HANOI –

Vietnam was back on high alert for the novel coronavirus on Saturday after medical officials in the central city of Danang detected the nation's first locally transmitted case in three months.

Thanks to strict quarantine measures and an aggressive and widespread testing program, the Southeast Asian country has kept its virus total to an impressively low 416 cases and had reported no locally transmitted infections for 100 days.

Vietnam has reported no deaths from the virus.

But on Friday, the health ministry said a 57-year-old man from Danang, a tourist hot spot, had tested positive, prompting the isolation of 50 people he came in contact with.

The ministry said 103 people connected to the patient were tested for the virus but all returned negative results.

The government said on Saturday a new test had confirmed the man's infection.

It did not say how the man contracted the virus but that he had not left Danang for nearly a month. He was initially diagnosed with pneumonia.

The case comes at a time when Vietnam was about to resume international commercial flights and as domestic tourism is surging.

Late on Friday, authorities in Hanoi reinstated a recommendation to wear masks in public places.

Vietnam's ban on international commercial flights is still in place, but foreign experts and skilled workers have been able to enter provided they undergo mandatory centralized quarantine.

Of the nearly 150 cases reported over the past three months, all were imported in people quarantined on arrival.

Earlier this week, Vietnam said it would repatriate about 130 Vietnamese citizens infected with the virus from Equatorial Guinea.

In March, Danang reported six local cases of the coronavirus as the U.S. aircraft carrier Theodore Roosevelt, which reported cases on board, conducted a port visit. There was no confirmation the six cases were linked to the ship.