Strengths and limitations of molecular subtyping in a community outbreak of Legionnaires' disease

An epidemiological and microbiological investigation of a cluster of eight cases of Legionnaires' disease in Los Angeles County in November 1997 yielded conflicting results. The epidemiological part of the investigation implicated one of several mobile cooling towers used by a film studio in the centre of the outbreak area. However, water sampled from these cooling towers contained L. pneumophila serogroup 1 of another subtype than the strain that was recovered from case-patients in the outbreak. Samples from two cooling towers located downwind from all of the case-patients contained a Legionella strain that was indistinguishable from the outbreak strain by four subtyping techniques (AP-PCR, PFGE, MAb, and MLEE). It is unlikely that these cooling towers were the source of infection for all the case-patients, and they were not associated with risk of disease in the case-control study. The outbreak strain also was not distinguishable, by three subtyping techniques (AP-PCR, PFGE, and MAb), from a L. pneumophila strain that had caused an outbreak in Providence, RI, in 1993. Laboratory cross-contamination was unlikely because the initial subtyping was done in different laboratories. In this investigation, microbiology was helpful for distinguishing the outbreak cluster from unrelated cases of Legionnaires' disease occurring elsewhere. However, multiple subtyping techniques failed to distinguish environmental sources that were probably not associated with the outbreak. Persons investigating Legionnaires' disease outbreaks should be aware that microbiological subtyping does not always identify a source with absolute certainty.     

Legionnaires' disease: evaluation of a quantitative microbial risk assessment model

Background: The quantities of Legionella vary considerably from natural waters to water in contaminated domestic hot water supplies, whirlpool spas and cooling towers, with the risk for LD rising as the Legionella counts grow. We currently report the results from our Quantitative Microbial Risk Assessment (QMRA) model evaluation. We developed the LD QMRA model to better understand Legionella exposure risks.     

A survey of methods used to detect nosocomial legionellosis among participants in the National Nosocomial Infections Surveillance System.

OBJECTIVE: To help define the scope of nosocomial legionnaire's disease (LD) and to assess use of recommended diagnostic methods and transmission control practices. METHODS: We surveyed 253 hospitals participating in the National Nosocomial Infections Surveillance (NNIS) System. The anonymous survey included questions about episodes of nosocomial LD, environmental sampling practices, maintenance of hospital water systems, and diagnostic techniques. RESULTS: Of 192 hospitals that responded, 29% reported at least one episode of nosocomial LD from 1990 through 1996, and 61% of these reported at least two episodes. Of 79 hospitals with transplant programs, 42% reported nosocomial LD, compared with 20% of hospitals without transplant programs. Environmental sampling had been conducted by 55% of hospitals, including 79% of those reporting nosocomial LD. Legionella were isolated in 34% that sampled potable water and 19% that sampled cooling system reservoirs. Supplemental potable-water decontamination systems were installed in 20% of hospitals. Only 19% routinely performed testing for legionellosis among patients at high risk for nosocomial LD. CONCLUSIONS: Nosocomial LD is relatively common among NNIS hospitals, especially those performing organ transplants. Environmental sampling for Legionella is a common practice among NNIS hospitals, and Legionella often are isolated from sampled hospital cooling towers and hospital potable-water systems. Hospitals have responded to suspected nosocomial LD infection with a variety of water sampling and control strategies; some have not attempted to sample or decontaminate water systems despite identified transmission.     

北京市大饭店空调冷却塔军团菌污染现况及人群感染水平研究

目的：了解北京市大饭店空调冷却塔军团菌污染现况及相关人群感染水平。方法：按分层随机抽样的方法,抽取北京市１４家大饭店（四五星级）中央空调３８个冷却塔;抽取相应饭店健康工作人员（暴露人群）和非从事饭店行业的健康群（对照人群）各４１４人,分别进行军团病的病原学及人群血清学检测。结果 所调查饭店中１２家空调冷却塔有军团菌污染,污染率８５．７％’有２１个冷却塔检出军团菌,阳性率５５．３％（２１／３８）;共     

Decreasing trend of Legionella isolation in a long-term microbial monitoring program in Greek hospitals

