Legionnaires’Disease: An Update for Plumbing Engineers
Most cases of Legionnaires’ Disease are not detected. Even when cases are detected, the public rarely hears about them, because only a small percentage of Legionnaires’ cases occur as part of the multi-case outbreaks that sometimes make the news. The disease is seldom publicized, even when lawsuits are involved, because most Legionnaires’ lawsuits are settled quickly and under terms of confidentiality.
Under-diagnosis makes it difficult to estimate the incidence of the disease; figures have varied widely. The U.S. Center for Disease Control and Prevention (CDC) in Atlanta has estimated that the disease infects 10,000 to 15,000 persons annually in the United States, but others have estimated as many as 100,000 annual U.S. cases.
Symptoms of Legionnaires’ are similar to those of other types of pneumonia, so undetected cases of Legionnaires’ Disease end up being classified merely as pneumonia with no apparent cause (“atypical” pneumonia). Based on CDC estimates, this means that eight to 39 pneumonia deaths each week occur without anyone knowing that the cause was Legionella. What’s worse is that many of these deaths could be prevented because, unlike most pneumonias, the source (e.g., a plumbing system) of Legionnaires’ cases can be identified. But if Legionella is not recognized as the cause, no investigation ensues to pinpoint and disinfect the source, so the same source remains a threat to other lives.
Specialized laboratory tests are required to identify Legionnaires’ Disease. Three types of tests are used: blood tests, urine tests and sputum tests. Sputum tests are the most sensitive and reliable, because if legionellae is in the sputum, it actually can be grown (cultured) in a laboratory. Unfortunately, most U.S. hospitals have not made the sputum tests available, possibly because the analysis is specialized. Urine tests are not as accurate as sputum cultures, but give results quicker. Blood tests are the least sensitive of the three. Another disadvantage of blood tests is that about six weeks are required for analysis; by the time the physician receives the results, the patient has already recovered or died.
Plumbing systems, first blamed for a nosocomial case of Legionnaires’ Disease in 1980, have since been implicated in numerous outbreaks. Of 20 hospital outbreaks of Legionnaires’ in the United Kingdom from 1980 to 1992, 19 were blamed on plumbing systems, according to the British Communicable Disease Surveillance Centre. Cases of Legionnaires’ have been attributed to plumbing systems in nursing homes, workplaces and private residences.
Plumbing systems provide a perfect habitat for legionellae. Legionellae can flourish in a hot-water tank, especially at the bottom, where a warm zone sometimes develops and scale and sediment accumulate. Piping presents an even more complex problem than tanks. Biofilm and scale that form in valves and fittings and on pipe walls not only feed legionellae but also protect them from hot water and chemical disinfectants. Biofilm is a slimy structure that is formed as microbes attach to underwater surfaces. As biofilm grows, fragments of it break off and flow into the water, releasing potentially high levels of legionellae into the system. Dead areas in the system also contribute to the problem because legionellae grow well in stagnant water.
Designing, operating and maintaining plumbing systems to prevent legionellae growth is crucial for reducing the risk of the disease. The objectives of most preventive measures are to avoid water temperatures in which legionellae grow best; eliminate scale, sediment or biofilm; avoid materials that provide food sources for legionellae; minimize water stagnation; or prevent legionellae transmission from water to people. (For specific recommendations, see “Legionella: Preventive Measures for Domestic Water Systems,” PM Engineer, Nov. 1997.) Preventive measures do not always control the disease, particularly in systems with scale and biofilm, so disinfection procedures are sometimes necessary.
An Update on Legionnaires’ Disease and Legionellae ControlPublic Awareness. Last November, “CNN & TIME,” a TV news magazine, aired a segment on Legionnaires’ Disease in hospitals. CNN reported that “every year, thousands of patients contract [Legionnaires’] Disease from contaminated hospital water systems.” The show included an interview with Dr. Victor Yu, a Legionnaires’ expert from the VA Medical Center in Pittsburgh.
“These outbreaks—they’re actually occurring all through the country every week,” Yu said. “It’s an explosive problem to realize that people are dying, to realize that the means are there for preventing all this from happening and that those means are not being exercised.” Indeed, more people are learning that Legionnaires’ Disease is widespread, and that preventive measures are not implemented in most buildings.
Outbreaks. The biggest outbreak of the year—and one of the biggest ever—occurred in the Netherlands in late February to early March 1999. It involved 242 cases of illness and 28 deaths. The outbreak was blamed on a whirlpool spa displayed at a trade show. Briefs on recent outbreaks are posted at www.hcinfo.com/outbreaks-news.htm.
Patient Testing. A new 15-minute test (by Binax Inc., www.binax.com) for a common strain of Legionella makes patient testing easy, which should result in more testing and more diagnoses. As more cases are detected, more attention will be given to cleaning plumbing systems and other potential sources of contamination.
Lawsuits. Legionnaires’ Disease is conducive to lawsuits; several are in process at this time. A case of Legionnaires’ can be linked to an environmental source (e.g., a plumbing system) by comparing the Legionella strain found in the victim to the strain found in a water sample. This may allow a plaintiff to rule out some water supplies (e.g., in the victim’s house) and implicate others (e.g., in the defendant’s building) as the source of the legionellae that caused the illness—similar to the way DNA tests are used to link criminal defendants to a murder scene. In a health facility, the length of a patient’s stay is another factor. Since a person gets Legionnaires’ Disease usually within two to 10 days after exposure, a hospital or nursing home will be recognized as the source of contamination if a victim is diagnosed with the disease after a stay of 11 or more days.
Water Sampling. The debate continues on whether or not to test water routinely for legionellae. CDC guidelines do not include a recommendation for routine sampling unless cases of the disease have been identified, but CDC officials have suggested recently that routine testing may be appropriate in hospitals that treat high-risk patients. Some building owners voluntarily test plumbing systems and cooling towers for Legionella in order to check preventive measures and establish a defense against lawsuits.
New Disinfection Technology. In plumbing systems, copper-silver ionization has outperformed chlorine, partly because of its apparent ability to disinfect systems laden with biofilm. Studies indicate chlorine dioxide is also more effective than chlorine, plus lower in cost, less harmful to ingest and less likely to cause pipe leaks. Suppliers claim it even removes biofilm over time. Chlorine dioxide has been used in drinking water in the United Kingdom, but is still uncommon in the United States, partly because of concerns about the safety of onsite generation. But new technology (by Halox in Chalfont, PA) makes the chlorine dioxide generation process much safer than before, so it may soon gain acceptance here. Look for reports on studies of actual plumbing systems rather than laboratory models.
Information. A free Legionella newsletter, sent by e-mail about once a month, covers new technology for legionellae control, outbreak briefs and new findings on Legionnaires’ Disease. To subscribe, go to www.hcinfo.com (the Web site of HC Information Resources) and click on “Subscribe to Legionella E-news.” Also, Denis Green of Australia has formed a Legionnaires’ discussion group. To participate, go to www.egroups.com/group/legionnaires_disease/.
Regulations. The New York State Department of Health was to send a letter of Legionnaires’ recommendations to some 250 hospitals and 650 nursing homes in January. A NYDOH official said it is recommending routine sampling in hospitals that treat high-risk patients. The State of Maryland has also begun the process of drafting Legionnaires’ guidance.