Asymptomatic COVID-19: Five Questions Answered
By William Petri
Blood tests that check for exposure to the coronavirus are starting to come online, and preliminary findings suggest that many people have been infected without knowing it. Even people who do eventually experience the common symptoms of COVID-19 don't start coughing and spiking fevers the moment they're infected.
William Petri is a professor of medicine and microbiology at the University of Virginia who specializes in infectious diseases. Here, he runs through what's known and what isn't about asymptomatic cases of COVID-19.
How common is it for people to contract and fight off viruses without knowing it?
In general, having an infection without any symptoms is common. Perhaps the most infamous example was Typhoid Mary, who spread typhoid fever to other people without having any symptoms herself in the early 1900s.
My colleagues and I have found that many infections are fought off by the body without the person even knowing it. For example, when we carefully followed children for infection by the parasite Cryptosporidia, one of the major causes of diarrhea, almost half of those with infections showed no symptoms at all.
In the case of the flu, estimates are that anywhere from 5 percent to 25 percent of infections occur with no symptoms.
For the most part, symptoms are actually a side effect of fighting off an infection. It takes a little time for the immune system to rally that defense, so some cases are more aptly considered presymptomatic rather than asymptomatic.
How can someone spread coronavirus if they aren’t coughing and sneezing?
Everyone is on guard against the droplets that spray out from a coronavirus patient's cough or sneeze. They're a big reason public health officials have suggested everyone should wear masks.
But the virus also spreads through normal exhalations that can carry tiny droplets containing the virus. A regular breath may spread the virus several feet or more.
Spread could also come from fomites — surfaces, such as a doorknob or a grocery cart handle, that are contaminated with the coronavirus by an infected person's touch.
What’s known about how contagious an asymptomatic person might be?
No matter what, if you've been exposed to someone with COVID-19, you should self-quarantine for the entire 14-day incubation period. Even if you feel fine, you're still at risk of spreading the coronavirus to others.
Most recently it has been shown that high levels of the virus are present in respiratory secretions during the "presymptomatic" period that can last days to more than a week prior to the fever and cough characteristic of COVID-19. This ability of the virus to be transmitted by people without symptoms is a major reason for the pandemic.
After an asymptomatic infection, would someone still have antibodies against SARS-CoV-2 in their blood?
Most people are developing antibodies after recovery from COVID-19, likely even those without symptoms. It is a reasonable assumption, from what scientists know about other coronaviruses, that those antibodies will offer some measure of protection from reinfection. But nothing is known for sure yet.
Recent serosurveys in New York City that check people's blood for antibodies against SARS-CoV-2 indicate that as many as one in five residents may have been previously infected with COVID-19. Their immune systems had fought off the coronavirus, whether they'd known they were infected or not — and many apparently didn't.
How widespread is asymptomatic COVID-19 infection?
No one knows for sure, and for the moment lots of the evidence is anecdotal.
For a small example, consider the nursing home in Washington where many residents became infected. Twenty-three tested positive. Ten of them were already sick. Ten more eventually developed symptoms. But three people who tested positive never came down with the illness.
When doctors tested 397 people staying at a homeless shelter in Boston, 36 percent came up positive for COVID-19 — and none of them had complained of any symptoms.
In the case of Japanese citizens evacuated from Wuhan, China and tested for COVID-19, fully 30 percent of those infected were aymptomatic.
An Italian pre-print study that has not yet been peer-reviewed found that 43 percent of people who tested positive for COVID-19 showed no symptoms. Of concern: The researchers found no difference in how potentially contagious those with and without symptoms were, based on how much of the virus the test found in individuals' samples.
The antibody serosurveys getting underway in different parts of the country add further evidence that a good number – possibly anywhere from around 10 percent to 40 percent — of those infected might not experience symptoms.
Asymptomatic SARS-CoV-2 infection appears to be common — and will continue to complicate efforts to get the pandemic under control.
Reposted with permission from The Conversation.
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In celebration of Earth Day, a star-studded cast is giving fans a rare glimpse into the secret lives of some of the planet's most majestic animals: whales. In "Secrets of the Whales," a four-part documentary series by renowned National Geographic Photographer and Explorer Brian Skerry and Executive Producer James Cameron, viewers plunge deep into the lives and worlds of five different whale species.
