Doctors take samples from a man for Covid-19 tests during a drill at Cu Chi field hospital in HCMC, March 4, 2020. Photo by VnExpress/Quynh Tran.

The number of new suspects since early March has ranged from 70 to 100 cases a day. A suspected person shows symptoms of cough, fever or shortness of breath, and has a history of travel from or through epidemic-stricken areas or has had come into close contact with an infected patient. Suspected persons are subject to compulsory isolation in hospitals specialized in treating Covid-19.

As of Tuesday, the country had 20,075 people placed under medical monitoring, either at home, military camps or certain general hospitals, up nearly 2,000 against the previous day.

Most of these people are in the major cities of Hanoi, HCMC, Da Nang and Can Tho.

Vietnam had gone 22 days without any new infection until 26-year-old Nguyen Hong Nhung was confirmed positive last Friday, making her Hanoi’s first Covid-19 patient and the country's 17th. Vietnam has since recorded 16 new infection cases, all but one related to Nhung.

Nhung had flown to Hanoi from London on Vietnam Airlines flight VN54, in the business class, on March 2. There were 201 passengers on the flight, including 21 in the business class.

12 people on the same flight, 11 of them foreigners, have tested Covid-19 positive.

Nhung's personal chauffeur and an aunt have also been infected.

A 24-year-old Vietnamese woman who'd met Nhung at a party in London is infected with the novel coronavirus, the Health Ministry confirmed Tuesday, after she arrived in Vietnam on a private jet.

The Covid-19 outbreak has thus far spread to 115 countries and territories around the world, killing over 4,000.