Norovirus — the single leading cause of gastrointestinal illness in the United States — is sweeping the country and this year there’s a new strain on the scene, according to the Centers for Disease Control and Prevention.

Locally, there have been no outbreaks of norovirus linked to the new Sydney strain, which was first identified in Australia, the CDC reported Thursday. But health officials are keeping their eyes and ears open for reported cases because the virus is highly contagious.