User talk:Bree061208

Causes of COVID-19
COVID-19 is caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus strain. The virus is transmitted mainly via the respiratory route, when people inhale droplets and particles that infected people release as they breathe, talk, cough, sneeze or sing. The closer people interact, and the longer they interact, the more likely they are to transmit COVID-19, but infection can occur over longer distances, particularly indoors. People are at their peak of infectiousness when their symptoms start, and are infectious for up to 3 days prior to this. Their infectiousness declines after the first week, but they remain contagious for up to 20 days, and can spread the virus even if they never developed any symptoms.

The size of the infectious particles is on a continuum, ranging from small airborne particles that remain suspended in the air for long periods, to larger droplets that may remain airborne or fall to the ground. This continuum between droplets and aerosols has redefined the traditional understanding of how respiratory viruses transmit. The largest droplets of respiratory fluid do not travel far, and can be inhaled, or land on mucous membranes on the eyes, nose, or mouth to cause new infection. The fine aerosol particles are in highest concentration when people are in close proximity, leading to the virus transmitting easier when people are physically close. However, airborne transmission does occur at longer distances, mainly in locations that are poorly ventilated (such as restaurants, choirs, gyms, nightclubs, offices, and religious venues). In those conditions small particles can remain suspended in the air for minutes to hours.

The number of people generally infected by one infected person varies; with only 10 to 20% of people responsible for the diseases spread. However, in September 2020 it was estimated that one infected person will, as a crude average, infect between two and three other people. This is more infectious than influenza, but less so than measles. It often spreads in clusters, where infections can be traced back to an index case or geographical location. There is a major role of "super-spreading events", where many people are infected by one person.

It is possible that a person might get COVID-19 indirectly by touching a contaminated surface or object before touching their own mouth, nose, or eyes, though strong evidence suggests this does not contribute substantially to new infections. Although it is considered possible, there is no direct evidence of the virus being transmitted by skin to skin contact. The virus is not known to spread through feces, urine, breast milk, food, wastewater, drinking water, or via animal disease vectors (although some animals can contract the virus from humans).[57] It very rarely transmits from mother to baby during pregnancy.