Viral load found to be higher in asymptomatic COVID-19 patients, lower in those who are older: Study

It took quite a while since the pandemic began for medical professionals to understand the transmissibility of the SARS-CoV-2 virus and how patients with or without symptoms help spread the disease further.

As more research related to this topic is conducted, our knowledge is expanding. In June 2020, the World Health Organisation (WHO) said in a news update that transmission occurs mostly from symptomatic people through close contact with others, while asymptomatic patients are much less likely to transmit the virus.

The WHO also mentioned that comprehensive studies on transmission from asymptomatic patients are difficult to conduct and may require more data to provide a better understanding.

In August 2020, a Korean study published in JAMA Internal Medicine suggested that many individuals with infection remained asymptomatic for a prolonged period and yet their viral load was similar to that in symptomatic patients. This study clearly recommended that isolation of infected persons and all protective measures should be performed regardless of symptoms.

A new study published in the journal Infection reveals that asymptomatic patients have a higher viral load than symptomatic patients, suggesting that this might make them even more potent as carriers of the disease than previously thought.

Viral load and asymptomatic patients

Viral load refers to the gross amount of a virus in the blood of an infected person. Having a higher viral load usually suggests that the infection is progressing and the risks of transmission are highest. Viral load measurements can be difficult to conduct since their levels can differ daily.

This is why only long-term, well-controlled assessments can explain how viral load correlates with transmission dynamics in different viral infections. Current research suggests that in , the viral load of SARS-CoV-2 appears to be highest between the first and third day after the onset of symptoms.

Viral load dynamics in asymptomatic patients are yet to be fully explored but this new study sheds much-needed light. The study, conducted by researchers at the Ankara City Hospital’s Department of Infectious Diseases and Clinical Microbiology, Turkey, aimed to evaluate the viral loads of six different sample types of patients of different ages to understand the relationship between SARS-CoV-2 viral load and disease course.

Symptomatic vs asymptomatic viral loads

The researchers collected a total of 360 samples from 60 patients who were hospitalised in the month of May 2020. Nasopharyngeal and oropharyngeal combined, oropharyngeal, saliva, stool, urine and blood samples were taken from all the patients at the time of admission.

While 45 of these 60 patients were symptomatic, 15 were asymptomatic. A total of 39 of these patients were able to confirm that they had been in direct contact with a patient, thus explaining how they got the infection.

The researchers found that there was a significant difference in the mean ages of the asymptomatic (26.4 years) and symptomatic patients (36.4 years). They found 80 percent viral load in the nasopharyngeal and oropharyngeal (combined), 50 percent in saliva, 13.3 percent in the oropharyngeal, 8.3 percent in stool and 1.7 percent in urine samples.

Only one asymptomatic patient showed viral load presence in urine samples. The researchers also found that the viral loads of asymptomatic patients were significantly higher when compared to symptomatic patients. However, as the patient age increased, the levels of viral load were found to be decreasing. The researchers correlated this decrease in viral load among older patients with increasing disease severity and adverse outcomes.

While the researchers concluded that asymptomatic patients do indeed have a higher viral load and are therefore more likely to transmit the disease to others, they recommend more virological studies be conducted to confirm this. They also suggest that as winter intensifies in many countries, proper isolation and treatment for asymptomatic patients should also be scaled up to meet the threat of their high viral load.

For more information, read our article on Viral load. 

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