Philadelphia and surrounding counties have been identified as a cluster area for a rare lung disease - one of seven such clusters a recent NIH study found in the U.S. The disease is caused by Mycobacterium avium complex (MAC). "The profile re-emerges time after time. Fifty-five to 75- or 80-year-old women, otherwise generally healthy, Caucasian, and not overweight," said John Hansen-Flaschen, MD, chief, Pulmonary, Allergy and Critical Care Division, in an interview with WHYY radio. Usually, patients are also of higher than average socioeconomic status. He said MAC infections can cause a persistent cough that, if left untreated by a long-term course of antibiotics, can become severe and progress to fever, shortness of breath, cavities in the lungs and, in rare cases, death. "For two decades now, pulmonary physicians in the Philadelphia area have been encountering this on a very regular basis," Hansen-Flaschen said. "We long suspected that the Philadelphia area might be a hot spot."