In a study released this month by the National Institute for Occupational Safety and Health (NIOSH), federal researchers identified more than 400 cases of complicated black lung in three clinics in southwestern Virginia between 2013 and 2017—the largest cluster ever reported.

However, the actual number of cases is likely much, much higher as the government analysis relied on self-reporting. An ongoing investigation from NPR has counted nearly 2,000 cases diagnosed since 2010 across Appalachia.