920), the Paris strain (n = 80), or the Lorraine strain (n = 90). Infection with the Paris strain was significantly associated with female sex (aOR, 1.98; 95% confidence interval [CI], 1.19-3.28), steroid therapy (aOR, 3.16; 95% CI, 1.76-5.68), and a history of cancer or hematologic malignancies (aOR, 2.08; 95% CI, 1.15-3.76). In addition, the mortality rate was higher among patients infected with the Paris strain than in the control group (38% vs. 25.5%). The Lorraine strain was associated with smoking (aOR, 1.82; 95% CI, 1.14-2.91) and reduced mortality (9.9%). ., Conclusion: Several host characteristics were associated with the risk of infection by endemic strains of L. pneumophila serogroup 1. These findings may help to guide preventive measures. Factors predisposing patients to infection by specific strains need to be explored further.

The Pittsburgh Veterans Affairs hospital administration closed the research laboratory directed by Victor Yu and Janet Stout and destroyed isolates collected as part of a series of clinical studies over 25 years. This article discusses the implications and protests such destruction as an affront to science and scientific study. A petition signed by 243 individuals accompanies this article.

Background: On 21 May 2005, the Norwegian health authorities were alerted by officials from a local hospital that several recent patients had received the diagnosis of legionnaires disease; all patients resided in 2 neighboring municipalities. We investigated the outbreak to identify the source and to implement control measures., Methods: We interviewed all surviving case patients and investigated and harvested samples from 23 businesses with cooling towers and other potential infection sources. The locations of the businesses and the patients' residences and movements were mapped. We calculated attack rates and risk ratios among people living within various radii of each potential source. Isolates of Legionella pneumophila were compared using molecular methods., Results: Among 56 case patients, 10 died. The case patients became ill 12-25 May, resided up to 20 km apart, and had not visited places in common. Those living up to 1 km from a particular air scrubber had the highest risk ratio, and only for this source did the risk ratio decrease as the radius widened. Genetically identical L. pneumophila serogroup 1 isolates were recovered from patients and the air scrubber. The air scrubber is an industrial pollution-control device that cleans air for dust particles by spraying with water. The circulating water had a high organic content, pH of 8-9, and temperature of 40 degrees C. The air was expelled at 20 m/s and contained a high amount of aerosolized water., Conclusions: The high velocity, large drift, and high humidity in the air scrubber may have contributed to the wide spread of Legionella species, probably for >10 km. The risk of Legionella spread from air scrubbers should be assessed.

We evaluated the impact of the copper-silver ionization system in a hospital where hyperendemic nosocomial legionellosis and was present and all previous disinfection measures had failed. After implementation of the copper-silver ionization system, environmental colonization with Legionella species decreased significantly, and the incidence of nosocomial legionellosis decreased dramatically, from 2.45 to 0.18 cases per 1000 patient discharges.

Background: During March 2004, a large outbreak of legionnaires disease and Pontiac fever occurred among hotel guests in Oklahoma. An investigation was conducted to identify the source and evaluate the utility of the Legionella urine antigen assay and serologic testing for the identification of Pontiac fever., Methods: A retrospective cohort investigation of hotel guests and employees and an environmental evaluation were performed. Participants were interviewed, and clinical specimens were collected from consenting individuals., Results: Six cases of legionnaires disease and 101 cases of Pontiac fever were identified. Exposure to the indoor pool and hot tub area was associated with legionellosis (relative risk, 4.4; 95% confidence interval, 2.8-6.9). Specimens from the pool and hot tub tested positive for Legionella pneumophila serogroup 1 by polymerase chain reaction. For Pontiac fever, the sensitivity and positive predictive value were 35.7% and 100%, respectively, for the urine antigen assay, and 46.4% and 90%, respectively, for serologic testing. The specificity and negative predictive value were 100% and 47.8%, respectively, for the urine antigen assay, and 89.3% and 45.5%, respectively, for serologic testing., Conclusions: Urine antigen testing, with or without serologic testing, can be used to confirm outbreak-associated cases of Pontiac fever caused by L. pneumophila serogroup 1.

