Legionella and Legionnaires' Disease: 25 Years of Investigation

Abstract

There is still a low level of clinical awareness regarding Legionnaires' disease 25 years after it was first detected. The causative agents, legionellae, are freshwater bacteria with a fascinating ecology. These bacteria are intracellular pathogens of freshwater protozoa and utilize a similar mechanism to infect human phagocytic cells. There have been major advances in delineating the pathogenesis of legionellae through the identification of genes which allow the organism to bypass the endocytic pathways of both protozoan and human cells. Other bacteria that may share this novel infectious process are Coxiella burnetti and Brucella spp. More than 40 species and numerous serogroups of legionellae have been identified. Most diagnostic tests are directed at the species that causes most of the reported human cases of legionellosis, L. pneumophila serogroup 1. For this reason, information on the incidence of human respiratory disease attributable to other species and serogroups of legionellae is lacking. Improvements in diagnostic tests such as the urine antigen assay have inadvertently caused a decrease in the use of culture to detect infection, resulting in incomplete surveillance for legionellosis. Large, focal outbreaks of Legionnaires' disease continue to occur worldwide, and there is a critical need for surveillance for travel-related legionellosis in the United States. There is optimism that newly developed guidelines and water treatment practices can greatly reduce the incidence of this preventable illness

Detection of Legionella pneumophila serogroup 1 in blood cultures from a patient treated with tumor necrosis factor-alpha inhibitor

“…The primary method of LD diagnosis is UAT since this modality identifies 81% to 97% of LD infections compared to only 5% to 9% by culture [15,28]. The UAT is simple and it can rapidly and accurately (sensitivity, 60% to 80%; specificity, >99%) identify L. pneumophila serogroup 1 [17,28]. However, culture remains important because 14% to 20% of LD infections are caused by non-serogroup 1 Legionella species [15,17] that UAT cannot detect.…”

“…The UAT is simple and it can rapidly and accurately (sensitivity, 60% to 80%; specificity, >99%) identify L. pneumophila serogroup 1 [17,28]. However, culture remains important because 14% to 20% of LD infections are caused by non-serogroup 1 Legionella species [15,17] that UAT cannot detect. Notably, L. pneumophila from the present patient survived in a non-selective medium for one week and another study has shown that L. pneumophila could survive in standard blood culture broth medium [29].…”

“…Among diagnostic tests for LD, the urinary antigen test (UAT) is the most useful [15] and it supposedly improves the outcomes and mortality rates of patients involved in LD outbreaks [16]. However, detection of the organism by culture is still important, because UAT can detect only L. pneumophila serogroup 1 and approximately 14% to 20% of LD is caused by non-serogroup 1 Legionella species [15,17].…”

Structural basis for substrate recognition by a unique Legionella phosphoinositide phosphatase

“…Several species, in particular Legionella pneumophila and Legionella longbeachae, are pathogenic to humans (1)(2)(3). Because of the development of artificial water systems, such as air conditioning, Legionnaires' disease has emerged as a significant health threat in modern societies (4). Inhalation of L. pneumophila in contaminated aerosols allows the pathogen to reach the alveoli of the lung, where they can be phagocytosed by host macrophages.…”

Risk of Hospital-Acquired Legionnaires' Disease in Cities Using Monochloramine Versus Other Water Disinfectants

“…5 Legionnaires' disease is caused by numerous species of Legionella, bacteria that are ubiquitous in natural and man-made aquatic environments. 6 Acquisition of legionnaires' disease usually occurs following the aspiration or inhalation of aerosols from contaminated potable water or cooling towers. [7][8][9][10][11][12][13][14] Most hospital-acquired outbreaks of legionnaires' disease have been associated with the contamination of hospital drinking water with Legionella species.…”