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ABSTRACTEstimates of the prevalence of Shigellaspp. are limited by the suboptimal sensitivity of current diagnostic and surveillance methods. We used a quantitative PCR (qPCR) assay to detect Shigellain the stool samples of 3,533 children aged <59 months from the Gambia, Mali, Kenya, and Bangladesh, with or without moderate-to-severe diarrhea (MSD). We compared the results from conventional culture to those from qPCR for the Shigella ipaHgene. Using MSD as the reference standard, we determined the optimal cutpoint to be 2.9 × 104ipaHcopies per 100 ng of stool DNA for set 1 (n= 877). One hundred fifty-eight (18%) specimens yielded >2.9 × 104ipaHcopies. Ninety (10%) specimens were positive by traditional culture for Shigella. Individuals with =2.9 × 104ipaHcopies have 5.6-times-higher odds of having diarrhea than those with <2.9 × 104ipaHcopies (95% confidence interval, 3.7 to 8.5; P< 0.0001). Nearly identical results were found using an independent set of samples. qPCR detected 155 additional MSD cases with high copy numbers of ipaH, a 90% increase from the 172 cases detected by culture in both samples. Among a subset (n= 2,874) comprising MSD cases and their age-, gender-, and location-matched controls, the fraction of MSD cases that were attributable to Shigellainfection increased from 9.6% (n= 129) for culture to 17.6% (n= 262) for qPCR when employing our cutpoint. We suggest that qPCR with a cutpoint of approximately 1.4 × 104ipaHcopies be the new reference standard for the detection and diagnosis of shigellosis in children in low-income countries. The acceptance of this new standard would substantially increase the fraction of MSD cases that are attributable to Shigella.

ABSTRACTThe large and growing number of viral and bacterial pathogens responsible for respiratory infections poses a challenge for laboratories seeking to provide rapid and comprehensive pathogen identification. We evaluated a novel application of the TaqMan low-density array (TLDA) cards for real-time PCR detection of 21 respiratory-pathogen targets. The performance of the TLDA was compared to that of individual real-time PCR (IRTP) assays with the same primers and probes using (i) nucleic acids extracted from the 21 pathogen strains and 66 closely related viruses and bacteria and (ii) 292 clinical respiratory specimens. With spiked samples, TLDA cards were about 10-fold less sensitive than IRTP assays. By using 292 clinical specimens to generate 2,238 paired individual assays, the TLDA card exhibited 89% sensitivity (95% confidence interval [CI], 86 to 92%; range per target, 47 to 100%) and 98% specificity (95% CI, 97 to 99%; range per target, 85 to 100%) overall compared to IRTP assays as the gold standard with a threshold cycle (CT) cutoff of 43. The TLDA card approach offers promise for rapid and simultaneous identification of multiple respiratory pathogens for outbreak investigations and disease surveillance.

ABSTRACTApproximately 84% of legionellosis cases are due to Legionella pneumophilaserogroup 1. Moreover, a majority of L. pneumophilaserogroup 1 clinical isolates react positively with monoclonal antibody 2 (MAb2) of the international standard panel. Over 94% of the legionellosis outbreaks investigated by the Centers for Disease Control and Prevention are due to this subset of L. pneumophilaserogroup 1. To date, there is no complete explanation for the enhanced ability of these strains to cause disease. To better characterize these organisms, we subtyped 100 clinical L. pneumophilaserogroup 1 isolates and 50 environmental L. pneumophilaserogroup 1 isolates from the United States by (i) reactivity with MAb2, (ii) presence of a lag-1gene required for the MAb2 epitope, and (iii) sequence-based typing analysis. Our results showed that the MAb2 epitope and lag-1gene are overrepresented in clinical L. pneumophilaserogroup 1 isolates. MAb2 recognized 75% of clinical isolates but only 6% of environmental isolates. Similarly, 75% of clinical isolates but only 8% of environmental isolates harbored lag-1. We identified three distinct lag-1alleles, referred to as Philadelphia, Arizona, and Lens alleles, among 79 isolates carrying this gene. The Arizona allele is described for the first time in this study. We identified 59 different sequence types (STs), and 34 STs (58%) were unique to the United States. Our results support the hypothesis that a select group of STs may have an enhanced ability to cause legionellosis. Combining sequence typing and lag-1analysis shows that STs tend to associate with a single lag-1allele type, suggesting a hierarchy of virulence genotypes. Further analysis of ST and lag-1profiles may identify genotypes of L. pneumophilaserogroup 1 that warrant immediate intervention.

