Colorado’s public health experts are urging awareness of the symptoms of norovirus, saying infections are climbing along with cases of seasonal respiratory illnesses. The virus primarily affects the digestive system — causing nausea, diarrhea and vomiting — and can be transmitted by coming into contact with or eating food prepared by an infected person. Serious infections can cause dehydration and other health problems.

Ned Calonge, chief medical officer for Colorado’s Department of Public Health and Environment, said norovirus has been reported more and more frequently in Colorado and other states since the end of the COVID-19 pandemic.

“During COVID, we just didn’t see many outbreaks, because people weren’t getting outside,” he said. “From then on, is there a new strain that’s more easily transmitted? We don’t have any information on that. Or have we just gotten really lax about hand hygiene and hand-washing since emerging from the pandemic?”

Before 2020, the state saw about 160 to 165 outbreaks per year, Calonge said. That number fell to 39 in 2020 but has since climbed, with 338 outbreaks reported in 2024. The agency primarily takes reports of outbreaks from schools, child care facilities and nursing homes, where it has also expanded its public health surveillance efforts.

At the same time, the state is dealing with a seasonal spike in respiratory illnesses, including influenza, COVID-19 and the respiratory syncytial virus, or RSV. By the end of last week, there were 246 reported hospital admissions involving a diagnosis of influenza plus 101 diagnoses of COVID-19 and 113 diagnoses of RSV, according to CDPHE.

Denver’s Department of Public Health and Environment also wrote about the increasing number of norovirus outbreaks in a blog post last week, urging people to stay hydrated and wash their hands often with soap and water for at least 20 seconds if they are experiencing norovirus symptoms. Calonge and Leslee Warren of Denver’s Department of Public Health and Environment both said that alcohol-based hand sanitizers are less effective against norovirus than other viruses. Diluted bleach can be used to disinfect surfaces touched by an infected person.

“It’s really all about hand-washing with soap and water as frequently as you can, especially before you’re going to handle food,” Warren said. “It’s prime norovirus season right now. It’s a seasonal bug, and it circulates with the respiratory viruses.”

More information about the virus is available on DDPHE’s website.