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Since first identified in early 1977, bacteria of the genus Legionella are recognised as a common cause of community-acquired pneumonia and a rare cause of hospital-acquired pneumonia. Legionella bacteria multisystem manifestations mainly affect susceptible patients as a result of age, underlying debilitating conditions, or immunosuppression. Water is the major natural reservoir for Legionella, and the pathogen is found in many different natural and artificial aquatic environments such as cooling towers or water systems in buildings, including hospitals. The term given to the severe pneumonia and systemic infection caused by Legionella bacteria is Legionnaires' disease. Over time, the prevalence of legionellosis or Legionnaires' disease has risen, which might indicate a greater awareness and reporting of the disease. Advances in microbiology have led to a better understanding of the ecological niches and pathogenesis of the condition. Legionnaires' disease is not always suspected because of its non-specific symptoms, and the diagnostic tests routinely available do not offer the desired sensitivity. However, effective antibiotics are available. Disease notification systems provide the basis for initiating investigations and limiting the scale and recurrence of outbreaks. This report reviews our current understanding of this disease., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Background: Many Legionella infections are acquired through inhalation or aspiration of drinking water. Although about 25% of municipalities in the USA use monochloramine for disinfection of drinking water, the effect of monochloramine on the occurrence of Legionnaires' disease has never been studied., Methods: We used a case-control study to compare disinfection methods for drinking water supplied to 32 hospitals that had had outbreaks of Legionnaires' disease with the disinfection method for water supplied to 48 control-hospitals, with control for selected hospital characteristics and water treatment factors., Findings: Hospitals supplied with drinking water containing free chlorine as a residual disinfectant were more likely to have a reported outbreak of Legionnaires' disease than those that used water with monochloramine as a residual disinfectant (odds ratio 10.2 [95% CI 1.4-460]). This result suggests that 90% of outbreaks associated with drinking water might not have occurred if monochloramine had been used instead of free chlorine for residual disinfection (attributable proportion 0.90 [0.29-1.00])., Interpretation: The protective effect of monochloramine against legionella should be confirmed by other studies. Chloramination of drinking water may be a cost-effective method for control of Legionnaires' disease at the municipal level or in individual hospitals, and widespread implementation could prevent thousands of cases.

Background: Outbreaks of travel-related Legionnaires' disease present a public-health challenge since rapid, sensitive, and specific diagnostic tests are not widely used and because detection of clusters of disease among travellers is difficult. We report an outbreak of Legionnaires' disease among cruise ship passengers that occurred in April, 1994, but that went unrecognised until July, 1994., Methods: After rapid diagnosis of Legionnaires' disease in three passengers by urine antigen testing, we searched for additional cases of either confirmed (laboratory evidence of infection) or probable Legionnaires' disease (pneumonia of undetermined cause). A case-control study was conducted to compare exposures and activities on the ship and in ports of call between each case-passenger and two or three matched control-passengers. Water samples from the ship, from sites on Bermuda, and from the ship's water source in New York City were cultured for legionellae and examined with PCR., Findings: 50 passengers with Legionnaires' disease (16 confirmed, 34 probable) were identified from nine cruises embarking between April 30 and July 9, 1994. Exposure to whirlpool spas was strongly associated with disease (odds ratio 16.2, 95% Cl 2.8-351:7); risk of acquiring Legionnaires' disease increased by 64% (95% Cl 12-140) for every hour spent in the spa water. Passengers spending time around the whirlpool spas, but not in the water, were also significantly more likely to have acquired infection. Legionella pneumophila serogroup 1 was isolated only from the sand filter in the ship's whirlpool spa. This isolate matched a clinical isolate from the respiratory secretions of a case-passenger as judged by monoclonal antibody subtyping and by arbitrarily primed PCR., Interpretation: This investigation shows the benefit of obtaining a recent travel history, the usefulness or urine antigen testing for rapid diagnosis of legionella infection, and the need for improved surveillance for travel-related Legionnaires' disease. New strategies for whirlpool spa maintenance and decontamination may help to minimise transmission of legionellae from these aerosol-producing devices.

