Spaulding Rehabilitation Hospital in Charlestown has been contending with a norovirus outbreak since Tuesday afternoon. The highly contagious gastrointestinal infection has sickened 22 out of 132 inpatients, as well as three staff within the past 24 hours. "We're trying to make sure we do the best we can to keep sick patients isolated in their rooms," said Paula Hereau, vice president of administration at Spaulding. "We've had no serious complications so far." Known as the "winter vomiting disease," the virus also causes severe diarrhea, nausea, and gastrointestinal cramps. It's usually short-lived and not serious, with symptoms resolving in an average of two days. Treatment usually involves keeping patients in bed and well hydrated.