Connecticut is seeing an unseasonable, "offseason" spike in a virus known to cause 10,000 deaths annually, according to data from the Centers for Disease Control and Prevention. There were an average of 14 cases a week of Respiratory Syncytial Virus, commonly called RSV, identified as of July 10. Out of an average of more than 250 weekly tests for the virus, more than 6 percent came back positive. "Still small numbers, but very unusual for us to see any this time of the year," said Rick Martinello, director of infection prevention for Yale New Haven Health. "We will likely see a rise in this over the next number of weeks and months. And then it will probably get worse as the weather gets colder." RSV, Martinello explained, was the second-most common cause of viral pneumonia, "prior to the COVID era." "RSV is a common cause of upper respiratory tract infections in both kids and adults," he said. But young kids, especially those who are less than six years of age, can develop bronchiolitis. It's not unusual in the winter time for children's hospitals to be 50 percent or more full of children with bronchitis most often due to RSV." Though children are most susceptible, older adults tend to have the worst outcomes. RSV "leads to about 10,000 deaths among adults each year in the United States," Martinello said. Last July, though COVID numbers were low, RSV surveillance showed zero cases of the illness. That, Martinello said, is not unusual. "RSV is a winter time virus," he said. Christoper Boyle, a spokesperson for the state Department of Public Health, said decreased masking, social distancing "and other COVID mitigation efforts have contributed to increased circulation of various respiratory viruses, including RSV, at levels not usually seen at this time of year." "These increased activity levels are higher than seen before the pandemic," Boyle said. All children are expected to catch RSV by the age of 6, and adults can expected to get sick with the virus every few years, health experts say. According to Martinello, the complete lack of immunity is likely the cause of the unseasonable spike this summer. "When we get sick with it, it provides some degree of immunity for us for subsequent infection," he said. "This past year, we have been distancing, we've had lockdowns, masking, we've been, I think, more careful with how we're protecting ourselves from infection. We have not had those infections. So as a population, we are more vulnerable to RSV now than what we typically would be this time of the year." There are no truly effective treatments for RSV. Monoclonal antibodies can provide some protection, but antivirals are largely ineffective and so are administered in only the worst cases. There are no vaccines yet approved, though there are some currently in late-stage trials. Unlike COVID, "RSV is spread mostly by contact," Martinello said. "It's not thought to be spread by aerosols, like we see flu and COVID being spread." It's not just RSV that is experiencing what Martinello called an "off-season" rise. "We are seeing, actually, a lot of Rhinovirus right now, which is most often responsible for the cold," he said. "And then also a lot of another virus called parainfluenza. We haven't seen any influenza yet, though. We're doing about 1,000 tests a month that include flu, and we have not seen a single flu case yet."