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The Flint Water Crisis-due to changes of water source and treatment procedures-has revealed many unsolved social, environmental, and public health problems for US drinking water, including opportunistic premise plumbing pathogens (OPPP). The true health impact of OPPP, especially in vulnerable populations such as the elderly, is largely unknown. We explored 10 8 claims in the largest US national uniformly collected data repository to determine rates and costs of OPPP-related hospitalizations. In 1991-2006, 617,291 cases of three selected OPPP infections resulted in the elderly alone of $0.6 billion USD per year of payments. Antibiotic resistance significantly increased OPPP illness costs that are likely to be underreported. More precise estimates for OPPP burdens could be obtained if better clinical, microbiological, administrative, and environmental monitoring data were cross-linked. An urgent dialog across governmental and disciplinary divides, and studies on preventing OPPP through drinking water exposure, are warranted.

Purpose of Review: The aim is to discuss the epidemiology of infections that arise from contaminated water in healthcare settings, including Legionnaires' disease, other Gram-negative pathogens, nontuberculous mycobacteria, and fungi., Recent Findings: Legionella can colonize a hospital water system and infect patients despite use of preventive disinfectants. Evidence-based measures are available for secondary prevention. Vulnerable patients can develop healthcare-associated infections with waterborne organisms that are transmitted by colonization of plumbing systems, including sinks and their fixtures. Room humidifiers and decorative fountains have been implicated in serious outbreaks, and pose unwarranted risks in healthcare settings., Summary: Design of hospital plumbing must be purposeful and thoughtful to avoid the features that foster growth and dissemination of Legionella and other pathogens. Exposure of patients who have central venous catheters and other invasive devices to tap water poses a risk for infection with waterborne pathogens. Healthcare facilities must conduct aggressive clinical surveillance for Legionnaires' disease and other waterborne infections in order to detect and remediate an outbreak promptly. Hand hygiene is the most important measure to prevent transmission of other Gram-negative waterborne pathogens in the healthcare setting.

Legionnaires' disease (LD) is a systemic infection caused by Legionella species especially colonized in the water systems. Hotels are common locations in which waterwork-associated sporadic or epidemic legionellosis can be detected. The aim of this study was to evaluate a small Legionella outbreak emerged in a recently opened 600-bed hotel in Alanya, a touristic county in Mediterranean part of Turkey. A 66 years old male patient who stayed in this hotel opened on May 15th, 2009, was admitted to our hospital on May 21st, 2009 with the complaints of high fever, headache and diarrhea lasting for three days. Since chest X-ray revealed non-homogenous density increase in left middle and inferior zone, the patient was diagnosed as atypical pneumoniae and LD was confirmed by positive urinary Legionella antigen test (Card test, BinaxNOW®Legionella Urinary Antigen Test; Alere Co, USA) result. Following the identification of the index case, the records of our hospital were reviewed and revealed another case being treated with the diagnosis of community acquired pneumonia who was also the guest of the same hotel. This patient was then diagnosed as LD by positive urinary antigen test. Since new cases were identified during the following days (May 22, 25 and 26) the Antalya County Health Department and hotel management were informed about a cluster of LD. In addition subsequent investigation for environmental surveillance and water sampling were conducted. The LD diagnosis and environmental inspections were performed according to the procedure described in the guideline from "Turkish Ministry of Health Travel-Associated Legionnaires' Disease Control Programme". Five definitive cases and one presumptive case of LD were identified during the outbreak period (May 20-26, 2009). All of the cases were successfully treated (intravenous ciprofloxacin or levofloxacin or clarithromycin), however one patient died due to sudden death during sleep after being discharged. Since sputum samples could not be obtained from the cases, the diagnosis were not confirmed by culture but by urinary antigen test. Besides high antibody titer in single serum sample was accepted as a diagnostic marker. Additionally 26 cases who accommodated in the same hotel and presented with high fever without pneumonia were treated in the outpatient clinics of our hospital. Urinary antigen test was performed in 11 of those patients to confirm the prediagnosis of pontiac fever, however all were found negative. Likewise convalescent phase sera for the confirmation of the diagnosis by seroconversion could not be obtained since they all were foreign tourists. Investigation of water sources of the hotel revealed that the municipal drinking water network had not been connected yet and the hotel supplied water from groundwater sources. The analysis of multiple samples from multiple sites of hotel's water system indicated that the water temperature was between 35-45°C and the iron level was beyond the acceptable limits (245 µg/L) recommended for drinking water in the regulation guides. These properties were considered as the factors that enhanced the growth and survival of Legionella species. Water samples were cultivated on BCYE-_ (Buffered Charcoal Yeast Extract a-Ketoglutarate) and GVPC (Glycine-Vancomycin-Polymyxin-Cycloheximide) agar plates and 11 out of a total 13 samples yielded Legionella spp. growth. All isolates were identified as L.pneumophila serogroup 1 by specific antisera. Legionella decontamination of hotel's water system was managed by implementation of hyperchlorination method as well as superheating (> 60°C) of water. The hotel was not closed during the outbreak and cultures of water samples obtained for one year later did not yield any Legionella spp. growth. This outbreak emphasized that hotel residents are at risk for acquiring LD in the presence of a colonized water system, even in a newly constructed building. In conclusion, effective control and decontamination programmes for the prevention of Legionella colonization should be applied even in new opening hotels.