Approximately 84% of legionellosis cases are due to Legionella pneumophila serogroup 1. Moreover, a majority of L. pneumophila serogroup 1 clinical isolates react positively with monoclonal antibody 2 (MAb2) of the international standard panel. Over 94% of the legionellosis outbreaks investigated by the Centers for Disease Control and Prevention are due to this subset of L. pneumophila serogroup 1. To date, there is no complete explanation for the enhanced ability of these strains to cause disease. To better characterize these organisms, we subtyped 100 clinical L. pneumophila serogroup 1 isolates and 50 environmental L. pneumophila serogroup 1 isolates from the United States by (i) reactivity with MAb2, (ii) presence of a lag-1 gene required for the MAb2 epitope, and (iii) sequence-based typing analysis. Our results showed that the MAb2 epitope and lag-1 gene are overrepresented in clinical L. pneumophila serogroup 1 isolates. MAb2 recognized 75% of clinical isolates but only 6% of environmental isolates. Similarly, 75% of clinical isolates but only 8% of environmental isolates harbored lag-1. We identified three distinct lag-1 alleles, referred to as Philadelphia, Arizona, and Lens alleles, among 79 isolates carrying this gene. The Arizona allele is described for the first time in this study. We identified 59 different sequence types (STs), and 34 STs (58%) were unique to the United States. Our results support the hypothesis that a select group of STs may have an enhanced ability to cause legionellosis. Combining sequence typing and lag-1 analysis shows that STs tend to associate with a single lag-1 allele type, suggesting a hierarchy of virulence genotypes. Further analysis of ST and lag-1 profiles may identify genotypes of L. pneumophila serogroup 1 that warrant immediate intervention.

ABSTRACTThe ResPlex I assay (Qiagen) was designed to amplify and detect DNA of six bacterial respiratory pathogens. This assay was compared with real-time PCR assays based upon the same target sequences for the ability detect the target bacteria by use of both stock strains and specimens from respiratory disease patients. The ResPlex I assay is somewhat less sensitive than real-time PCR assays but offers the advantage of multiple assays in a single reaction.

Previous studies have shown that monochloramine disinfection of municipal water supplies is associated with decreased risk of healthcare‐associated Legionnaires— disease. A twoyear, prospective environmental study was conducted to determine whether converting from chlorine to monochloramine for water disinfection would decrease Legionella colonization of hot water systems. Water and biofilm samples were collected from 53 buildings. Prevalence ratios comparing Legionella colonization before and after monochloramine disinfection were adjusted for water system characteristics. Legionella colonized 60% of the hot water systems before monochloramine conversion versus 4% after conversion. The median number of colonized sites per building declined significantly with monochloramine disinfection. Increased prevalence of Legionella colonization was associated with water heater temperatures below 50oC, buildings taller than 10 stories, and interruptions in water service. Although no outbreaks of Legionnaires— disease were found, the study provides support that use of monochloramine in water supplies may reduce Legionella transmission and incidence of Legionnaires— disease.

There is still a low level of clinical awareness regarding Legionnaires' disease 25 years after it was first detected. The causative agents, legionellae, are freshwater bacteria with a fascinating ecology. These bacteria are intracellular pathogens of freshwater protozoa and utilize a similar mechanism to infect human phagocytic cells. There have been major advances in delineating the pathogenesis of legionellae through the identification of genes which allow the organism to bypass the endocytic pathways of both protozoan and human cells. Other bacteria that may share this novel infectious process are Coxiella burnetti and Brucella spp. More than 40 species and numerous serogroups of legionellae have been identified. Most diagnostic tests are directed at the species that causes most of the reported human cases of legionellosis, L. pneumophila serogroup 1. For this reason, information on the incidence of human respiratory disease attributable to other species and serogroups of legionellae is lacking. Improvements in diagnostic tests such as the urine antigen assay have inadvertently caused a decrease in the use of culture to detect infection, resulting in incomplete surveillance for legionellosis. Large, focal outbreaks of Legionnaires' disease continue to occur worldwide, and there is a critical need for surveillance for travel-related legionellosis in the United States. There is optimism that newly developed guidelines and water treatment practices can greatly reduce the incidence of this preventable illness.

