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Legionnaire’s Disease at the Luxor: What Causes It?

The views expressed are those of the author and are not necessarily those of Scientific American.


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The slinky rods of Legionalla pneumophila. If you didn't know better, you might assume these were extruded by a Play-Doh Fun Factory. CDC Public Health Image Library Image #11151. CDC/ Margaret Williams, PhD; Claressa Lucas, PhD;Tatiana Travis, BS

In July 1976, a convention of members of the American Legion — a veterans’ group — was meeting in Philadelphia at the Belleville Stratford Hotel in honor of America’s bicentennial. Soon, 221 attendees would be sickened and 34 dead of an illness it was believed no one had ever seen before. Swine flu was suspected, as were toxic chemicals or terrorism of some sort. None of these proved to be the cause.

The CDC sprang into action and by January of 1977 the culprit was identified: Legionella pneumophila. The bacteria had been living in the warm water of the hotel’s air conditioning cooling tower, whence they were aerosolized and spread through the building via air ducts.

Just yesterday, these bacteria made headlines again when they were discovered to have infected at least three and killed one last year at the Luxor Hotel and Casino in Las Vegas, where the bacteria were dwelling in “water samples” — most likely the plumbing or A/C system. Although this sounds scary, you have to put things in perspective: Legionnaire’s Disease, or legionellosis, already sends up to 18,000 people a year to the hospital in the United States, and doctors may overlook the diagnosis in others. But most of these infections do not take place at high-profile pyramidal Las Vegas casinos.

L. pneumophila, a gammaproteobacterium like E. coli or Salmonella, is actually quite an interesting organism in and of itself. It is related to no other respiratory pathogen, and in fact, its usual host is not a bird or a pig or a human. It’s an amoeba. Legionella live within and, in fact, parasitize free-living amoebae in nature*. We are accidental hosts.

Their preferred home in amoebas may explain why they like invading our macrophages so much. Macrophages are amoeba-like immune cells that wander through your body at will — often slithering between tissue cells — looking for invading microbes to engulf and digest, just as amoebas feed. Legionella bacteria get taken up by our macrophages and then parasitize them — and in turn us — just as they do wild amoebas.

If the infection progresses (which in many healthy people it does not), the consequences for a human shake out in one of two delightfully-named ways. The first is Pontiac Fever (I actually have this, but it’s because I drive a suh-weet Pontiac), a flu-like syndrome that usually resolves on its own. It was named for an outbreak in Pontiac, Michigan, that pre-dated that the Philadelphia outbreak and was identified ex post facto. The second option is Legionnaire’s Disease, which also begins with flu-like symptoms before progressing to pneumonia accompanied by sky-high fevers of up to about 107F. This option kills somewhere between 5 and 30% of the people who develop the symptoms. People sickened by the bacteria are typically middle-aged or older, and often have weakened immune systems.

In addition to water towers used in industrial air-cooling systems, the bacteria-parasitized amoebae can also hang out in shower heads, medical respiratory devices, spas, hot tubs, large central air conditioning systems, fountains, swamp coolers, ice machines(!), misting equipment, domestic plumbing, swimming pools, and humidifiers (another reason you should use only boiled or distilled water in them). The bacteria (and of course, their amoeba hosts) also thrive in freshwater ponds and creeks.

Legionella get into the air after an infected water source is disturbed mechanically. Any fine droplets produced may evaporate quickly, leaving the bacteria suspended and easily inhaled. The bacteria thrive between 77 and 112 F, so one simple strategy for keeping water free of the disease is to maintain a temperature hotter or colder than that.

It used to be thought the Legionella bacteria couldn’t travel far by air. But the investigation into an epidemic in Pas-de-Calais, northern France in 2003-2004 traced 86 confirmed cases and 18 resulting deaths to a cooling tower in a petrochemical plant, and found that some of the victims lived as far as 7 km from it. Once airborne, those bacteria can really move — or at least can survive a long time as the wind moves them. Perhaps it is a natural dispersal strategy for reaching new amoeba hosts.

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*In fact, the first amoeba-parasitizing giant viruses were found by scientists investigating a local pneumonia outbreak and looking for Legionella in amoebas found in an area water tower. They found large particles inside amoebas in the cooling tower they assumed were bacteria. It was only when the “bacteria” failed to respond to bacteria-specific molecules (PCR primers) that the scientists realized they had a new (and entirely harmless to humans) super-giant virus on their hands.

Jennifer Frazer About the Author: Jennifer Frazer is a AAAS Science Journalism Award-winning science writer. She has degrees in biology, plant pathology/mycology, and science writing, and has spent many happy hours studying life in situ.
Nature Blog Network
Follow on Twitter @JenniferFrazer.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. kdimoff 10:54 pm 01/31/2012

    doing what you do best: fascinating me and freaking me the eff out all at the same time :)

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  2. 2. Jennifer Ouellette 11:14 pm 01/31/2012

    Mental note: avoid the Luxor on next trip to vegas. :) Yeah, I know it’s unfair….

    Link to this
  3. 3. Jennifer Frazer in reply to Jennifer Frazer 12:24 pm 02/1/2012

    Awww. . . it’s actually one of my favorite casinos on the strip. How could you not love a pyramid shaped hotel? I’ve got a thing for ancient Egypt so not much surprise there. Plus I bet in mere days they’ll have the cleanest water and a/c system on the strip. It’s not like casinos are ever strapped for cash. They of all people can afford to throw money at the problem.

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  4. 4. mtw4107 3:36 pm 02/1/2012

    MGM International also owns: MGM Grand, Luxor, Monte Carlo, Excalibur, Mirage, Aria, Bellagio, Treasure Island (off the top of my head).
    I contracted Legionnaire’s disease at the Aria Hotel. I was exposed to the Legionella bacteria June 2011 l. I had full blown 102 fever, vomitting, diarrhea, headache, deep hacking cough (which became a two month long bout with bronchitis), lost 20 pounds, and other physical symptoms. The Legionella exposure is difficult to trace after a certain amount of time, and the Aria had the minimal response to the outbreak considering they had a Legionella scare at the Aria in 2009.

    It is apparent, because of the ongoing outbreaks in the MGM International Las Vegas hotels, that the hotels are not concerned about the health of their customers. The money MGM would have to shell out to have a safe water maintenance program outweighs a few Legionella outbreak reports and a handful of deaths. Of course, the MGM International’s only concern is the bottom line – it’s a business, but if their cutting corners where their cost effective measures endanger the health, well-being and life of a client, they should be

    The water maintenance is expensive, the testing is expensive and they are not under any enforced water maintenance regulations – the MGM owned hotels just have “guidelines” from the Southern Nevada Health District. When corporations have a choice between profit and the public safety, profit always trumps safety.

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  5. 5. CM doran 3:48 pm 02/1/2012

    Recently some infections too in Milwaukee hospital–water wall had it (read about in recent Washington Post)
    and more famously…an outbreak at Playboy Mansion–Jenny McCarthy fundraiser last year

    Thanks for writing about Legionnare’s disease.

    Link to this
  6. 6. N0Naame 12:50 am 02/2/2012

    Which is why you should always put washer fluid in your windshield washer reservoir. It sits just outside the engine compartment — its filler pipe in the compartment — and it is like Jamaica for these guys in plain water. Imagine spritzing your windshield with your window open a tad. Or — thanks for the additional info — the guys driving behind you with their elbows getting tanned.

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