|Photo 1: L. pneumophilia. Source|
Legionella pneumophila, is a member of Legionellaceae, which represents a group of highly fastidious gram negative bacteria often seen to be associated with aquatic environment. They survive intracellularly in protozoans, especially amoeba. Being a natural outdoor organism, associated with water, they are almost ubiquitous in distribution. L pneumophilia is non-acid-fast, non-sporulating, flagellated, non-capsulated gram negative bacilli.
|Photo 2: Publicity of the 1976|
Legion outbreak. Source
This infection is not transmitted from person to person but rather from air conditioning systems by inhalation. The infection on an average has an incubation time of 10 days.
One of the well known outbreaks in the recent history was from Quebec City, Canada in 2012. The outbreak caused 182 declared cases of Legionnaire's disease and included 13 fatalities. Another recent one is in Berthierville. As of on Aug 28, 2015, 16 cases have been reported with 2 deaths. Another outbreak of interest in news is the Bronx outbreak. The outbreak was identified in late July 2015, in South Bronx which is a part of NY city. More than 100 cases had been identified with 12 deaths. Of the 12 deaths only one was of age below 40 years, with all cases known to be suffering from other health problems. The assessment team had found that the infection was traced to a contaminated cooling tower on top of the Opera House Hotel on East 149th Street. No new cases has been reported and by Aug 20, 2015 health officials had declared the outbreak to be over. This massive outbreak has led to new considerations in legislative and regulatory efforts intended to prevent similar outbreaks. It has also lead to proposal of measure requiring building owners to conduct quarterly inspections of cooling towers.
The heightened awareness of the outbreaks has lead to screening of water tanks and cooling systems in several regions. The best example, once again covered in news is closing of 3 schools in Chicago area. The report says, "Three schools in Illinois' U-46 school district, which covers 11 communities in Cook, DuPage and Kane counties, shut down Wednesday after test results showed higher than normal levels of Legionella bacteria."
|List 1: Legionnaires' disease- What you should know|
Diagnosis is by preferentially by cultivation of bacteria in Buffered charcoal-yeast extract (BCYE) agar from sputum or lavage samples. Biochemically, they are oxidase- and catalase-positive. They are more readily identified by a test called DFA (Direct fluorescent antibody test). The confirmation is usually by PCR. They are mostly susceptible to Erythromycin, Macrolides, Tetracyclines, Trimethoprim-sulfamethoxazole, Rifampacin, and Fluoroquinolones.
Newton HJ, Ang DK, van Driel IR, & Hartland EL (2010). Molecular pathogenesis of infections caused by Legionella pneumophila. Clinical microbiology reviews, 23 (2), 274-98 PMID: 20375353
Lévesque S, Plante PL, Mendis N, Cantin P, Marchand G, Charest H, Raymond F, Huot C, Goupil-Sormany I, Desbiens F, Faucher SP, Corbeil J, & Tremblay C (2014). Genomic characterization of a large outbreak of Legionella pneumophila serogroup 1 strains in Quebec City, 2012. PloS one, 9 (8) PMID: 25105285