Legionnaires' disease is a known cause of severe pneumonia in a nosocomial setting. This study examined Legionella isolation in Greek hospitals. Water samples and swabs of showerheads from 41 hospitals were collected over a four-year period (2004-2007) from hot and cold water systems and cooling towers in Greece. In total, 1058 samples were examined for the presence of Legionella. From the hot water samples examined, 166 out of 607 (27.3%) were positive for Legionella, including 111 (18.3%) positive for Legionella pneumophila sg1 samples. The temperature of hot water samples less than 55°C was statistically significant, associated with Legionella spp. isolation (RR 4.01, 95%CI 2.33-6.92). Ten out of 17 (58.8%) hospital cooling towers required remedial actions due to Legionella colonization. Reemergence of Legionella spp. colonization was evident in more than half of the hospitals where frequent monitoring and appropriate risk assessment plans were absent or lacking. Hospitals that were monitored continuously over the study period presented a decreasing trend of Legionella colonization. Environmental risk assessment together with Legionella isolation should be enforced systematically in hospitals.     

Soil as a source of Legionella pneumophila serogroup 1 (Lp1)

OBJECTIVE: To investigate the potential source of a case of Legionnaires' disease caused by an unusual serotype of Legionella pneumophila serogroup 1 (Lp1) in regional Victoria in May 2001. METHOD: Epidemiological and environmental investigation of the source of infection of a case of Legionnaires' disease in regional Victoria in May 2001. RESULTS: Extensive environmental investigations did not reveal any cooling water tower systems close to the residence or the shopping centre that the case visited prior to illness. The sputum culture and a soil sample from the field at the plant nursery where the case worked prior to illness were both positive for Legionella pneumophilia serogroup 1, MDU pulsovar 97:103. CONCLUSION: Legionella pneumophila has been found in soil and was further found to be associated with a case of Legionella pneumophila. IMPLICATIONS: Public health authorities should consider exposures to soil and potting mixes when investigating cases of Legionella pneumophila where the case has no apparent association with cooling towers. Safe gardening practices should be promoted among the community.     

Environmental investigation of a legionellosis outbreak in western Sydney: the role of molecular profiling

This investigation used DNA profiling in an attempt to identify the environmental source of a community outbreak of 11 cases of Legionnaires? disease. Nine of these cases were culture positive and a single strain (DNA profile) of Legionella pneumophila serogroup 1 was isolated from eight cases. Spot water samples were collected from 51 cooling towers implicated by case exposure histories; this same strain was isolated from four towers at three separate locations up to 6 km apart. None of these locations had been frequently implicated by case histories. Because we did not perform an analytic epidemiological investigation, we were unable to identify a single environmental source for the outbreak. It is also possible that this outbreak was multifocal. The use of molecular profiling should not overshadow the importance of epidemiological methods in these environmental investigations. More data is needed regarding the prevalence, distribution, and clinical significance (virulence) of environmental L. pneumophila strains. This would aid interpretation of molecular profiling used in investigations of community legionellosis outbreaks.     

Legionellosis prevention in France

Since 1997, both the prevention of legionellosis and the control of Legionella in water networks and cooling towers have greatly improved in France. The epidemiological surveillance of Legionnaires' disease showed an increase, which was followed by a decrease in the incidence after a maximum was reached in 2005 (incidence rate of 2.5 per 10(5)). A steady decrease in the incidence rate has been observed since 2006, mainly due to the efficacy of control measures both for cooling towers and hospital water networks. In hospitals, a proactive approach was proposed in 1998 and quantitative limit values with systematic survey were put into force in 2002. The percentage of nosocomial cases has decreased dramatically and is now around 6-7% of all cases recorded in France. No nosocomial outbreak has been reported in recent years. However, this is not the case for community cases linked to diverse exposure sources, including cooling towers.     

