>> we're all a little overwhelmed, not only the practitioners, but the caregivers in general. >> reporter: numbers are so great, he isn't even administering flu tests but handing out treatment. >> a lot of what we do is simple supportive care, making them feel better. >> reporter: the most vulnerable patients, children and the elderly. but this flu can also have deadly consequences for healthy adults. strong immune systems can sometimes overreact and destroy healthy tissues along with the flu itself. this year, there's a double threat. not only is flu rampant, so is a nasty stomach bug called the norovirus. now widespread throughout the country. it's also very contagious, and another serious concern for hospitals. a perfect storm of sickness, which is why 45,000 people in boston got an automated call from the city. >> residents who have not been vaccinated against the flu this year are urged to get