Background: Public health officials will normally take action at accommodation sites following an association with a cluster of cases of Legionnaires' disease. This paper seeks to determine the likelihood of such a cluster occurring at a site once it has been associated with a single case of the disease, and therefore whether more should be done at sites following individual cases., Methods: Information for UK residents reported to the EWGLINET system between 1993 and 2000 was included in a dataset. The size and country of hotel visited by the cases were divided into six country groups (France, Italy, Spain, Turkey, other Europe and other World), and eight size groups (<20 rooms, 20-49, 50-99, 100-199, 200-299, 300-399, 400-499, 500+). The data were investigated using Cox proportional hazards regression to model the probability of at least one further case following the first., Results: The dataset comprised 793 cases that had stayed at 605 sites in 51 countries between 1993 and the end of 2000. This included 605 cases that were the first case associated with a site, and 188 subsequent cases. Following the first case, 16.6% of sites were associated with at least one subsequent case during the period under study. The probability of a subsequent case occurring within 6 months of the first varied by country and size group, with some combinations returning a probability >30%; the probability of a subsequent case occurring within 2 years of the first reached over 50% in some instances., Conclusions: There may be support for early intervention at some accommodation sites following a first case of Legionnaires' disease, in specific country and size groups.

A community-wide outbreak of legionnaires disease occurred in Pas-de-Calais, France, in November 2003-January 2004. Eighteen (21%) of 86 laboratory-confirmed cases were fatal. A case-control study identified smoking, silicosis, and spending >100 min outdoors daily as risk factors for acquiring the disease. Legionella pneumophila strain Lens was isolated from cooling towers, wastewater, and air samples from plant A. This unique strain matched all 23 clinical isolates, as assessed by pulsed-field gel electrophoresis subtyping. Modeling of atmospheric dispersion of aerosols emitted from plant A cooling towers showed good coverage of the communes where patients lived and showed that the dispersion extended over a distance of at least 6 km from plant A. No other aerosol-producing installation was identified as a plausible source, and no common source of indoor exposure was found. These findings implicate plant A as the most likely outbreak source and suggest that the distance of airborne transmission of L. pneumophila may be greater than previously reported.

We investigated 3 cases of legionnaires disease (LD) that developed in travelers who stayed at a hotel in the United States Virgin Islands where cases of LD occurred in 1981-1982 and in 1998. The temperature of the potable water at the hotel was in a range that could optimally support the growth of Legionella species, and the potable water was colonized with Legionella pneumophila in 1981-1982 and in 2002-2003.

This case-control study investigated a cluster of respiratory illness among patrons of a restaurant. Of 173 patrons interviewed, 117 (68%) were ill. Symptoms included myalgias (93%), headache (87%), and fatigue (79%). The mean incubation period was 49 h and the mean duration of illness was 71 h. Patrons aged >15 years were more likely to have been ill than younger patrons (odds ratio [OR], 2.96; P=.002); 58% of persons who were ill sat near a large fountain, compared with 18% of respondents who were not ill (OR, 7.5; P=.005). Legionella anisa was cultured from water samples obtained from the fountain pool. Of 22 individuals who were ill, 11 (50%) had a > or =4-fold increase in the titer of antibody to that strain of L. anisa from acute-phase to convalescent-phase serum samples; 3 others (14%) had persistently elevated titers of > or =512; of a group of 20 individuals who had not been exposed to the restaurant, none had titers of >128. Pontiac fever should be considered as a diagnosis during acute outbreaks of influenza-like illness with a high attack rate and no other identified etiology.

Optimal therapy against Legionella infection is based on agents with a high intrinsic activity, an appropriate pharmacokinetic and pharmacodynamic profile (including the ability to penetrate phagocytic cells), a low incidence of adverse reactions and an advantageous cost-efficacy relationship. Newer macroazalides and fluoroquinolones are among the first-line therapies and in severe infections, particularly those occurring in immunocompromised patients, azithromycin and later fluoroquinolones are the agents of choice. Delay in the onset of adequate therapy is a key factor associated with a poor outcome. Thus, all patients with pneumonia associated with respiratory failure, shock or underlying disease causing severe immunodeficiency should initially receive an agent active against Legionella spp., at least while the aetiology remains unknown. Adjunctive measures improve outcome in critically ill patients. In intubated patients with delayed resolution, superinfection by Pseudomonas aeruginosa or co-infection caused by other pathogens should be excluded.

