Indirect Transmission of COVID-19

There has been a lot of talk in the news about how to avoid COVID-19. Recommendations include social distancing, minimizing time in groups, and maintaining at least six feet of distance between people.

While it seems obvious that coronavirus can spread if someone sneezes on you or if someone coughs on their hands and then shakes your hand, one nonobvious way coronavirus can transfer is through indirect contact.

Source: Atkinson et al. WHO 2009.

For example, someone with COVID-19 can sneeze on to their hands and then wipe their hands on a door knob. If you touch that door knob and wipe your face, you have the potential to also get infected with the virus.

Persistence of COVID-19 on Surfaces

Human coronaviruses can remain infectious on inanimate surfaces at room temperature for days. Recently, van Doremalen et al. showed that the SARS-CoV-2 virus remained in aerosols for more than 3 hours, can remain on on plastic and stainless steel for more than 3 days, similar to the 2003 SARS virus. See for more details.

Source: van Doremalen et al. NEJM 2020.

Coronaviruses have the capacity to survive on a wide variety of materials including metals, plastics, fabric, paper, wood, glass, stethoscopes, and tissue paper. Ye et al. examined how many objects were contaminated with COVID-19 during the outbreak in Wuhan, China and found that printers, keyboards, door knobs, and medical equipment were frequently contaminated with SARS-CoV-2 RNA. Source:

Ye et al. 2020

They also found that personal protective equipment like gloves and hand sanitizer dispensers frequently contained positive samples of SARS-CoV-2 RNA.

Ye et al. 2020

Indirect Transmission

This is particularly problematic because humans inadvertently touch their faces 23 times per hour and contact mucous membranes 44% of the time (Kwok et al, Journal of Infection Control 2014). Source:

We do not have the full estimate of how many people contracted COVID-19 from indirect contact with surfaces, but we do know that in the previous previous 2003 SARS outbreak, some individuals who contracted the virus were hospital cleaners who had no direct contact with patients (Ho et al, Annals of Internal Medicine 2003). Source:


Vigilant hygiene is the solution to prevent unneeded spread of COVID-19.

Kampf et al. showed that surface disinfection with 0.1% sodium hypochloride can reduce coronavirus infectivity more than 1000 fold in less than 1 minute (Kampf et al. Journal of Hospital Infection. 2020). Source:

For the general public, the WHO recommends to wash your hands frequently, maintain social distancing, avoid touching eyes, nose, and mouth, and practicing good respiratory hygiene.

In the hospital, my personal opinion is that we should avoid unnecessary physical exams, tools, and procedures. Dr. Jeremy Faust got a lot of flak for this recent tweet:

My opinion is that the evidence supports that he is right.

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