The Centre for Health Protection said her husband, 75, could have been the source of the family outbreak, which had also infected the engineer’s wife. He travelled via the Lo Wu border checkpoint to Dongguan, Guangdong province, six times from January 14 to January 25 and fell ill afterwards.

He attended family gatherings in Hong Kong on January 27 and 29 during the Lunar New Year, and his symptoms later subsided.

Chuang Shuk-kwan, head of the centre’s communicable diseases branch, said it was possible that people who contract the virus could recover on their own.

“Otherwise everybody would be going to hospital, like during Sars [in 2003],” she said.

Sources said the husband, who was admitted to the same hospital on Tuesday evening, initially returned a preliminary negative on a first test, and a “weak positive” on a second, requiring a further test.

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The case has raised eyebrows because the elderly couple’s infected son-in-law, 54, and a colleague from his architectural firm attended a meeting at the Hospital Authority’s headquarters on February 6.

Six patients who shared a ward with the woman during the four days she was in hospital for surgery – but before the virus diagnosis – were placed in isolation. Nine of the 15 medics who treated her tested negative, while results for the remaining six had not come back.

“When she was admitted [for the surgery], there was no infection and her lung scan was clean, so it was not listed as suspected,” Dr Lau Ka-hin, the Hospital Authority’s chief manager for quality and standards, said. “After our medics talked with the family and confirmed other relatives had contracted the disease, she was sent to isolation and received tests on February 18.”

Separately, a couple who live in Sui Moon House, Siu Sai Wan Estate, were confirmed to be infected with the virus. The 68-year-old man and 70-year-old woman had no recent travel history.

Meanwhile, a spokesman for Princess Margaret Hospital said the city’s second virus-related fatality died on Wednesday morning after his condition deteriorated.

The Hospital Authority said the 70-year-old man, who had diabetes and kidney problems, died at about 7am, but the exact cause of death was yet to be determined.

According to information previously released by the health authorities, he lived alone in Shek Yi House, Shek Lei (II) Estate, in Kwai Chung.

He had fallen ill on February 2, and was sent to Princess Margaret Hospital 10 days later, after suffering a fall. He was in a critical condition when his case was confirmed on February 14.

The man had taken a day trip to mainland China through Lok Ma Chau on January 22.

Identified as the 13th confirmed case in the city, he lived at Whampoa Garden.

He travelled to Wuhan in Hubei province, where the virus originated, on January 21 and returned to Hong Kong two days later via the Guangzhou-Shenzhen-Hong Kong Express Rail Link.

There was no definitive link between the coronavirus and diabetic patients, the Hospital Authority said.

Both men’s deaths were referred to the Coroner’s Court to determine the cause.

A fifth patient has recovered from the disease, and was discharged on Wednesday, the authority said. The latest recovery involved a 63-year-old Wuhan man who took the high-speed rail to Hong Kong on January 22. His wife, also from Wuhan and also infected, was still in hospital.