SUMMARYThere is still a low level of clinical awareness regarding Legionnaires' disease 25 years after it was first detected. The causative agents, legionellae, are freshwater bacteria with a fascinating ecology. These bacteria are intracellular pathogens of freshwater protozoa and utilize a similar mechanism to infect human phagocytic cells. There have been major advances in delineating the pathogenesis of legionellae through the identification of genes which allow the organism to bypass the endocytic pathways of both protozoan and human cells. Other bacteria that may share this novel infectious process are Coxiella burnettiand Brucellaspp. More than 40 species and numerous serogroups of legionellae have been identified. Most diagnostic tests are directed at the species that causes most of the reported human cases of legionellosis, L. pneumophilaserogroup 1. For this reason, information on the incidence of human respiratory disease attributable to other species and serogroups of legionellae is lacking. Improvements in diagnostic tests such as the urine antigen assay have inadvertently caused a decrease in the use of culture to detect infection, resulting in incomplete surveillance for legionellosis. Large, focal outbreaks of Legionnaires' disease continue to occur worldwide, and there is a critical need for surveillance for travel-related legionellosis in the United States. There is optimism that newly developed guidelines and water treatment practices can greatly reduce the incidence of this preventable illness.

ABSTRACTChlamydiapneumoniaeis an important respiratory pathogen recently associated with atherosclerosis and several other chronic diseases. Detection of C. pneumoniaeis inconsistent, and standardized PCR assays are needed. Two real-time PCR assays specific for C. pneumoniaewere developed by using the fluorescent dye-labeled TaqMan probe-based system. Oligonucleotide primers and probes were designed to target two variable domains of the ompAgene, VD2 and VD4. The limit of detection for each of the two PCR assays was 0.001 inclusion-forming unit. Thirty-nine C. pneumoniaeisolates obtained from widely distributed geographical areas were amplified by the VD2 and VD4 assays, producing the expected 108- and 125-bp amplification products, respectively. None of the C. trachomatisserovars, C. psittacistrains, other organisms, or human DNAs tested were amplified. The amplification results of the newly developed assays were compared to the results of culturing and two nested PCR assays, targeting the 16S rRNA and ompAgenes. The assays were compared by testing C. pneumoniaepurified elementary bodies, animal tissues, 228 peripheral blood mononuclear cell (PBMC) specimens, and 179 oropharyngeal (OP) swab specimens obtained from ischemic stroke patients or matched controls. The real-time VD4 assay and one nested PCR each detected C. pneumoniaein a single, but different, PBMC specimen. Eleven of 179 OP specimens (6.1%) showed evidence of the presence of C. pneumoniaein one or more tests. The real-time VD4 assay detected the most positive results of the five assays. We believe that this real-time PCR assay offers advantages over nested PCR assays and may improve the detection of C. pneumoniaein clinical specimens.

Use of monochloramine as a residual disinfectant could prevent Legionnaires' disease in communities throughout the United States. Legionnaires' disease is caused by Legionellabacteria, which live in biofilm in natural and synthetic aquatic environments. The most frequent route of infection is inhalation of contaminated aerosol, which is often produced by faucets, showers, or cooling towers. Although the disease can be disseminated in potable water, the effects of the disinfection methods used by municipal water treatment facilities on the occurrence of Legionnaires' disease have not been studied. This article describes an epidemiological study in which methods for disinfecting potable water supplied to 32 hospitals where outbreaks of Legionnaires' disease have occurred are compared with methods for water supplied to 48 randomly selected control hospitals. Hospitals supplied with drinking water containing free chlorine were 10.2 times more likely to have reported an outbreak of Legionnaires' disease associated with potable water than hospitals that used water with monochloramine as a residual disinfectant (odds ratio—10.2; 95 percent confidence interval—1.4–460).

The etiology of Kawasaki syndrome (KS), the leading cause of acquired coronary artery disease in children, is unknown. Recent studies have suggested that Chlamydia pneumoniae,a common respiratory pathogen associated with an increased risk of heart disease, might lead to KS.

