Duong Tan Hau, 29, is being investigated for "spreading dangerous infectious diseases in humans."

Hau was placed under house arrest after he recovered from Covid-19 and completed a 14-day isolation.

Ho Chi Minh City police officially launched the investigation into Hau more than a month after they began investigating the case.

According to the police, Hau had breached regulations when staying at the airline’s quarantine facility and continued to do the same after returning home for a designated self-isolation period. His irresponsibility is believed to have triggered a new outbreak of the novel coronavirus in the community.

Hau had returned to Vietnam from Japan on November 14 and was quarantined for four days at a facility managed by Vietnam Airlines in HCMC's Tan Binh District. While he was there, he broke the rules by visiting another quarantine area and ended up contracting the virus from another crew member who’d returned from Romania, police said.

However, after two tests showed he was negative for the novel coronavirus, Hau was released from the airline’s facility, but told to isolate himself at home for another 14 days.

As per Vietnam’s protocols on Covid-19 prevention, pilots and attendants need to use dedicated restrooms and their own vehicles on getting off the plane. No contact is allowed with passengers during flights.

On arriving in Vietnam, they are quarantined and tested for the novel coronavirus twice 72 hours apart. If both tests return negative, they are allowed to self-isolate at home for 14 days.

However, when he was at home, Hau failed to isolate himself. He made contact with his mother and two friends, including an English language teacher who came to stay with him for a few days.

On November 29, 15 days after he returned from Japan, he tested positive for the virus, becoming "Patient 1342" and the the teacher followed suit the next day. The teacher had later spread the virus to a nephew and a student.

The outbreak broke Vietnam's 89-day and HCMC's 120-day streak of having no community transmissions.

Hau has been suspended from his job and will be considered for dismissal.

However, Hau claims he has told investigators more than once that he did not visit another quarantine area when at the airline’s facility and that he "had only met several colleagues when getting water for drinking at a mutual area."

During those face-to-face meetings, Hau said he was struggling with stomach-ache and therefore had been enquired after and been taken care of by several colleagues. One of them, he said, was the attendant returning from Romania.

"I understand that I have made mistakes. But I shouldn’t be the only one to be blamed for this. Errors in quarantine management have allowed me to neglect and let my guard down. I hope that the investigators will clarify this and assess the nature and extent of my violation," Hau told VnExpress Tuesday after receiving the decision to be placed house arrest pending further investigation.

His lawyer Dao Thi Bich Lien said: "I hope the investigation agency will clarify the causes, conditions, context, subjective and objective reasons as well as the responsibilities of the management units in this case. And in case Hau is convicted, it will be a warning for all other flight attendants."

Vietnam has recorded 1,520 Covid-19 cases so far with 35 deaths. Many of the deaths were of elderly patients with underlying conditions like diabetes and kidney failure.

As of Tuesday, the nation has gone 40 days without recording any community transmission of the novel coronavirus.