Public health officials have begun contact tracing to identify people who may have been exposed to hantavirus after an outbreak on a cruise ship killed three people, with health agencies in multiple countries working to follow people who may have come into contact with sick or deceased passengers. Hantaviruses, officials said, typically do not pass easily from one person to another, which has led them to say they are not expecting the outbreak to turn into an epidemic. Still, because rare person-to-person transmission has been documented for the Andes virus in rare cases, authorities are trying to prevent secondary spread by finding potentially exposed contacts and monitoring them for symptoms.
In general, contact tracing aims to alert people who may have been exposed, keep tabs on them if they develop symptoms, and reduce the chance they spread illness further. Officials said that task is difficult because people move between crowded settings, travel, and spend time with others—conditions that can make it hard to determine who was in close contact with whom before authorities identified the cause.
For the cruise-ship outbreak, authorities said fewer than a dozen people were thought to have shown symptoms and there have been five confirmed cases, but they warned many more may have been exposed. About 140 people remained on the cruise ship headed to the Canary Islands for disembarkation, and none had been reported sick. Authorities also faced the challenge that contact tracing had to extend to dozens of potentially exposed passengers who already left the ship about two weeks after a passenger died and before hantavirus was identified as the culprit, according to infectious disease experts and state public health officials.
Among those left earlier, officials said the displaced passengers came from at least 12 different countries, including several U.S. states. Health agencies in St. Helena, where passengers got off, said they were monitoring a small group of “higher-risk contacts” and told them to isolate for 45 days, according to the St. Helena government. In the U.K., health officials said two passengers who flew home midway through the journey were self-isolating and did not have symptoms, and they said a small number of contacts of the two were also self-isolating without showing symptoms, according to the U.K. Health Security Agency.
Singaporean authorities said they were monitoring two men who disembarked at St. Helena, then traveled to South Africa and later returned home. The two men arrived in Singapore at different times, were tested for hantavirus, and were isolated at the country’s National Center for Infectious Diseases, officials said. The U.S. government, officials said, had released few details about its contact-tracing work.
In the United States, Texas officials said on Thursday that public health workers had reached two people who left the ship on April 24. Those passengers told officials they were not experiencing symptoms and did not have contact with a sick person while aboard, and Texas officials said they planned daily self-monitoring and told them to contact public health officials if they developed symptoms. Arizona officials said they were following a person who disembarked but did not know when the person arrived in the state; the Arizona officials said the Centers for Disease Control and Prevention notified the state on May 5, when monitoring began, and that it will continue for 42 days. In Canada, a provincial health minister said two Canadians who disembarked were in Ontario and had been advised to self-isolate after returning home.
Alongside tracing people, scientists are studying the virus involved in the outbreak—an Andes virus case linked to the cruise-ship outbreak that researchers said may be among the rare hantaviruses that can spread between people in uncommon circumstances. Officials in Argentina believe initial cases may have been contracted on a birdwatching trip in Ushuaia, but Argentina’s Health Ministry said it had not yet dispatched a team there. The ministry told The Associated Press that scientists from the Malbrán Institute planned to travel to Ushuaia “in the coming days.”
Researchers are also analyzing the virus’s genetics to determine whether it has changed and possibly become more transmissible, according to the reporting. Dr. Jeanne Marrazzo, chief executive officer of the Infectious Diseases Society of America, said scientists are working to understand how the virus spreads. She said officials believe people become infectious mainly when they have symptoms and that, if the virus spreads between people, it may be transmitted through small liquid particles released from an infected person when they talk, cough or sneeze.