AbstractBackground:In 1994, a hospital reported an increase in nosocomial legionnaires' disease after implementing use of a rapid urinary antigen test for Legionella pneumophilaserogroup 1 (Lp-1). This hospital was the site of a previous nosocomial legionnaires' disease outbreak during 1980 to 1982.Methods:Infection control records were reviewed to compare rates of nosocomial pneumonia and the proportion of cases attributable to legionnaires' disease during the 1994 outbreak period with those during the same period in 1993. Water samples were collected for Legionellaculture from the hospital's potable water system and cooling towers, and isolates were subtyped by monoclonal antibody (MAb) testing and arbitrarily primed polymerase chain reaction (AP-PCR).Results:Nosocomial pneumonia rates were similar from April through October 1993 and April through October 1994: 5.9 and 6.6 per 1,000 admissions, respectively (rate ratio [RR], 1.1; P=.56); however, 3.2% of nosocomial pneumonias were diagnosed as legionnaires' disease in 1993, compared with 23.9% in 1994 (RR, 9.4; P<.001). In 1994, most legionnaires' disease cases were detected by the urinary antigen testing alone. MAb testing and AP-PCR demonstrated identical patterns among Lp-1 isolates recovered from a patient's respiratory secretions, the hospital potable water system, and stored potable water isolates from the 1980 to 1982 outbreak.Conclusions:There may have been persistent transmission of nosocomial legionnaires' disease at this hospital that went undiscovered for many years because there was no active surveillance for legionnaires' disease. Introduction of a rapid urinary antigen test improved case ascertainment. Legionellaspecies can be established in colonized plumbing systems and may pose a risk for infection over prolonged periods.

AbstractBackground:In 1994, a hospital reported an increase in nosocomial legionnaires' disease after implementing use of a rapid urinary antigen test for Legionella pneumophilaserogroup 1 (Lp-1). This hospital was the site of a previous nosocomial legionnaires' disease outbreak during 1980 to 1982.Methods:Infection control records were reviewed to compare rates of nosocomial pneumonia and the proportion of cases attributable to legionnaires' disease during the 1994 outbreak period with those during the same period in 1993. Water samples were collected for Legionellaculture from the hospital's potable water system and cooling towers, and isolates were subtyped by monoclonal antibody (MAb) testing and arbitrarily primed polymerase chain reaction (AP-PCR).Results:Nosocomial pneumonia rates were similar from April through October 1993 and April through October 1994: 5.9 and 6.6 per 1,000 admissions, respectively (rate ratio [RR], 1.1; P=.56); however, 3.2% of nosocomial pneumonias were diagnosed as legionnaires' disease in 1993, compared with 23.9% in 1994 (RR, 9.4; P<.001). In 1994, most legionnaires' disease cases were detected by the urinary antigen testing alone. MAb testing and AP-PCR demonstrated identical patterns among Lp-1 isolates recovered from a patient's respiratory secretions, the hospital potable water system, and stored potable water isolates from the 1980 to 1982 outbreak.Conclusions:There may have been persistent transmission of nosocomial legionnaires' disease at this hospital that went undiscovered for many years because there was no active surveillance for legionnaires' disease. Introduction of a rapid urinary antigen test improved case ascertainment. Legionellaspecies can be established in colonized plumbing systems and may pose a risk for infection over prolonged periods.

