West Virginia
Infectious Disease Epidemiology Program
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Public Health Action
Disease Control ObjectivesPrevent additional cases of legionellosis by early recognition and investigation of outbreaks of legionellosis so that control measures can be applied in a timely fashion. Disease Prevention ObjectivesThere is very little that can be done to prevent sporadic cases of legionellosis at the community level. Early identification of outbreaks can prevent occurrence of additional cases if a thorough investigation is performed and a common source is identified. Surveillance Objectives
Public Health SignificanceLegionnaires' disease accounts for two to 15% of cases of community acquired pneumonia. Due to difficulty with diagnosis and ready availability of broad spectrum antibiotics effective against Legionella, the disease is often under-diagnosed and under-reported. Since the dramatic outbreak at the American Legion Convention in Philadelphia in 1976, large community based outbreaks and nosocomial outbreaks of legionellosis have been documented. Mortality ranges from five to 15%; higher mortality rates have occurred in nosocomial outbreaks. Outbreaks have been recognized in association with cooling towers, potable water, whirlpools, humidifiers, fountains, grocery store misters, and other sources of water aerosol. Clinical DescriptionLegionellosis is a bacterial disease that is more common in adults over the age of 50 and is extremely rare in those under age 20. Most cases occur in males, with an estimated male:female ratio of 2.5:1. Legionella can cause two clinically distinct syndromes: Legionnaires' disease and Pontiac fever. Legionnaires' disease is a type of pneumonia which may be accompanied by fever, cough, and chest pain. Classified among the atypical pneumonias, early symptoms may include low grade fever, malaise, anorexia, headaches, and myalgias. Gastrointestinal symptoms are sometimes prominent in the early phase of illness and may lead to delayed recognition. Patients with severe disease may progress to stupor, respiratory failure, and multiorgan failure. The case-fatality rate may be as high as 39% in some hospitalized patients. By contrast, Pontiac fever results in flu-like symptoms that spontaneously resolve without treatment in two to five days. This syndrome is usually recognized only in association with outbreaks. The table below provides a quick comparison of the two syndromes:
Etiologic AgentLegionellae bacteria is associated with Legionnaires' disease and Pontiac fever. Forty-three species of Legionella with at least 65 serogroups have been identified. Legionella pneumophila serogroup 1 is most commonly associated with disease. ReservoirThis bacteria has been isolated in water from hot water systems, air conditioning cooling towers, evaporative condensers, humidifiers, whirlpool spas, respiratory therapy devices, decorative fountains, hot and cold water taps and showers, and hot tubs. Legionella has also been isolated in creeks, ponds, and soil from their banks. Testing of environmental sources is expensive and should not be undertaken unless the source is implicated through an epidemiological investigation. Mode of TransmissionLegionella transmission is airborne through contaminated aerosols and possibly through aspiration of contaminated water. There is no person-to-person transmission. Incubation PeriodThe incubation period for Legionnaires' disease is two to 10 days, usually five to six days. The incubation period for Pontiac fever is five to 66 hours, usually 24 to 48 hours. Infectious PeriodLegionella is not transmitted person-to-person. Outbreak RecognitionOutbreaks of Legionella pneumonia have been associated with contaminated cooling towers and evaporative condensers, showers, decorative fountains, humidifiers, respiratory therapy equipment, and whirlpool spas. Outbreaks may present to public health as reports of increased numbers of cases of pneumonia, sometimes without a specific diagnosis. Prompt investigation must include case-finding, case confirmation, and a detailed review of all the patient's activities during the two to 10 days prior to onset of symptoms. These investigations are difficult and time consuming; however, community based outbreaks of legionellosis are associated with substantial mortality, so the quality and timeliness of the investigation is important. By contrast, outbreaks of Pontiac fever present as an outbreak of influenza-like illness (usually in healthy adults) shortly after a common exposure. Sporadic cases and outbreaks of Legionella are seen more often during the summer and fall, but it is possible for cases of Legionella to occur anytime during the year. Multiple outbreaks have been noted among hospitalized patients. Case Definition for LegionellosisClinical Description Legionellosis is associated with two clinically and epidemiologically distinct illnesses: Legionnaires’ disease, which is characterized by fever, myalgia, cough, and pneumonia; and Pontiac fever, a milder illness without pneumonia. Laboratory Criteria for Diagnosis
Case Classification Confirmed: a clinically compatible case that is laboratory confirmed. Comment The previously used category of "probable case," which was based on a single IFA titer, lacks specificity for surveillance and is no longer used. Nosocomial Legionella Case Definition Laboratory confirmed legionellosis that occurs in a patient who has spent > 10 days continuously in the hospital prior to onset of illness is considered definite nosocomial Legionnaires’ disease, and laboratory-confirmed infection that occurs two to nine days after hospitalization is possible nosocomial infection. Laboratory DiagnosisThere are multiple tests available to diagnose legionellosis, as summarized in the table below (Am J Med. 2001;110:41-48):
Testing notes:
Preventive InterventionsWhile prevention of legionellosis is not always practical at the community level, much has been written about preventive measures in hospitals. The issue is quite controversial, and there are at least two schools of thought to be considered for hospitals that have had no nosocomial cases of Legionella (primary prevention) (MMWR, 1997: 46(RR-1): 1-79). According to one school of thought, hospitals can institute routine, periodic culturing of the potable water system, and take action if > 30% of samples are positive for Legionella species. Actions should include:
Proponents of this method argue that physicians are more likely to test for legionellosis if Legionella is known to be present in the hospital water system. In addition, infrequent culturing of a limited number of water samples on an infrequent basis may be less expensive than routine laboratory diagnostic testing for legionellosis in all patients with nosocomial pneumonia in hospitals that have never had a case. Others argue that in the absence of cases, the risk from Legionella in the water supply is undefined. Other factors, including the proximity of contaminated water to the host, the debility of the host, and the virulence of the strain may be just as, if not more, important. A second school of thought recommends maintaining a high index of suspicion for legionellosis through appropriate use of diagnostic tests coupled with routine maintenance of cooling towers AND use of only sterile water for nebulization devices. If one definite or two possible nosocomial cases are identified:
Proponents of this method argue that this offers hospitals flexibility based on patient population and the ability to link environmental Legionella with Legionnaires’ disease in patients before initiating expensive cleanup. Methods to clean contaminated water systems include superheating water to 65 °C and flushing each distal outlet for > five minutes or hyperchlorination (flushing all outlets with > 10 mg/L free residual chlorine). In addition, cleaning of water pipes and cooling systems may be necessary, as well as removal of deadlegs. Surveillance Indicators
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State
of West Virginia (WV) A-Z Listing of West Virginia's Reportable Diseases
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