Many Asymptomatic COVID-19 Cases Are Undetected: Study
Thu, February 2, 2023

Many Asymptomatic COVID-19 Cases Are Undetected: Study



Many countries are ramping up their efforts for coronavirus mass testing, mainly focusing on people who are exhibiting known symptoms of the disease. But health experts have reminded governments to also focus on those who haven’t exhibited the symptoms because there’s a huge possibility that they are infected. 

Back in January, a 20-year-old woman from Wuhan tested positive for coronavirus and passed it to five of her family members but never got physically sick herself. Reports showed that the woman traveled to Anyang on January 10 together with her family members. On January 17, one of the woman's family members came down with a fever and sore throat. The other four relatives developed a fever and respiratory symptoms the following week.

All of the family members tested positive for COVID-19. The woman, who also tested positive for the virus, still wasn’t showing any symptoms. By February 11, the woman still had no fever, cough, sore throat, or gastrointestinal issues. The researchers from China said that this is the first concrete evidence that a person showing no symptoms can pass the coronavirus to others.

Health experts have also documented other instances in which people tested positive for the virus without showing symptoms. A report from the Chinese Center for Disease Control and Prevention, for instance, analyzed records of all China’s reported cases of the disease from December 8 to February 11. The researchers found out that 1.2% of patients confirmed to be infected showed no symptoms. 

Huge numbers of asymptomatic cases were also found on the Diamond Princess cruise ship, where 322 of 621 people tested positive but showed no symptoms. "It's very clear that the people who are getting caught in that umbrella of reporting are the people that present themselves to a hospital. There's another whole cohort that is either asymptomatic or minimally symptomatic,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said.



Rates of ‘Symptomless’ COVID-19

After the World Health Organization (WHO) declared COVID-19 a global pandemic, it released the results of the COVID-19 testing on an expedition cruise ship. The cruise departed from Argentina in mid-March with 217 passengers and crew members. The researchers explained that the cruise ship took certain precautions, including taking everyone’s temperature before embarking and making hand-sanitizing stations readily available onboard.

Despite these measures, the first case of fever was reported on day eight of the expedition. After this, the management decided to confine passengers to their cabins and required crew members in contact with any sick passengers to wear personal protective equipment (PPE). The results of the coronavirus testing showed that 59% of those on board tested positive for coronavirus. Of those who tested positive, 81% had no symptoms while 19% had symptoms. 

The researchers from Macquarie University, Sunshine Coast University Hospital, and the Royal Australian College of General Practitioners also reported that the rate of ‘silent’ symptomless COVID-19 infection may be much higher than previously thought. “As countries progress out of lockdown, a high proportion of infected, but asymptomatic, individuals may mean that a much higher percentage of the population than expected may have been infected with COVID,” Prof. Alan Smyth, joint editor-in-chief of Thorax, said.

Robert Redfield, the director of the Centers for Disease Control and Prevention, said that asymptomatic carriers are most likely contributing to the rapid spread of the coronavirus worldwide. According to Science Alert, a leading scientific publisher dedicated to publishing peer-reviewed significant research work, an article by Bill Gates recently published in the New England Journal of Medicine stated that the prevalence of asymptomatic transmission doesn't bode well for global containment efforts.

"That means COVID-19 will be much harder to contain than the Middle East respiratory syndrome or severe acute respiratory syndrome (SARS), which were spread much less efficiently and only by symptomatic people," Gates said.

Experts say that statistics or data about coronavirus cases suggest that the disease may be similar to the flu virus in one way: the asymptomatic rate. According to Forbes, a global media company, focusing on business, investing, technology, entrepreneurship, leadership, and lifestyle, a study published in the journal Emerging Infectious Disease estimated that the asymptomatic rate for influenza is 19.1% with a 95% confidence interval of 5.2% to 35.5%. 



Why It Is Important to Identify Asymptomatic Cases 

While there are several studies being conducted about asymptomatic cases, health experts aren’t sure how common it is. This is also considering the fact that there are different asymptomatic rates in many countries. For instance, 40% of people were asymptomatic in a study from Iceland, while 30.8% of people in a study of Japanese evacuees from Wuhan were asymptomatic.

“So it’s hard to know which is right. And although we are getting closer to understanding the proportion of asymptomatic cases with Covid-19, we still don’t know for sure the magnitude of the impact that they have on the further transmission of cases. Do they generate lots of secondary cases or only a small proportion?” Sanjaya Senanayake, an associate professor of medicine at the Australian National University, said.

According to The Guardian, a British daily newspaper, it is important to identify asymptomatic cases because the virus can spread whether a person exhibits symptoms or not. Peter Collignon, an infectious disease doctor, said that speaking, shouting, and singing were all ways someone with no symptoms could spread the virus.



“Although patients who were asymptomatic experienced less harm to themselves, they may have been unaware of their disease and therefore not isolated themselves or sought treatment, or they may have been overlooked by healthcare workers and thus unknowingly transmitted the virus to others,” the JAMA study found.

While new studies about asymptomatic cases are still not enough, these could help state how common asymptomatic infections of COVID-19 are or how much these contribute to transmission.

“The answers to these questions are not only essential for getting a better picture of how many people have already been exposed, but will also greatly affect our predictions on how the Covid-19 pandemic may develop over the coming months, and what interventions are most important to prevent the second wave of cases and deaths,” Prof. Ivo Mueller, an epidemiologist at the Walter and Eliza Hall Institute of Medical Research in Melbourne, said.