While the flu continues its attack on Iowa and the rest of the country, the state Department of Public Health is warning of norovirus. The department says it has received numerous reports of the illness largely associated with upset stomach issues. Norovirus activity occurs year round but it's generally higher in the colder months because people are indoors and in closer contact more often. Health officials say norovirus spreads easily so they advise people to stay home when sick and wash hands regularly.