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="b102b19b2719f50272ab718c44703dd0"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/xOySOlB78dM?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
Herring are a primary food source for Norway's orcas. Luis Lamar / National Geographic for Disney+
Belugas are extremely social creatures with a varied vocal range. Peter Kragh / National Geographic for Disney+
A Southern Right whales is pictured in the accompanying book, "Secrets of the Whales." Brian Skerry / National Geographic
The coronavirus has isolated many of us in our homes this year. We've been forced to slow down a little, maybe looking out our windows, becoming more in tune with the rhythms of our yards. Perhaps we've begun to notice more, like the birds hopping around in the bushes out back, wondering (maybe for the first time) what they are.
A Coeligena helianthea hummingbird is photographed during a birdwatching trail at the Monserrate hill in Bogota on November 11, 2020. Colombia is the country with the largest bird diversity in the world, home to about 1,934 different bird species, a fifth of the total known. JUAN BARRETO / AFP / Getty Images
1. Choosing the Right Binoculars<p>Binoculars are a relatively indispensable tool for most birders – but, for those just starting out, it might not yet be worth the several-hundred-dollar investment. If you aren't able to scour the attics of friends or borrow a pair from a fellow bird watcher, some local birding and naturalist groups have <a href="https://vashonaudubon.org/all-about-vashon-birds/binoculars-check-out/" target="_blank">binocular loaning programs</a> for members, allowing you to plan ahead for a day (or week) of birding.</p><p>When you're ready to take the plunge, choosing a pair or binoculars should take some careful deliberation based on your needs and preferences; some <a href="https://www.birdwatchersdigest.com/bwdsite/explore/optics/top-10-tips-buying-binoculars-bird-watching.php" target="_blank">major considerations</a> might include size, ease of use, <a href="https://www.rei.com/learn/expert-advice/binoculars.html" target="_blank" rel="noopener noreferrer">magnification</a>, and price. While professional binoculars can easily run north of $1,000, there are plenty of perfectly suitable entry-level binoculars under $200. You might not get the perfect precision and clarity of more elite models, but a less expensive pair will allow you to strengthen your birding skills while deciding if you're interested in investing in a premium pair.</p><p>For a budget-friendly option, check out resale options on eBay, Facebook marketplace, or neighborhood yard sales: you might find a nicer pair whose retail price isn't within your budget.</p>
2. Know What Birds Are in Your Area<p>When I began to pay more attention to the birds just outside my apartment building, I started to learn what species have always been around me: European starlings, house sparrows, blue jays, black capped chickadees, and the occasional red-bellied woodpecker. They had always been there, but I hadn't ever taken the time to identify them. Once you learn to <a href="https://www.audubon.org/news/get-know-these-20-common-birds_" target="_blank" rel="noopener noreferrer">recognize common birds</a> in your area, you'll be able to identify the typical species right outside your window and in your community. Of course, permanent residential birds in your neighborhood will <a href="https://nestwatch.org/learn/focal-species/" target="_blank" rel="noopener noreferrer">vary by region</a>, as will those migrating through it.</p>
3. Get Out and Explore<p>Venturing elsewhere might allow you to spot some different species beyond those frequenting your backyard. Anywhere with water or greenery offers a place for birding; as an urbanite myself, I've found that even small- and mid-sized parks in New York City allow me to find more elusive birds (although Central Park takes the crown for an afternoon of urban birding).</p><p>If you are able to travel a bit further from home, <a href="https://www.fws.gov/refuges/" target="_blank">national wildlife refuges</a> and <a href="https://www.americasstateparks.org/" target="_blank" rel="noopener noreferrer">state/national parks</a> are excellent places to explore bird habitats and perhaps log some less-common sightings. The American Birding Association also lists <a href="https://www.aba.org/aba-area-birding-trails/" target="_blank" rel="noopener noreferrer">birding trails by state</a>, and Audubon and BirdLife International identify <a href="https://www.audubon.org/important-bird-areas" target="_blank" rel="noopener noreferrer">Important Bird Areas (IBAs)</a> across the country – important bird habitats and iconic places that activists are fighting to protect – where birders can spot birds of significance.</p>
