"Patient 416" is a 57-year-old man in Da Nang who has tested positive with the novel coronavirus five times as of Saturday morning, the National Institute of Hygiene and Epidemiology said.

The patient is a retired man living with his wife, daughter, her husband and a 18-year-old grandson in Lien Chieu District. He said he has not left Da Nang in recent months, but went to three healthcare facilities and attended a wedding in Hai Chau District from July 7 to July 20.

On the morning of July 20, he visited Hospital C in Da Nang with fever, cough and phlegm. After diagnosing him with pneumonia, doctors took his samples to test for Covid-19, and the result turned up positive.

He has since been transferred to the Da Nang Hospital after his condition took a turn for the worse. He is now on ventilators and doctors from HCMC's Cho Ray Hospital, who treated Vietnam's first Covid-19 patients as well as the country's most critically ill case - the British pilot, have come to the Da Nang Hospital with additional equipment, including an extracorporeal membrane oxygenation (ECMO) machine, to assist with the case.

The patient has had mediastinal cysts before. Authorities have yet to confirm the source of transmission.

105 people who had had close contact with the patient have been tested by the Da Nang Center for Disease Control (CDC), all coming back negative.

Da Nang authorities have put Hospital C under lockdown, with no admissions or discharges allowed. The city has closed its airport from international flights and is preparing large-scale testing among the community.

With the Da Nang case confirmed, Vietnam now has 51 active cases.