A fatal nosocomial infection with Legionella pneumophila serogroup 5 occurred in a patient with leukemia. Isolates recovered from both the potable water supply and the patient showed an identical genomic profile. With no other exposure identified, the water from the washbasin was evidently the source of infection.

Problem/condition: Since 1971, CDC, the U.S. Environmental Protection Agency (EPA), and the Council of State and Territorial Epidemiologists have maintained a collaborative Waterborne Disease and Outbreak Surveillance System (WBDOSS) for collecting and reporting data related to occurrences and causes of waterborne-disease outbreaks (WBDOs) and cases of waterborne disease. This surveillance system is the primary source of data concerning the scope and effects of waterborne disease in the United States., Reporting Period: Data presented summarize 28 WBDOs that occurred during January 2005--December 2006 and four previously unreported WBDOs that occurred during 1979--2002., Description of System: The surveillance system includes data on WBDOs associated with recreational water, drinking water, water not intended for drinking (WNID) (excluding recreational water), and water use of unknown intent. Public health departments in the states, territories, localities, and Freely Associated States (FAS) (i.e., the Republic of the Marshall Islands, the Federated States of Micronesia, and the Republic of Palau, formerly parts of the U.S.-administered Trust Territory of the Pacific Islands) are primarily responsible for detecting and investigating WBDOs and voluntarily reporting them to CDC by a standard form. Only cases and outbreaks associated with drinking water, WNID (excluding recreational water), and water of unknown intent (WUI) are summarized in this report. Cases and outbreaks associated with recreational water are reported in a separate Surveillance Summary., Results: Fourteen states reported 28 WBDOs that occurred during 2005--2006: a total of 20 were associated with drinking water, six were associated with WNID, and two were associated with WUI. The 20 drinking water-associated WBDOs caused illness among an estimated 612 persons and were linked to four deaths. Etiologic agents were identified in 18 (90.0%) of the drinking water-associated WBDOs. Among the 18 WBDOs with identified pathogens, 12 (66.7%) were associated with bacteria, three (16.7%) with viruses, two (11.1%) with parasites, and one (5.6%) mixed WBDO with both bacteria and viruses. In both WBDOs where the etiology was not determined, norovirus was the suspected etiology. Of the 20 drinking water WBDOs, 10 (50) were outbreaks of acute respiratory illness (ARI), nine (45%) were outbreaks of acute gastrointestinal illness (AGI), and one (5.0%) was an outbreak of hepatitis. All WBDOs of ARI were caused by Legionella, and this is the first reporting period in which the proportion of ARI WBDOs has surpassed that of AGI WBDOs since the reporting of Legionella WBDOs was initiated in 2001. A total of 23 deficiencies were cited in the 20 WBDOs associated with drinking water: 12 (52.2%) deficiencies fell under the classification NWU/POU (deficiencies occurred at points not under the jurisdiction of a water utility or at the point-of-use), 10 (43.5%) deficiencies fell under the classification SWTDs (contamination at or in the source water, treatment facility, or distribution system), and for one (4.3%) deficiency, classification was unknown. Among the 12 NWU/POU deficiencies, 10 (83.3%) involved Legionella spp. in the drinking water system. The most frequently cited SWTD deficiencies were associated with a treatment deficiency (n = four [40.0%]) and untreated ground water (n = four [40.0%]). Three of the four WBDOs with treatment deficiencies used ground water sources., Interpretation: Approximately half (52.2%) of the drinking water deficiencies occurred outside the jurisdiction of a water utility. The majority of these WBDOs were associated with Legionella spp, which suggests that increased attention should be targeted towards reducing illness risks associated with Legionella spp. Nearly all of WBDOs associated with SWTD deficiencies occurred in systems using ground water. EPA's new Ground Water Rule might prevent similar outbreaks in the future in public water systems., Public Health Actions: CDC and EPA use surveillance data to identify the types of water systems, deficiencies, and etiologic agents associated with WBDOs and to evaluate the adequacy of current technologies and practices for providing safe drinking water. Surveillance data also are used to establish research priorities, which can lead to improved water-quality regulation development. The majority of drinking water deficiencies are now associated with contamination at points outside the jurisdiction of public water systems (e.g., regrowth of Legionella spp. in hot water systems) and water contamination that might not be regulated by EPA (e.g., contamination of tap water at the POU). Improved education of consumers and plumbers might help address these risk factors.

