Seven fishermen were sent to a designated hospital for medical observation and treatment on Thursday after they tested positive to COVID-19 upon their return to shelter in Nan'ao county, an island in Shantou, Guangdong province.

According to a statement released by the county government on Friday, the infections include four people with mild symptoms and three asymptomatic carriers.

Epidemic prevention personnel boarded the fishing boat to collect samples for testing. Nine fishermen had been aboard the boat, the statement said, seven of whom had abnormal screening results on Thursday.

Medical experts later confirmed the infections when COVID-19 test results came out positive again on Friday, it said. The two fishermen whose test results were negative have been quarantined, it said.

Combined with the epidemiological history, clinical manifestations and laboratory test results, local medical experts have confirmed that the seven infections were imported — men meeting other fishermen from outside the mainland during their trip to sea, the statement said.

The county government has urged fishermen to pay special attention to preventing infection, including through vaccination, which remains an effective path to prevention, or at least resulting in milder infections, the statement said.

Earlier, eight fishermen from the island also tested positive for COVID-19 when they returned to shelter earlier this month.