Novel coronavirus (COVID-19) transmission
Updated Aug. 3, 2020

COVID-19 may be transmitted when people touch surfaces – such as doorknobs, countertops, railings, etc. – contaminated by novel coronavirus and then touch their face, nose or mouth. The Centers for Disease Control and Prevention says while it is possible to be infected by touching a surface or object that has the novel coronavirus on it, it isn’t considered the main way the virus spreads. But it can happen.

Rigorous handwashing, good house cleanings and disinfecting high-touch surfaces help guard against possible surface contamination and transmission. The CDC has information about cleaning your home and high-touch areas.

Airborne transmission requires an infectious pathogen to remain viable in the air for extended periods of time and can infect people at distances greater than 3 feet. The evidence is not yet clear if COVID-19 can easily become truly airborne and can be transmitted over long distances and time. Currently, COVID-19 is primarily spread through direct contact and short distances by respiratory droplets when an infected person coughs or sneezes. The respiratory droplets land in the nose or mouth of people who are near the infected individual.

Based on the most recent information available, both asymptomatic and presymptomatic transmission of the novel coronavirus may occur. Based on CDC studies, about 60% of COVID-19 cases are transmitted by people without symptoms. The possibility of COVID-19 transmission from people who are presymptomatic (meaning they have COVID-19 before symptoms appear) or asymptomatic (meaning a person is infected but their symptoms never develop) reinforces the value of masking, social distancing and the avoidance of large gatherings to reduce COVID-19 spread.

With asymptomatic spread, it all depends on how much virus is coming out of a person’s cough, breath, speech, etc. that is putting people at risk. People are commonly infectious just before they are symptomatic (also known as presymptomatic). We see that with chickenpox, the flu and other illnesses, where people can transmit before there are symptoms. If you stay 6 feet apart from people, unless they are shedding a ton of coronavirus, you are likely not going to get it. However, it’s not just proximity, but also duration of time spent with an infected person. We consider it exposure if people are face-to-face for at least 15 minutes. It’s very unlikely you will contract COVID-19 walking by a person on the street.

Contact tracing is the process of tracking down an individual who has had an infectious disease and the people that person has potentially been in contact with. It’s a confidential process that has been used by health departments for years to help stop the spread of infectious diseases and avoid outbreaks.

Learn more about contact tracing related to COVID-19 

Researchers haven’t been able to distinguish superspreaders from other infected individuals; meaning it’s hard to identify specific people responsible for multiple COVID-19 transmissions. Superspreaders could be widely spreading coronavirus in two ways: by their behavior and not following health guidelines, or by the fact that they can more effectively replicate and shed the virus. It’s difficult to separate those who potentially have more capacity to physically replicate the virus from those who are in close quarters and not following medical best practices.

Listen as UC Davis School of Medicine associate dean Dr. Brad Pollock discusses superspreaders and the coronavirus pandemic

Mostly likely, yes. Compared to adults, fewer children have become infected with coronavirus, and most who did become infected generally suffered mild symptoms. Worldwide, children younger than 10 years old make up only 1% of COVID-19 cases. But several studies, according to research from China and other countries, offer evidence that children can transmit the virus. We know a good amount of transmission has occurred through close household contact, which likely includes children. Our understanding of the disease is still limited, as the virus was only discovered in December 2019, but we can’t ignore the role of children in spreading the virus. We should not assume that just because a child is relatively asymptomatic doesn’t mean they can’t spread coronavirus.

The summer heat will not end the spread of viruses like COVID-19. It would have to be unbearably hot (potentially at least 130° F) to get rid of coronavirus. However, higher temperatures help degrade viruses’ genetic material so they become less infectious. The higher the temperature, the less likely COVID-19 can survive. Researchers have found that the fastest transmission of COVID-19 was in places with dry, cool weather up to 62 degrees. Lower humidity dries out our mucus membranes and causes other issues with the respiratory tract, making humans more susceptible to infection.

There’s no evidence that shows COVID-19 can be transmitted in open water, like swimming pools. It also hasn’t been proven that a specific amount chlorine in a pool can eliminate coronavirus. However, pools are typically large, and the amount of viable virus that someone would come in contact with would likely be very low. Most public pools are heavily chlorinated specifically to kill viruses and bacteria that may be in the water.

If you’re in a pool, the same principles of social distancing apply as when you’re out of the pool. For extra safety, check to see if the pool facility has any requirements for swimmers, like health screenings. Of course, there’s always the risk that even if COVID-19 isn’t transmitted in the water, you can catch the virus before getting in the pool – from touching a door handle or chair arm. In this age of the coronavirus pandemic, there’s no perfect way to know if something is 100% safe. Use common sense and good judgement while experts continue to advance their understanding of COVID-19 and its transmission.

There’s no evidence that dogs and cats can transfer COVID-19 back to people. We know that coronavirus infections of dogs and cats can occur and that they can shed virus. However, it may be that dogs and cats can become infected, but they can’t shed enough virus or shed the virus in a way that it can be transmitted to other animals. Overwhelmingly, COVID-19 transmission is driven by person-to-person contact, which presents a much greater risk than holding a dog or cat.