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Transcript
Legionella Risk Management Review Group Project May 10, 2002 ENV 711 Prof. David M. Hassenzahl Amy Klima Jeff Geller McClain Peterson Rob Boehlecke Vanessa Stevens Abstract Legionella refers to a group of bacteria commonly found worldwide in freshwater aquatic environments. Legionella pneumophila is the most important member of this group because it is commonly associated with Legionnaires’ Disease. Legionnaires’ Disease is a severe form a pneumonia that first came to prominence in 1976, when it affected people attending an American Legion Conference in Philadelphia, Pennsylvania. Favorable conditions for Legionella can be found in many everyday situations including grocery store misters, casinos, and hospitals. Anyone who is exposed to the bacteria could contract Legionellosis, however, individuals that are immunodeficient, have chronic lung disease, the elderly, smokers, or individuals that are receiving immunosuppressive medication are at a greater risk of contracting Legionellosis. The population characteristics of Las Vegas (e.g., high percentage of retired persons, heavy drinkers, and smokers including tourists) as compared to other cities, may lead to an increased risk of infection. Reducing the potential that susceptible persons are exposed, implementing engineering controls, and properly maintaining water systems through such measures and water treatment can mitigate the risk of contracting Legionellosis. Because of the many uncertainties associated with sampling and analysis, clinical identification, susceptibility factors, strain virulence, minimal epidemiological data, and near absence of specific toxicological data sets there is no known model for the risk of contracting Leginellosis if exposed. The risk of contracting Legionellosis cannot be eliminated; however, by following the proper steps it can be reduced. Introduction Legionellae refers to a group of bacteria commonly found in aquatic environments. Legionellae pneumophila is the most important member of this group because it is commonly associated with the disease Legionellosis. There are two forms of Legionellosis, Legionnaires’s Disease and Pontiac Fever. Legionnaires’ Disease is a severe form of pneumonia caused by Legionellae pneumophila. Legionnaries’ Disease first received public awareness in 1976, when it affected people attending an American Legion Conference in Philadelphia, Pennsylvania. Currently, there are 43 species of Legionellae and 65 serogroups. However, Legionellae pneumophila is responsible for 90% of the Legionellosis cases in the United States (Marston, et al 1994). 2 The major reservoir for Legionellae is water. The bacteria are found in freshwater environments worldwide (Steele et al 1990). Water containing the organism is aerosolized in respirable droplets (1-5um) and inhaled by a susceptible host (CDC, 1997). These sources can be showers, faucets, misters, spas, air conditioning units, water fountains, and cooling towers. People may be exposed at home, hospitals or nursing homes, work environments, grocery stores or other public places such as casinos. For instance the following outbreaks occurred during the period between 1984 and 1898 in the United States, see Table 1. Legionellae basically has two “lifestyles”. The Planktonic Legionellae bacteria are free-floating and unprotected. The sessile form of the Legionellae bacteria is attached to a surface or is considered protected (Barbaree et al, 1993). The intracellular habitat provides protection for Legionellae against the biocidal effects of chlorine and heat (Kuchta et al, 1993). The conditions that are required for amplification of Legionellae bacteria include a water temperature of 32C-45C, stagnation, the presence of sediment, and the presence of biofilms and amoebae (Yanamoto et al, 1992). In an aquatic environment, the amoebae/protozoa feed on the biofilm and engulf the Legionellae bacteria. The Legionellae bacteria are resistant to digestion. Inside of the amoebae the bacteria then proliferate and break down the cell wall of the amoebae. They are then released back out into the water (Beer, 2002). The mechanism that the Legionellae bacteria uses to infect and multiply in protozoa is similar to the mechanism the bacteria uses to infect human phagocytic cells (Barbaree et al, 1993) 3 Overall, the population as a whole is at risk. However, individuals that are immune deficient or have chronic lung disease, elderly, smokers, or individuals who are receiving immunosuppressive