How it gets around: COVID-19 transmission
Viruses are tiny germs that can invade our bodies and make us sick by hijacking cells and using them to make copies of themselves. This can damage, change, or even kill those cells so they no longer do for us what they are supposed to do. Some viruses make us sicker than others. Different viruses attack different kinds of cells, causing diseases ranging from the common cold to warts to hepatitis (a liver disease) to COVID-19.
Unlike bacteria, which are one-cell microorganisms that live in many different environments, viruses can’t exist for long without a living plant, animal, or human host. Antibiotics (medicines that kill bacteria) do not work against viruses.
Just as fires need three things in order to burn — fuel, heat, and oxygen — infections caused by viruses need three things: a source, a way into our bodies, and transmission, that is, a way to get from one person to another. Also, there must be enough virus to result in infection.
Virus transmission happens in various ways. The SARS-CoV-2 virus is transmitted mostly by directly touching a contaminated surface and then touching our faces; by sprays or splashes from coughing or sneezing, generally within 6 feet; and by breathing particles carried at greater distances on air currents.
When COVID-19 was first identified, we did not know how it was transmitted. Handwashing is always our first line of defense against infections because we touch so many things around us and touch our own faces so often. The easiest routes for germs to enter our bodies are the mucous membranes of our noses and mouths, which are not only exposed to the outside world, but offer perfect conditions for viruses to thrive. The eyes are another possible access point.
When early studies showed that the virus could survive on surfaces, sometimes for several days, we started quarantining our mail and groceries and wiping down everything we could with disinfectant. The news showed us vivid images of hazmat-suited people spraying the interiors of buses, subway cars and buildings. These common-sense measures are important and effective, but the pandemic developed in spite of them. Contaminated surfaces, especially ones touched often, can collect enough virus to transmit COVID-19 when someone touches them and then touches their own face. However, this has turned out to be an uncommon route of transmission. The likelihood of getting COVID-19 from your mail or a package or a bag of groceries is low, especially if the people who handle them before you are properly masked, which keeps most virus from getting on them in the first place.
The SARS-CoV-2 virus fits perfectly into cells that line our noses and easily converts them to make copies of itself. If enough virus particles take hold before our immune systems can bring up the defenses to defeat them, we develop COVID-19. From the nose the infection can spread deeper into our bodies, causing pneumonia and other problems and too often, unfortunately, death.
When we breathe, speak, and sing, we expel air and droplets of moisture. If we have a respiratory infection, we cough and sneeze out more droplets along with the germs that made us sick. The heavier droplets soon fall to the floor, usually within 3-6 feet. This is why the guidelines call for staying 6 feet apart when we are with other people. At this distance, the chance of inhaling the virus is greatly reduced. But the larger droplets carry more virus, so when they fall on frequently touched surfaces, they are a potential source of infection by contact.
Smaller, lighter droplets can go farther through the air, especially when propelled more forcefully, as when singing or speaking loudly in a crowded bar. Not only that, but particles can remain in the air for fairly long times, making it possible to inhale enough to cause infection. Fans and air conditioners that just move the air around can make things worse. Ventilation that exchanges room air with fresh air from outside is needed to dilute the virus to safer levels. This is the reason for limiting indoor gatherings and for wearing masks.
We just reached the one-year anniversary of the COVID-19 pandemic. The progress made toward understanding and controlling this disease is remarkable; more is being learned every day. We know that COVID directly attacks the respiratory system and spreads mostly through close contact and to some extent through the air at greater distances and/or concentrations. We need to learn more about how people without symptoms transmit the virus, how long people remain infectious after recovering, and whether vaccinated people can still carry and transmit the virus. Because viruses mutate, new variants that may be more easily transmitted or may cause more severe disease, are a continuing threat. But victory is in sight. Like the second-place runner who helped the faltering leader cross the last few feet to the finish line, we need to help each other by wearing masks, washing our hands, social distancing, and avoiding crowds and indoor gatherings. Let’s end COVID!
Michael Heyd, a retired medical librarian from Fairfield Township, spent more than 40 years searching professional literature for doctors, nurses, educators and others at Williamsport Hospital and Susquehanna Health. He is a member of Let’s End COVID, a group of people in Northcentral PA working to overcome the COVID-19 pandemic through education, outreach and mitigation.