AbstractObjective:To investigate an increase in reports of legionnaires' disease by multiple hospitals in San Antonio, Texas, and to study risk factors for nosocomial transmission of legionnaires' disease and determinants for Legionellacolonization of hospital hot-water systems.Setting:The 16 largest hospitals in the cities of San Antonio, Temple, and Austin, Texas.Design:Review of laboratory databases to identify patients with legionnaires' disease in the 3 years prior to the investigation and to determine the number of diagnostic tests for Legionellaperformed; measurement of hot-water temperature and chlorine concentration and culture of potable water for Legionella. Exact univariate calculations, Poisson regression, and linear regression were used to determine factors associated with water-system colonization and transmission of Legionella.Results:Twelve cases of nosocomial legionnaires' disease were identified; eight of these occurred in 1996. The rise in cases occurred shortly after physicians started requesting Legionellaurinary antigen tests. Hospitals that frequently used Legionellaurinary antigen tests tended to detect more cases of legionnaires' disease. Legionellawas isolated from the water systems of 11 of 12 hospitals in San Antonio; the 12th had just experienced an outbreak of legionnaires' disease and had implemented control measures. Nosocomial legionellosis cases probably occurred in 5 hospitals. The number of nosocomial legionnaires' disease cases in each hospital correlated better with the proportion of water-system sites that tested positive for Legionella (P=.07) than with the concentration of Legionellabacteria in water samples (P=.23). Hospitals in municipalities where the water treatment plant used monochloramine as a residual disinfectant (n=4) and the hospital that had implemented control measures were Legionella-free. The hot-water systems of all other hospitals (n=11) were colonized with Legionella. These were all supplied with municipal drinking water that contained free chlorine as a residual disinfectant. In these contaminated hospitals, the proportion of sites testing positive was inversely correlated with free residual chlorine concentration (P=.01). In all hospitals, hot-water temperatures were too low to inhibit Legionellagrowth.Conclusions:The increase in reporting of nosocomial legionnaires' disease was attributable to increased use of urinary antigen tests; prior cases may have gone unrecognized. Risk of legionnaires' disease in hospital patients was better predicted by the proportion of water-system sites testing positive for Legionellathan by the measured concentration of Legionellabacteria. Use of monochloramine by municipalities for residual drinking water disinfection may help prevent legionnaires' disease.

We studied the ability ofLegionella to multiply in potable water samples obtained from investigations of nosocomial legionellosis. AutochthonousLegionella multiplied in three of 14 hospital water samples after incubation at 35°C and 42°C. All three samples were from hot water tanks. Multiplication did not occur when a selected sample was filtered through a 0.45-µm membrane and reinoculated with indigenousLegionella. We isolated bothLegionella pneumophila and one or more species of free-living amoebae, primarity members of theHartmannellidae, from each of these hot water tank samples. Amoebae from a total of six hot water tank samples were used for cocultivation studies withL. pneumophila. All amoebae supported multiplication ofLegionella in coculture at 35°C. Four of six isolates of amoebae supported multiplication oflegionella at 42°C, while none supported multiplication at 45°C. Gimenez staining and electron microscopy showed thatLegionella multiplied intracellularly in amoebae. Control of these amoebae in potable water may prevent colonization and multiplication ofLegionella in domestic hot water systems.

Pathogenesis of Legionnaires» disease is strictly related to the ability of the legionellae to infect phagocytic cells, yet surface markers of virulence inLegionellaisolates are currently unknown. Rabbit antibodies raised against purified flagella ofLegionella pneumophilaserogroup 1 recognized a total of 24 of 30 laboratory-maintained isolates ofL. pneumophilaserogroups 1–15 and 16 of 24 otherLegionellaspecies tested by rapid immunoblot and indirect immunofluorescence assay. All isolates possessing flagella detectable with these anti-flagella antibodies, regardless of species, were capable of infectingHartmannella vermiformis. Isolates lacking immunologic cross-reactivity were shown to lack purifiable flagella. The majority of aflagellate isolates were not motile and failed to multiply intracellularly in co-culture withHartmannella vermiformis. Some isolates characterized as aflagellate when harvested from BCYE agar were able to multiply in amoebae, and flagella were subsequently detectable by immunologic methods. These data suggest that lack of immunologic recognition of flagella in laboratory-maintained isolates ofLegionellais due to their attenuation and a corresponding loss of expression of flagella. More importantly, the presence of flagella can serve as a positive predictive marker for strain virulence and is useful in determining the virulence status ofLegionellaisolates.

ABSTRACTWe compared the performances of three recently optimized real-time PCR assays derived from distinct genomic regions of Mycoplasma pneumoniaeduring an outbreak. Comprehensive evaluation established that a newly described toxin gene represents a superior target for detecting M. pneumoniaeDNA in clinical specimens, although use of multiple targets may increase testing confidence.

ABSTRACTThe Binax and the Biotest urinary antigen kits for the detection of Legionnaires' disease caused by organisms other than Legionella pneumophilawere compared by testing 45 urine samples from non-Legionella pneumophilaserogroup 1 patients previously positive in a broad-spectrum enzyme-linked immunosorbent assay (ELISA). Eighteen were positive with the Binax kit, and 13 were positive with the Biotest. Although neither kit is as sensitive as ELISA, these results extend the number of serogroups and species ofLegionellathat can be diagnosed with the Binax or Biotest kit.

