A viral outbreak has so far sickened about 575 residents and staff at nursing homes, retirement centers and care facilities in Spokane and North Idaho.

Health officials are closely monitoring the norovirus, which may be best known for hitting cruise ships. It is highly contagious and results in a 24- to 48-hour bout of vomiting and diarrhea.

No one has been hospitalized, though health officials say the sickness merits close monitoring among the elderly to ensure against dehydration. The numbers include about 300 cases in Spokane and 275 in North Idaho.

Norovirus, which causes most cases of gastroenteritis, is among of group of viruses that cause what’s sometimes called “stomach flu,” although it is not related to influenza. The viruses are found in the vomit or stool of infected people. It’s difficult to contain because the viruses become “aerosolized” after a person vomits, for example, and awaits contact by another person.

Officials at the U.S. Centers for Disease Control and Prevention say that while the vomiting and diarrhea may last just a couple of days, people can remain contagious for two weeks after they recover.

There is no medication to fight norovirus, nor is there a vaccine to prevent infection.

(The Spokesman-Review)