How COVID-19 spreads

Knowledge of the novel coronavirus continues to evolve.  Current understanding supports that COVID-19 is primarily transmitted by respiratory droplets. Information about COVID-19 transmission from the CDC and WHO  is compiled below.

  1. Droplet: Respiratory droplets are >5-10 μm in diameter and are produced when an infected person has respiratory symptoms (e.g. coughing or sneezing) or is talking, shouting, or singing.
        • This form is the most significant mode of transmission.
        • Infection can occur when respiratory droplets that include virus are inhaled or deposited on mucous membranes, such in the nose, mouth, or eyes.
        • The risk of transmission diminishes as the distance from the infected person increases and with the passage of time as respiratory droplets fall out of the air, disperse, and decrease in concentration.
        • Risk is improved by wearing a face covering/mask over the mouth and nose by people within 6 feet of each other as a general recommendation.
  2. Airborne: Droplet nuclei or aerosols are <5μm in diameter and remain in the air for a longer period of time than do respiratory droplets, but they disperse quickly. The virus does not seem to remain viable in aerosols as long as it does in respiratory droplets.
        • Not a significant mode of transmission.
        • Infection can occur when a high enough concentrations of aerosol droplets that contain viable virus are inhaled or deposited on mucous membranes, such in the nose, mouth, or eyes.
        • The risk of airborne transmission increases with poor ventilation and with exposure duration.
        • Risk is improved with medical grade, well-fitting, N95 mask or higher (without vents), and by improving ventilation when indoors.
  3. Fomite: Fomites are contaminated surfaces.
        • Not a significant mode of transmission
        • Infection can occur when virus particles land on a surface and someone touches the surface and then transfers viable virus to mucous membranes, such as their nose, mouth, or eyes.
        • Risk is improved with handwashing and avoiding hand contact with face, mouth, nose, and eyes.
  4. Fecal/urine: Though the virus that causes COVID-19 has been found in urine and fecal sample of infected individuals, there is no documentation of transmission from this source.
        • Not a documented mode of transmission
  5. Bloodborne: Though virus has been detected in low levels in plasma or serum, and has been able to replicate in blood cells, there is no clear evidence of bloodborne transmission.
        • Uncertain mode of transmission
  6. Mother-to-child: There is no evidence a fetus can contract COVID-19 in utero. Fragments of virus RNA have been found in breast milk, but there has been no documentation of transmission to an infant from this source.
        • Not a documented mode of transmission (thought transmission through respiratory droplets remains a risk).
  7. Animal-to-human: There are a small number of reports of transmission from pets to humans.
        • Not a significant mode of transmission and is considered rare.