Legionnaires' Disease associated with potting soil--California, Oregon, and Washington, May-June 2000

Since Legionnaires' Disease (LD) was first reported in 1976, outbreaks have been associated with airborne transmission of Legionella bacteria through cooling towers, showers, and other aerosolizing devices (1). However, most LD cases are sporadic, and the source and mode of infection in many cases are unknown. Infections with one species, Legionella longbeachae, have been associated with gardening and use of potting soil in Australia and Japan (2,3). This report summarizes the findings of LD investigations in California, Oregon, and Washington, that suggest that transmission from potting soil has occurred for the first time in the United States, and that active surveillance and case finding are warranted to explore this association.     

Community-acquired Legionnaires' disease associated with a cooling tower: evidence for longer-distance transport of Legionella pneumophila

In the period August 10-29, 1986, 29 confirmed cases of Legionnaires' disease occurred in Sheboygan, Wisconsin; two cases were fatal. No common source of indoor exposure was identified. Water specimens were obtained from all known cooling tower units in Sheboygan; Legionella pneumophila serogroup 1 was isolated at 1 x 10(6) colony-forming units per liter from a specimen obtained August 27 at plant A. This isolate was identical to the only clinical isolate by monoclonal antibody and isoenzyme subgrouping. Of 29 persons with Legionnaires' disease, 21 lived or worked within one mile (1.6 km) of plant A; seven of the remaining eight visited within one to two miles (1.6 to 3.2 km) of plant A from three to seven days before onset of illness. Attack rates were highest for persons living within 0.5 mile (0.8 km) of plant A. These findings associate a cooling tower with community-acquired Legionnaires' disease and suggest that dissemination of Legionella may occur over longer than previously recognized distances.     

Sampling and detection of Legionella pneumophila aerosols generated from an industrial cooling tower

Cooling tower water has frequently been cited as a source of infection in outbreaks of Legionnaires' disease. However, there have been few reports on the presence of legionellae in aerosols from cooling towers. This paper describes our use of an impinger or a six-stage microbial impactor for detecting legionellae in air around a cooling tower contaminated with L. pneumophila (1.2+/-0.3x10(5) CFU/100 ml). Phosphate-buffered saline, Page's saline, 2% yeast extract solution and buffered yeast extract (BYE) broth were tested to evaluate their collection efficiency. These solutions were compared in laboratory experiments using an aerosol of L. pneumophila serogroup (SG) 1. Because BYE broth was the most efficient and storable collecting fluid among them, it was used for outdoor air sampling. In the outdoor air sampling, aerosolized L. pneumophila SG 6 was detected in the air around the cooling tower by the impinger (0.09 CFU/l. air). No legionellae were detected by the impactor with Legionella-selective agar plates (WYOalpha) because the plates were overgrown with fungi. Repetitive element PCR (rep-PCR) and arbitrarily primed PCR (AP-PCR) were employed to assess the epidemiological relationship among Legionella isolates from the air sample and the cooling tower water samples. L. pneumophila SG 6 isolated from the aerosols produced rep-PCR and AP-PCR fingerprints identical to those of L. pneumophila SG 6 strains from the cooling tower water, suggesting that the bacterium was aerosolized from the cooling tower.     

公共场所中央空调系统冷却塔水及气溶胶军团菌污染的风险评估和预警研究

目的 构建中央空调系统冷却塔水及气溶胶军团菌污染的风险评估指标体系和风险预警模型.方法 于2008、2009年的5-9月采集马鞍山市16户宾馆、商场、公共浴室冷却塔水样70份,冷却塔气溶胶样品110份,分别进行军团菌分离培养和嗜肺军团菌mip基因的PCR检测.分析冷却塔水军团菌检出与气溶胶军团菌检出之间的关系,筛选可能...     

Outbreak detection and secondary prevention of Legionnaires' disease: a national approach

BACKGROUND: To stop a possible outbreak of Legionnaires' disease (LD) at an early stage an outbreak detection programme was installed in The Netherlands. METHODS: The programme consisted of sampling and controlling of potential sources to which LD patients had been exposed during their incubation period. Potential sources were considered to be true sources of infection if two or more LD patients (cluster) had visited them, or if available patients' isolates and environmental Legionella spp. were indistinguishable by amplified fragment length polymorphism genotyping. RESULTS: Rapid sampling and genotyping as well as cluster recognition helped to target control measures. Despite these measures, two small outbreaks were only stopped after renewal of the water system. The combination of genotyping and cluster recognition lead to 29 of 190 (15%) patient-source associations. CONCLUSION: Systematic sampling and cluster recognition can contribute to outbreak detection and lead to cost-effective secondary prevention of Legionnaires' disease.     

