A series of studies of the coronavirus suggest it is infectious for longer periods than pathogens from the same family, such as Sars, presenting added challenges for containing it.
Researchers found that on average, people with SARS-CoV-2 – the virus that causes Covid-19, a pneumonia-like disease – can expel or “shed” virus particles from their bodies for a relatively long period of 20 days, spreading it even before symptoms appear.
The virus also remains persistent in the faeces of some children, suggesting it can be transmitted through a faecal-oral transmission route – meaning that contaminated faeces from the infected child is somehow ingested by another person.
This indicates longer quarantine periods may be needed for patients, according to a study by a team from the China-Japan Friendship Hospital, which included China National Health Commission expert Cao Bin.
The more contagious nature of the virus as indicated in the study is reflected in the growing number of cases globally: as of Thursday, Covid-19 had infected over 200,000 people in more than 172 countries and regions, and killed nearly 9,000.
The research included 191 patients in Wuhan, 137 of which were discharged and 54 had died in hospital by January 31. For patients who received antiviral treatment, the medication did not reduce the duration of viral shedding, according to the paper published in medical journal The Lancet.
“A period of 20 days completely exceeds the expected viral shedding duration for acute respiratory virus infections,” Cao Bin said in an interview with Caixin magazine on March 11. “The relatively longer viral shedding duration means longer antiviral treatment time and quarantine period are needed.”
The paper said there were limitations to the study, although it was reportedly the largest retrospective analysis of Covid-19 patients who have experienced a definitive outcome.
Another study observed the highest viral load in throat swabs at the initial sign of symptoms, inferring that infectiousness peaked on or before symptom onset, according to researchers from Guangzhou and the University of Hong Kong. That finding was published in a so-called preprint paper, or one which has not been peer-reviewed.
Researchers estimated that 44 per cent of the transmissions could occur before an infected person displayed symptoms. This pattern bore a greater similarity to the transmission of influenza than Sars, the study suggested.
The preprint research, which involved 94 patients in Guangzhou, said containing the virus was made more difficult by the high rate of transmissions occurring before symptoms were evident. Mitigation measures such as social distancing may be more effective, it said.
“Contact tracing and isolation alone are less likely to be successful if more than 30 per cent of transmission occurred before symptom onset,” the paper said.
“With a substantial proportion of pre-symptomatic transmission, measures such as enhanced personal hygiene among the general population and social distancing would likely be the key instruments for disease control in the community.”
In another paper published by the journal Nature Medicine last week, Guangzhou researchers studied 10 children aged 2 months to 15 years old and found that eight of them persistently tested positive for the virus on rectal swabs after nasal samples had returned negative results.
“[This] suggests that the gastrointestinal tract may shed virus and faecal – oral transmission may be possible,” the study said.
“These findings also suggest that rectal swab-testing may be more useful than nasopharyngeal swab-testing (in the area behind the nose and mouth that connects to the oesophagus) in judging the effectiveness of treatment and determining the timing of termination of quarantine.”
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