Insight
Serology tests: Keep track of COVID-19 recovery
During the second wave of COVID-19 infection, suspected re-positive cases were found in the community. In April, the Hospital Authority had collaborated with the School of Public Health of the University of Hong Kong to conduct a viral study and literature review, with the following two pieces of scientific evidence being concluded and presented to the Scientific Committee on Emerging and Zoonotic Diseases (SCEZD) under the Centre for Health Protection of the Department of Health. After a thorough discussion and review, the SCEZD concluded that a serology test can help keep track of the recovery progress of patients with COVID-19; and should be included as one of the criteria for releasing the patients from isolation.
1. The viral load of COVID-19 patients attains the highest level at the early stage of infection and gradually decreases in the second week after symptom onset. Patients will start to produce neutralising antibodies to fight against the virus seven to ten days after symptom onset, which implies that the patient is in recovery.
2. Reverse transcription polymerase chain reaction (RT-PCR) test was performed on patients’ respiratory specimens for analysis in the study. For specimens with the Ct (Cycle threshold) value equals or above 30, viral culture test would be conducted. It was observed that the culture results were negative for these specimens. In other words, viable SARS-CoV-2 (the COVID-19 virus) was not detected in the specimens that the virus was therefore proved to be no longer infectious. Nevertheless, some patients might continue to have positive RT-PCR test results even after recovering from COVID-19 due to the high sensitivity of the RT-PCR test, ribonucleic acid fragments of dead virus could be detected.
Dr Vivien Chuang, Chief Manager (Infection, Emergency & Contingency) mentions, “By assessing the infectiousness of patients based on the above-mentioned scientific evidence as well as the clinical conditions of patients, we can safely discharge clinically recovered patients so as to facilitate the usage of isolation beds. It is noted that the average length of stay of patients during the third wave of infection is significantly shorter after implementation of the new criteria for releasing patients from isolation.”
1. The viral load of COVID-19 patients attains the highest level at the early stage of infection and gradually decreases in the second week after symptom onset. Patients will start to produce neutralising antibodies to fight against the virus seven to ten days after symptom onset, which implies that the patient is in recovery.
2. Reverse transcription polymerase chain reaction (RT-PCR) test was performed on patients’ respiratory specimens for analysis in the study. For specimens with the Ct (Cycle threshold) value equals or above 30, viral culture test would be conducted. It was observed that the culture results were negative for these specimens. In other words, viable SARS-CoV-2 (the COVID-19 virus) was not detected in the specimens that the virus was therefore proved to be no longer infectious. Nevertheless, some patients might continue to have positive RT-PCR test results even after recovering from COVID-19 due to the high sensitivity of the RT-PCR test, ribonucleic acid fragments of dead virus could be detected.
Dr Vivien Chuang, Chief Manager (Infection, Emergency & Contingency) mentions, “By assessing the infectiousness of patients based on the above-mentioned scientific evidence as well as the clinical conditions of patients, we can safely discharge clinically recovered patients so as to facilitate the usage of isolation beds. It is noted that the average length of stay of patients during the third wave of infection is significantly shorter after implementation of the new criteria for releasing patients from isolation.”
