The invisible part of the iceberg of the pandemic
Infectious disease specialists told which of the infected with SARS-CoV-2 revealed the highest viral load
Maria Azarova, Naked Science
As the coronavirus pandemic develops, we are learning more and more details about it. For example, at first Covid-19 was positioned mainly as a respiratory infection, but it soon became clear that the virus affects not only the respiratory system, but also, in particular, the brain, endothelium, affects the heart, causes anosmia, thrombosis and even delirium and stroke.
Although a proportion of patients suffer from coronavirus heavily and have concomitant symptoms, in some cases the infection practically does not manifest itself in any way. Such people are called asymptomatic carriers – and it is they who help the pathogen spread around the world, infecting more and more others.
Earlier, a team of scientists from the United States analyzed the viral load in hospitalized patients with Covid-19, as well as in asymptomatic patients. As a result, both groups were found to have "strikingly similar viral load distributions." Viral load is the total amount of virus in the blood of an infected person. Its higher rates usually imply the progression of the disease and the risk of transmission.
A new study of infectious disease specialists from the Ankara City Hospital (Turkey) at Yildirim Bayazit University, in turn, showed that the viral load in asymptomatic patients is even higher. The work was published in the journal Infection (Hasanoglu et al., Higher viral loads in asymptomatic COVID-19 patients might be the invisible part of the iceberg). Scientists collected samples of saliva, urine and blood, and also took swabs from the nasopharynx / oropharynx, oral cavity, rectum from 60 infected with coronavirus (48 percent – men, 52 percent – women). The biomaterials were sent to the laboratory of the Institute of Public Health of Turkey for research.
25 percent of the subjects did not have any symptoms of the disease. A total of 39 people were able to confirm that they had been in direct contact with Covid-19 patients and thus became infected.
As a result, experts revealed a significant difference in the average age of asymptomatic carriers (26.4 years) and patients with obvious signs of the disease (36.4 years). The highest concentrations of SARS-CoV-2 (80 percent) were found in the nasopharynx and oropharynx combined, 50 percent – in saliva, 13.3 percent – in the oropharynx, 8.3 percent – in the rectum, 1.7 percent – in urine samples.
Correlation of viral load and age (NP – nasopharynx, OP – oropharynx; red – men, blue – women). Drawings from an article in Infection.
The viral load in the oropharynx/nasopharynx of asymptomatic patients was significantly higher than in patients with symptoms (however, when comparing other samples, for example from the oral cavity or saliva, there was no difference in values). In addition, the concentration decreased depending on age, as well as the time that has elapsed since the appearance of signs of Covid-19 and before admission to a medical institution. According to scientists, the drop in viral load in the elderly can be explained by a more severe course of Covid-19.
Correlation of viral load and time from the onset of symptoms to admission to the hospital (NP – nasopharynx, OP – oropharynx).
"The viral load in patients with at least one concomitant pathology (hypertension, diabetes, malignant neoplasms, chronic lung disease) was significantly lower than in patients without them. In addition, such patients were more at risk of severe Covid-19. A significant decrease in viral load was observed with an increase in the severity of the disease when comparing samples from patients with mild or pneumonia. <...> In patients with bilateral "frosted glass" with chest CT, this indicator was much lower compared to patients with unilateral "frosted glass" or normal chest CT," virologists said.
Thus, the authors of the study concluded that carriers of the coronavirus without signs of Covid-19, apparently, are more likely to infect others. However, they recommend confirming the received data once again.
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