A British couple on holiday in Vietnam have been told they “left infections everywhere” over several days after unknowingly contracting coronavirus from a fellow passenger on their flight from Heathrow.

Graham Craddock, 68, and his wife, Mary, 69, are in quarantine in Hanoi where conditions have been poor at times, , although the couple praised the no-nonsense response of the Vietnamese authorities.

After touching down in Hanoi on 2 March on Vietnam Airlines flight VN54 – where they sat two rows behind the woman, 26, from Hanoi who was carrying the virus – the couple visited attractions in the capital before moving on to Sapa in north-west Vietnam. They were contacted on Saturday and told that someone on their flight had tested positive for coronavirus.

The Craddocks were taken by ambulance to Lao Cai hospital, where they were placed in what they believed to be an unused wing which was dirty and had no hot water.

Graham Craddock told the Guardian: “We stayed in the room we were given that night even though the toilet only worked with the use of bucket and bailer. I complained to the doctors and the following day we were upgraded to the VIP room. Well at least it had a functioning toilet. The best thing about the hospital wing is that we were alone in it. I am very concerned about picking up infections, not only the virus.”

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Despite the conditions, Craddock said they preferred to be there than at a busier, better-equipped hospital because they feared infection. But on Monday morning they were forced to move to the Hanoi central hospital for tropical diseases, four hours away.

He said: “Last night [Sunday] we were told that we had the virus, although my wife and I do not have symptoms. I asked how can that be? I was told 80% of people carrying the virus do not have symptoms. So it’s like catching a ghost if that’s correct.

“Before we left Lao Cai I had a call from the district foreign office official who said that everywhere we had been we had left people with infection. He emphasised it was not our fault but one of the reasons he wanted us out of the Lao Cai hospital was to accommodate 54 more suspected cases.”

The 26-year-old woman from Hanoi had visited London, Milan and Paris, the Vietnamese health ministry said. Vietnam had not had a case for more than three weeks before she tested positive on Thursday and had been praised for its response. On 25 February it announced that all 16 cases in the country had recovered but the number of confirmed cases has now almost doubled to 30, including seven Britons who were on the flight that landed on 2 March.

Craddock said the Vietnamese action appeared draconian but was “much better than letting it drift”. However, he expressed dismay that the infected woman on his flight was allowed to travel.

“When we checked in at Heathrow we were asked if we had been near infected people, [or] had we been recently to China, Iran or Italy. We answered no,” he said. “I asked what would have happened if we had [said yes]. We were told we would not be able to board the flight.”

The woman has been named in the Vietnamese press as a wealthy socialite whose 27-year-old chauffeur and 64-year-old aunt have also tested positive. It was reported that she had suffered from a cough and fever before travelling but not at the time of the flight.

Vietnam has temporarily suspended visa-free travel for citizens from eight European countries, including the UK.

• This article was amended on 11 March 2020. The picture caption mistakenly said that Graham and Mary Craddock were taken to “Lao Cai hospital in Hanoi”. The couple were taken from Lao Cai hospital, in north-west Vietnam, to Hanoi. In addition, errors introduced in the editing process led an earlier version to say that the quarantine conditions in Hanoi “had been poor at times, with no toilet or hot water”. As the article said elsewhere, those complaints related to conditions in Lao Cai hospital, not in quarantine in Hanoi.