Although raw sewage and gastrointestinal illnesses are rarely topics broached in polite conversation, they’re having a glaring impact in hundreds of towns and cities in the United States. The risk of acute gastrointestinal illness increases by up to 62% after certain kinds of sewer overflows, according to recent research led by a team at the School of Public Health at Boston University. And with increasing extreme rainfall events in the forecast, climate change could make the problem worse.