ABSTRACTThree methods for the recovery of Chlamydia pneumoniaefrom spiked nasopharyngeal and blood specimens, including extended culture and additional centrifugations, were compared. Additional centrifugations and a 7-day culture time resulted in a 500- to 5,000-fold increase in the number of detectable inclusion-forming units.

Guidelines for the prevention of nosocomial pneumonia specify that only sterile fluids should be used for aerosol therapy; however, this recommendation may not be uniformly followed. Thirteen patients with nosocomial pneumonia due to Legionella pneumophila serogroup 3(Lp3) were identified at a community hospital in the period from 1984 through 1988; 12 patients (92%) had chronic obstructive pulmonary disease; and 9 patients(69%) died. Anepidemiologic investigation suggested that the use of nebulizers to deliver medication was associated with acquiring legionnaires' disease. The hospital potable water system was contaminated with Lp3, and a survey indicated that tapwater was commonly used to wash medication nebulizers. Lp3 in respirablesize droplets was isolated from aerosols generated bya nebulizer containing Lp3 at one-tenth the concentration found in the hospital potable water. These findings support the recommendation that only sterile fluids be used forfilling or cleaning respiratory care equipment and suggest that this guideline is not universally followed.

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.

Legionella pneumophila is an intracellular parasite of Hartmannella vermiformis. Attachment to the amebae and entry of L. pneumophila were studied by two quantitative assays: One used plate counts to measure the number of bacteria attaching to amebae at 4°C; the other determined the number of intracellular bacteria by use of transmission electron microscopy (TEM). The attachment assay showed that L. pneumophila are inefficient in attachment to amebae. About 0.05% of the bacteria were bound after 1 h with a 10- to 40-fold increase over the next 11 h. Attachment of both virulent and avirulent strains of L. pneumophila occurred at a similar rate. Uptake of L. pneumophila was measured by counting intracellular bacteria using TEM. Limited numbers of virulent L. pneumophila were found intracellularly before 4 h, but the numbers increased logarithmically after this time. The number of amebae containing virulent L. pneumophila increased linearly during the 12-h co-incubation. Avirulent L. pneumophila were rarely detected within amebae throughout the 12-h incubation. Results indicate that entry, not attachment, of virulent L. pneumophila is the limiting step in infection of axenically grown H. vermiformis.

In June 1992, 13 (38%) of 34 resort guests experienced illness that met a symptom-based case definition of Pontiac fever. Each ill guest reported using an indoor hot tub compared with 6 (29%) of 21 nonill guests (P < .001). Water samples from the indoor hot tub were culture-negative for legionellae using standard techniques, coculture with amebae, and intraperitoneal inoculation of guinea pigs. However, polymerase chain reaction (PCR) testing of the water samples indicated the presence of Legionella pneumophila. Direct fluorescent antibody testing identified the organism as serogroup 6. Seroconversion to L. pneumophila serogroup 6 occurred in 7 (64%) of 11 ill guests and none of 5 nonill guests (P = .03). These results suggest that in certain circumstances, culture of environmental samples should be supplemented with additional tests such as PCR. These results are also consistent with the concept that Pontiac fever can be caused by nonviable legionellae.

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.

Epidemiologic studies have suggested that legionnaires' disease can betransmitted to susceptible hosts by contaminated aerosolized water from cooling towers and evaporative condensers; however, epidemic strains of Legionella have not been isolated by air sampling at such sites during epidemiologic investigations. An outbreak of legionnaires' disease occurred at a retirement hotel; Legionella pneumophila serogroup 1 was isolated from an evaporative condenser and from potable water. A case-control study showed that the only significant exposure risk was in area A. L. pneumophila serogroup 1 was isolated during air sampling near the evaporative condenser exhaust site, the air conditioning intake vent, and an air vent in area A, but not in shower stalls. Monoclonal antibody subtype patterns of L. pneumophila serogroup 1 isolates from patients matched those from the evaporative condenser but not from shower water. Air sampling and monoclonal antibody subtyping results support epidemiologic evidence that the evaporative condenser was the source of this outbreak.