Each week we answer some of your pressing questions about the coronavirus and how to stay safe. Email us your questions at goatsandsoda@npr.org with the subject line: "Weekly Coronavirus Questions."
Does the size of a viral dose make a difference? That is, if you're exposed to lots of viral particles, will you get sicker?
While there is a lot we don't know about SARS-CoV-2, experts believe they can answer this question with confidence: Yes – the amount of virus a person is exposed to makes a difference in whether they get sick and how sick they get.
"Dose is important in everything we are doing in life," says Peter Palese, a leading virologist who is professor and chair of microbiology at the Icahn School of Medicine at Mount Sinai in New York. "The same is also true for coronaviruses. It makes a lot of sense because if you have a lot of virus [in your environment], such as when you are working in an intensive care unit, then you get many more virus particles in your system and the disease is usually much worse."
"Most viruses, there's some form of graded response depending on how big your initial exposure is," explains Dr. Joshua Rabinowitz, a professor of chemistry and genomics at Princeton. "Every virus, if you get one particle of virus, you're likely to never know it – you're also likely to really never get sick and never develop an immune response. And for most acute viruses, there is a gray area where you get some version of sick but not horribly sick — and develop an immune response that is protective against the virus in the future."
There have been cases of young, healthy health-care workers getting severely sick with COVID-19. That's what scientists would expect with a virus in which dose plays an important role.
"If you have someone working in an intensive care unit and the poor physician or the poor nurse gets a hefty dose, then the severity of the disease really is much worse than if one just gets a single particle," says Palese.
But there are still some unknowns in the matter of dose. Rabinowitz says researchers don't yet know exactly how the symptoms of the current coronavirus correlate with the size of the initial dose. Nor is it known how much of a viral dose causes a person to get sick from COVID-19, though "we have very good reason to believe that it requires many virus particles," he says.
Understanding the role of dose is important, he says, because during an epidemic where much is out of one's control, individuals can act to reduce the risk of high-dose exposure — through social distancing and protective measures like masks. While six feet of distance is recommended, even four feet is better than two feet, Rabinowitz says. "They're probably radically different in terms of both your chance of getting sick and your chance of getting horribly sick if you do get sick."
And masks, even if they're far from 100% effective? "They're likely to be super important," says Rabinowitz, "because they're dose-reducing agents."
How many people are walking around with coronavirus but no symptoms? How much are they driving transmission?
"Somewhere between 25 and 50%" of people with coronavirus are out there with no symptoms, estimated Dr. Anthony Fauci, the immunologist helping to steer the U.S. pandemic policy, at a White House press briefing April 5, though he acknowledged there's not much scientific data to back up the claim.
"Even among good friends, we differ about that," he said. "Right now, we're just guessing."
The issue is that, with limited testing available, people who have the virus but show no symptoms are hard to find. Researchers have confirmed their existence through contact tracing and mass testing in places like nursing homes and the Diamond Princess cruise ship.
People who show no symptoms can fall into two categories — they can be presymptomatic, which means that they're in the incubation phase and will develop symptoms over the next few days, or asymptomatic, which means they never develop symptoms.
Based on available data, the World Health Organization thinks that presymptomatic cases are more common than asymptomatic cases, and that some people who are presymptomatic can spread the virus one to three days before showing symptoms. It's less clear whether people who are totally asymptomatic are contributing significantly to spread.
The extent to which symptom-less cases are driving transmission is an open question — and it seems to depend on behavior. In China before lockdown, a modeling paper in Science suggests that undiscovered cases (including people with mild or no symptoms) may have been responsible for 79% of transmission because many of them attended gatherings or traveled while contagious. Other papers from Singapore and China, from late January on, suggest that presymptomatic cases accounted for 6% to 13% of transmission in times of greater COVID-19 awareness.
I have a toothache. Should I go to the dentist right now?
If you're experiencing pain or swelling in your mouth, you should see a dentist, says Mary-Jane Hanlon, associate dean for clinical affairs at Tufts School of Dental Medicine and president-elect of the Massachusetts Dental Society.
"Especially if the pain or the swelling is increasing," she says. "If you go to bed and you're woken up in the middle of the night because of pain, that's another indication that, yes, you should see a dentist."
As with everything else, coronavirus has complicated dental visits. The American Dental Association has recommended that dentists restrict their practices to all but urgent and emergency care through April 30.
Some dentists are not seeing even emergency patients right now because the dentists themselves have underlying medical conditions that put them at risk to COVID-19, Hanlon says.
So if you are in pain, you should call your dentist — but may be referred to a different dentist handling emergency care.
But if it's not an emergency, don't go to the dentist right now, says Hanlon. The American Dental Association has a list of dental issues that can wait, and those that can't.
"Believe it or not, there are patients getting upset with us because we can't they can't have their teeth cleaned, but we just can't take the chance," she says. "There's no reason why a patient can't wait a couple months to have their teeth cleaned."
If you do make an appointment for emergency dental care, expect your dentist to ask you whether you have symptoms of COVID-19. When you arrive at the office, you'll likely be handed a mask, hand sanitizer and gloves.
And don't expect to hang out reading a magazine before your appointment.
"You should not go into the office until it is your time to go in," says Hanlon. "What we're trying to do is make sure we stagger appointments and have adequate time to clean up between patients."
Some dental practices may resume regular appointments in the coming weeks, as some state and local governments allow re-opening certain businesses considered "essential." Last week, the ADA released updated guidance that in states considering reopening, "dentists should exercise professional judgment and carefully consider the availability of appropriate PPE [personal protective equipement] to minimize risk of virus transmission."
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