Among asymptomatic patients, 2% could account for 90% of the viral load in the community

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Approximately 2% of asymptomatic college students carried 90% of COVID-19 viral load levels on a Colorado campus last year, new research reveals. In addition, viral loads in these students were as high as those observed in hospitalized patients.

“University campuses were one of the few places where the virus was detected in people without symptoms or suspicion of exposure. This allowed us to make some powerful comparisons between symptomatic and healthy carriers of the virus,” said author Sara Sawyer, doctor. , said professor of virology at the University of Colorado Boulder Medscape Medical News.

“It turns out that walking around a college campus can be as dangerous as walking through a hospital COVID room, as you’ll experience these viral‘ super carriers ’alike in both environments,” he said.


Dr. Thomas Giordano

“This is an important study to advance our understanding of how SARS-CoV-2 is distributed in the population,” said Thomas Giordano, MD, MPH, professor and section head of infectious diseases at Baylor College of Medicine. Houston. Medscape Medical News when asked to comment on the research.

The study “adds to the evidence that viral load is not too closely correlated with symptoms.” In fact, Giordano added, “this study suggests that viral load has nothing to do with symptoms.”

Viral load may also not be related to transmissibility, Raphael Viscidi, MD, said when asked to comment. “This is not a transmissibility study. They did not show that viral load is the transmission-related factor.”

“It is true that 2% of the population they studied carried 90% of the virus, but it does not establish any biological importance in that 2%,” added Viscidi, a professor of pediatrics and oncology at Johns Hopkins University School of Medicine. Baltimore. , Maryland.

The 2% could just be the top end of the tail of a normal bell-shaped distribution curve, Viscidi said, or there could be something biologically unique in that group. But the study does not make that distinction, he said.

The study was published online May 10 a PNAS, the official journal of the National Academy of Sciences.

A similar picture in hospitalized patients

Of the more than 72,500 saliva samples taken during COVID-19 screening at the University of Colorado Boulder between August 27 and December 11 last year, 1405 were positive for SARS-CoV- 2.

The researchers also compared the viral loads of the students with those of the hospitalized patients according to the published data. They found that the distribution of viral loads between these groups was indistinguishable.

“Surprisingly, these data sets demonstrate dramatic differences in viral levels between individuals, with a very small minority of infected individuals harboring the vast majority of infectious virions,” the researchers write. The comparison “really represents two extremes: one group is mostly hospitalized, while the other group represents a young and healthy (but infected) university population.”

“It would be interesting to adjust public health recommendations based on a person’s viral load,” Giordano said. “It could be speculated that a person with a very high viral load could be more or less thoroughly isolated, while someone with a very low viral load could be minimally isolated.

“This is speculation and more data is needed to prove this concept,” he added. In addition, quantitative viral load testing should be standardized before it can be used to guide this decision making.

Preceding the era of the COVID-19 vaccine

It should be noted that the research was conducted in the fall of 2020, prior to access to vaccination against COVID-19.



Dr. David Hirschwerk

“The study was conducted before vaccine availability in a cohort of young people. It adds more data to support previous observations that most infections are spread by a much smaller group of individuals,” he said. said David Hirschwerk, MD, Medscape Medical News when asked to comment.

“Now that vaccines are available, I think it’s very likely that a repeated study like this will show a decrease in the transmission of infected but asymptomatic vaccinated people,” added Hirschwerk, an infectious disease specialist at Northwell Health in New Hyde Park. , New York, which was not affiliated with the research.

The mechanism is still a mystery

“This finding has been in the literature in a fragmentary way since the beginning of the pandemic,” Sawyer said. “I just think we were the first to realize the bigger implications of these viral load plots that we’ve all been seeing over and over again.”

It goes unanswered as a minority of people walk asymptomatically with a majority of viruses. Are there any special people who can harbor these extremely high viral loads? Or do many infected people experience a short period of time when they have such high levels?

The highest viral load observed in the current study was more than 6 trillion virions per ml. “It is remarkable to note that this individual was on campus and showed no symptoms at our test site,” the researchers write.

In contrast, the lowest viral load detected was 8 virions per ml.

While more research is needed, the researchers note that “a strong implication is that these people who are ‘super viral carriers’ can also be ‘super propagators.’

Some of the study’s authors have financial ties to companies that offer commercial testing for SARS-CoV-2, including Darwin Biosciences, TUMI Genomics, Faze Medicines, and Arpeggio Biosciences.

PNAS. Published online May 10, 2020. Full text

Damian McNamara is a staff Miami-based journalist. It covers a wide range of medical specialties, including infectious diseases, gastroenterology, and critical care. Follow Damian on Twitter: @MedReporter.

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