medication are at a much greater risk of contracting Legionellosis. Most cases that have been reported have occurred in the 40-70 year old range. This is significant because Las Vegas has a large population of retired persons in this age category and many of the tourists who frequent Las Vegas also fall into this age category. Therefore, the Las Vegas region needs to have an increased awareness of Legionnaire’s Disease. Four conditions must be met in order for an individual to contract Legionnaires’ Disease. The bacteria must be in an environment were it is able to amplify (i.e., reproduce). There must be a way for the Legionellae bacteria to be disseminated, such as a showerhead or mister. The Legionella bacteria must be virulent, and the individual must have susceptibility such as a weakened immune system. 4 Table 1: Legionellae outbreak and source Outbreak Location Epidemic Source Hospital Potable water system Hospital Respiratory therapy device Spa Whirlpool Banking Trust Building Cooling Tower Prison Cooling Tower Tourist Lodges Potable water system Hotel for the elderly Evaporative condenser Hospital Shower heads Hospital Respiratory therapy device Grocery store Mist machine above produce Source: Barbaree 1991 5 Information and Data There are numerous conditions and factors that make people more susceptible to the effects of Legionnaires’ Disease. In this research we will focus on the most common conditions and characteristics including people 40 – 70 years of age, alcoholics, smokers, persons with human immunodeficiency virus (HIV), and individuals who suffer from cancer (Beer, 2002). As a large city it would be expected that Las Vegas will have a significant population that is susceptible to contracting Legionellae. Therefore, a quantification of these individuals was necessary to ascertain how many individuals in the Las Vegas region are most susceptible to the Legionellae bacteria. Las Vegas is home to every age group, attracting young people with a flourishing economy, and attracting retired people with an inviting climate and a plethora of senior level activities. The age group that is the most susceptible to this disease, 40 – 70, is prominent. In Clark County out of the 1,375,765 people, 617,516 (or 45%) are within this category (USCB, 2002). Heavy drinkers are at a higher risk for contracting the disease once they come into contact with Legionella pneumophila. In Las Vegas there are approximately 77,042 people who are classified as “heavy drinkers” (SAMHA). These individuals, who drink five or more drinks on the same occasion on at least five different days a month, would be more prone to contracting this disease and experiencing its effects. This classification of heavy drinkers is one way to quantify the at risk groups to Legionnaires’ Disease. It is important however to note that anyone drinking alcohol is more susceptible to 6 Legionnaires’ Disease because of a decrease in the immune systems performance (NIAAA 2002). Cigarette smoking is also a habit that makes individuals more susceptible to Legionnaires’ Disease and its subsequent effects. In Las Vegas, 331,559 citizens or 24.1% of the total population have an increase susceptibility to the disease because of smoking habits (Yahoo Health, 2002). Immunodeficiency, which compromises the body’s ability to fight Legionella pneumophila, is another factor in determining susceptibility to the disease. As with any city, a significant portion of the population will have some disease or condition that has comprised their body’s immunity. Human immunodeficiency virus (HIV) is one such condition and in Las Vegas approximately 3,773 individuals suffer from HIV. Cancer is another form of an immunodeficiency that makes individuals more susceptible to Legionnaires’ Disease, and in Las Vegas there have been 32,076 cases of cancer reported to the state health department since 1995 (NVDH, 2002). The health department considers this an accurate representation of the total population inflicted with cancer. As the primary source of revenue for the city of Las Vegas, tourism attracts people from around the world and from various backgrounds, ethnicities, and health related conditions. In 2001, 35,017,357 visitors came to Las Vegas (LVCVA, 2002). It is important to include these visitors in the population of people who could be adversely affected by Legionellae pneumophila. However, it is unknown what percentages of these 7 visitors have characteristics that make them more susceptible to Legionnaires’ Disease, but it is certain that a portion of them