Legionnaires' disease is a form of atypical pneumonia caused by any species of Legionella bacteria, quite often Legionella pneumophila. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Nausea, vomiting, and diarrhea may also occur. This often begins 2–10 days after exposure.
A legionellosis is any disease caused by Legionella, including Legionnaires' disease (a pneumonia) and Pontiac fever (a related upper respiratory tract infection), but Legionnaires' disease is the most common, so mentions of legionellosis often refer to Legionnaires' disease.
Legionella is found naturally in fresh water. It can contaminate hot water tanks, hot tubs, and cooling towers of large air conditioners. Typically, it is spread by breathing in mist that contains Legionella, and can also occur when contaminated water is aspirated. It typically does not spread directly between people, and most people who are exposed do not become infected. Risk factors for infection include older age, a history of smoking, chronic lung disease, and poor immune function. Those with severe pneumonia and those with pneumonia and a recent travel history should be tested for the disease. Diagnosis is by a urinary antigen test and sputum culture.
No vaccine is available. Prevention depends on good maintenance of water systems. Treatment of Legionnaires' disease is commonly conducted with antibiotics. Recommended agents include the fluoroquinolones levofloxacin and moxifloxacin, and the macrolide azithromycin. Hospitalization is often required. The fatality rate is around 10% for previously healthy people, but up to 25% in those with underlying conditions.
The numbers of cases that occur globally is not known. Legionnaires' disease is the cause of an estimated 2–9% of pneumonia cases that are acquired outside of a hospital. An estimated 8,000 to 18,000 cases a year in the United States require hospitalization. Outbreaks of disease account for a minority of cases. While it can occur any time of the year, it is more common in the summer and autumn. The disease is named after the outbreak where it was first identified, at a 1976 American Legion convention in Philadelphia.
Signs and symptoms The length of time between exposure to the bacteria and the appearance of symptoms (incubation period) is generally 2–10 days, but more rarely can extend to as long as 20 days. For the general population, among those exposed, between 0.1 and 5.0% develop the disease, while among those in hospital, between 0.4 and 14% develop the disease.
Those with Legionnaires' disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Almost all experience fever, while around half have cough with sputum, and one-third cough up blood or bloody sputum. Some also have muscle aches, headache, tiredness, loss of appetite, loss of coordination (ataxia), chest pain, or diarrhea and vomiting. Up to half of those with Legionnaires' disease have gastrointestinal symptoms, and almost half have neurological symptoms, including confusion and impaired cognition. "Relative bradycardia" may also be present, which is low to normal heart rate despite the presence of a fever.
Laboratory tests may show that kidney functions, liver functions, and electrolyte levels are abnormal, which may include low sodium in the blood. Chest X-rays often show pneumonia with consolidation in the lower portion of both lungs. Distinguishing Legionnaires' disease from other types of pneumonia by symptoms or radiologic findings alone is difficult; other tests are required for definitive diagnosis.
People with Pontiac fever, a much milder illness caused by the same bacterial genus, experience fever and muscle aches without pneumonia. They generally recover in 2–5 days without treatment. For Pontiac fever, the time between exposure and symptoms is generally a few hours to two days.
Cause
Over 90% of cases of Legionnaires' disease are caused by Legionella pneumophila. Other types include L. longbeachae, L. feeleii, L. micdadei, and L. anisa.
Transmission Legionnaires' disease is usually spread by the breathing in of aerosolized water or soil contaminated with the Legionella bacteria. Experts have stated that Legionnaires' disease is not transmitted from person to person. In 2014, one case of possible spread from someone sick to the caregiver occurred. Rarely, it has been transmitted by direct contact between contaminated water and surgical wounds. The bacteria grow best at warm temperatures and thrive at water temperatures between , with an optimum temperature of . Temperatures above kill the bacteria. Sources where temperatures allow the bacteria to thrive include hot water tanks, cooling towers, and evaporative condensers of large air conditioning systems, such as those commonly found in hotels and large office buildings. Before 1988, energy conservation programs from the late 1970s and early 1980s still mandated a maximum hot water generation, storage, and distribution temperature of , unknowingly Legionella bacteria's ideal breeding temperature. To minimize risks of bacterial growth, the American Society of Heating, Refrigerating and Air-Conditioning Engineers' 1988 ASHRAE Standard 188 and subsequent ASHRAE Guideline 12-2000 increased recommended hot water generation and storage temperatures to with minimum distribution temperatures of .
Though the first known outbreak was in Philadelphia, cases of legionellosis have occurred throughout the world.
Reservoirs
L. pneumophila thrives in aquatic systems, where it is established within amoebae in a symbiotic relationship. Legionella bacteria survive in water as intracellular parasites of water-dwelling protozoa, such as amoebae. Amoebae are often part of biofilms, and once Legionella and infected amoebae are protected within a biofilm, they are particularly difficult to destroy.