Human Legionella infections mainly consist of community-acquired and nosocomial pneumonia and rarely affect children. We describe a nosocomial infection with Legionella pneumophila, serogroup 1, subgroup OLDA, in an immunocompromized 2-y-old girl at a paediatric clinic. L. pneumophila identical to that of the patient was found in the hospital's cold-water but not in the hot-water distribution system. Transmission of Legionella to the girl most probably occurred by Legionella-contaminated cold water mixed and heated by water from the hot-water system. Mixing of hot and cold water probably occurred through thermostatic water mixing valves connected to showers regulated by a handle at the shower head. Nosocomial Legionella infection might thus have occurred, although circulating hot water temperatures never dropped below 53 degrees C and cultures for surveillance of Legionella from central parts of the hot-water system have been consistently negative. Legionellae were successfully eliminated from the hospital's cold-water distribution system by hot water flushing at 73 degrees C for 1h.

We investigated Legionella and Pseudomonas contamination of hot water in a cross-sectional multicentric survey in Italy. Chemical parameters (hardness, free chlorine, and trace elements) were determined. Legionella spp. were detected in 33 (22.6%) and Pseudomonas spp. in 56 (38.4%) of 146 samples. Some factors associated with Legionella contamination were heater type, tank distance and capacity, water plant age, and mineral content. Pseudomonas presence was influenced by water source, hardness, free chlorine, and temperature. Legionella contamination was associated with a centralized heater, distance from the heater point >10 m, and a water plant >10 years old. Furthermore, zinc levels of <100 microg/L and copper levels of >50 microg/L appeared to be protective against Legionella colonization [corrected]. Legionella species and serogroups were differently distributed according to heater type, water temperature, and free chlorine, suggesting that Legionella strains may have a different sensibility and resistance to environmental factors and different ecologic niches.

Objective: To study the epidemiologic manifestations of a large outbreak of Legionnaires' disease due to an inadequate circulating and filtration system for bath water., Patients: In June 2000 at Ishioka City, Ibaraki Prefecture, a large outbreak of Legionnaire's disease occurred, as a result of an inadequate circulating and filtration system for communal bath water. This outbreak was the worst ever experienced in Japan, involving a total of 34 patients (20 confirmed, 14 probable), 3 of whom died., Measurements and Results: Legionella pneumophila serogroup 1 was isolated from sputum culture in two patients. Bacteriological culture of the public bath water subsequently yielded large numbers of Legionella species. Cleavage of genomic DNA showed that restriction fragment patterns coming from clinical and environmental isolates of L. pneumophila serogroup 1 were closely related, focusing the inquiry to a public bathhouse where a circulating filtration system was suspected as the source of infection., Conclusions: It was later concluded that the circulating filtration system adopted for bath water was marred by a serious design flaw that subsequently caused the mass outbreak. Specifically, a line of the bath water was being returned to the bath without undergoing heat exchange or sterilization by chlorine; and the Legionella species that had proliferated in the filter and the bright stone filtration unit were allowed to return to the bath, eventually culminating in a mass infection.

