Saturday, September 26, 2015

Wanted suspect: L pneumophilia


Photo 1: L. pneumophilia. Source
If you had been following the infections news, you had probably already noted that there is a lot of news articles on Legionnaires'. The recently famous "Bronx Legionnaires’ Outbreak" has been an eye opener. This has increased the stress on surveillance, which is making more news. Having never talked about in this blog about Legionella pneumophila, this is the right time, to put up a few facts of interest.

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
The first account dates back to 58th annual meeting of the legion (July 21 to 24, 1976). In a couple of days participants attending the meeting at the hotel, started developing flu like symptoms. in the following days, the wives of attending people also began to feel sick with respiratory symptoms. The outbreak rang a bell when about 221 people associated had developed unexplained respiratory symptoms with no explaining etiology. 34 people died from the illness. CDC came into picture, and with clever epidemiology and bacteriology studies finally an environmental organism was identified. in 1977, Dr. Joseph McDade identified as the causative organism. They also identified that it thrives in hot, damp places like the water of the cooling towers which spread the disease throughout the hotel. Sudden mass onset of symptoms, deaths and unexplained cause- together they made great cover stories and headlines. The reputation of Bellevue-Stratford Hotel, was blown down and was closed just 4 months after the outbreak. Since then, several outbreaks have been identified.

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
L pneumophilia is not a bonafide human pathogen but an accidental pathogen. The organism has been recovered from several places (aquatic associated) such as lakes, ponds, rivers, cooling towers, fountains, spa baths etc. Moreover, they are not found as free living systems. They are almost always found intracellularly thus making them resistant to many different environmental insults. They are natural beta lactamase producers and in context of human infection, forms complex biofilms. These are the set of properties that makes the organism difficult to tackle.

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

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