In the built environment, central air conditioning systems in office buildings, hotels, and hospitals are sources of contaminated water. Other places the bacteria can dwell include cooling towers used in industrial cooling systems, evaporative coolers, nebulizers, humidifiers, whirlpool spas, hot water systems, showers, windshield washers, fountains, room-air humidifiers, ice-making machines, and misting systems typically found in grocery-store produce sections.
The bacteria may also be transmitted from contaminated aerosols generated in hot tubs if the disinfection and maintenance programs are not followed rigorously.Silivanch v. Celebrity Cruises, Inc., 171 F.Supp.2d 241 (S.D.N.Y. 2001) (plaintiff successfully sued cruise line and manufacturer of filter after catching disease on cruise) Freshwater ponds, creeks, and ornamental fountains are potential sources of Legionella. The disease is particularly associated with hotels, fountains, cruise ships, and hospitals with complex potable water systems and cooling systems. Respiratory-care devices such as humidifiers and nebulizers used with contaminated tap water may contain Legionella species, so using sterile water is very important. Other sources include exposure to potting mix and compost.
Mechanism Legionella species enter the lungs either by aspiration of contaminated water or inhalation of aerosolized contaminated water or soil. In the lung, the bacteria are consumed by macrophages, a type of white blood cell, inside of which the Legionella bacteria multiply, causing the death of the macrophage. Once the macrophage dies, the bacteria are released from the dead cell to infect other macrophages. Virulent strains of Legionella kill macrophages by blocking the fusion of phagosomes with lysosomes inside the host cell; normally, bacteria are contained inside the phagosome, which merges with a lysosome, allowing enzymes and other chemicals to break down the invading bacteria.
Diagnosis
People of any age may develop Legionnaires' disease, but the illness most often affects middle-aged and older people, particularly those who smoke cigarettes or have chronic lung disease. Immunocompromised people are also at higher risk. Pontiac fever most commonly occurs in those who are otherwise healthy.
The most useful diagnostic tests detect the bacteria in coughed-up mucus, find Legionella antigens in urine samples, or allow comparison of Legionella antibody levels in two blood samples taken 3–6 weeks apart. A urine antigen test is simple, quick, and very reliable, but only detects L. pneumophila serogroup 1, which accounts for 70% of disease caused by L. pneumophila, which means use of the urine antigen test alone may miss as many as 30% of cases. This test was developed by Richard Kohler in 1982. When dealing with L. pneumophila serogroup 1, the urine antigen test is useful for early detection of Legionnaire's disease and initiation of treatment, and has been helpful in early detection of outbreaks. However, it does not identify the specific subtypes, so it cannot be used to match the person with the environmental source of infection. The Legionella bacteria can be cultured from sputum or other respiratory samples. Legionella spp. stain poorly with Gram stain, stain positive with silver, and are cultured on charcoal yeast extract with iron and cysteine (CYE agar).
A significant under-reporting problem occurs with legionellosis. Even in countries with effective health services and readily available diagnostic testing, about 90% of cases of Legionnaires' disease are missed. This is partly due to the disease being a relatively rare form of pneumonia, which many clinicians may not have encountered before, thus may misdiagnose. A further issue is that people with legionellosis can present with a wide range of symptoms, some of which (such as diarrhea) may distract clinicians from making a correct diagnosis.
Prevention Although the risk of Legionnaires' disease being spread by large-scale water systems cannot be eliminated, it can be greatly reduced by writing and enforcing a highly detailed, systematic water safety plan appropriate for the specific facility involved (office building, hospital, hotel, spa, cruise ship, etc.) Some of the elements that such a plan may include are: Keep water temperature either below or above the range in which the Legionella bacterium thrives. Prevent stagnation, for example, by removing from a network of pipes any sections that have no outlet (dead ends). Where stagnation is unavoidable, as when a wing of a hotel is closed for the off-season, remedial measures are recommended, e.g., maintaining elevated temperatures throughout the hot-water distribution system and periodic disinfection or permanent chlorination of cold-water systems. Prevention of biofilms is crucial because once established they become more difficult to remove from piping systems. The likelihood of formation is increased by pipe scale and corrosion; warm water temperatures; stagnation and the quantity of nutrients that enter the system. Periodically disinfect the system, by high heat or a chemical biocide, and use chlorination where appropriate. Monochloramine is likely more effective than free chlorine (sodium hypochlorite), being more resistant with residuals likely to persist to the point of delivery. Monochloramine is also more likely to penetrate legionella biofilms. Treatment of water with copper-silver ionization or ultraviolet light may also be effective. System design (or renovation) can reduce the production of aerosols and reduce human exposure to them, by directing them well away from building air intakes.