We investigated 4 cases of legionnaires' disease (LD) reported among workers at an Ohio automotive plant in March 2001. A "confirmed" case of LD was defined as x-ray-confirmed pneumonia and a confirmatory laboratory test. A "possible" case of LD was defined as elevated titers of antibody and respiratory symptoms. Legionella pneumophila serogroup 1 (LP1) was isolated from 1 case patient. Legionella was isolated from 18 (9%) of 197 environmental samples; 3 isolates were LP1 but did not match the case isolate. We conducted a case-control study; 17 case patients with confirmed or possible LD and 86 control subjects (workers with low antibody titers and without symptoms) were enrolled. Visiting a specific cleaning line (odds ratio, [OR], 7.29; 95% confidence interval [CI], 2.31-23.00) and working in the cleaning region of the plant (OR, 3.22; 95% CI, 1.11-9.38) were associated with LD. LD can be transmitted in industrial settings in which aerosols are produced. Clinicians should consider LD when treating persons from these settings for pneumonia.

Legionella pneumophila serogroup 6 was recovered from a bronchoalveolar lavage specimen from a 1-week-old, full-term newborn with pneumonia, as well as from water samples from the maternity hospital and the newborn's home (an apartment). Amplified fragment-length polymorphism typing revealed that the strains isolated from the newborn and her home were indistinguishable from each other but were clearly different from the hospital and control strains. To our knowledge, this is the first report of domestic acquisition of legionnaires disease in a newborn to have been confirmed by molecular typing.

A follow-up study of 122 survivors of an outbreak of legionnaires disease (LD) in The Netherlands was conducted to determine persistence of symptoms, health-related quality of life (HRQL), and presence of posttraumatic stress disorder (PTSD). Seventeen months after diagnosis of LD, survivors completed a questionnaire assessing symptoms and HRQL and a questionnaire assessing PTSD. The most prevalent new symptoms were fatigue (in 75% of patients), neurologic symptoms (in 66%), and neuromuscular symptoms (in 63%). HRQL was impaired in 7 of the 8 dimensions assessed by the HRQL questionnaire, and 15% of patients experienced PTSD. Symptoms and impaired HRQL persisted for >1.5 years. As a result of the design of this study, it could not be inferred whether Legionella pneumophila infection, severe pneumonia in general, or the outbreak situation was responsible for impaired well-being. However, awareness of this problem by health care providers may improve the aftercare of patients.

Internet resources that focus on Legionella and legionnaires disease are presented. Web sites were selected on the basis of their content and adherence to suggested standards of medical Internet publishing. Free, accessible, English-language Web sites were categorized according to users' needs as follows: (1) those with comprehensive information on Legionella infection (including pathophysiologic characteristics, symptoms, and treatment of legionnaires disease), (2) those with information on outbreaks and epidemiology (including information for travelers), (3) those with information for researchers, (4) those about prevention, and (5) those with information for laypersons.

Legionella pneumophila is naturally found in fresh water were the bacteria parasitize within protozoa. It also survives planctonically in water or biofilms. Upon aerosol formation via man-made water systems, L. pneumophila can enter the human lung and cause a severe form of pneumonia, called Legionnaires' disease. The pathogenesis of Legionnaires' disease is largely due to the ability of L. pneumophila to invade and grow within macrophages. An important characteristic of the intracellular survival strategy is the replication within the host vacuole that does not fuse with endosomes or lysosomes. In recent times a great number of bacterial virulence factors which affect growth of L. pneumophila in both macrophages and protozoa have been identified. The ongoing Legionella genome project and the use of genetically tractable surrogate hosts are expected to significantly contribute to the understanding of bacterium-host interactions and the regulation of virulence traits during the infection cycle. Since person-to-person transmission of legionellosis has never been observed, the measures for disease prevention have concentrated on eliminating the pathogen from water supplies. In this respect detection and analysis of Legionella in complex environmental consortia become increasingly important. With the availability of new molecular tools this area of applied research has gained new momentum.