上海市16个冷却塔水中军团菌脉冲场凝胶电泳分型及基因型监测

目的 研究上海市公共场所16个空调冷却塔水中军团菌的脉冲场凝胶电泳(PFGE)分型,并连续监测该菌基因型变化.方法 2007年5-10月连续6个月以每月1次的频率采样,从16个公共场所空调冷却塔水中分离军团菌,经血清学凝集试验、胶乳凝集试验分型后,使用PFGE技术对酶切后的军团菌全染色体DNA进行电泳获得指纹图谱,利用BioNumerics软件进行聚类分析.结果 16个冷却塔水中共分离出131株军团菌,包括嗜肺军团菌、博杰曼军团菌、米克戴德军团菌和茴香军团菌,分为52个PFGE型别,其中37个PFGE型别(71.15%)仅分布于1个冷却塔中,即为该冷却塔所特有;15个PFGE型别(28.85%)分布于2个或以上冷却塔中.16个冷却塔具有2个或以上的PFGE型,13个冷却塔(81.25%)中多次出现相同的PFGE型别.2007年6-10月连续5个月从6个冷却塔中分离出18株PFGE型为LPAs.SH0078型的军团菌.结论 冷却塔水中的军团菌基因型具有多样性和复杂性,81.25%的冷却塔水中PFGE型具有持续性,且LPAs.SH0078型广泛分布,可能为优势PFGE型.     

大连市集中空调场所军团菌污染及人群健康状况影响调查

目的调查大连市集中空调场所冷却塔水军团菌污染状况及暴露人群中军团菌隐性感染状况,研究军团菌对人群健康的影响因素。方法2005年8～9月,随机采集大连市使用集中空调的32所公共场所集中空调冷却塔水,采用分离病原培养法进行军团菌检测;随机抽取使用集中空调场所的工作人员血样,采用微量凝集试验法,进行血清军团菌抗体检测。结果大连市公共场所集中空调冷却塔水军团菌检测的场所阳性率为53.13%,军团菌血清型分别为嗜肺军团菌(Legionella pneumophila,Lp)Lp7、Lp8、Lp9和Lp10型。其中,Lp9型28株,占总菌株的77.78%,为优势菌株。人群血清学抗体检测显示,使用集中空调的公共场所人群Lp10感染率较高。结论大连市使用集中空调的场所存在军团菌污染,人群中存在军团菌隐性感染。     

Isolation of Legionella species/serogroups from water cooling systems compared with potable water systems in Spanish healthcare facilities

Surveillance of Legionella spp. in hospital water systems was performed in forty-four inpatient healthcare facilities in Spain during 2005-2006. A total of 2,341 samples were collected: 470 from cooling systems (cooling towers) and 1,871 from potable water systems. The latter included 211 from cold-water tanks and 260 from hot-water tanks, totalling 471 from central water reservoirs 136 from showers, 1,172 from unfiltered taps and 92 from filtered taps, totalling 1,400 from peripheral points. Temperature, chlorine levels and the presence of Legionella spp. were determined. In all, 373 (15.9%) samples yielded Legionella spp. Significantly higher isolation rates were obtained from cooling towers (23.8%) versus cold- and hot-water tanks (approximately 4.7%), due to the significantly higher number of samples positive for serogroup 1 (19.4 vs 0.9-3.5%). In potable water systems, no differences were found between central water tanks and showers, but significant differences in isolation rates between central water tanks and unfiltered taps were observed (4.7 vs 19.6%) due to differences in non-serogroup 1 L. pneumophila. Filters significantly decreased isolation rates of these serotypes (11 vs 0%). Some seasonal differences were noted, with higher isolation rates in summer for legionella serogroup 1 in cooling systems and for L. pneumophila serogroups 2-14 in potable water systems. In regression models, higher temperatures were associated with colonisation in cooling systems, while lower chlorine levels were associated with colonisation in potable water systems.     

