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Once considered the most glorious hotel in the nation, Philadelphia’s Bellevue-Stratford took a crashing reputation hit after nearly 200 members of the American Legion who’d attended a 1970s conference there sickened, and more than two dozen died.

A hunt for the cause was taken up by scientists and medical doctors in Philly and around the region. Theories proliferated, and it wasn’t until months later that someone discovered the pneumonia-like bacteria responsible, and described its spread via the building’s air-conditioning system.

The hotel, now called the Hyatt at the Bellevue and greatly downsized from its original 1,000-plus rooms, is still a locus for high-end society events. But it never quite regained its initial glory as the “Grande Dame of Broad Street.”

The disease discovered there is now treatable with antibiotics. Here’s how its discovery unfolded.

Avi Wolfman-Arent is co-host of Studio 2 and a broadcast anchor on 90.9 FM. He was previously an education reporter with WHYY, where he's worked since 2014. Prior to that he covered nonprofits for the...