Keeping Cool Under Pressure: NYC Legionnaires’ Disease Outbreak, Summer 2015

In the summertime when the weather is hot, having air conditioning to help keep you cool can be a sweet relief. Have you ever felt a fine mist when walking past large buildings in the heat of the summer? That mist may have been water droplets from rooftop cooling towers that keep large air conditioning systems―like those found in hotels―running efficiently, even when temperatures are soaring outside. When these cooling towers are not properly maintained, they can become a home for Legionella bacteria, which thrive in untreated warm water. If people with certain health risks breathe in water droplets contaminated with these bacteria, they may develop Legionnaires’ disease. If people are getting sick with Legionnaires’ disease, how can health officials find out the source of the bacteria? A team of city, state, and CDC epidemiologists (disease detectives), laboratory scientists, and environmental health experts was able to do just that with an outbreak this summer in New York City.

Recognizing the Outbreak

Legionella bacteria are found naturally in fresh water and can live in most any warm water that isn’t properly treated with chemicals. Most people exposed to Legionella bacteria don’t get sick, but those who are older or already have health problems are at risk for developing Legionnaires’ disease. It’s not surprising for large cities to report several cases of the disease every year. However, epidemiologists are always on the lookout for an increase in cases that might suggest an outbreak of the disease. This past July, after noticing a spike in reports from clinics and hospitals in the Bronx, New York City investigators sprang into action.

Identifying the Source

After mapping the places of work and residence of all the patients identified, the investigators noticed a pattern that indicated the source was likely a cooling tower. Then, using state-of-the-art computer modeling programs, the geographic area most likely to contain the contaminated cooling tower was identified. A team of environmental health experts from New York and CDC then collected samples from every cooling tower in that area and sent those samples to public health laboratories. Legionella are very challenging bacteria to work with, but after weeks of testing, city, state, and CDC laboratories were able to solve the mystery. The DNA “fingerprint” from the bacteria found in each of the patients was identical to that of the bacteria found in one of the cooling towers, confirming that it was the specific Legionella bacteria from that cooling tower that infected each of those patients.

Containing the Outbreak

Even before the source was confirmed, the suspected cooling tower and those in the surrounding area were cleaned and treated. Then officials worked with the building owners to ensure industry standards for treatment of their cooling tower were met. After weeks of a collaborative epidemiologic, environmental health, and laboratory investigation by the city, state, and CDC, the outbreak was declared over by New York City officials.

Keeping an Eye on Cooling Towers

With 128 people infected and 12 deaths attributable to the outbreak as of August 20, 2015, this was the largest outbreak of Legionnaires’ disease ever recorded in New York City. In response, the city passed new legislation that requires registration of all cooling towers and defines maintenance standards. The collaborative efforts of public health professionals from city, state, and federal agencies made it possible for this outbreak to be identified, solved, and contained as quickly as possible. Investigators like these, stationed all over the United States, at CDC, and across the globe are working every day to detect, respond to, and prevent public health threats. Now, THAT is cool.