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FAQ's Regarding Legionnaires' Disease

WHAT IS LEGIONELLOSIS (LEGIONNAIRES' DISEASE)?

Legionnaires' disease is a type of pneumonia that is caused by Legionella, a bacterium found primarily in warm water environments. Both the disease and the bacterium were discovered following an outbreak traced to a 1976 American Legion convention in Philadelphia. Pontiac fever, a flu-like illness, is also caused by Legionella organisms (legionellae), but is not as serious as Legionnaires' disease. Most people who get Pontiac fever recover within five days, without having to be hospitalized.

HOW SEVERE IS THE ILLNESS?

The severity of legionellosis can range from a mild respiratory illness (Pontiac fever) to pneumonia (Legionnaires' disease). Up to 20% of healthy adults have antibodies showing previous exposure to the bacteria, but only a small percentage have a history of previous pneumonia. Fatality rates for persons with Legionnaires' disease can be as high as 15%. Persons with Pontiac fever generally recover in 2-5 days without treatment.

WHERE ARE LEGIONELLA BACTERIA FOUND?

Legionella can be found in any type of water system. They have been found in the environment in creeks and ponds. The bacteria are prevalent in warm stagnant water (90°-105° F), such as those found in most plumbing systems, hot water tanks, water in cooling towers, evaporative condensers of large air conditioning systems and hot tubs. Home and automobile air conditioners are NOT a source of legionella bacteria. The most common amplifiers and disseminators of the Legionella bacteria are:

  • Cooling Towers
  • Evaporative Condensers
  • Domestic Hot Water Systems
  • Spas and Whirlpools
  • Humidifiers
  • Decorative Fountains and Waterscapes
  • Reservoir Misters In Supermarkets
  • Portable Cooling Units With Stagnant Water
  • Faucets and Showerheads
  • Condensate Drip Pans
  • Safety Showers and Eyewash Stations
  • Fire Sprinkler Systems

WHO GETS LEGIONELLOSIS?

The disease occurs most frequently in older adults. The disease most often affects those who smoke heavily, have chronic lung disease or have underlying medical conditions that lower their immune system resistance to disease such as diabetes, cancer or renal dysfunction. Persons taking certain drugs that lower their immune system resistance, such as steroids, have an increased risk of being affected by legionellosis.

HOW SOON DO SYMPTOMS OCCUR?

The period between exposures and onset of illness for Legionnaires' disease is 2-10 days, but most often 5-6 days; for Pontiac fever it is 5-6 hours, but most often 24-48 hours.

WHAT IS THE TREATMENT FOR LEGIONELLOSIS?

Antibiotics such as erythromycin are effective for treating Legionnaires' disease, especially when cases are detected early. Pontiac fever requires no specific treatment.

WHAT ARE THE SYMPTOMS OF LEGIONNAIRES' DISEASE?

Legionnaires' disease develops within 2 to 10 days after exposure to legionellae. Initial symptoms may include loss of energy, headache, nausea, aching muscles, high fever (often exceeding 104°F), and chest pains. Later, many bodily systems as well as the mind may be affected. The disease eventually will cause death if the body's high fever and antibodies cannot defeat it. Victims who survive may suffer permanent physical or mental impairment.

IS LEGIONNAIRES DISEASE COMMON?