Travel-associated outbreaks of legionnaires disease (LD) and combined outbreaks of LD and Pontiac fever (PF) are rarely identified. During one travel-associated combined outbreak at a hotel, a cohort study of potentially exposed persons and an environmental investigation were performed. Two LD and 22 PF cases were identified. Legionella pneumophila serogroup 6 (Lp6) isolates from the index patient and the hotel whirlpool spa were found to be identical by amplified fragment-length polymorphism typing. Disease occurred in 10 of 26 guests who were exposed to the spa versus 2 of 29 guests who were exposed only to the pool area (38% vs. 7%; P=.005). Immunoglobulin M (IgM) antibody to the outbreak Lp6 strain was more common among persons with PF (4 of 9) than among non-ill persons (2 of 32) (44% vs. 6%; P=.02). Spa exposure correlated with disease (P=.001) and IgM seropositivity (P=.007). New laboratory techniques facilitate outbreak investigation; to expedite outbreak interruption and measure the impact of travel-associated legionellosis, surveillance must be improved.

An epidemiologic investigation was conducted in response to a case of Legionella pneumonia in a scientist working at a federal research facility. A survey of 80 individuals working at the facility revealed that 13 (16%) had sustained prior infections with Legionella pneumophila serogroup 1 (Lps1) as measured by anti-Lps1 antibodies. Antibody-positive individuals' offices clustered around an air cooling tower and a heating, ventilation, and air conditioner unit (odds ratio = 5). On multivariate logistic regression analysis, individuals of non-white race (adjusted odds ratio = 8) and smokers (adjusted odds ratio = 36) were also found to be at higher risk of past infection. Marked Legionella growth was noted in the cooling tower's water reservoir and potable hot water system, where suboptimal operating temperatures were noted. Subsequent increase in the hot water temperatures as well as a complete renovation of the affected building's air handling and potable water systems led to a reduction in Legionella species colonization.

A survey was conducted of exhibitors at a 1999 floral trade show, where a whirlpool spa on display caused a large outbreak of legionnaires disease (LD). In total, 742 exhibitors without LD returned a questionnaire on their whereabouts during the fair and their health afterward and supplied blood samples for the detection of IgM and IgG antibodies against Legionella pneumophila. The exhibitors had higher average antibody levels than did the general population. The closer to the whirlpool that the exhibitors worked, the higher their antibody levels. Both high-normal and high titer levels were found more frequently among workers with more exposure, suggesting that serosurveys among potentially exposed subjects are a valuable tool for outbreak investigation. Some differences in health complaints were observed between the more and less exposed groups, as estimated by the workplace location, but few differences were found between groups with different antibody levels.

Phenotypic and genotypic methods identify subtypes of Legionella pneumophila, serogroup 1, and match patient and environmental isolates from suspected sources. The strength of this association is limited by the lack of information regarding the frequency and distribution of isolates belonging to various subtypes. In this study, 62 clinical isolates of L. pneumophila, serogroup 1, were subtyped by using pulsed-field gel electrophoresis (PFGE), to determine the distribution and degree of diversity of PFGE patterns among monoclonal antibody (MAb) subtypes. Unexpectedly, 8 of 21 MAb Philadelphia 1 isolates had a common PFGE pattern, and, among 12 MAb OLDA isolates, only 2 PFGE patterns were seen. Our hypothesis was that PFGE patterns were distributed randomly; however, statistical analysis showed that the distribution of subtypes was not random (Fisher's exact test 0.13; P>.05). In light of these results, researchers who do epidemiological investigations should use caution when interpreting the significance of matching PFGE patterns of L. pneumophila, serogroup 1.

