Asymptomatic and pre-symptomatic individuals primarily drive the coronavirus disease 2019 (COVID-19) pandemic by unknowingly transmitting the virus to others. Asymptomatics are those infected people that manifest no symptoms over the course of infection and recovery. Meanwhile, pre-symptomatic individuals are those who have been infected with the virus but who are yet to present symptoms. The incubation period for COVID-19 - that is, the period of time between exposure and symptom onset - can be as long as 14 days. This means that pre-symptomatics, in the same way as asymptomatics, can unwittingly transmit the virus to others.
The risk of this is occurring is especially high among healthcare workers on the frontline of the pandemic as they are at high risk of viral exposure and of passing it on to vulnerable patients.
Given the major role asymptomatics and pre-symptomatics play in viral transmission, developing effective measures that prevent this dynamic of its spread will be crucial in getting on top of the pandemic while the logistics of mass vaccination at the national and global level are still being hashed out.
A new study on frontline healthcare works by researchers at the Karolinska University Hospital in Sweden shows that testing for the presence of SARS-CoV-2 nucleic acid can help in containing the virus spread. Detecting the presence of high amounts of SARS-CoV-2 nucleic acid predicts future symptomatic disease, they found.
Since pre-symptomatic individuals are spreaders of SARS-CoV-2 infection, it is crucial to identify methods that could identify them, especially in hospital settings.
The study, published on the preprint medRxiv* server, showed a strategy to identify potentially contagious individuals among asymptomatic healthcare workers. This way, infected healthcare workers will be immediately isolated and treated to reduce the virus's transmission risk.
The researchers tested more than 9,400 employees at the Karolinska University Hospital in Sweden for SARS-CoV-2 RNA and antibodies. They also tied the Polymerase Chain Reaction (PCR) screening results to sick leave records and evaluated the link between screening results and past or future sick leave.
Asymptomatic healthcare workers
Detecting asymptomatic or pre-symptomatic carriers are vital to reduce the risk of spreading the virus to others. In the hospital setting, since healthcare workers are at risk of infection with SARS-CoV-2, finding those infected should be prioritized.
The study highlights a new strategy to detect potentially infected healthcare workers. The team found that healthcare workers with high amounts of SARS-CoV-2 virus, had the highest risk for sick leave in the two weeks after being tested.
Meanwhile, those who had low amounts of the virus had the highest risk for sick leave in the past three weeks before testing.
The team also revealed that screening asymptomatic healthcare workers identified a few people who had SARS-CoV-2. Among these, more than half were only positive for low levels of the virus and had already been infected, or known as post-symptomatic.
Hence, the researchers noted that the amounts of virus are crucial for distinguishing between post-symptomatic and pre-symptomatic people. Pre-symptomatic healthcare workers are at a higher risk of transmitting the virus to other people, including the patients.
We conclude that the amount of virus as determined by the Ct value of the PCR test and also the serology status are useful testing results for distinction between post-symptomatic, asymptomatic, and pre-symptomatic subjects."
"Healthy healthcare workers with low amounts of SARS-CoV-2 nucleic acids will previously have had the disease. Presence of a high amount of SARS-CoV-2 nucleic acids predicts future symptomatic disease," they concluded.
Evaluating the amount of virus in the PCR test can help identify people who may carry the virus. This way, virus transmission can be controlled and stemmed. As infectivity declines rapidly after symptom onset, it is more useful to detect infected individuals before the symptoms begin.
The team proposed that systematic SARS-CoV-2 screening of healthy individuals may be necessary for a phase of the epidemic where many people had previous COVID-19.
To date, over 73.67 million cases have been confirmed worldwide, and 1.63 million have lost their lives.
The United States reports the highest number of cases, reaching 16.73 million, with more than 304,000 deaths. India and Brazil have more than 9.93 million and 6.97 million cases, respectively.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Dillner, J., Elfstrom, M., Blomqvist, J., Engstrand, L., Uhlen, M., Eklund, C. et al. (2020). Screening for high amounts of SARS-CoV-2 identifies pre-symptomatic subjects among healthy healthcare workers. medRxiv preprint server. doi: https://doi.org/10.1101/2020.12.13.20248122,