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A. 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. Return to top
A. 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. Return to top
A. 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. Return to top
A. Erythromycin and Azithromycin, antibiotics, have been effective, especially when cases are detected early. Return to top
A. 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. Return to top
A. 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 drinkers have a moderately higher risk.
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A. 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, Unviersity of Pittsburgh; Chief, Infectious Disease Section, VA Medical Center, Pittsburgh, PA, USA.Return to top
Q. I have had Legionnaire's disease and been treated with large doses of erythromycin. The disease nearly killed me. My temperature was 107 degrees F; I was at death's door. Luckily, I had a physician who stayed by my side for days and suspected Legionnaire's. After having a near-death experience, I want to make sure that this never happens to me or any of my loved ones again. Is there any chance that the bacteria are still in my system, remaining a threat? Deborah Newman
A. I am sorry that you had such a punishing experience with Legionnaires' disease (LD) , but I am also thankful that you survived since the mortality can be high. The answer to your question has only been clearly elucidated in the last decade. In 1978, when I saw my first case, we wondered if this could occur and our blood antibody tests suggested that it might have occurred in two patients. But, more complete studies with newer and more powerful lab tests have shown that once you are cured with antibiotics, the bacteria are cleared. So, you do not have to worry about this. We have data on the largest collection of patients with LD in the world and have followed them for many years. Somewhat to our surprise, virtually none of them have become reinfected. Apparently, they developed immunity with their first infection. It appears that you have some residual protection if you contract Legionnaire's disease; however, the most effective method of prevention is stopping cigarette smoking. Smokers are much more likely to contract LD (as they are to contract other respiratory infections including the flu). Fever exceeding 104.5 is a hallmark of LD, so you should thank your MD for making that fine diagnosis. Answer provided by Victor L. Yu, MD, Professor of Medicine, Unviersity of Pittsburgh; Chief, Infectious Disease Section, VA Medical Center, Pittsburgh, PA, USA. Return to top
Q. I have a friend who has been diagnosed with Legionnaires disease and is in the critical care department of a local hospital. Is this a disease that is mandated to be reported to the (U.S.) CDC? Will there be follow up on the source of the bacteria?
A. In the United States, Legionaires' disease is a reportable disease by law to the local public health department and the CDC. Most health departments will not do a follow-up unless many patients contract the illness. Answer provided by Victor L. Yu, MD, Professor of Medicine, Unviersity of Pittsburgh; Chief, Infectious Disease Section, VA Medical Center, Pittsburgh, PA, USA.Return to top
A. The plumbing system (via showers and faucets), whirlpool spas and bathtubs, and humidifiers present a potential risk of legionellae exposure in homes. A number of measures can be taken to minimize legionellae growth. The long list of risk reduction options for homes cannot be covered in this brief FAQ. Return to top
A. 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. Return to top
A. 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. Return to top
A. 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 Legionaires disease. High-risk individuals, however, should consider taking every reasonable precaution. For information on avoiding exposure in public places and at home, see the book Protect Yourself from Legionnaires' Disease: The waterborne illness that continues to kill and harm. Return to top
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