Medical doctor Lim Boon Hee wrote in Straits Times Forum today criticising the Ministry of Health (MOH) for making mistakes in relying only on viral load and serology test to allow an infected COVID-19 patient be discharged from hospital prematurely (‘Forum: Don’t rely on viral load and serology test alone‘, 23 Apr).
“It takes only one positive Covid-19 case to start another wave of community infections if we let our guard down,” Dr Lim cautioned.
“I am referring to the imported case who was probably reinfected in India, infectious on return to Singapore and released into the community as he was deemed to be no longer infectious. Unfortunately he was, and thus infected two others, starting a new cluster.”
“Any person with a positive PCR, or polymerase chain reaction, swab must be assumed to be infectious and immediately isolated”, Dr Lim added.
Dr Lim was referring to a 43 year-old Indian expat on Work Pass who arrived in Singapore from India on 2 Apr and was tested positive for COVID-19 on arrival. His serology test result also came back positive suggesting that it was an old infection (‘Expat from India discharged from hospital as recovered COVID case, who later goes on to infect 2 others‘).
The authorities then deemed that the Indian expat was a recovered case based on his high Ct value indicating a low viral load. They discharged him from the hospital on 6 Apr, as he was deemed to have been shedding only minute fragments of the virus RNA, which were no longer transmissible to others.
But 10 and 12 days later, his sister-in-law and her husband who are staying together with him, were infected. In fact, just yesterday (22 Apr), it was reported that his nephew, an 11 year-old Indian national on Student’s Pass also staying with them, is the latest victim. He is a student at Dimensions International College.
After his sister-in-law was tested positive, the Indian expat was re-tested which showed that his COVID-19 viral load has increased and that his Ct value was lower than that of his earlier test. This suggests that he was exposed to a new infection which boosted his antibody levels.
Later, MOH said that the Indian expat was “probably re-infected when he was in India, and had been infectious when he returned to Singapore”.
Dr Lim commented, “The doctors who deemed him as non-infectious were probably misled by two red herrings – the low viral load, and the positive serology test, which tests for antibodies to the virus. They probably concluded the very low viral load meant he was recovering from infection.”
“But a low viral load can equally mean an early acute infection before the virus replicates,” Dr Lim explained.
“In the current situation of multiple variants of the virus, positive serology, or having antibodies to the virus, just means the patient was infected before and does not rule out a new acute infection. It could very well still be a sub-acute case and the patient could still be infectious, as this case has shown.”
Dr Lim added that relying on the viral load and positive serology test to release imported Covid-19 patients is unwise. He advised that all tested positive for Covid-19 upon entering Singapore be treated as people with acute infection, and be quarantined appropriately until proven otherwise.
“We cannot afford to have another reinfected case starting a new wave of Covid-19 in our community,” he said.