will. Mitigation Measures As pointed out by the American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) in their 1998 position paper on Legionellosis, the most effective control for most diseases is to prevent transmission at as many points as possible (ASHRAE, 1998). Butler et. al. also echoed this idea in stating that interrupting the transmission from the environment to people is the foundation of prevention of Legionellosis (Butler et.al, 1997). Prevention can be accomplished though several methods including engineering controls on water system equipment, regular cleaning and maintenance of water systems, addition of inhibitors into water systems, or reducing the potential that susceptible people will be exposed. According to Butler et.al, 1997 there are currently two schools of thought regarding the most effective way to prevent hospital acquired Legionellosis (nosocomial infection). The first is to routinely culture water samples for the hospitals potable water system. The second is to maintain a high suspicion for Legionellae bacteria by using clinical diagnostic tests on potential Legionellosis patients. When a case of disease is confirmed, initiate an investigation for the exposure source and correct the maintenance problem(s) that led to the exposure (Butler et.al, 1997). We will first discuss how reducing the potential that susceptible persons are exposed to Legionellae can be aided by sampling and analysis of both water systems and people. 8 While it may be obvious that the risk of contracting Legionellosis can be mitigated by knowing if the water supply is contaminated, it is not exactly that straight forward due to factors such as incubation time and turnaround time for sampling and analysis. It is also difficult to determine whether a particular person is sick due to legionella or some other pathogen. However, in both cases it can be shown that increased knowledge of the existence of Legionellae in a system or a patient’s body can reduce the risk. The risk to the individual is reduced through the identification and proper treatment of the disease. Clinical features (e.g., symptoms) described for Legionnaires’ Disease cannot be distinguished from those due to pneumonia caused by other agents. Therefore, serological tests are the only way to confirm Legionellosis. Most tests are run on lower respiratory tract secretions; however, they may also be done on blood, serum and urine samples. As reported by the EPA in 1999, early initiation of appropriate treatment for individuals infected with Legionellae pneumophila is recognized as crucial for the successful outcome of the disease. In fact as reported in EPA, 1999 after multiple logistic regression analysis of seriologically confirmed cases of Legionnaires’ Disease; the only factor associated with increased mortality in Legionellosis patients was a delay in initiation of appropriate treatment (EPA, 1999). Proper identification is also important to the mitigation of the risk to others in the community as well. Additional nosocomial (hospital contracted) cases are typically 9 identified once several cases have been reported (EPA, 1999). Active surveillance of Legionella infection, especially among hospital patients at high risk is an important tool for minimizing risk of Legionnaires’ Disease because it also allows for prompt remedial actions (EPA, 1999). In hospitals where Legionellae was acquired, additional cases have only been recognized after increased testing of patients who had pneumonia. Recognition of such cases can lead to interventions to limit growth of the organism and transmission to other patients (Butler et al, 1997). However, it should be noted that the incubation period for Legionellae pneumophila is usually 2-10 days, therefore, a patient must have spent greater than 10 days in a hospital prior to onset of Legionellosis, before it can be concluded that the patient acquired the disease in the hospital (Butler, 1997). When a case of hospital-transmitted Legionellosis is confirmed, Butler et. al (1997) indicates that in order to support a link between a human illness and a specific source, subtype matching between the Legionellae bacteria isolated from the patient and that from the environmental (i.e., potential exposure source) sample should be completed. Proper identification of non-hospital contracted Legionnaires’ Disease can also lead to risk mitigation for other potentially exposed populations. For example, a person goes into the hospital with pneumonia and it is proven through testing that the person suffers