Legionella Critical Review

Abstract

Legionella pneumophila (L. pneumophila) is of increasing concern due to its ability to cause Legionnaires’ disease, a severe pneumonia, and the difficulty in removing L. pneumophila from water systems. L. pneumophila thrives within the biofilm of premise plumbing systems, utilizing protozoan hosts for protection from disinfectants and other environmental stress. While there is a plethora of information regarding how L. pneumophila interacts with protozoa and human macrophages (causing Legionnaires’ disease), this information has yet to be used for a comprehensive quantitative microbial risk assessment (QMRA) model for L. pneumophila in drinking water systems. This review article seeks review the available information regarding how L. pneumophila invades host cells.

Background

Legionellosis, a respiratory disease caused by the inhalation of Legionella bacteria, incorporates both Pontiac Fever and Legionnaires’ disease (LD) a severe form of pneumonia. Pontiac Fever, a self-limiting flu-like illness, is characterized by a non-pneumonia respiratory infection lasting two to five days. Those affected may experience fever, chills, malaise, myalgia, headache, cough, or chest pain. The typical incubation period is one to two days. The disease was first discovered in Pontiac Michigan in 1968. At the time of discovery, the etiological agent of the disease was unable to be identified. It was not until the LD outbreak in 1976 that Legionella pneumophila (L. pneumophila) was identified as the causative agent 1,2.  LD is named so as it was discovered after an outbreak of pneumonia at a Legionnaires’ convention in Philadelphia. During this outbreak 29 of the 182 cases were fatal, and a gram-negative bacillus was isolated and determined to be the cause. It was also determined that the same bacterium was the previously unknown etiological agent of Pontiac Fever3–5.

LD has similar symptoms to Pontiac Fever with the addition of a severe pneumonia. Though LD may cause sub-clinical infections, more serious cases can cause long-term symptoms including easy fatigue, shortness of breath, muscle or joint pain, productive cough, and memory loss 6–8. LD can have an incubation time ranging from two days to two weeks, depending on the patient’s immuno-health and if antibiotic therapy was administered 8,9. There is an increased risk of contracting legionellosis in those with a non-municipal water supply, recent residential plumbing repair , electric water heaters (as opposed to gas), and those who work more than 40 hours a week 10–12. Elderly, males, those with nosocomial infections, renal disease or immunodeficiency have increased risk from Legionaries’ 10,13.

Legionellosis is the most common cause of all reported waterborne diseases in the US, and its incidence is steadily increasing 14,15.  The US average 10,000 – 15,000 cases year, and L. pneumophila was the cause of half of all reported waterborne disease outbreaks in 2005-20016–18. Due to the prevalence and seriousness of LD, L. pneumophila has been added to the United States Waterborne Disease Outbreak Surveillance System in 2001 and the US Environmental Protection Age