4. Finding a Bird: Stop, Look, Listen, Repeat<p>The National Audubon Society recommends the "<a href="https://www.audubon.org/news/how-find-bird" target="_blank">stop, look, listen, repeat</a>" mantra when seeking and identifying birds.</p><p>First and foremost, spotting birds requires attention. Stopping – getting out of the car, pausing on the sidewalk, trail, or in the backyard to look up – is the most important step.</p><p>When looking for birds, try to avoid gazing wildly around; rather, scan your surroundings, focusing on any odd shapes or shadows, trying to think about where a bird might perch (power lines, fence posts, branches), or keep an eye on the sky for flying eagles and hawks. In open areas like fields and beaches, you might have a more panoramic view, and can take in different sections of the landscape at a time. Look around with the naked eye before reaching for the binoculars to hone in.</p><p>While it can be hard to sift through the noise, listening for birds is perhaps an even more important element of bird watching than looking. Once you spend more time in the field, you'll be able to parse apart the racket and identify specific species, especially aided by Audubon's Bird Guide app or by learning from their <a href="https://www.audubon.org/section/birding-ear" target="_blank">Birding by Ear series</a>.</p><p>Repeat this pattern as you continue on your way, stopping to look and listen for birds as you go, rather than waiting for them to come to you. </p>
5. Identification<p>When you head out for a day of bird watching – especially when you're hoping to spot some new species – you'll want to be armed with the tools to identify what you see. <a href="https://www.audubon.org/news/how-identify-birds" target="_blank" rel="noopener noreferrer">Major considerations when identifying birds</a> are their group (such as owls, hawks, or sparrow-like birds), size and shape, behavior, voice, field marks, season, and habitat.</p><p>The <a href="https://www.sibleyguides.com/about/the-sibley-guide-to-birds/" target="_blank" rel="noopener noreferrer">Sibley Guide to Birds</a> and the <a href="https://www.hmhbooks.com/shop/books/peterson-field-guide-to-birds-of-north-america-second-edition/9781328771445" target="_blank" rel="noopener noreferrer">Peterson Field Guide</a> are widely considered the best books for identifying birds in North America, although many <a href="https://www.audubon.org/news/what-bird-guide-best-you" target="_blank" rel="noopener noreferrer">specialized guides</a> focus on specific species or regions as well.</p><p>Plenty of <a href="https://blog.nature.org/science/2013/05/27/boucher-bird-blog-apps-smart-birder/" target="_blank" rel="noopener noreferrer">bird identification apps</a> have popped up in recent years – including National Geographic Birds, Sibley eGuide to Birds, iNaturalist, Merlin Bird ID, and Birdsnap – which are basically a <a href="https://www.audubon.org/news/the-best-birding-apps-and-field-guides" target="_blank" rel="noopener noreferrer">field guide in your pocket</a>. I'm partial to the Audubon Bird Guide, which allows users to filter by common identifiers, including a bird's habitat, color, activity, tail shape, and general type, adding them all to a personal map to view your sightings.</p>
6. Recording Your Sightings<p><span>As you deepen your commitment to birding, you might join the community of birders that track and quantify their sightings, building their </span><a href="https://www.thespruce.com/what-birds-count-on-a-life-list-386704#:~:text=A%20life%20list%20is%20a,which%20birds%20you%20have%20seen." target="_blank" rel="noopener noreferrer">life list</a><span>.</span></p><p>While a standard notebook noting the date, species name, habitat, vocalizations, or any other data you wish to include will suffice, some birders opt for a more <a href="https://www.riteintherain.com/no-195-birders-journal" target="_blank" rel="noopener noreferrer">structured birder's journal</a> with pre-determined fields to record your encounters, take notes, draw sketches, etc.</p><p>Many birders also choose to record their sightings online and in shared databases (which include many of the field guide apps), often pinpointing them on a map for others to view. Launched by the Cornell Lab of Ornithology and Audubon, <a href="https://ebird.org/home" target="_blank" rel="noopener noreferrer">eBird is one of the largest databases and citizen science projects around birding</a>, where hundreds of thousands of birders enter their sightings, and users can explore birds in regions and hotspots around the world. Users can also record their sightings on the <a href="https://apps.apple.com/us/app/ebird/id988799279" target="_blank" rel="noopener noreferrer">eBird app</a>.</p>
7. Attracting Birds to Your Own Yard<p>Feeding birds is a common phenomenon: more than 40% of Americans maintain a birdfeeder to attract birds and watch them feast.</p><p>Not all birdfeed is created equal, however. Many commercial varieties are mostly made with "fillers" (oats, red millet, etc.) that birds will largely leave untouched. After researching what birds to expect in your area – and which ones you want to attract – you can create your own birdfeed with <a href="https://www.allaboutbirds.org/news/types-of-bird-seed-a-quick-guide/?pid=1142" target="_blank">seeds that will appeal to them</a>.