Legionnaires' is not rare. It is perceived as rare only because most cases are never detected, and not all detected cases are reported to public health authorities. Because underdiagnosis and under-reporting make incidence of the disease difficult to estimate, figures have varied widely. The (U.S.) Centers for Disease Control and Prevention (CDC), 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. Another reason that Legionnaires' is falsely perceived as rare is that when cases are detected, the public rarely hears about them. Most cases—at least 65 to 80 percent in the United States and the United Kingdom—occur sporadically (one or two at a time). Thus, only a small percentage of cases occur as part of the multicase outbreaks that sometimes make the news. Cases of the disease are seldom publicized even when lawsuits are involved, because most Legionnaires' lawsuits are settled quickly and under terms of confidentiality. A case of Legionnaires' disease will go undetected unless special laboratory tests are performed. Unfortunately, most U.S. hospitals still have not made these tests routinely available. It is reasonable to assume that undetected cases of Legionnaires' are occurring because experience has shown that increased suspicion of the disease among physicians, when combined with increased patient testing, leads to more diagnoses. Some hospitals have recognized cases of Legionnaires' disease only after increased testing of patients with pneumonia. Likewise, in hospitals where only one to three cases of Legionnaires' were identified over several months, numerous additional cases were recognized after surveillance was intensified. Studies of community-acquired pneumonia (cases acquired outside hospitals) have also indicated that increased surveillance leads to more diagnoses. A large-scale study in Ohio (U.S.A.) suggested that only 3 percent of sporadic cases of Legionnaires' disease were correctly diagnosed. By comparison, in studies in which diagnostic tests have been consistently used, Legionella has been recognized among the top three or four microbial causes of community-acquired pneumonia. Because the symptoms of Legionnaires' are similar to those of other types of pneumonia, undetected cases of Legionnaires' disease end up being classified merely as pneumonia with no apparent cause. Based on CDC estimates, this means that 8 to 39 pneumonia deaths occur each week in the United States 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 hot-water 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.

HOW DOES A PERSON GET LEGIONNAIRES' DISEASE?

Legionnaires' disease is contracted by inhaling airborne water droplets containing legionellae. Some investigators believe that the disease may be acquired also by drinking legionellae-contaminated water, particularly if legionellae aspirated from the water are inhaled before the water enters the stomach. Cases have also been blamed on contact between contaminated water and incisions or skin wounds. The disease is not contagious.

WHO IS AT RISK OF CONTRACTING LEGIONNAIRES DISEASE?

The risk of infection is based on two key factors: the number of legionellae reaching the body and the resistance of the individual. Young and healthy people can get Legionnaires' disease, but persons who are immunocompromised either because of illness (e.g., cancer) or medical treatment (e.g., chemotherapy) are at a much higher risk because they can be infected by relatively low legionellae counts. HIV-infected patients, for example, have a 40-fold increased risk; organ transplant recipients have a 200-fold increased risk. Smokers, persons over 65 years of age, and heavy drink have a moderately higher risk. Children have contracted Legionnaires' disease. Most cases have occurred in immunosuppressed children, but a number of immunocompetent children, particularly newborns, have acquired the disease, most often after surgeries, or through the use of legionellae-contaminated ventilators.

WHAT IS THE DEATH RATE?

Underlying disease and advanced age not only increase the risk of contracting Legionnaires' disease but also the risk of dying from it, so it is not surprising that a CDC study of reported cases indicated a death rate of 40 percent for cases acquired during a hospital stay (nosocomial cases), but a death rate of 20 percent for community-acquired cases. Some outbreaks have claimed more than 50 percent.

CAN THE RISK OF LEGIONNAIRES' DISEASE BE DETERMINED BY GEOGRAPHICAL LOCATION?

No. Legionnaires' disease is not specific only to certain areas. Although some areas have reported more cases of LD than other areas, the geographic location is relatively insignificant. What's more, the number of cases reported from a given area could indicate the level of awareness among physicians and the availability of laboratory testing, as opposed to the level of legionellae in the water supply. Legionella contamination is usually tied to the condition of a building's mechanical system, which is independent of geographical location.

WHAT IS THE SIZE OF LEGIONELLA ORGANISMS?

The average Legionella cell is 0.5-1.0 micrometer wide and 1.0-3.0 micrometers long (Barbaree, J. M. "Controlling Legionella in Cooling Towers," ASHRAE Journal, June 1991; 38-42).

WHAT ARE THE LONG-TERM SIDE EFFECTS OF LEGIONNAIRES DISEASE? I HEARD ASTHMA IS ONE SIDE EFFECT.

