麻豆影院

A few 鈥渟uper carriers鈥� with off-the-charts viral loads are likely responsible for the bulk of COVID-19 transmissions, while about half of infected people aren鈥檛 contagious at all at the time of diagnosis, suggests of more than 72,000 test samples.

A second, lends further credence to the idea that viral load, or the amount of virus particles a person carries, drives contagion. It found that only one in five university students who tested positive while living in a residence hall infected their roommate. And their viral load was nearly seven times higher than those who didn鈥檛 spread the virus.

鈥淭he takeaway from these studies is that most people with COVID don鈥檛 get other people sick, but a few people get a lot of people sick,鈥� said Sara Sawyer, a professor of molecular, cellular and developmental biology and senior author of the first study. 鈥淚f you don鈥檛 have a viral super-carrier sitting near you at dinner, you might be OK. But if you do, you鈥檙e out of luck. It鈥檚 a game of roulette so you have to continue to be careful.鈥�

For the studies鈥攁mong the largest to date to examine trends in asymptomatic people鈥攔esearchers analyzed saliva samples collected from students, and some faculty and staff, on the CU 麻豆影院 campus between Aug. 17 and Nov. 25.

Asymptomatic students in residence halls are required to test weekly, using a free, highly-sensitive saliva-based screening test called RT-qPCR (reverse transcription polymerase chain reaction), which detects and quantifies genetic material from the virus that causes COVID-19.听

In the fall, out of 72,500 samples taken from asymptomatic people, 1,405 cases of COVID-19 were identified.

鈥淲hat is so special about these samples is that they are all from infected people with no symptoms鈥攁 snapshot of all these seemingly healthy people you assume it is safe to be around,鈥� said Sawyer.

Super-carriers = super-spread

Sawyer and her team quantified just how many viral particles, or virions, each of those samples contained, plotted it and compared it to samples from hospitalized patients. A few surprising patterns emerged. First, the distribution of viral loads in the asymptomatic sample was indistinguishable from that of highly symptomatic patients.

鈥淭his means that symptoms tell you very little about what is going on inside a person鈥檚 body,鈥� said Sawyer. 鈥淪ome of these asymptomatic people are carrying a viral load as high as someone who is intubated with COVID in a hospital bed.鈥�

Just 2% of all the COVID-positive individuals at CU 麻豆影院 carried 90% of the circulating virus. One student with the highest load carried 5%.

Meanwhile, about half of those who tested positive had viral loads so low (below 106 virions per millilieter) that they were probably not carrying live virus anymore鈥攊nstead they may have just been shedding viral fragments from tissue under repair. Thus, they were probably not contagious.

鈥淭his provides another example of why you don鈥檛 necessarily need super sensitive tests that may take longer to process,鈥� said coauthor Roy Parker, director of the BioFrontiers Institute and Howard Hughes Medical Institute investigator. 鈥淓ven a faster but less sensitive test will catch all the people who are contagious.鈥�

Dorm life, with precautions, still safe

For a second study, researchers used the same samples to explore how often one roommate infected another.听

In all, 1,058 students living in the dorms tested positive, constituting 16.5% of the population.

Students in single rooms were about half as likely to be infected. But this was not because the virus was spreading between roommates. (Previous research has shown that students who live alone tend to have fewer social contacts).

In fact, only 20% of infected students鈥攖hose with significantly higher viral loads鈥攖ransmitted the virus to their roommate.

Notably, CU 麻豆影院鈥攚hile allowing students to have roommates in the fall鈥攔equired that students diagnosed with COVID-19 move into a dedicated isolation dorm for 10 days. But it can take time for a student flagged through screening to get a follow-up diagnostic, get notified and move out.

鈥淥ne might think that students who were co-housed with another student longer before isolating would be more likely to transmit the virus to their roommate but we saw no impact,鈥� said lead author Kristen Bjorkman, COVID scientific director for CU 麻豆影院.

This does not mean that isolation has no impact at all on the spread of the virus, she said, but it does provide a ray of optimistic news for people who want to live with other people but are worried about safety.

鈥淭his is important for us and other universities to know because it tells us we can continue to offer on-campus housing and roommate pairing,鈥� she said.

The findings may also offer relief to those who have received a positive COVID-19 test and fear for people they live with.

鈥淧eople feel a lot of guilt about this but our study suggests that getting a positive test is not a guarantee you will infect your loved ones or roommates,鈥� Bjorkman said.

Neither paper has been published in a peer-reviewed journal yet.

Collectively, the research shows that, in some cases it might be prudent to contact those with high viral loads fast鈥攁nd encourage them to isolate quickly.

鈥淭his could go a long way in preventing large outbreaks,鈥� said Bjorkman.