As India and other parts of the world depart from the lockdown, the identification and isolation of asymptomatic and pre-symptomatic novel coronavirus cases are emerging as a major cause for concern. Two recent studies from China on asymptomatic and pre-symptomatic Covid-19 cases show there is more to these cases than we think we know.

First Study

A retrospective study on Covid-19 patients in China shows that the treatment cycle of asymptomatic patients was longer than that for most patients who had moderate symptoms.

Asymptomatic cases involved people who have been infected with the virus without any clinical symptoms such as fever, cough, sore throat, etc. but were tested positive as the result of an RT-PCR test.

Conducted by researchers from Zunyi Medical University in Guizhou, the study asserted that the average treatment cycle for asymptomatic patients was 16 days, while a majority of these varied between 11 and 20 days. On the other hand, the average treatment cycle for symptomatic cases was 13 days, with an interquartile range of 10-15 days.

Currently, the average treatment cycle of infections with recovering moderate type of confirmed Covid-19 patients is considered to be less than 14 days.

The study was done at Guizhou Provincial Staff Hospital in Guiyang, China, between January 29 and March 31 while a final follow-up was conducted on April 22. The researchers studied a cohort of 52 Covid-19 patients at the hospital, who were recovering from the infection and consisted of similar demography. The pre-print study has been registered with the Chinese Clinical Trial Registry. The study was funded by the Science and Technology Support Plan of Chinese Province Guizhou.

Researchers noted that a higher incubation period in asymptomatic cases could be one of the reasons behind the variance which also makes the detection of Covid-19 tough in such cases. “The prolonged incubation period of asymptomatic infections was more likely to cause SARS-CoV-2 to survive in the body for a long time,” the study found. Trends show that a large number of cases of Covid-19 are asymptomatic. In India, 14 days’ quarantine is advisable for all asymptomatic suspected cases.

The Second Study

The second peer-reviewed study published by the US Centre for Diseases Control’s (CDC) journal, Early Infectious Diseases, revealed that patients without symptoms had the ability to spread the virus. A medical investigation noted that two asymptomatic Chinese students who were asked to quarantine for 14 days after returning from overseas, left traces of virus on 8 surfaces of the two hotel rooms they were housed in during the quarantine period.

According to the study, the students who had no symptoms left traces of the virus on the pillow covers, sheets, and duvet covers. The two students were later admitted to a hospital where one of them ran mild temperatures (99.5 C and 100.2 C) and the other had a mild cough sometime later.

Researchers from the Beijing Institute of Microbiology and Epidemiology took samples from 22 surfaces of the two hotel rooms, giving a 36 per cent surface infection by the two students. The viral load on frequently and prolonged contact surfaces such as sheets and pillow covers were higher than intermittent contact surfaces such as door handle and light switch.

To minimize the possibility of dispersing virus through the air, the researchers recommended: “used linens not to be shaken upon removal and laundered items can be thoroughly cleaned and dried to prevent additional spread”.

“Our study demonstrates that pre-symptomatic patients have high viral load shedding and can easily contaminate environments. Our data also reaffirm the potential role of surface contamination in the transmission of SARS-CoV-2 and the importance of strict surface hygiene practices, including regarding linens of SARS-CoV-2 patients,” the study had concluded.