Background: Recognized outbreaks of Legionnaires' disease (LD) are rare; when they occur, they provide opportunities to understand the epidemiology of the illness and improve prevention strategies. We investigated a population-based outbreak., Methods: After the confirmation of LD in October 1996 in five people in neighbouring towns in southwest Virginia, active surveillance for additional cases was undertaken. A case-control study was conducted to identify exposures associated with illness, followed by a cohort study among employees of the facility at which the source of the outbreak was located in order to assess unrecognized exposure and illness. Samples of likely sources of LD in the facility were cultured for LEGIONELLA:, Results: In all, 23 laboratory-confirmed cases of LD were eventually identified. Of the 15 cases in the case-control study, 14 (93%) reported visiting a home-improvement store, compared with 12 (27%) of 45 controls (matched odds ratio [MOR] = 23.3; 95% CI : 3-182). Among home-improvement centre patrons, 10 (77%) of 13 cases questioned recalled either visiting or walking by a display whirlpool spa, compared with 3 (25%) of 12 controls (MOR = 5.5; 95% CI : 0.7-256.0). Two cases' sputum isolates were an exact match, by monoclonal antibody subtyping and arbitrarily primed polymerase chain reaction, to a whirlpool spa filter isolate from the store. Employees reporting more exposure to the display spas were more likely to report symptoms of LD or to have an elevated titre., Conclusions: This investigation shows that LD can be transmitted from a whirlpool spa used for display only, and highlights the need for minimizing the risk of transmission of LD from all water-filled spas. Key messages This paper describes an investigation of a population-based outbreak of Legionnaires' disease (LD). A case-control study first identified a home-improvement store as the likely source of the outbreak. An environmental investigation later confirmed that finding, as two cases' sputum isolates were an exact match, by monoclonal antibody subtyping and arbitrarily primed polymerase chain reaction, to a whirlpool spa filter isolate from the store. The spa was intended and used for display only.

Background: From July to September 1994, 29 cases of community-acquired Legionnaires' disease (LD) were reported in Delaware. The authors conducted an investigation to a) identify the source of the outbreak and risk factors for developing Legionella pneumophila serogroup 1 (Lp-1) pneumonia and b) evaluate the risk associated with the components of cumulative exposure to the source (i.e. distance from the source, frequency of exposure, and duration of exposure)., Methods: A case-control study matched 21 patients to three controls per case by known risk factors for acquiring LD. Controls were selected from patients who attended the same clinic as the respective case-patients. Water samples taken at the hospital, from eight nearby cooling towers, and from four of the patient's homes were cultured for Legionella. Isolates were subtyped using monoclonal antibody (Mab) analysis and arbitrarily primed polymerase chain reaction (AP-PCR)., Results: Eleven (52%) of 21 case-patients worked at or visited the hospital compared with 17 (27%) of 63 controls (OR 5.0, 95% CI : 1.1-29). For those who lived, worked, or visited within 4 square miles of the hospital, the risk of illness decreased by 20% for each 0.10 mile from the hospital; it increased by 80% for each visit to the hospital; and it increased by 8% for each hour spent within 0.125 miles of the hospital. Lp-1 was isolated from three patients and both hospital cooling towers. Based on laboratory results no other samples contained Lp-1. The clinical and main-tower isolates all demonstrated Mab pattern 1,2,5,6. AP-PCR matched the main-tower samples with those from two case-patients., Conclusion: The results of our investigation suggested that the hospital cooling towers were the source of a community outbreak of LD. Increasing proximity to and frequency of exposure to the towers increased the risk of LD. New guidelines for cooling tower maintenance are needed. Knowing the location of cooling towers could facilitate maintenance inspections and outbreak investigations.

The occurrence of legionnaires' disease has been described previously in passengers of cruise ships, but determination of the source has been rare. A 67-year-old, male cigarette smoker with heart disease contracted legionnaires' disease during a cruise in September 1995 and died 9 days after disembarking. Legionella pneumophila serogroup 1 was isolated from the patient's sputum and the ship's water supply. Samples from the air-conditioning system were negative. L. pneumophila serogroup 1 isolates from the water supply matched the patient's isolate, by both monoclonal antibody subtyping and genomic fingerprinting. None of 116 crew members had significant antibody titers to L. pneumophila serogroup 1. One clinically suspected case of legionnaires' disease and one confirmed case were subsequently diagnosed among passengers cruising on the same ship in November 1995 and October 1996, respectively. This is the first documented evidence of the involvement of a water supply system in the transmission of legionella infection on ships. These cases were identified because of the presence of a unique international system of surveillance and collaboration between public health authorities.

