A South Bay resident from Santa Clara County was on the MV Hondius cruise ship but disembarked before the outbreak. Two other Californians were also on the ship and disembarked over the weekend in the Canary Islands. They are now in quarantine at a federal facility in Nebraska.
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The fourth Californian, a Sacramento County resident, has returned home. That person was not on the ship but was exposed to someone who was ill on a plane in South Africa, according to health officials.
All four individuals are being closely monitored.
State health officials addressed questions about the two people who have returned home to California and whether they are in quarantine. Dr. Erica Pan said, "They're doing modified activities in alignment with our Centers for Disease Control guidance as well. So they are limiting activities outside the home. They're doing daily temperatures and are in contact with their local health departments."
Federal officials emphasized that the risk to the general public remains low.
"Let me clear, let me be crystal clear the risk to the general public remains very, very low," said Adm. Brian Christine with the U.S. Department of Health and Human Services.
Health experts said hantavirus typically requires close and prolonged contact with someone who is symptomatic, which may explain how it spread on the ship.
"It was a much smaller cruise ship than what we often envision with these large cruises and, really a lot of interaction and activities that were close contact with each other, but we'll be learning more over time," Dr. Pan said.
Officials said there have been nine confirmed cases tied to the outbreak, including three deaths. The two people being monitored in California are not currently showing symptoms, but health officials said it can take up to 42 days for symptoms to appear. They will be monitored during that time.