Transmission of SARS-CoV-2
Note: A COVID-19 (SARS-CoV-2) particle is 0.125 micrometers (μm); influenza virus size is 0.08 – 0.12 μm; a human hair is about 150 μm.
*1 nm = 0.001 micron; 1000 nm = 1 micron; Micrometer (μm) is the preferred name for micron (an older term)
1 meter is = 1,000,000,000 nm or 1,000,000 microns
Virus is transmitted through respiratory droplets produced when an infected person coughs, sneezes or talks. Larger respiratory droplets (>5 μm) remain in the air for only a short time and travel only short distances, generally <1 meter. They fall to the ground quickly. https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30245-9/fulltext
This idea guides the CDC's advice to maintain at least a 6-foot distance.
Virus-laden small (<5 μm) aerosolized droplets can remain in the air for at least 3 hours and travel long distances. https://www.nejm.org/doi/pdf/10.1056/NEJMc2004973?articleTools=true
In air conditioned environment these large droplets may travel farther.
However, ventilation — even the opening of an entrance door and a small window can dilute the number of small droplets to one half after 30 seconds. (This study looked at droplets from uninfected persons). This is clinically relevant because poorly ventilated and populated spaces, like public transport and nursing homes, have high SARS-CoV-2 disease transmission despite physical distancing. https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30245-9/fulltext
Objects and surfaces
Person to person touching
The CDC's most recent statement regarding contracting COVID-19 from touching surfaces: "Based on data from lab studies on Covid-19 and what we know about similar respiratory diseases, it may be possible that a person can get Covid-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose or possibly their eyes," the agency wrote. "But this isn't thought to be the main way the virus spreads. https://www.cdc.gov/media/releases/2020/s0522-cdc-updates-covid-transmission.html.
Chinese study with data taken from swabs on surfaces around the hospitalhttps://wwwnc.cdc.gov/eid/article/26/7/20-0885_article?deliveryName=USCDC_333-DM25707The surfaces where tested with the PCR (polymerase chain reaction) test, which greatly amplifies the viral genetic material if it is present. That material is detectable when a person is actively infected. This is thought to be the most reliable test.
Computer mouse (ICU 6/8, 75%; General ward (GW) 1/5, 20%)
Trash cans (ICU 3/5, 60%; GW 0/8)
Sickbed handrails (ICU 6/14, 42.9%; GW 0/12)
Doorknobs (GW 1/12, 8.3%)
81.3% of the miscellaneous personal items were positive:
Medical equipment (spirometer, pulse oximeter, nasal cannula)
PC and iPads
Cellular phones (83.3% positive for viral RNA)
Remote controls for in-room TVs (64.7% percent positive)
Toilets (81.0% positive)
Room surfaces (80.4% of all sampled)
Bedside tables and bed rails (75.0%)
Window ledges (81.8%)
Plastic: up to 2-3 days
Stainless Steel: up to 2-3 days
Cardboard: up to 1 day
Copper: up to 4 hours
Floor – gravity causes droplets to fall to the floor. Half of ICU workers all had virus on the bottoms of their shoes