Legionella pneumophila is an important pathogen that may cause nosocomial and community-acquired pneumonia in patients with normal or altered immunity. The epidemiology of 40 cases of legionella pneumonia in patients hospitalized between 1986 and 1994 was studied. Fourteen patients (35%) were solid organ transplant recipients. The calculated annual incidence of L. pneumophila infection was highest among lung transplant recipients (2.07 cases per 1,000 transplant-years). There was a trend toward reduced mortality rates and less severe disease among transplant patients vs. nontransplant patients: mortality rate, 36% vs. 54%; incidence of intubation, 50% vs. 69%; rate of concurrent infections, 29% vs. 38%; and overall rate of complications, 86% vs. 96%; respectively. In a multivariate analysis, factors independently associated with an increased mortality rate were nosocomial acquisition, need for intubation, formation of lung abscess or cavitation, and presence of pleural effusion. Thus, despite differing host immune responses, the most important prognostic factors affecting the outcome of legionellosis are nosocomial acquisition and the development of pulmonary complications.

In July 1995 we investigated a pneumonia outbreak in a Pennsylvania town. We conducted epidemiological and molecular microbiological studies to determine the outbreak source and interrupt transmission of disease. Legionnaires' disease (LD) was quickly identified by urine antigen testing, and a newly developed immunohistochemical stain confirmed nosocomial transmission to a hospital inpatient. LD was confirmed in 22 patients. Case-patients were more likely than controls to have been within 1,000 feet of the hospital (matched odds ratio, 21.0; 95% confidence interval, 2.9-368) during the 2 weeks prior to illness. Legionella pneumophila serogroup 1 (Lp-1) was isolated from hospital cooling towers (CTs) and rooftop air samples but not from hospital potable water or community CTs. Hospital CT and air Lp-1 isolates matched all five patient isolates by monoclonal antibody, arbitrarily primed polymerase chain reaction, and pulsed-field gel electrophoresis subtyping. Strategies to prevent LD must include minimizing transmission from CTs.

In August and September 1993, we investigated an outbreak of legionnaires' disease in Fall River, Massachusetts, that involved 11 persons; the attack rate was highest in Flint, a community of Fall River. All cases were infected with Legionella pneumophila serogroup 1 (Lp-1). A case-control study revealed that cases were more likely than matched controls to have visited sites in neighborhood A of Flint. Environmental sampling in Flint found that four of nine aerosol-producing devices sampled contained legionellae; only two, conjoined cooling towers on building A, contained Lp-1. Three independent methods of subtyping--monoclonal antibody subtyping, arbitrary primer polymerase chain reaction, and pulsed-field gel electrophoresis--revealed that Lp-1 isolates from three cases with culture-positive legionnaires' disease matched those from the cooling towers on building A. Water samples from the homes of cases with culture-positive legionnaires' disease contained no legionellae. The results of this epidemiologic and laboratory investigation indicate that the cooling towers on building A were the source of the outbreak of legionnaires' disease and confirm the importance of cooling towers in the transmission of legionnaires' disease.

Background: An outbreak of legionnaires' disease occurred in central London in January and February 1989. An Infection Control Committee was established to investigate the outbreak and institute control measures. The objective of this paper is to describe the investigation and control of the outbreak., Methods: An epidemiological survey and case-control study were carried out. The subjects were cases of community acquired pneumonia associated with central London with onset of illness in January and February 1989., Results: Thirty-three confirmed cases, including five deaths, and ten suspected cases, including three deaths, were identified with dates of onset from 1 January to 11 February. A clustering of visits by cases to the vicinity of Piccadilly Circus was noted, and a case-control study demonstrated a strong association between illness and visits to this area in the two weeks before onset of symptoms. The causative organism, Legionella pneumophila serogroup 1, was isolated from six patients. Legionella pneumophila of the same serogroup was isolated from water samples from five wet cooling systems (cooling towers) in the area under investigation, but in only two systems was the organism indistinguishable by subtyping from the patients' strains. Many of the cooling towers examined were inadequately maintained, including one of the two above a building adjacent to Piccadilly Circus from which a strain indistinguishable from the outbreak strain was isolated. All cooling towers in the area were shut down until inspected, and only allowed to restart after appropriate maintenance had been instigated., Conclusions: This outbreak showed the continuing risk of legionnaires' disease posed by wet cooling systems, including cooling towers, and highlighted the need to assess this risk so that appropriate maintenance is carried out. Regulations have recently been introduced, under the Health and Safety at Work Act, requiring notification of all wet cooling systems to the local authority to facilitate the investigation of outbreaks of legionnaires' disease.