As with any acute illness, patients who recover from Legionnaires' disease can suffer long-term side effects. The most common are fatigue and lack of energy for several months. However, asthma of new onset is uncommon, although I know of a few cases who have persistent chest x-ray abnormalities with sustained wheezing. It is unclear as to whether this can be blamed solely on Legionnaires' disease; asthma may be due to a number of stresses besides Legionnaires' disease. Answer provided by Victor L. Yu, MD, Professor of Medicine, University of Pittsburgh; Chief, Infectious Disease Section, VA Medical Center, Pittsburgh, PA, USA.

ARE CERTAIN TYPES OF BUILDINGS MORE PRONE THAN OTHERS TO HAVE PROBLEMS WITH LEGIONELLAE?

Cases of Legionnaires' disease have been linked to many types of equipment that contain water, but plumbing systems and air conditioning systems are most often blamed. Although it is possible to contract the illness from legionellae growing in home plumbing systems, most cases have been traced to large buildings. This may be because larger piping networks are generally more conducive to legionellae growth. Also, the air conditioning systems for large buildings often include cooling towers, which contain a pool of warm water in which legionellae can flourish.

WHAT PRECAUTIONS CAN BE TAKEN TO PREVENT LEGIONNAIRES' DISEASE?

Legionnaires' is considered an environmental disease because its causative agent (legionellae) is transmitted from an environmental source (water) to a person (in contrast with communicable diseases, such as AIDS, which are transmitted from person to person). Therefore, keeping legionellae out of water is the key to preventing the disease. For example, plumbing systems can be maintained to minimize the growth of legionellae. And if preventive measures alone do not control the bacteria, disinfection procedures can be implemented.

HOW CAN I REDUCE MY RISK OF GETTING LEGIONNAIRES' DISEASE?

You can reduce your risk of Legionnaires' disease by (a) lowering your susceptibility to infection and (b) avoiding exposure to Legionella bacteria. The most important factor in lowering your susceptibility to infection is to stop smoking. Among persons who are not immunocompromised, smoking is the number one factor in acquiring Legionnaires disease. A study of 146 adults with Legionnaires' disease indicated that smoking sharply increased the risk of contracting the disease. As for avoiding exposure to legionellae, you have several options. Some measures cost nothing and should be implemented out of good sense. Expensive measures could be a waste of money for healthy nonsmoking adults, who are at low risk of contracting Legionaries disease. High-risk individuals, however, should consider taking every reasonable precaution. For more information on avoiding exposure to legionellae in public places, see our electronic publication entitled How to reduce your risk of Legionnaires' disease in public places. For information on reducing your exposure to legionellae at home, see our publications for homes.

WHAT PRECAUTIONS SHOULD BE TAKEN IN WORKING ON COOLING TOWERS?

Experts recommend wearing a high-efficiency particulate air (HEPA) protective mask while cleaning cooling towers or collecting samples from them, unless the tower fans are shut off, especially if legionellae contamination is suspected or hyperchlorination is in process. Full masks allow less leakage and thus filter more than half masks. A good fit is critical with any mask. Be aware, however, that HEPA filters will not block all bacteria. Gloves, goggles, and other body coverings have also been suggested for cooling tower work.

HOW IS LEGIONELLOSIS DIAGNOSED?

The diagnosis of legionellosis requires special tests not routinely performed on persons with fever or pneumonia. Therefore, a physician must consider the possibility of legionellosis in order to obtain the right tests. Several types of tests are available. The most useful tests detect the bacteria in sputum, find Legionella antigens in urine samples, or compare antibody levels to Legionella in two blood samples obtained 3 to 6 weeks apart.

WHAT IS BEING DONE TO PREVENT LEGIONELLOSIS?

Improved design and maintenance of cooling towers and plumbing systems to limit the growth and spread of Legionella organisms are the foundations of legionellosis prevention.

During outbreaks, CDC and health department investigators seek to identify the source of disease transmission and recommend appropriate prevention and control measures, such as decontamination of the water source. Current research will likely identify additional prevention strategies.



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