from Legionnaires’ Disease, then it can be assumed the person was exposed to the disease through exposure to a contaminated water system. Although results may not necessarily be conclusive, sampling of potentially infected water systems may lead to identification of the source of the exposure. The source can then be cleaned and/or 10 treated thus mitigating the risk. Once the source system is identified those people who are in high-risk groups could also be isolated from the system. In order to identify the exposure source, samples must be collected and analyzed. ASHRAE states that currently the most reliable method of testing for viable (the bacteria must be alive to cause the disease) Legionellae in a system is culturing (ASHRAE, 1998). This is supported by the CDC, which considers bacteria culturing the only reliable method for detecting viable organisms (Beer, 2002). However, culture-based techniques require 10-14 days from the time of sample collection until results are available (CTI, 2000). In their paper CTI states this period is too long a time for sampling and analysis to serve as an effective tool for treatment control. Most of the documentation supports this stance and indicates routine culturing of water systems should not be performed (Yu, 1997; Cohen, 1997; ASHRAE, 2000) because the concentration of Legionellae bacteria in a system may not be predictive of risk transmission (ASHRAE, 2000). ASHRAE (2000) and other documentation (e.g., Butler et.al, 1997) indicate that routine culturing cannot be directly correlated with the risk of contracting the disease because of several factors. The first is that the presence of the organism cannot be directly related to risk of infection (ASHRAE, 2000). Among a study reported by EPA (1999) the study authors noted that among 900 samples from building water systems, some of the samples with the highest hazard level were obtained from a building without any reported Legionnaires’ Disease cases. The second is that interpretation of results is 11 complicated by use of different collection and analysis methods and fluctuations of results within samples collected from the same source (ASHRAE, 2000). Also the risk of illness is influenced by a number of factors as previously discussed, and finally, test results only represent the counts at the time the sample was collected (ASHRAE, 2000). Results of a specific test must be interpreted cautiously because the concentration of organisms can increase substantially in a short period of time (e.g., days) (ASHRAE, 1998). Butler et.al (1997) adds several other factors influencing the rate of infection including strain virulence and how efficiently the bacteria are aerosolized. In an earlier position paper on Legionellae, ASHRAE stated that there is currently not enough information to adopt a position on what is a “safe” or “unsafe” number of Legionellae bacteria or how long that number would be valid. In some cases, small numbers caused disease and in others large numbers did not result in a disease outbreak (ASHRAE, 1998). Then why sample water systems at all? Even those opposed to routine sampling state that there is some utility in water system sampling. Butler et.al (1997) states, “culturing in a water system may be appropriate if performed to evaluate a suspected source of infection, as part of an outbreak investigation, to assess the effectiveness of treatment or decontamination, or to evaluate the potential for transmission in health care facilities with high risk patients.” ASHRAE also indicates “culturing for Legionellae may be appropriate if carried out for a specific purpose, such as tracing the source of an infection, evaluating the potential amplifier or transmission sources, verifying the effectiveness of a water treatment system, 12 verifying that decontamination procedures have been effective, or at health care facilities with patients at high risk.” Yu (1997) indicates that the presences of Legionellae within a hospital water supply system invariably leads to infections and recommends routine environmental culturing in hospitals to raise the index of suspicion. Water system sampling and analysis can never be a substitute for sound maintenance and water treatment (ASHRAE, 2000). A variety of engineering controls are recommended to help reduce the risk of Legionellae transmission from common systems such as cooling towers, evaporative condensers, humidifiers, potable water heaters and holding tanks, pipes containing stagnant warm water, showerheads, faucet aerators and whirlpool baths can