A medical staff disinfects an area at Binh Thuan General Hospital in Binh Thuan Province, south central Vietnam, which is treating nine Covid-19 patients, March 12, 2020. Photo by VnExpress/Viet Quoc.

Four of new cases are: the 59-year-old husband, 28-year-old son, two-year-old granddaughter and an in-law of the businesswoman who tested positive after a trip back from Washington D.C. The fifth is a 12-year-old boy, her neighbor.

On Wednesday, her house-help, an employee and daughter-in-law were confirmed infected.

All nine patients are being treated in quarantine at the Binh Thuan General Hospital.

The businesswoman, 51, had flown from Ho Chi Minh City to New York on February 22, transiting at the Incheon International Airport in South Korea for three hours.

On February 29, she flew back from Washington D.C., transiting at the Doha International Airport in Qatar. She landed at the Tan Son Nhat Airport in HCMC on March 2 and took a car home to the resort town of Phan Thiet in the south central Binh Thuan.

On March 5, she developed high fever and a cough. Four days later, she was admitted to the Binh Thuan General Hospital and placed under quarantine pending Covid-19 tests, and the results came back positive.

Vietnam has recorded 28 infection cases over the past six days, after going 22 clean days with no infections. Sixteen of the previous Covid-19 patients had been discharged from hospitals by February 26.

The Thursday additions made Binh Thuan the worst hit locality in Vietnam, followed by Hanoi with five cases. Other active cases have been reported in Lao Cai, Ninh Binh and Quang Ninh Provinces in northern Vietnam; Da Nang, Thua Thien-Hue and Quang Nam in central Vietnam, and HCMC.

On Thursday morning, the health ministry confirmed that a male tour guide in Hanoi who’d been in contact with an infected British tourist on flight VN54 from London to Hanoi on March 2 has tested positive for the novel coronavirus.

A Da Nang saleswoman who served two other infected British tourists on the same flight was confirmed infected on Wednesday.

Thus far, 14 passengers on the Vietnam Airlines flight have tested positive for the novel coronavirus, 13 being treated in Vietnam while a British woman had left for Cambodia before she was confirmed positive.

26-year-old Hanoian Nguyen Hong Nhung, one of the passengers, spread the virus to a personal chauffeur and an aunt.

A 24-year-old Vietnamese woman who had met Nhung at a party in London last month before falling sick and being put on a private plane to Saigon on Monday tested positive the same day.

The other infection case is a Vietnamese man who returned from Daegu, South Korea.

Covid-19, which WHO has declared a pandemic, has spread to 125 countries and territories, killing more than 4,700 people.