An outbreak of infections caused by Legionella pneumophila serogroup 5 was detected in a university hospital, and nosocomial reservoirs of the legionella epidemic were examined. Clinical isolates from two patients who had been affected by the L. pneumophila serogroup 5 outbreak, and from another patient with a legionella infection caused by the same serogroup 3 years later, were compared to L. pneumophila serogroup 5 isolates from the hospital water supply by two molecular methods, amplified fragment length polymorphism (AFLP) analysis and random amplified polymorphic DNA analysis (RAPD). Genotyping confirmed the epidemiological linkage of the first two patients, and linked their infections with the hospital water supply. The third clinical strain, which was also linked to the hospital water, was very similar to the epidemic strain. Even though the water distribution system was sanitized (superheat and flush sanitation), the epidemic strain was shown to be persisting in the hospital water outlets several years after its initial discovery.

There have been reported outbreaks of Legionnaires' disease at hospitals and industrial facilities, which prompted the development of various preventive measures. For example, Ford has been developing and implementing such a measure at its facilities worldwide to provide technical guidance for controlling Legionella in water systems. One of the key issues for implementing the measure is the selection of a disinfectant(s) and optimum conditions for its use. Therefore, available publications on various disinfectants and disinfection processes used for the inactivation of Legionella bacteria were reviewed. Two disinfection methods were reviewed: chemical and thermal. For chemical methods, disinfectants used were metal ions (copper and silver), oxidizing agents (halogen containing compounds [chlorine, bromine, iodine, chlorine dioxide, chloramines, and halogenated hydantoins], ozone, and hydrogen peroxide), non-oxidizing agents (heterocyclic ketones, guanidines, thiocarbamates, aldehydes, amines, thiocyanates, organo-tin compounds, halogenated amides, and halogenated glycols), and UV light. In general, oxidizing disinfectants were found to be more effective than non-oxidizing ones. Among oxidizing agents, chlorine is known to be effective and widely used. Among non-oxidizing agents, 2,2-dibromo-3-nitropropionamide appears to be the most effective followed by glutaraldehyde. Isothiazolin (known as Kathon), polyhexamethylene biguanide, and 2-bromo-2-nitropropionamide (known as Bronopol) were found to be less effective than glutaraldehyde. Thermal disinfection is effective at > 60 degrees C (140 degrees F).

As part of a case-control study of community-acquired Legionnaires' disease, several factors related to residential water distribution systems and public drinking water systems were studied in the homes of 124 patients with community-acquired Legionnaire's disease and in the homes of 354 controls. The presence of water reservoirs and hot water tanks was studied in residential systems. Factors such as deficient chlorine levels, pipe repairs and other work, water flow interruptions, the use of alternative water sources, inadequate cleaning operations in public water reservoirs, and the position of the home within the public network (and whether this location constituted an endpoint) were studied in public water supply systems. Levels of legionellae in domestic water samples were also measured. Although the use of water reservoirs and hot water tanks promotes colonization by legionellae in residential systems, none of the variables studied seems to increase the incidence of community-acquired Legionnaires' disease.

A case of community-acquired Legionnaires' disease (LD) is described. The source of infection was traced to a push-on tap at the end of a long spur from the hot circulation system in a large old residential building which had been unoccupied for several weeks. Legionella pneumophila serogroup 1 subgroup Pontiac was isolated from the patient's sputum and from the contaminated water supply. Isolates were shown to be indistinguishable from one another when subtyped by pulsed field gel electrophoresis of chromosomal DNA.

A lack of standardization of environmental monitoring techniques for Legionella spp. complicates the interpretation of results and comparisons of results from different institutions. A comparative assessment of techniques recommended by the Centers for Disease Control and Prevention, the Hygiene Institute (Graz, Austria), and our laboratory was performed. Variables investigated were sampling method (swabbing and collection of water samples [250 ml] before and after swabbing), method of concentration (none, filtration, and centrifugation), acid buffer treatment (no acid treatment, treatment for 3 min, and treatment for 15 min), and choice of medium (five formulations of buffered charcoal yeast extract agar with glycine, vancomycin, polymyxin B, anisomycin, or cycloheximide). Thirty-three sites in seven hospital buildings were studied. Recovery by swab correlated with recovery from water after swabbing (P < 0.05). However, the quantity of Legionella spp. recovered from swab specimens (mean, 3.0 x 10(4) CFU per swab) was greater than that recovered from water (mean, 4.7 x 10(3) CFU/250 ml). Filtration resulted in recovery rates (mean, 5.2 x 10(3) CFU/250 ml) higher than those by centrifugation (mean, 2.3 x 10(3) CFU/250 ml). Three minutes of acid buffer treatment to reduce overgrowth by commensal flora did not improve selectivity or sensitivity for Legionella spp. if glycine-containing selective media were used. Fifteen minutes of acid buffer treatment reduced recovery compared with that after a 3-min treatment. All glycine-containing media tested effectively inhibited background flora, but one selective medium containing dyes, glycine, vancomycin, and polymyxin B (DGVP) resulted in the greatest quantitative recovery of Legionella pneumophila. Use of buffered charcoal yeast extract agar and the acid buffer treatment gave the greatest recovery of non-pneumophila species. A standardized protocol with an emphasis on the culturing of swab samples is presented.

