Many people who contract the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease (COVID-19), do not manifest symptoms. Called asymptomatic carriers, these individuals are tied to the growing number of cases across the globe.
On the other hand, some people are at a higher risk of developing severe symptoms, resulting in viral pneumonia, acute respiratory distress syndrome (ARDS), and death.
A new study by researchers at the University of Bern and published in the journal PLOS Medicine reports that while some people never experience any symptoms, most of those infected with the novel coronavirus do develop symptoms. The study suggests that asymptomatic cases of the infection comprise only a minority of the infections.
Previous reports have shown the magnitude of asymptomatic spread that has been tagged as the cause of the skyrocketing cases. The research team wanted to know the proportion of people who will remain asymptomatic throughout infection with SARS-CoV-2.
Definitions of symptom status in infected people
People who are symptomatic means that they experience and report symptoms of COVID-19, including cough, fever, and difficulty of breathing. Some symptoms may include headache, sore throat, body pains, vomiting, diarrhea, and loss of smell and taste, among others.
Asymptomatic patients are those who tested positive with SARS-CoV-2 via the reverse transcriptase PCR (RT-PCR) test. However, they do not manifest any symptoms at all.
Pre-symptomatic patients are those who were asymptomatic at first, but as the disease progressed, they develop symptoms.
Asymptomatic SARS-CoV-2 carriers
To arrive at the study findings, the team conducted a living systematic review and meta-analysis to determine what proportion of infected people does not experience symptoms at all during the disease process, and the number of people who develop symptoms later, called pre-symptomatic carriers.
The team used a database of SARS-CoV-2 evidence from March to June, including 79 studies spanning 6,616 people, wherein 1,287 were tagged as asymptomatic. The database searched included Embase, PubMed, bioRxiv, and medRxiv. Studies of people with COVID-19 diagnosed by reverse transcriptase PCR (RT-PCR) that documented follow-up and symptoms status at the start and end of follow-up or modeling studies were included.
The study findings showed that the proportion of people who became infected with SARS-CoV-2 and remained asymptomatic throughout the infection was 20 percent at follow-up. Meanwhile, the team reported that in even studies, 31 percent of the patients remained asymptomatic at follow-up.
Further study findings also showed that SARS-CoV-2 infection in contacts of people with asymptomatic infection is likely than in contacts of people who develop symptoms.
“The findings of this living systematic review suggest that most people who become infected with SARS-CoV-2 will not remain asymptomatic throughout the infection,” the researchers concluded.
“The contribution of pre-symptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand hygiene, masks, testing tracing, and isolation strategies and social distancing, will continue to be needed,” they added.
Determining asymptomatic carriers
More studies are needed to specifically determine the actual proportion of asymptomatic infections, using methods to minimize biases in selecting participants.
The accurate predictions of true asymptomatic and pre-symptomatic infections are important to provide a better understanding of SARS-CoV-2 transmission at the population level. This way, communities, and countries can adopt suitably modified public health strategies to stem the spread of the infection. These preventive measures include enhanced hand hygiene, wearing masks, contact tracing and testing, isolation strategies, and social distancing.
Global case toll
The coronavirus pandemic is still actively spreading globally, with more than 31.76 million confirmed cases and more than 973,000 deaths. Still, the United States has the highest number of cases, with more than 6.93 million cases and at least 201,000 deaths.
Other countries with high case tolls include India, with more than 5.64 million cases, and Brazil, with more than 4.59 million cases.
The illness has now reached 188 countries and territories, and with many countries slowly lifting restrictions, some have reported a second wave of infections. Health experts recommend that proper hand hygiene, social distancing, and the wearing of masks are the best ways to prevent infection and stem the spread of the virus.
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Journal reference:
Limited impact of prenatal COVID-19 exposure on child neurodevelopmental outcomes