北京市东城区公共场所冷却塔使用状况及健康风险评估

目的了解北京市东城区公共场所冷却塔使用及卫生状况,评估各场所冷却塔军团菌病健康风险。方法2018年5—9月,采集东城区内三类共26家公共场所冷却塔冷却水,填写相关调查问卷,通过冷却塔军团菌病健康风险指数模型计算各场所健康风险。结果本次研究中各场所冷却水样本嗜肺军团菌检测均为阴性,合格率为100%。游离性余氯平均为0.15 mg/L。酒店类场所冷却塔规模、加药方式和频率与其他场所有明显差别。26家公共场所健康综合风险平均为61.49,其中军团菌增殖风险、含菌气溶胶传播风险、暴露人群易感风险分别为16.13、22.66和22.70。不同场所冷却塔军团菌病健康风险评估结果存在一定差异,医院类场所健康风险指数高于酒店和商场(F=3.78,P<0.05)。结论冷却塔军团菌病健康风险高低主要受公共场所周围易感人群影响,该地区相关卫生部门应加强对相关易感人群的保护,对各类场所相关政策法规进行制定、完善和实施。     

Legionnaires' disease outbreak in Murcia,Spain

An explosive outbreak of Legionnaires' disease occurred in Murcia, Spain, in July 2001. More than 800 suspected cases were reported; 449 these cases were confirmed, which made this the world's largest outbreak of the disease reported to date. Dates of onset for confirmed cases ranged from June 26 to July 19, with a case-fatality rate of 1%. The epidemic curve and geographic pattern from the 600 competed epidemiologic questionnaires indicated an outdoor point-source exposure in the northern part of the city. A case-control study matching 85 patients living outside the city of Murcia with two controls each was undertaken to identify to outbreak source; the epidemiologic investigation implicated the cooling towers at a city hospital. An environmental isolate from these towers with an identical molecular pattern as the clinical isolates was subsequently identified and supported that epidemiologic conclusion.     

A hospital outbreak of Legionella from a contaminated water supply

The authors performed a cross-sectional epidemiological survey to investigate the source of a hospital Legionella outbreak originating in contaminated water. Water temperature and air humidity were measured around possible contamination sources. A dead-end pipe was found to contain Legionella pneumophila serogroup 1. All individuals who acquired legionellosis had spent at least 30 min within 2 m of the contamination source. Among staff, 41 of 71 were exposed, and 31 of these fell ill. All 7 patients exposed to the contaminated water acquired legionellosis. None of the 94 bed-ridden patients from the same units developed the disease. An aerosol with 60% relative air humidity was formed near the suspect water faucets, but the humidity fell rapidly farther from the water source, suggesting that desiccation decreased the risk of infection. The healthy personnel and patients closest to the source acquired legionellosis, suggesting that risk was related less to compromised patients than to exposure.     

北京某区部分医院和宾馆中央空调系统冷却塔水军团菌污染状况监测

[目的]了解北京市某区部分医院和宾馆冷却塔水的军团菌污染状况,为军团病的防控提供科学依据。[方法]选取北京某区3家医院和44家宾馆于2007年6月至2007年9月每月对上述场所的冷却塔水进行军团菌污染状况监测,同时对冷却塔的环境和冷却水处理方式进行调查。[结果]3家医院在监测期间均曾检出过军团菌,44家宾馆中有26家检出过军团菌,47家单位总的合格率为38.30%。采集的265件样本中,有76件检出军团菌,阳性率为28.68%。其中医院共采集样本17件,阳性样本9件,阳性率为52.94%;宾馆共采集样本248件,阳性样本67件,阳性率为27.02%。76件阳性样本中,63件为LP1型菌株污染,7件为LP2-14型菌株污染,LP1和LP2-14均检出的样本6件。冷却塔的工作环境有利于军团菌生长,冷却水的处理主要采取化学方式进行,使用的大部分化学制剂成分不明。[结论]北京某区部分医院和宾馆受军团菌污染较为严重,医院比宾馆的检测阳性率高。军团菌分型以LP1型为主。冷却塔水的处理方法需规范。