</p><p>Beyond filling a birdfeeder, <a href="https://www.ecowatch.com/eco-friendly-lawn-2651194858.html" target="_self">transforming your yard into an eco-friendly oasis</a> is by far the best way to attract birds. Choosing to forgo mowing your lawn, planting native flowers and grasses, and ditching the pesticides will bring back the bugs that birds feed on, and provide a safe haven in which birds can happily live and eat.</p><p>While it's widely considered acceptable – and even beneficial – to feed birds with appropriate seeds, communal birdfeeders often <a href="https://www.audubon.org/news/to-feed-or-not-feed" target="_blank" rel="noopener noreferrer">foster unlikely interactions between different species</a>, who can then transmit harmful diseases and parasites to one another. Maintaining several bird feeders with different types of seeds might keep different species from coming into contact, and feeders can be <a href="https://www.allaboutbirds.org/news/how-to-clean-your-bird-feeder/" target="_blank" rel="noopener noreferrer">cleaned to prevent the spread of infection</a>.</p>
8. Inclusivity and Anti-Racism in the Birding Community<p>Like all outdoor activities and areas of scientific study, birding communities are subject to racist and discriminatory ideologies. Black birders have long experienced discrimination and underrepresentation in outdoor spaces. The work of organizations like the <a href="https://www.instagram.com/birdersfund/" target="_blank">Black & Latinx Birders Fund</a>, <a href="https://www.instagram.com/birdability/" target="_blank">Birdability</a>, and <a href="https://www.instagram.com/feministbirdclub/" target="_blank">Feminist Bird Club</a> highlight the contributions and importance of birders of color, birders with disabilities, and women and LGBTQ+ birders to the birding community, as do activists and naturalists like <a href="https://www.instagram.com/hood__naturalist/" target="_blank">Corina Newsome</a> and <a href="https://www.instagram.com/tykeejames/" target="_blank">Tykee James</a>. The work of <a href="https://www.audubon.org/news/its-bird-new-comic-written-central-park-birder-christian-cooper" target="_blank">Christian Cooper</a>, <a href="https://camilledungy.com/publications/" target="_blank">Camille Dungy</a> (read her poem <a href="https://www.poetryfoundation.org/poetrymagazine/poems/58363/frequently-asked-questions-10" target="_blank">Frequently Asked Questions: 10</a>), and <a href="https://orionmagazine.org/article/9-rules-for-the-black-birdwatcher/" target="_blank">J. Drew Lanham</a> – including his essay "<a href="https://lithub.com/birding-while-black/" target="_blank">Birding While Black</a>" – are a great place to start.</p><p>Getting involved in birding means educating ourselves on these issues and taking meaningful action; the work of <a href="https://www.audubon.org/news/its-bird-new-comic-written-central-park-birder-christian-cooper" target="_blank">Christian Cooper</a> and <a href="https://orionmagazine.org/article/9-rules-for-the-black-birdwatcher/" target="_blank">J. Drew Lanham</a> – including his essay "<a href="https://lithub.com/birding-while-black/" target="_blank" rel="noopener noreferrer">Birding While Black</a>" – are a great place to start. Just as birders are activists for protecting habitats and natural areas, we must also be active and aware of inclusivity in these spaces.</p>
9. Get Involved<p>To learn from and enjoy the company of other birders, check out local birding groups in your area to join. Many Audubon chapters host trips, meetings, and bird walks for members. The American Birding Association even maintains a <a href="https://www.aba.org/festivals-events/" target="_blank">directory of birding festivals</a> across the country.</p><p>Volunteering for birds is also a great way to meet other birders and take action for birds in your community; local organizations might have opportunities for assisting with habitat restoration or helping at birding centers.</p><p>Like all wildlife, climate change and habitat destruction threaten the livelihood of birds, eliminating their breeding grounds and food sources. A <a href="https://www.audubon.org/climate/survivalbydegrees" target="_blank">2019 report released by the National Audubon Society</a> found that two-thirds of North American birds may face extinction if global temperatures rise 5.4 degrees Fahrenheit by 2100. Staying informed about and taking action for legislation designed to protect birds and our climate – such as the recent <a href="https://www.congress.gov/bill/116th-congress/house-bill/5552/text" target="_blank" rel="noopener noreferrer">Migratory Bird Protection Act</a> – is important for ensuring a livable future for wildlife and humans alike.</p><p><em>Linnea graduated from Skidmore College in 2019 with a Bachelor's degree in English and Environmental Studies, and now lives in Brooklyn, New York. Most recently, Linnea worked at Hunger Free America, and has interned with WHYY in Philadelphia, Saratoga Living Magazine, and the Sierra Club in Washington, DC. </em><em>Linnea enjoys hiking and spending time outdoors, reading, practicing her German, and volunteering on farms and gardens and for environmental justice efforts in her community. Along with journalism, she is also an essayist and writer of creative nonfiction.</em></p>
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