foster Legionellae growth (ASHRAE, 1998). Controlling temperature in any of the many potable water supply systems mentioned above helps to minimize growth of the bacteria (ASHRAE, 2000). Studies have indicated that temperature plays a potential role as an amplifier. Temperature ranges between 68 F and 131 F can produce favorable conditions for Legionellae to colonize. Therefore, plumbing in any water system must be routinely checked and have devices installed that control temperature. Insulation should also be installed, especially in colder regions. Another simple engineering practice that can reduce the ability of the Legionellae bacteria to colonize is to remove any dead pipes that do not receive continued flow. 13 Another way to reduce the transmission potential of Legionellae is to avoid aerosolization via water droplets since this is the primary means by which Legionellae are transmitted to humans (Butler et.al, 1997). Therefore, regulating climatic conditions around the potential locations of the bacteria, such as conditions in the air, humidity and harsh solar radiation would help to minimize risk of exposure. Other engineering controls may include maintenance and routine inspections of air filters, especially those associated with the air intake of cooling towers (ASHRAE, 2000). Designing cooling towers that do not discharge their air near the buildings air intake should be a must. This would further reduce the chance of distributing Legionellae into other parts of the building. Finally, there is speculation that a variety of water treatment measures could be effective in the control of Legionellae. Ozone, chlorine, ultraviolet light and heavy metal ions have been shown to be effective in some cases; nonetheless, further research needs to determine if this is true (Butler et.al, 1997). Chlorine treatment is recommended in emergency situations using 1 ppm to 2 ppm free chlorine at the tap for several hours (ASHRAE, 1998). However, chlorine treatment should not be used as a long-term solution to an area heavily contaminated. Use of chlorine is the current method used by the Southern Nevada Water Authority for treating potable water. However, an ozone treatment facility is currently being built. Ozone is the current treatment of choice for controlling the Legionellae bacteria. 14 Conclusion Clearly, Legionellosis is a potentially preventable disease but there is still a great deal of uncertainty in why outbreaks occur. Most if not all lakes and streams harbor Legionellae naturally and it would be impossible to eradicate the bacteria entirely from the outdoor environment (ASHRAE, 1998), not to mention that eradication could have negative effects. There could be some societal benefit to the Legionellae bacteria, where it fights off other potentially more harmful microorganisms. However, more speculation will only lead to more debate amongst the scientific community. The engineering controls and water treatment mitigation measures discussed in this paper can limit the amount of bacteria in our water systems. Culturing water samples can be useful to pinpoint the origin of an exposure and thus limit further exposures. In addition, if we can maintain a high degree of suspicion for Legionellosis when diagnosing human illness, exposed people can get the proper treatment and reduce their individual risk of succumbing to the direst consequences of infection. For the Las Vegas region it is important that a more comprehensive evaluation of the associated risks be completed. We must know who in the valley is at risk for exposure to this bacteria and whether or not appropriate measures are being taken to protect these individuals. We must also evaluate our water sources for possible contamination points and evaluate the treatment facilities currently employed. In addition, we must know whether the Las Vegas climate and yearly temperatures make it 15 more susceptible to Legionella contaminations and whether the increased use of cooling towers and misting systems provides the valley with an increased risk. One must remember that the risk of Legionellae pneumophila can never be eradicated completely, we can only reduce the risk. Furthermore, a threshold infective dose has not been established and animal models show great interspecies variation in susceptibility to infection with Legionellae (EPA, 1999). In order to increase our understanding of why and when outbreaks occur, government and industry need to develop sampling standards and acceptable infectious dose levels. More information is also needed