Philadelphia, located in eastern Pennsylvania, United States, is a city of great historical significance. The Declaration of Independence was signed there in 1776, and it served as the nation’s capital from 1790 to 1800. Although Philadelphia was the capital for only about ten years, numerous events are held there each year on Independence Day. On July 4, 1976, the 200th anniversary of American independence, one notable event was a veterans’ meeting held at a luxury hotel from July 21 to 24. Among the 4,400 attendees, 255 developed severe pneumonia symptoms, including high fever and cough, between July 22 and August 3, and 34 of them died.