Based on the results of 95 studies, which comprised almost 30,000,000 people, the average percentage of patients with COVID-19 that were symptomatic was 0.25 percent in the test population , and 40.5% in confirmed cases.
Asymptomatic infections could be a source of COVID-19 transmission, particularly when communities reopen and public life resumes, but the percentage of these infections among the who have been tested and those diagnosed with COVID-19 has not been studied, according to Qiuyue Ma, PhD, and colleagues from Peking University, Beijing, China.
In a paper published in JAMA Network Open, the researchers identified 44 cross-sectional studies and 41 cohort studies, seven case series, and three case series on transmission studies. There were 74 research studies conducted in countries that are developed, including North America, Asia, Europe and North America. A third (37) of the studies were conducted among patients in hospitals or healthcare workers 17 of them were among staff or residents of nursing homes, and 14 among residents in the community. 13 studies were conducted with pregnant women, eight of them with air or cruise travelers and six who had close contacts of those with confirmed infections.
The meta-analysis covered 29,776,306 individuals. Of them, 11,516 were suffering from asymptomatic infection.
Overall, the pooled percentage of asymptomatic infections among the population that was tested was 0.25%. In a study of various study populations, the percentage was higher among nursing home residents or staff (4.52%), air or cruise ship passengers (2.02%)) and pregnant women (2.34 percent), compared against the percentage of the pooled population.
The proportion of an asymptomatic infection in the population that was confirmed to have it was 40.50%. This was more for women who were pregnant (54.11%) and air or cruise passengers (52.91%), as well as staff or residents in nursing homes (47.53%).
The pooled percentage of the tested population was higher than the overall percentage when the average age of the study population was 60 years old or older (3.69%). The percentage of the pooled population in the confirmed population was, however higher than the overall percentage when the the study population was younger than 20, (60.2%) or older than 39 years old (49.5 percent).
The researchers mentioned in their discussion that the varying percentage of asymptomatic people based on the prevalence of the community could impact the heterogeneity of studies. They also highlighted the large number of studies conducted in nursing home populations. These groups are more likely to have asymptomatic patients.
Researchers have noted the possibility of missing studies, that were not published at the time of meta-analysis, and the study that was written by Chinese authors. Other limitations included the absence of follow-up of presymptomatic or hidden infections, as well as the focus on specific populations, factors that may limit the extent of the results that can be generalized.
However, the results highlight the need to check for asymptomatic infections, especially in countries where COVID-19 is better managed, the researchers stated. They recommended that asymptomatic infections be treated with contact tracing and isolation, similar to the treatment of confirmed cases.
More Testing is Required to Catch Cases Early
“During the initial phase of the COVID-19 pandemic the testing was not widely available in the United States or the rest of the world,” Setu Patolia, MD, of Saint Louis University School of Medicine, St. Louis, Missouri, said in an interview. A large portion of the world does not have access to COVID-19 tests, and early in the pandemic, only severely affected patients were tested, he said. “With new variants, especially the Omicron variant, which can be mild or not so symptomatic disease Asymptomatic carriers play a significant role in spreading the pandemic,” he explained. He added, “It is important that we know the asymptomatic rate of the general population in order to manage the pandemic.”
Patolia said he was astonished by the study finding that one in 400 in the general population could be asymptomatic carriers of COVID-19.
“Also, nursing home patients are at a higher risk of complications of COVID and I had hoped that they would have a higher incidence of symptomatic disease when compared to the general population,” said Patolia. He was equally shocked by the high prevalence of asymptomatic infection among travelers.
He suggested that doctors be more aware of carriers who are not symptomatic, particularly in travelers and nursing home patients. “Travelers carry high risk of passing on infection from one region to another of the world, and doctors should advise them to get tested regardless of the absence of symptoms,” Patolia emphasized. He also said that COVID-19 has been found in a variety of nursing home patients. Physicians should be more cautious with patients who are suffering from COVID and test them even if they do not have symptoms.
Patolia also recommended that pregnant women wear masks to avoid transmission of disease when visiting a physician’s office or labor center.
Patolia stated that there is a need to make at-home testing kits less expensive so that all vulnerable populations can get tested quickly and frequently.
The National Natural Science Foundation of China was a major contributor to the study. Researchers did not have financial conflicts to disclose. Patolia has not disclosed any relevant financial relationships.
JAMA. Published online on December 14 2021. Abstract
Heidi Splete is a freelance medical journalist with over 20 years of experience.
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