The Ha Nam Centre for Disease Control has collected his nasal swab for the second time and sent the sample to the National Institute of Hygiene and Epidemiology for confirmation, Truong Thanh Phong, deputy director of the provincial Department of Health told local media outlets.
More than 200 people who had directly or indirectly come into contact with the patient were transferred to a concentrated quarantine facility for medical surveillance, said Phong.
The patient, 28, returned from Japan to Vietnam on April 7 after his labour contract had expired.
He was taken to Alisia Beach hotel in Da Nang, central Vietnam, for a 14-day quarantine period according to the COVID-19 rules.
Following his three negative tests, the man was allowed to return home and self-isolate locally.
However, he tested positive after showing virus-like symptoms such as a cough and a sore throat.