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Legionnaires' Disease and You

By Laureano Andrade Vicenty 7/31/2015

picture of the alveoli infected with bacterium

     So, there have been a lot of reports (currently 46 people sick, 2 dead) of a spreading legionnaires' disease in NYC, albeit “spreading” is probably a bad word to use, since the disease does not spread via human contact. Nonetheless, this is today's topic. The following information to be presented was inspired by the work of Hawley, H. Bradford, M.D., which can be found in the Magill's Medical Guide(2013).

What is it?

     Legionnaires' disease (named after the event of its first known occurrence, leaving 25 dead and ~130 sick) is an acute (fast onset) bacterial pneumonia via the legionellosis bacterium. A pneumonia, for clarity, is an inflammation of the air sacs of the lungs, which normally exchange air coming into the lungs with the blood vessels that lead to the heart. This leads to a fluid buildup in these air sacs. The real problem with this is that oxygen, the stuff we breathe, is very insoluble in water, and this prevents a sufficient amount of oxygen to exchange with the blood vessels that lead to the heart and the rest of the body, and we all know that's bad news, because all of our cells need oxygen to function. What is more, in serious cases, some of the air sacs in Legionnaires' disease actually become necrotized (or die), increasing difficulty in breathing, as the air sacs lose their elasticity. That said, the molecular mechanisms with respect to the legionellosis bacterium remain largely unclear, although their is some research, which can be found here

How is it Transferred?

schematic of transfer method

     Legionnaires' disease is transferred via a respiratory route (i.e. breathing, see figure to right). The source of infection tends to be contaminated water supplies such as AC cooling units, but not things like drinking water, as the bacterium can do nothing in your stomach. It is thought that the disease can rarely be spread from person to person, as the likelihood of coming into such close contact with another person's air that they breathe out(with a high enough concentration of bacterium) is very unlikely. To that point, it is estimated that only 5% of those exposed individuals actually contract legionnaires' disease, although, given the current circumstances, I'd estimate that to be a little higher now.The rationale behind the older percentage is that most immune systems are capable of dismantling this bacterium before it can begin to do damage.


schematic of transfer method

     The symptoms include a dry cough, muscle aches, a rising fever, possibly vomiting, and possibly diarrhea. If anyone from NYC has these symptoms, they would be well advised to call a doctor.


     While the prognosis (the outlook) of patients with legionnaires' is favorable with early treatment, delayed intervention can prove fatal(range 5-30% fatal). The treatment is simple really, as this bacterium acts very similar to common ones, and so the antibiotics erythromycin and/or rifampin usually do the trick!


Hawley, H. M., & Alder, R. P. (2013). Legionnaires' disease. Magill's Medical Guide (Online Edition),

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