From July through October 1993, outbreaks of Legionnaires' disease (LD) were reported from communities in Massachusetts and Rhode Island and from a state prison in Michigan. Cooling towers (CTs) were identified as the source of all three outbreaks. This report summarizes investigations by state and local health officials and CDC and efforts to control these outbreaks.

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.

We determined the natural history of the colonization of our hospital's potable water by culturing water approximately biweekly from 20 sites throughout the hospital for 4 years. Overall, 545 (24.7%) of the 2200 samples grew Legionella pneumophila. During hyperchlorination, 11.7% of the samples were positive while 41.6% were positive in the absence of chlorination. There was no seasonal trend towards positivity, but there was marked inter-site variation in the semi-quantitative culture results. However, a single strain of legionella (as defined by plasmid profiling) tended to persist at a site. Such a site was a unique ecological niche in that different sites in the same wing were populated by distinct strains. The two wings of our hospital had a significantly different distribution of strains of legionella-plasmid profile type III predominated in the Victoria Wing while types II and VI predominated in Centennial Wing. Twenty-four of our 28 cases of nosocomial Legionnaires' disease occurred in the Centennial Wing. Three of the four cases in the Victoria Wing were caused by plasmid profile type III while 18 of the 24 isolates from patients who acquired their infection in the Centennial Wing were type II. We conclude that each water outlet serves as its own ecological niche of L. pneumophila.

Hospital-acquired legionella pneumonia is emerging as a major problem; potable water distribution systems have been shown to be the primary reservoirs for the legionella organisms. As a result, disinfection measures have been developed to eradicate the organism from the hospital water supply. Each disinfection modality differs in its design and application such that choosing an appropriate cost-effective control measure requires careful analysis and planning. We assess in comparative fashion the disinfection modalities of thermal eradication ("heat-and-flush"), instantaneous steam-heating system, chlorination, ultraviolet light irradiation, ozonation and metal ionization. The theoretical bases, the actual procedure or system, the logistics of implementation, the costs and personnel requirements and the advantages and disadvantages are presented for each modality. Criteria for selection of a method, the use of combinations of methods, parameters for installation, pitfalls in implementation and a plan for subsequent environmental surveillance are discussed in detail.

In late April 1984, an outbreak of Pontiac fever was investigated in an office building in lower Manhattan (New York City). The outbreak was characterized by a high attack rate (78 per cent overall); the predominant symptoms were myalgias, chills, fatigue, fever, and headache. There was a clustering of cases in an office that was air cooled by a dedicated cooling tower separate from the remainder of the building. A high concentration of live L. Pneumophila cells in the cooling tower was quantified. Airborne spread via settle plates placed along the air intake system and within the office was demonstrated. Legionella pneumophila serogroup 1 antigen was found in the urine of two cases, and identical monoclonal antibody reactivity patterns of isolates from all sources was observed. Difficulty was experienced in eliminating the organism from the tower.

An epidemiological link was found between contamination of a hospital water-supply by Legionella pneumophila and by Pittsburgh pneumonia agent (PPA) and subsequent cases of nosocomial legionnaires' disease and Pittsburgh pneumonia. The extent of L pneumophila isolation from the water-supply paralleled the occurrence of disease. Whenever L pneumophila was isolated from more than 30% of ten selected water sites, nosocomial legionellosis occurred. The temperature of the hot water tanks was raised to 60-77 degrees C for 72 h, and water outlets were flushed for 30 min with hot water. A decline in numbers of L pneumophila and PPA in the water-supply was followed by a fall in the incidence of legionnaires' disease and Pittsburgh pneumonia. In addition, intermittent raising of the temperature in the hot water system decreased both the number of months in which disease occurred and the proportion of nosocomial pneumonias caused by these organisms.

