Health workers wear hazmat suits as residents of a neighborhood queue up for a mandatory COVID-19 test, after a spike in cases within the Jordan district of Kowloon in Hong Kong on Jan 20, 2021. (ANTHONY WALLACE / AFP)

HONG KONG – Hong Kong’s health authorities are looking into incidents where people who tested negative for COVID-19 at community testing centers were later found to be infected with the coronavirus.

The first incident was brought to light when Dilip Rai, 42, told the media that he, along with his wife and son, tested positive at the hospital a few hours after their tests conducted at mobile stations in Yau Ma Tei all came back negative.

He said the negative results were returned around 2 pm Monday, but they were all confirmed infected after being hospitalized roughly five hours later.

Rai, who developed a fever last Thursday, said he also tested negative last Friday at the Yau Ma Tei community testing center.

I think the situation would not be as bad if I had (tested) positive on Saturday and started my treatment three days earlier.

Dilip Rai, a 42-year-old Hong Kong resident

“I am questioning the reliability of the testing. ... It’s not just me. My son and my wife also face the same situation. I think the situation would not be as bad if I had (tested) positive on Saturday and started my treatment three days earlier,” he told local media.

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The city’s Food and Health Bureau (FHB) said in a statement on Thursday night: “The government has immediately contacted the Hospital Authority and the testing service providers (Hong Kong Molecular Pathology Diagnostic Centre and KingMed Diagnostics (Hong Kong) Limited) to obtain more information.”

Yuen Kwok-yung, a prominent microbiologist at the University of Hong Kong, said the university’s laboratory test and the station’s second test of Rai’s condensed sample both indicated that his viral load was very low.

Yuen is one of the four experts who advise the government on its anti-epidemic strategies and has been looking into the false-negative cases. The FHB said further information will be disclosed once available to allay public concerns.

He reminded doctors to arrange COVID-19 testing for their patients even if they only display mild suspected symptoms because their viral load could decline to one-tenth its initial level seven days after they develop the first symptoms.

The FHB said they are looking into three other similar cases. According to authorities’ records, they involved two women, aged 42 and 52 respectively, and a 52-year-old man. All of them were confirmed infected on Jan 18 and at least two were residents in Yau Ma Tei, a hard-hit area where mandatory COVID-19 testing notices have been issued to many old residential buildings.

The two testing service providers involved in the cases “have participated with satisfactory performance in the external quality assurance program of the Department of Health, and have the medical testing accreditation of the Hong Kong Laboratory Accreditation Scheme,” the FHB said.

“Furthermore, the Public Health Laboratory Services Branch of the Centre for Health Protection of the Department of Health also regularly sends specimens to all service providers of the community testing centers for comparison tests to ensure that their sensitivity and specificity meet the criteria. Three rounds of comparison tests have been conducted in the past two months.”

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As of Jan 20, the Henry G. Leong Community Centre in Yau Ma Tei, operated by KingMed Diagnostics, had provided swabbing and testing service to nearly 90,000 residents and identified 312 patients. Hong Kong Molecular Pathology Diagnostic Centre, which has mobile testing stations across the city, had provided specimen collection and testing services for more than 180,000 people. It has identified 186 positive cases.

The FHB said that most of the residents under compulsory testing orders were swabbed by professionals, while all the community testing centers have adopted professional swab sampling of combined nasal and throat swab since mid-November last year.

Contact the writer at jefferygu@chinadailyhk.com