An illness characterized by high fever and pneumonia struck 2.9% of a group of the Independent Order of Odd Fellows attending a convention held in Philadelphia, in September, 1974. The convention headquarters was the hotel where the American Legion met in July, 1976. The epidemiological, clinical, and laboratory characteristics of the illness were nearly identical to those of the disease in American legionnaires in 1976. Illness was significantly associated with attendance at one convention activity held on Monday morning, Sept. 16, 1974, in the grand ballroom of the hotel. A serological survey in February and March, 1977, showed that people who had attended the convention and became ill were more likely to have raised indirect fluorescent antibody titres than persons who had attended and remained well. The illness seen in Odd Fellows members in September, 1974, was caused by the legionnaire's disease organism.

Legionnaires' disease is reported in five renal-transplant recipients. All had febrile respiratory illnesses with pulmonary infiltrates and one died. The diagnosis was made on clinical features and by indirect fluorescent antibody titres. Symptoms started after maximum immunosuppressive therapy.

The community incidence of legionnaires' disease (L.D.) was estimated by a retrospective study of stored paired sera from 500 patients treated for pneumonia in Seattle in 1963--75. The patients were all members of a prepaid medical-care group; 84% were treated as outpatients. Only 5 (1%) had a fourfold rise in antibody titre to the L.D. antigen. Seroconversion to influenza A virus also occurred in 3 of the 5 cases. The course of illness in 4 of the 5 patients with confirmed infection was milder than that previously reported with legionnaires' disease. In addition, 1 child had a fourfold fall in titre, and 23 patients had titres of greater than or equal to 256 without significant change in titre. Only 8 of the 23 had their first serum collected later than 2 weeks after onset of illness, which suggests that the majority had acquired their antibodies before their attack of pneumonia. Prevalence of antibody in the 500 patients was not affected by age, sex, or year in which illness occurred. The incidence of legionnaires' disease based on 5 patients with rises in titre was estimated to be 0.4--2.8/10 000 persons/year.

Analysis of case histories from 187 people who had visited a hotel and leisure complex in Lochgoilhead, a village on the west coast of Scotland, indicated that 170 had had an acute illness characterised by headache, fatigue, arthralgia, myalgia, cough, and breathlessness. These symptoms were consistent with Pontiac fever-like illness. Legionella micdadei was isolated from the leisure complex whirlpool spa at the time that 60 of 72 individuals with symptoms seroconverted to L micdadei antigen. This outbreak is thought to be the first of a Pontiac fever-like illness ascribed to L micdadei and the first large-scale outbreak of its kind to have occurred outside North America. Whirlpool spas can be a major reservoir of legionella organisms; they must therefore be properly maintained and operated to prevent outbreaks of infection.

Of 33 patients infected in an outbreak of legionellosis in Glasgow in 1984, 26 lived in the Dennistoun district and the remainder either worked in or visited there. There were three main clusters of cases, the onset of illness being in early and mid June in two clusters and early September in the third. Most patients were not severely ill, but 1 patient died. The likely source of infection was a cooling tower from which Legionella pneumophila serogroup 1 was isolated. Strains indistinguishable from the cooling-tower strain were isolated from 2 of the patients. Cases occurred downwind of this cooling tower up to a distance of 1700 m. It is suggested that airborne infection with L pneumophila may extend further from the source than has hitherto been recognised.

An epidemiological link was found between contamination of a hospital water-supply by Legionella pneumophila and by Pittsburgh pneumonia agent (PPA) and subsequent cases of nosocomial legionnaires' disease and Pittsburgh pneumonia. The extent of L pneumophila isolation from the water-supply paralleled the occurrence of disease. Whenever L pneumophila was isolated from more than 30% of ten selected water sites, nosocomial legionellosis occurred. The temperature of the hot water tanks was raised to 60-77 degrees C for 72 h, and water outlets were flushed for 30 min with hot water. A decline in numbers of L pneumophila and PPA in the water-supply was followed by a fall in the incidence of legionnaires' disease and Pittsburgh pneumonia. In addition, intermittent raising of the temperature in the hot water system decreased both the number of months in which disease occurred and the proportion of nosocomial pneumonias caused by these organisms.