on the virulence characteristics, of specific subtypes and of the Legionellae bacteria itself. Finally, the usefulness of non-culture methods such as antigen detection or polymerase chain reaction for detecting viable Legionellae needs to be defined (Butler et.al, 1997). Local Update! An outbreak of Legionnaires’ Disease at the Polo Towers in 2001 is currently being investigated. This incident is still under evaluation by the CDC and the final report will not be public record until the end of May. Currently, the Southern Nevada Water Authority conducts weekly sampling to determine Legionellae and other microbial levels. However, their sampling technique is to analyze bulk water samples and not biofilm where there is a greater likelihood for Legionellae to occur. 16 References ASHRAE, see American Society of Heating, Refrigerating and Air-Conditioning Engineers American Society of Heating, Refrigerating and Air-Conditioning Engineers. 1998. Legionellosis: Position Statement, updated August 3, 1998, as found at http://www.ashrae.org/ABOUT/leg_stmt.htm, (Visited on 4/1/2002). American Society of Heating, Refrigerating and Air-Conditioning Engineers. 2000. Minimizing the Risk of Legionellosis Associated with Building Water Systems, as approved by the ASHRAE Standards Committee February 5, 2000. Atlanta, GA. Barbaree, J.M. 1991. Controlling Legionella in Cooling Towers. ASHRAE Journal, 1991: pp 3841. Barbaree J. M., Breiman R. F., Dufour A. P. editors. Current status and emerging perspectives of Legionaella. Washington D. C.: ASM; 1993 p. 129-36. Beer, William. 2002. Reduction of Risks Associated with Legionella, Do You Have a Legionella Risk Management Program? William Beer is the Cooling Technology Manager at BetzDearborn, A Division of Hercules Incorporated. Butler, Jay, Barry Fields, and Robert Breiman. 1997. “Prevention and Control of Legionellosis”. In Infectious Diseases in Clinical Practice. Vol. 6, No. 7, September – October 1997. Williams & Wilkens. Baltimore, MD. CDC Legionnaires’ disease association with a whirlpool spa display – Virginia, Sept-Oct, 1996. MMWR 1997. 46:83-86. CDC, United States Centers for Disease Control. http://www.cdc.gov/scientific.htm, (Visited on 04/1/2002). CTI, see Cooling Technology Institute Cooling Technology Institute. 2000. Legionellosis Guideline: Best Practices for Control of Legionella. February, 2000. Houston, TX. EPA, see U.S. Environmental Protection Agency Fiore, AE, PJ Nuorti, OS, Levine, et al. 1998. Epidemic Legionnaires' Disease Two Decades Later: Old Sources, New Diagnostic Methods. Clinical Infectious Diseases 26:426-433. Kuchta J. M., Navratil J. S., Shepherd M. E., et. al. Impact of chlorine and heat on the survival of Hartmannella vemiformis and subsequent growth of L. pneumophila. Appl. Environ. Micro. 1993. 59:4096-100. 17 LVCVA, Las Vegas Convention and Visitors Authority. http://www.vegasfreedom.com/learn-5.asp, (Visited on 04/2/2002). Marston B. J., Lipman H. B., Breiman R. F., Surveillance for Legionnaires’ disease: risk factors for morbidity and mortality. Arch Intern Med. 1994. 154: 2417-22. NVDH, Nevada State Department of Health. http://health2k.state.nv.us/scripts/hi_iq_func.exe, http://health2k.state.nv.us/cancer/Canstats00.pdf, (Visited on 04/2/2002). OSHA Technical Manual. Section II, I Chapter 7, Legionnaires' Disease. http://www.osha-slc.gov SAMHA, see U.S. Dept. of Heath & Human Services: Substance Abuse and Mental Health Administration Southern Nevada Water Web Site. 2002. http://www.snwa.com/water_tests.html. (Visited on 4/1/2002). Steele T. W., Langser J., Sangster N. Isolation of L. longbeachae serogroup 1 from potting mixes. Appl. Env. Micro. 1990. 56:219-53. USCB, see United States Census Bureau U.S. Census Bureau. http://quickfacts.census.gov/qfd/states/32000.html, (Visited on 04/2/2002). U.S. Department of Health and Human Services: Substance Abuse and Mental Health Administration (SAMHA). http://www.drugabusestatistics.samhsa.gov/, (Visited on 04/2/2002). U.S. Environmental Protection Agency. 1999. Legionella: Human Health Criteria Document, EPA-822-R-99-001. Washington, DC. Yahoo Health. http://health.yahoo.com/health/tobacco/index.html, (Visited on 04/3/2002). Yanamoto H., Sugiura M., Kusunoki S., et al. Factors stimulating propagation of legionellae in cooling tower water. Appl. Env. Micro. 1992. 58:1394-7. Yu, Victor. 1997. “Prevention and Control of Legionella: An Idea Whose Time Has Come”. In Infectious Diseases in Clinical Practice. Vol. 6, No. 7, September – October 1997. Williams & Wilkens. Baltimore, MD. 18