A deadly Legionnaires' disease outbreak in New York City has set health and community leaders on a campaign to educate the public on ways to prevent the bacteria from growing and spreading. Health leaders hit the streets of Harlem for a third straight day Friday with fliers urging people to take precautions as the number of infections continues to rise.

Here’s what to know about Legionnaires’ disease, how it spreads, and the East Harlem cooling tower outbreak under investigation.

The source of the illness has not been conclusively identified more than a week after people began getting sick.