infectious diseases
COVID 19
Transmission of COVID 19
The SARS-CoV-2 virus spreads by close person-to-person contact, mainly via respiratory droplets produced when an infected person coughs, sneezes, sings, exercises, or talks. The spread occurs through large respiratory droplets that can travel short distances and land directly on mucosal surfaces or through small respiratory particle aerosols that can linger in air for several hours and travel longer distances (> 6 feet) before being inhaled. Spread of the virus could also occur via contact with surfaces contaminated (fomites) by respiratory secretions, if a person touches a contaminated surface and then touches a mucous membrane on the face (eyes, nose, mouth). The SARS-CoV-2 virus spreads easily between people. The risk of transmission is directly related to the amount of virus to which a person is exposed. In general, the closer and longer the interaction with an infected person, the higher the risk of virus spread. Both asymptomatic and symptomatic patients can transmit the virus, making it difficult to control spread. A symptomatic person is most contagious for the several days before and after the onset of symptoms, at which time the viral load in respiratory secretions is greatest. Factors such as distance from an infected person, the number of infected people in the room, the duration of time spent with infected people, the size of the air space, aerosol-generating activity (eg, singing, shouting, or exercising), ventilation in the location, and the direction and speed of airflow can contribute to this risk. Genetic variants of the SARS-CoV-2 virus emerge as it evolves. Variants with the potential for increased transmissibility, more severe disease, diagnostic detection failures, or reduced response to available treatments and/or vaccines are tracked as Variants of Concern and are commonly referred to by their WHO-designated Greek alphabet label or their Pango lineage number. A genetic mutation that confers a fitness advantage, namely increased transmissibility, can rapidly replace previously circulating variants. The progression of dominant variants in the United States and much of the world includes Alpha, Beta, Delta, and Omicron. The Omicron variant has predominated worldwide since March 2022, with newer and more transmissible Omicron subvariants (eg, BA.4 and BA.5) replacing the original Omicron (B.1.1.529). See alsoCDC: Variants & Genomic Surveillance. Situations with high risk of transmission include congregate living facilities (eg, elder care or other long-term care facilities, residential schools, prisons, ships) as well as crowded, poorly ventilated environments, such as indoor religious services, gyms, bars, nightclubs, indoor restaurants, and meat-packing facilities. Such situations have a high population density in which maintaining distance and ventilation precautions is difficult. The residents of elder care facilities are also at high risk of severe disease because of age and underlying medical disorders. Large indoor events or private gatherings such as meetings or weddings have also been associated with high transmission rates. These so-called super-spreader events or situations are probably due to a combination of biological, environmental, and behavioral factors. Social determinants of health (conditions in the places where people are born, live, learn, work, and play) impact a wide range of health risks and outcomes, such as exposure to SARS-CoV-2 infection, severe COVID-19, and death, as well as access to testing, vaccination, and treatment. In the United States, COVID-19 case, hospitalization, and death rates are higher in some racial and ethnic minority groups, including among people who are Black, Hispanic or Latino, American Indian, and Alaska Native. For people infected with COVID-19, isolation and precaution measures are recommended in an attempt to limit the spread of SARS-CoV-2 infection. (See alsoCDC: Isolation and Precautions for People with COVID-19.) For people exposed to COVID-19, precautions are recommended to help reduce the risk of spreading the virus. (See alsoCDC: What to Do If You Were Exposed to COVID-19.) 