With input from Dr Monica Vasudev

1104: Nearly 80% of Asymptomatic Individuals Develop COVID-19 Symptoms

1. Around 20% of asymptomatic COVID 19 positive people will remain symptom-free over time, suggested two studies published September 22.
2. Hence, most asymptomatic patients should be considered pre-symptomatic.
3. People with asymptomatic infection are infectious.
4. Nicola Low, MD, Institute of Social and Preventive Medicine at the University of Bern in Switzerland conducted a living systemic review and meta-analysis to determine the occurrence and transmission of asymptomatic and pre-symptomatic patients and published their findings in PLOS Medicine. Sung-Han Kim, MD, PhD, and colleagues conducted a study comparing levels of SARS-CoV-2 in the nose and throat of asymptomatic and symptomatic individuals, and published the results in the journal Thorax. 
5. Low et al searched PubMed, Embase, bioRxiv and MedRxiv for relevant studies in March, April, and June using RT-PCR testing. The data included a statistical modeling study of all 634 passengers from the Diamond Princess cruise ship with RT-PCR positive results. In 79 studies conducted in various settings, 20% of people with SARS-CoV-2 infection remained asymptomatic during follow-up. Restricting to seven studies that screened defined populations with follow-up, around 31% remained asymptomatic over time.
6. A subset of five studies included detailed contact tracing. The group calculated that the risk of asymptomatic people transmitting SARS-CoV-2 was lower (summary risk ratio, 0.35, compared with symptomatic people at 0.63).
7. Since SARS-CoV-2 can be transmitted a few days prior to an infected person develops symptoms, pre-symptomatic transmission likely appears to have a major contribution to overall SARS-CoV-2 epidemics.
8. Kim et al found that 19% of the 213 patients who did not have severe symptoms of COVID-19 remained asymptomatic through potential exposure, lab confirmation, and hospital admission. The upper respiratory tract viral load was not significantly different between asymptomatic and symptomatic individuals in upper respiratory tract samples in South Korea.
9. The mean cycle threshold (Ct) values of SARS-CoV-2 genes, reflecting the viral load, were found to be very similar between asymptomatic individuals and symptomatic patients. This points that asymptomatic individuals have a comparable potential for spreading the virus as symptomatic patients. To prevent the transmission from asymptomatic individuals, the use of face masks by general public, irrespective of the presence of symptoms, is recommended.
10. The study included outbreak in Daegu City traced to a single religious group. The 3000 close contacts that were identified reported symptoms from none to severe, and the asymptomatic individuals were isolated and assessed in dedicated facilities. A subset of 183 patients, including 39 asymptomatic and 144 symptomatic, were subjected to follow-up RT-PCR testing. As most asymptomatic people with COVID-19 continue to live in a community setting, such individuals may potentially contribute to the community spread. As the study population largely comprised of people in their 20s and 30s, the generalizability to other age groups is not known.

[Excerpts from Medscape]

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA