Legionella: Water culture advocates defend practice
CDC taken to task for discouraging routine testing
Challenging current infection control recommendations to the contrary, advocates of routine culturing for legionella in hospital water distribution systems say the practice can help identify and prevent nosocomial Legionnaires' disease in high-risk patients.
Indeed, the Centers for Disease Control and Prevention position not to endorse the practice in its nosocomial pneumonia guidelines was strongly questioned by a veteran legionella researcher recently in Washington, DC, at the annual conference of the Society for Healthcare Epidemiology of America (SHEA).1
"The whole idea is prevention -- isn't CDC supposed to be [the] Centers for Disease Control and Prevention?" said Victor Yu, MD, chief of infectious disease at Veterans' Administration Medical Center in Pittsburgh. "I advocate culturing the water supply because it will give us information as to whether or not we can prevent the disease."
Use Allegheny County guidelines
Yu recommended using water culturing and laboratory analysis guidelines developed by Allegheny County public health officials in Pittsburgh.2 (See guidelines and flowcharts, pp. 74-76.) Indeed, three Pittsburgh-area hospitals that followed the guidelines found positive cultures in water and cases of Legionnaires' disease in patients, reported Angela Goetz, RN, MNEd, CIC, infection control practitioner at the Pittsburgh VA Medical Center.
A total of 15 cases of Legionnaires' disease were diagnosed, including 12 caused by the highly pathogenic serogroup 1. Positive diagnostic tests results included urinary antigen, respiratory tract cultures, and serologies. Molecular typing available from two of the hospitals confirmed the source of the patient infection was the water supply, Goetz reported, adding that water decontamination was done by all three hospitals.
"These were three non-teaching community hospitals which had never identified nosocomial legionella before," she told SHEA attendees. ". . . We encourage the use of guidelines similar to those developed by the Allegheny County health department to ascertain if legionella exists in all medical facilities. Remember, if you look for it, you will find it."
That may be part of the problem from the CDC perspective. In general, the CDC guidelines recommend initiating a epidemiologic investigation that would include water system culturing after one laboratory-confirmed case of nosocomial Legionnaires' disease or two suspected cases. Routine water culturing is not supported by current data -- some of which suggest that the pathogen is ubiquitous in water supplies and natural reservoirs, and may be present in hospital systems without causing disease, according to the CDC.
"The level of risk of transmission in buildings where legionella is isolated from the water is not clearly defined," said Robert Breiman, MD, medical epidemiologist in the CDC division of childhood and respiratory diseases. Representing the CDC position in a SHEA debate with Yu, Breiman also warned that finding legionella species in hospital water -- even in the absence of associated infections -- opens the door to public overreaction and costly decontamination efforts that may not be necessary.
"We get these calls all of the time, and many of you are probably familiar with this, too, where there is a hysterical response -- inappropriately so -- when legionella are isolated from the water in the building," he told SHEA attendees. "Oftentimes recently, there have been a number of circumstances where people have demanded that the facility close until the site can be certified. . . . So without knowing what the attributable risk is, at least, one has to consider the fact that finding the bug in the water will lead to a certain cascade of events."
There also may be natural fluctuations in the concentration of legionella in the water, and laboratory test reliability may vary, he added.
"So a negative [test] result doesn't necessarily mean that legionella isn't there or won't be there tomorrow," he said. "Rapid blooms of legionella in water can lead to explosive outbreaks of Legionnaires' disease."
A troublesome pathogen
Indeed, despite the questions about water testing, there is little debate that legionella has caused considerable morbidity, mortality, and expense in common-source hospital outbreaks. Multiplying by taking over the "internal machinery" of host amoeba, the pathogen flourishes in water temperature that range from 78° to 105° F, Breiman noted. If the water reservoir is connected to a device that is capable of producing an aerosol -- such as showerheads, whirlpools, humidifiers, or faucets --legionella can be inhaled as respirable droplets. High-risk patients for infection include those immunocompromised due to HIV, chronic lung disease, the elderly, and transplant recipients. There are levels of risk within those groups, as HIV-infected patients have an estimated 40-fold increased risk of infection, and organ transplant recipients have a 200-fold increased risk. Overall, the CDC estimates that somewhere between 1% to 5% of all community-acquired pneumonia is due to legionella.
"About 10,000 to 15,000 cases occur annually in the United States, yet less than 10% are diagnosed," Breiman said. "No one really knows what the incidence is of nosocomial Legionnaires' disease. There is really not a very effective, comprehensive database on which one could establish that."
Yu argued that many of those nosocomial cases could be identified if hospital infection control programs routinely cultured potable water distribution systems, raised suspicion for cases, and beefed up in-house laboratory capabilities or linked up with outside reference labs. Patient, meticulous investigation will ultimately link cases in patients back to the hospital potable water supply, he emphasized.
"It's the effect of time when the index of suspicion gets higher," he said. "We have it -- we've found the reservoir. For how many diseases can we identify the reservoir so precisely?"
Addressing cost issues, Yu noted that a 500-bed hospital could spend as little as $32 for materials to test 15 distal water sites and all hot water tanks. Sending samples to a commercial reference laboratory would raise the cost another $400-$500, he noted. While Breiman raised questions about the subsequent cost and efficacy of the various water decontamination systems, Yu underscored the costs and liability associated with a single serious infection.
"If a heart transplant patient dies of Legionnaires' disease, he not only lost his life, but $90,000 to $200,000 were spent in that transplant," he said, adding that lawsuits resulting from such cases are usually settled in the "six figure" range.
Yu also implied the CDC selectively cited data and studies in its guidelines that favor its position, but Breiman denied the agency had any vested interest in whether hospitals culture water or not.
"We don't have any specific bias," he said. ". . . CDC does not just do things in order to appear to be preventing something. Basically, there really needs to be some good justification. People rely on us for careful, rational consideration of existing data and to make recommendations that will lead to measurable prevention and not just an expenditure of money."
Advocating a multifactorial approach, Breiman reminded that large buildings in particular are likely to become contaminated with legionella at some point, and ongoing maintenance should included raising water temperatures to the safest permissible level, keeping cooling towers disinfected, and using sterile water for respiratory therapy equipment.
"One might also culture the water periodically," he conceded. "Our perspective about this is that it isn't a bad thing to do as long as someone is aware of the other side of it; that by doing that, one could create a problem. You might not necessarily be finding information that is going to help you prevent further cases of disease, and it may end up costing you a fair bit."
While some in the SHEA audience noted a standing position against water culturing would certainly be open to critical questioning after a patient was infected, others pointed out that a routine culturing policy does not ensure prevention. John Sellick, MD, epidemiologist at Buffalo (NY) General Hospital, cited an anecdotal account of a legionella infection occurring within a month of negative water culturing of the implicated water fixture in a patient's room.
"We do routine culturing on a somewhat periodic basis, but I have been jaded against relying on it entirely," he said.
References
1. Centers for Disease Control and Prevention. Hospital Infection Control Practices Advisory Committee. Guideline for prevention of nosocomial pneumonia. Infect Control Hosp Epidemiol 1994; 15:587-627.
2. Allegheny County Health Department. Approaches to Prevention and Control of Legionella Infection in Allegheny County Health Care Facilities. Pittsburgh; 1993. *
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