‘Silent spreaders’ may account for HALF of all coronavirus cases in the US as nearly 50,000 people a day test positive, study suggests
- Researchers created a model on transmission and determined that between 17.9% and 30.8% of all COVID-19 cases are asymptomatic
- If 17.9% have no symptoms, then presymptomatic cases account for 48% of transmission,and asymptomatic accounts for 3.4%
- If 30.8% have no symptoms, then 47% of transmission is due to presymptomatic cases and 6.6% is due to asymptomatic cases
- At least one-third of all asymptomatic cases have to be identified and isolated for the outbreak to be brought under control
Silent spreaders may account for half of all cases of the novel coronavirus in the US, a new study suggests.
Transmission through people with no symptoms, or right before symptoms begin, is one of the main drivers of COVID-19, the disease caused by the virus.
What’s more, the team, led by the Yale School of Public Health, says more than one-third of silent infections would need to be identified and isolated to keep the coronavirus outbreak under control.
It comes as 50,000 Americans test positive every day, the highest rate recorded since the pandemic began and double the number that was testing positive last month.
If 17.9% of coronavirus cases have no symptoms, then presymptomatic cases account for 48% of transmission and asymptomatic accounts for 3.4%. If 30.8% have no symptoms, then 47% of transmission is due to presymptomatic cases and 6.6% is due to asymptomatic cases (above)
At least one-third of all asymptomatic cases have to be identified and isolated for the outbreak to be brought under control. Pictured: A healthcare worker tends to a patient in the Covid-19 Unit at United Memorial Medical Center in Houston, Texas, July 2
For the study, the team created models to examine how much of a role silent transmission played in the coronavirus outbreak.
The model presumes that people with COVID-19 are most likely to be contagious during the presymptomatic stage.
Additionally, the model mimicked New York City demographics and assumed all who were infected isolated immediately and stayed in isolation until after they recovered.
Researchers determined that between 17.9 percent and 30.8 percent of all COVID-19 cases are asymptomatic.
If the minimum 17.9 percent of cases are asymptomatic, they calculated that presymptomatic cases would be responsible for 48 percent of transmission and that asymptomatic would account for 3.4 percent.
If the maximum 30.8 percent of cases are asymptomatic, they estimated 47 percent of transmission is from presymptomatic cases and 6.6. percent is from asymptomatic cases.
The team says isolating all symptomatic cases of coronavirus is not enough to bring the spread under control.
For the virus to infect no more than one percent of the population, at least 33 percent of presymptomatic and asymptomatic cases would also need to be identified and isolated.
Researchers say the findings provide evidence for why outbreak control measures such as testing and contract tracing need to be ramped up.
‘Our findings highlight the urgent need to scale up testing of suspected cases without symptoms as noted in revised guidelines by Centers for Disease Control and Prevention,’ the authors wrote.
‘Furthermore, symptom-based surveillance must be supplemented by rapid contact-based surveillance that can identify exposed individuals prior to their infectious period.’
The findings were published in the journal Proceedings of the National Academy of Sciences.
In the US, there are more than 2.9 million confirmed cases of the virus and more than 130,000 deaths.