Silent Spreaders are individuals who are asymptomatic i.e. they don’t display signs or symptoms of COVID-19, yet they harbour SARS-CoV-2 in large enough quantities to be infectious to others. So if you’re not coughing, don’t have a fever and feel pretty okay, how do you know if you have COVID-19 and could spread it to others? You don’t unless you get tested. 

Studies have shown that people with no symptoms tend to have viral loads similar to those who have symptoms. These “silent spreaders” move through the community unbeknownst to themselves that they are spreaders of COVID-19. Only testing asymptomatic people will identify these silent spreaders. Frighteningly, studies have shown that 25-40% of people with COVID-19 can be asymptomatic while they are infectious, and over 8% of people never develop symptoms.  

In a study conducted by the renowned Cleveland Clinic in the U.S, researchers examined the timeline for infectiousness in individuals who contract SARS-Cov-2. They posed the question: when in the course of infection do people become infectious, and at what stage of their recovery do they no longer pose as a risk for transmitting the virus to others? The study concluded that viral load is highest closer to the onset of symptoms, and the vast majority of the viral load-time lies within 10 days of symptom onset. Transmission potential is negligible after seven to ten days have elapsed since the onset of symptoms1.

Identifying Silent Spreaders

Mass screening or serial testing in people who are at-risk or work in at-risk environments such as meat-processing factories or long-term care facilities is a valuable practice that is already being adopted in countries around the world.  For this, Rapid Antigen Detection Testing (RADT) is ideal. A high-quality RADT such as DropTech has a sensitivity of over 92.5%, accurate enough to detect ‘silent spreaders’ and eliminate from the community this mode of transmission. 

The aim of rapid antigen test is to identify individuals who have a viral load that is large enough for them to be infectious to others. Some people have lower viral loads than others throughout the course of the disease, rendering them less infectious. Importantly, the gold-standard test to detect SARS-CoV-2 (RT-PCR) is so sensitive it can detect the virus even weeks after the person is no longer infectious. Herein lies the value of the somewhat less sensitive RADT. It is sensitive enough to detect almost all people who have high viral loads, thus identifying people who pose the most risk to others. 

False Negative Test

A false-negative test result using rapid antigen tests is the main reason why certain governments have not adopted widespread RADT use. However, some in the scientific community view this as a positive.  The false-negative could be due to the lower viral load in certain individuals who are not infectious anyway. Widespread RADT use is a pragmatic adjunct to RT-PCR when access to RT-PCR is limited to people with symptoms or their close contacts.  


(1) Clin Infect Dis. 2020 Jun 29 : ciaa886. Published online 2020 Jun 29. doi: 10.1093/cid/ciaa886 PMCID: PMC7337652 PMID: 32594116. Accessed at: 

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