Several lines of evidence have been examined in attempts to implicate potable water as a source for legionellosis. Success has been mixed. The strongest evidence has been the similarity of strains recovered from patients and from potable water and the cessation of outbreaks following institution of measures to eradicate Legionella from potable water systems. Epidemiologic efforts to identify the effective mode of exposure to water (e.g. ingestion) have been remarkably unsuccessful. Although L pneumophila can clearly be acquired on occasion from potable water, the proportion of cases traceable to this source is unknown, as is the role of potable water as a source of infection by other Legionellae. Hyperchlorination, raising hot water temperatures to greater than 55 degrees C, and replacing rubber gaskets are useful methods for controlling outbreaks of legionellosis traced to potable water systems but are not yet justified as routine preventative methods in the absence of such an outbreak.

Two patients with sporadic community-acquired legionnaires' disease are described. Legionella pneumophila was isolated from sputum specimens, and seroconversion of antibody titers was demonstrated for both patients. Legionella pneumophila was also recovered from the residential water supply of both patients. In each case, the serogroup of the environmental organism matched that of the infecting organism. In one patient, serogroup 3 was isolated--a rare cause of legionnaires' disease, and in the second case, monoclonal antibody testing confirmed that the serogroup 1 organisms isolated from sputum and residential water supply samples were identical. The incubation period of legionnaires' disease is presumed to be up to two weeks. Because of medical problems, both patients had been confined to their homes for the entire two weeks before the onset of symptoms. This is the first report that links acquisition of community-acquired legionnaires' disease to contaminated water supplies within the homes of susceptible patients.

Five cases of Legionnaires' disease caused by Legionella dumoffii were identified within an 11-month period in a hospital in the Quebec City area. In four cases bacterial isolates were obtained from clinical specimens, and in one case seroconversion was demonstrated. All the patients had been admitted to hospital within 10 days before diagnosis. Two of the patients were immunosuppressed children. Only 1 of the 40 hot water samples from the hospital yielded L. dumoffii; however, 6 of 11 distilled water samples contained the bacterium. All the patients had been exposed to distilled water, four through respiratory therapy equipment and one through a room humidifier. Following the use of sterile distilled water in the apparatus, no further cases were identified. This is the first reported outbreak of Legionnaires' disease caused by L. dumoffii, and it is the first time that nosocomial legionellosis has been linked to contaminated distilled water in Canada.

In 1 year 12 of 48 patients who developed fatal pneumonia following admission with non-respiratory disorders to the Hospital Molinette, Torino, yielded Legionella pneumophila serogroup 1 from lung at autopsy. Patients were hospitalized on seven different wards for different conditions; only two of the wards had air conditioning but legionellas were not isolated from these. All patients were in poor health or immunocompromised. Some patients had inhaled humidified oxygen from piped supplies and three had undergone surgery. Legionella pneumophila serogroup 1 was detected in the water of oxygen bubble humidifiers and an underwater chest drain. The contaminated devices had been filled with tap or distilled water and the hospital water supply was found to be contaminated with L. pneumophila serogroup 1. Our findings suggest that filling bubble humidifiers or underwater chest drains with tap water is a potential hazard and should be avoided.

Over a 10-month period, 24 cases of Legionnaires' disease pneumonia occurred among patients admitted to an Iowa hospital, most of whom were immunosuppressed. Eleven patients died. Twenty-one patients were admitted to a recently completed hospital addition, 16 of these to a new hematology-oncology unit. Legionella pneumophila serogroup 1 was isolated from the patients, water outlets, and hot water in the new addition. Water quality variables in the hospital addition were adequate. Shock chlorination, temporary elevation of the hot water temperature, and continuous chlorination of hospital water decreased the frequency of isolation of Legionella. Water use by patients in the hematology-oncology unit was restricted until the water was free of Legionella. The incidence of Legionnaires' disease decreased. Indirect evidence supports an hypothesis of water-borne disease in this cluster of cases. Current variables of acceptable water potability may not guarantee water free of L. pneumophila.