There are two likely ways that infected people transmit the virus to infect healthy people.
Mucus like saliva and snot. These are primarily expressed two ways:
- As droplets that spray into the air when people cough and sneeze. This is thought to be the primary way that people transmit the virus, but we don’t know for certain yet. Viruses have evolved to force your body to cough and sneeze uncontrollably. They have evolved to spread and reproduce by modifying your behavior! The CDC thinks this is the main way that the disease is spread and although infected people can spread it when they are asymptomatic, the CDC believes that that is rare.
- Onto the hands (primarily) after touching the nose or mouth or after sneezing onto the hands. Again, viruses have evolved to force your nose to produce a stream of virus-laden snot that you will have the impulse to wipe away thereby spreading itself to your hands.
Through poop. At least two studies have found the virus in human poop and many viruses and bacteria exclusively transmit this way which again can get into the bodies of new hosts via two main vectors.
- As droplets that are sprayed into the air by toilets or faulty sewage pipes. These droplets are then inhaled. A major outbreak in the SARS epidemic happened in a housing estate in Hong Kong called Amoy Gardens where over 300 people caught the virus via the fecal-air route.
- The fecal-oral route which usually means that people aren’t washing their hands completely after using the toilet. Almost nobody lathers soap over their for the full 20 seconds recommended by the CDC. Brian Resnick wrote a great explainer about why soap is “a brutally effective coronavirus killer.” In countries without proper sewage treatment, most fecal-oral transmission happens when water sources are contaminated.
There are three main ways that you could get infected:
Getting the virus on your hands (as described above) and then touching your mucus membranes like those of your eyes, mouth, etc.
You prevent this by:
- Washing your hands properly. Ordinary respiratory illnesses are reduced 15-20% simply by washing hands!
- Stop touching yourself! It is hard to avoid unconsciously touching vulnerable bodily openings such as on the face. One way to help remember to not touch your eyes and mouth is to wear ordinary cloth gloves. They should be laundered regularly to prevent them from becoming sinks of virus, but at least they could help remind you not to touch your eyes and mouth and food because it would be weird to feel the fabric of gloves on the face (or have it touch your food). It is possible that the virus doesn’t survive as well on fabric as it does on skin, but we don’t know that yet, so if gloves don’t help you remember to stop touching yourself, then they probably aren’t worth wearing.
Breathing in the virus of which there are two possibilities:
droplets of virus-laden moisture. This is thought to be the most common route of infection.
- It is surprisingly easy to guard against breathing in droplets because they generally only travel less than three feet horizontally and they soon fall out of the air (where they can contaminate surfaces that lead to the next route of infection) and the Taiwanese authorities are recommending that everyone always try to maintain one meter of “social distance” from others. The CDC recommends that if you stay six feet away from infected people, you can nearly eliminate this risk. A surgical mask or cloth over your mouth and nose could help reduce this route of transmission, but droplets can still be inhaled if a mast is not well-sealed on the face and that is usually impossible with most designs because they aren’t designed to protect the wearer. Surgical masks are designed to prevent droplets from spreading from the people wearing the masks, such as surgeons, to others, such as their patients who have open wounds that are literally right under the surgeons’ noses in operating rooms. They are not designed to protect the wearer of the mask. But if someone gets sick, then by all means, they should wear a mask at all times to protect others around them.
dried airborne viruses.
- Moisture droplets rapidly desiccate in the air leaving the remaining solids such as virus particles. We don’t know if (nor how long) the corona virus can survive in the air after the moisture evaporates out of droplets, but if it can survive as a dry particle in the air, it would be very difficult to stop because it airborne viruses are so small that they can float on air currents indefinitely and only high-performance HEPA filters can screen them out of the air. Ordinary surgical masks are completely useless to stop dried airborne virus particles. In actuality, some airborne viruses are not completely dried out because the viruses form a little wall that retains a tiny amount of protective moisture around them, but the effect is the same. It becomes dry particles that don’t stick to the fibers of surgical masks and which are tiny enough to float on the air currents for hours or days. Airborne viruses cannot survive indefinitely, particularly when exposed to sunlight which typically kills them rapidly with ultraviolet light, but they only need to survive long enough for someone to inhale them back into the hospitable habitat of the lungs.
- So far there is no hard evidence that airborne transmission is happening, which is good because it is very hard to prevent. You prevent airborne transmission by breathing outside air, using high-efficiency HEPA air filtration or staying out of buildings that share air with infected people.
The oral route whereby the virus gets on your food, typically after hitching a ride on someone’s hands, but also possibly as a result of sneeze droplets that fall onto food.
- You prevent this by properly washing hands and making sure your food is never around sick people after it is cooked.
Although a few bacteria and fungi can directly inflect people through unbroken skin, it is highly unlikely that the corona virus can. Most viruses die harmlessly after only about 20 minutes on the skin which is less hospitable to viruses than non-porous surfaces like stainless steel and plastic where viruses stay moist longer than on cloth or dry wood which tends to suck out the moisture which sustains them. So cleaning hard surfaces that people often touch could help. Be particularly aware of things that you touch frequently like your phone. It might be a good time to break that habit of using your phone while on the toilet unless you are going to wash your phone along with your hands afterwards.
Now would also be a fantastic time to quit smoking:
Among Chinese patients diagnosed with COVID-19 associated pneumonia, the odds of disease progression (including to death) were 14 times higher among people with a history of smoking compared to those who did not smoke. This was the strongest risk factor among those examined.
In fact, a HEPA air purifier to clean indoor air might even help. They can actually filter out some fraction of airborne viruses and even if that doesn’t help, there is some evidence that just getting rid of particulates in the air could help reduce the risk of respiratory infections, at least for people living in polluted areas.
Given that it is possible that people could get their initial infections through different organs, such as via the lungs or the eyes or the digestive track, it would be interesting to see if the mortality of the disease is different for people who are initially infected in different places on their bodies. Most people who have died of covid-19 were killed when the virus invaded the deep lung tissues and if the virus were to initially infect the lower part of the lungs, perhaps it’s symptoms might become more severe and life-threatening than when it begins somewhere else such as in the digestive track and only later finds a way to the lungs after the body has already begun to develop defensive antibodies which could help protect the lungs which is the organ that is the most vulnerable to covid-19.
Julia Belluz has even more information and recent research about how covid-19 is spread.