Legionnaires’ disease is a rare condition, and incidence is hard to estimate because diagnosis requires a suspicion of disease and ordering of the tests needed for confirmation, said Krishna Thavarajah, MD, a pulmonologist and director of the Interstitial Lung Disease Program at Henry Ford Hospital, Detroit, in an interview.

Three people in central Harlem have already died from legionnaires’ disease, according to the NYC Health Department.

The health department offered five ZIP codes in central Harlem — 10027, 10030, 10035, 10037, 10039 – that were at the center of the cluster, as officials stressed the disease was airborne