Here's the truth behind the Legionnaires' disease outbreak everyone is panicking about

Legionnaires' disease bacteria culturePascal Rossignol / ReutersA technician holds a culture dish with colonies of legionella in a laboratory at the Water and Environment Department at the Institut Pasteur in Lille, January 5, 2004.

New York City is now in the throes of its largest-ever outbreak of Legionnaires’ disease, with 86 reported cases and seven deaths in the Bronx since July 10.

The outbreak is sparking necessary action in New York, but Legionnaires’ is an ongoing problem around the world — not a new one.

Smokers as well as people who are elderly and chronically ill are most at risk, but in the vast majority of cases doctors can treat the disease with antibiotics.

Legionnaires’ is a form of pneumonia that is caused by Legionella pneumophila, a bacterium that thrives in water and is spread when people inhale contaminated droplets. Symptoms include headache, fever, coughing, and shortness of breath.

In the current Bronx outbreak, the bacteria have been found in five water cooling towers, which are a component of of the heating and cooling systems used in many large buildings. (Workers have since decontaminated all five.)

“Legionella love water systems, particularly old, clunky and corroded ones that are not well maintained and have a little sludge,” Dr. Glenn Morris, the director of the Emerging Pathogens Institute at the University of Florida told The New York Times. “Cooling towers in particular are a great place to live from a legionella’s perspective, because it’s nice, warm water year-round.”

Still, The Times noted, “cooling towers account for a relatively small proportion of Legionnaires’ outbreaks. More often … the disease spreads through the systems that supply water for drinking, cooking and bathing.”

Legionnaires’ disease cannot be spread from person-to-person or from actually drinking water; people tend to fall ill after inhaling water from sources like showers, fountains, air conditioners, hot tubs, and misting machines in supermarkets.

Legionnaires' disease lungsCDC / Betty PartinChest X-ray of a patient with Legionnaires’ disease.

Legionnaires’ disease has been on the rise in recent years, but public health researchers say a growing population of older and chronically ill people may be why. In the Bronx outbreak, officials said, everyone who fell sick was in fact already unwell.

Researchers estimate that there are somewhere between 8,000 and 18,000 people hospitalized for Legionnaires’ in the US each year; between 5% and 30% of those cases are fatal. Most of those cases, however, are not diagnosed. Official counts still show an upward trend, from 1,127 cases in 2000 to 4,548 in 2013. Summer and early fall are peak seasons.

In New York City, where the highest incidence of Legionnaires’ is in lower-income areas, there was a 230% increase in cases from 2002 to 2009. Between 2002 and 2011, a total of 1,449 cases of Legionnaires’ disease were reported to the New York City Department of Health; 88% of those infected had at least one “underlying medical condition that is recognised as a risk factor.”

Legionnaires' disease bacteriaCDC / Margaret Williams, PhD; Claressa Lucas, PhD; Tatiana Travis, BSColorized scanning electron micrograph image showing a group of Gram-negative Legionella pneumophila bacteria.

A 2014 study by the New York City Department of Health served as a warning for the current South Bronx outbreak, and officials are now beginning to focus on some of the study’s suggestions.

“Socioeconomic disparities in disease should be of concern to public health policy makers,” the authors wrote in November. “If environmental issues in high-poverty neighbourhoods contribute to the disparity, greater effort may be warranted, for example, on the upkeep of cooling towers and water systems in the buildings in these areas.”

This year, a national study from the Center for Public Health Preparedness and Research at Emory University came to a similar conclusion: Legionnaires’ disease targets the most vulnerable among us, and it “deserves [to be] a higher public health priority.”

Just last month, an industry group suggested a new standard to make building cooling systems safer, and the ongoing outbreak in New York City is already bringing belated attention to the safety of cooling towers throughout the city.

Legionnaires’ disease got its name in 1976, when a number of American Legionnaires fell sick after a conference in Philadelphia.

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