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Respiratory syndrome and infectious disease in humans, caused by SARS coronavirus 2

Top 10 COVID-19 related articles

Coronavirus disease 2019
Other namesCOVID, (the) coronavirus
Transmission and life-cycle of SARS-CoV-2 causing COVID-19.
SpecialtyInfectious disease
SymptomsFever, cough, fatigue, shortness of breath, loss of taste or smell; sometimes no symptoms at all[2][3]
ComplicationsPneumonia, viral sepsis, acute respiratory distress syndrome, kidney failure, cytokine release syndrome, respiratory failure, pulmonary fibrosis, pediatric multisystem inflammatory syndrome, chronic COVID syndrome
Usual onset2–14 days (typically 5) from infection
Duration5 days to 10+ months known
CausesSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
Diagnostic methodrRT-PCR testing, CT scan
PreventionFace coverings, quarantine, physical/social distancing, ventilation, hand washing,[4] vaccination[5]
TreatmentSymptomatic and supportive
Frequency131,593,180[6] confirmed cases

Coronavirus disease 2019 (COVID-19) is a contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first case was identified in Wuhan, China, in December 2019.[7] The disease has since spread worldwide, leading to an ongoing pandemic.[8]

Symptoms of COVID-19 are variable, but often include fever, cough, fatigue, breathing difficulties, and loss of smell and taste. Symptoms may begin one to fourteen days after exposure to the virus. At least a third of people who are infected do not develop noticeable symptoms.[9] Of those people who develop noticeable symptoms, most (81%) develop mild to moderate symptoms (up to mild pneumonia), while 14% develop severe symptoms (dyspnea, hypoxia, or more than 50% lung involvement on imaging), and 5% suffer critical symptoms (respiratory failure, shock, or multiorgan dysfunction).[10] Older people are more likely to have severe symptoms. Some people continue to experience a range of effects—known as long COVID—for months after recovery, and damage to organs has been observed.[11] Multi-year studies are underway to further investigate the long-term effects of the disease.[11]

The virus that causes COVID-19 spreads mainly when an infected person is in close contact[a] with another person.[15][16] Small droplets and aerosols containing the virus can spread from an infected person's nose and mouth as they breathe, cough, sneeze, sing, or speak. Other people are infected if the virus gets into their mouth, nose or eyes. The virus may also spread via contaminated surfaces, although this is not thought to be the main route of transmission.[16] The exact route of transmission is rarely proven conclusively,[17] but infection mainly happens when people are near each other for long enough. People who are infected can transmit the virus to another person up to two days before they themselves show symptoms, as can people who do not experience symptoms.[18][19] People remain infectious for up to ten days after the onset of symptoms in moderate cases and up to 20 days in severe cases.[20]

Several testing methods have been developed to diagnose the disease. The standard diagnostic method is by detection of the virus' nucleic acid by real-time reverse transcription polymerase chain reaction (rRT-PCR), transcription-mediated amplification (TMA), or by reverse transcription loop-mediated isothermal amplification (RT-LAMP) from a nasopharyngeal swab.

Preventive measures include physical or social distancing, quarantining, ventilation of indoor spaces, covering coughs and sneezes, hand washing, and keeping unwashed hands away from the face. The use of face masks or coverings has been recommended in public settings to minimise the risk of transmissions. Several vaccines have been developed and several countries have initiated mass vaccination campaigns.

Although work is underway to develop drugs that inhibit the virus, the primary treatment is symptomatic. Management involves the treatment of symptoms, supportive care, isolation, and experimental measures.

COVID-19 Intro articles: 173


During the initial outbreak in Wuhan, China, the virus and disease were commonly referred to as "coronavirus" and "Wuhan coronavirus",[21][22][23] with the disease sometimes called "Wuhan pneumonia".[24][25] In the past, many diseases have been named after geographical locations, such as the Spanish flu,[26] Middle East Respiratory Syndrome, and Zika virus.[27] In January 2020, the WHO recommended 2019-nCov[28] and 2019-nCoV acute respiratory disease[29] as interim names for the virus and disease per 2015 guidance and international guidelines against using geographical locations (e.g. Wuhan, China), animal species, or groups of people in disease and virus names in part to prevent social stigma.[30][31][32] The official names COVID-19 and SARS-CoV-2 were issued by the WHO on 11 February 2020.[33] Tedros Adhanom explained: CO for corona, VI for virus, D for disease and 19 for when the outbreak was first identified (31 December 2019).[34] The WHO additionally uses "the COVID-19 virus" and "the virus responsible for COVID-19" in public communications.[33]

COVID-19 Name articles: 4

Signs and symptoms

Symptoms of COVID-19

Symptoms of COVID-19 are variable, ranging from mild symptoms to severe illness.[35][36] Common symptoms include headache, loss of smell and taste, nasal congestion and rhinorrhea, cough, muscle pain, sore throat, fever, diarrhea, and breathing difficulties.[37] People with the same infection may have different symptoms, and their symptoms may change over time. Three common clusters of symptoms have been identified: one respiratory symptom cluster with cough, sputum, shortness of breath, and fever; a musculoskeletal symptom cluster with muscle and joint pain, headache, and fatigue; a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea.[37] In people without prior ear, nose, and throat disorders, loss of taste combined with loss of smell is associated with COVID-19.[38]

Most people (81%) develop mild to moderate symptoms (up to mild pneumonia), while 14% develop severe symptoms (dyspnea, hypoxia, or more than 50% lung involvement on imaging) and 5% of patients suffer critical symptoms (respiratory failure, shock, or multiorgan dysfunction).[39] At least a third of the people who are infected with the virus do not develop noticeable symptoms at any point in time.[40][41][42][43] These asymptomatic carriers tend not to get tested and can spread the disease.[43][44][45][46] Other infected people will develop symptoms later, called "pre-symptomatic", or have very mild symptoms and can also spread the virus.[46]

As is common with infections, there is a delay between the moment a person first becomes infected and the appearance of the first symptoms. The median delay for COVID-19 is four to five days.[47] Most symptomatic people experience symptoms within two to seven days after exposure, and almost all will experience at least one symptom within 12 days.[47][48]

Most people recover from the acute phase of the disease. However, some people continue to experience a range of effects for months after recovery—named long COVID—and damage to organs has been observed. Multi-year studies are underway to further investigate the long-term effects of the disease.[49]

COVID-19 Signs and symptoms articles: 11


COVID-19 is caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus strain.


Transmission of COVID-19

Coronavirus disease 2019 (COVID-19) spreads from person to person mainly through the respiratory route after an infected person coughs, sneezes, sings, talks or breathes.[50][51] A new infection occurs when virus-containing particles exhaled by an infected person, either respiratory droplets or aerosols, get into the mouth, nose, or eyes of other people who are in close contact with the infected person.[52] During human-to-human transmission, an average 1000 infectious SARS-CoV-2 virions are thought to initiate a new infection.[53][54]

The closer people interact, and the longer they interact, the more likely they are to transmit COVID-19. Closer distances can involve larger droplets (which fall to the ground) and aerosols, whereas longer distances only involve aerosols.[52] Larger droplets can also turn into aerosols (known as droplet nuclei) through evaporation.[55] The relative importance of the larger droplets and the aerosols is not clear as of November 2020; however, the virus is not known to spread between rooms over long distances such as through air ducts.[56] Airborne transmission is able to particularly occur indoors, in high risk locations[56] such as restaurants, choirs, gyms, nightclubs, offices, and religious venues, often when they are crowded or less ventilated.[55] It also occurs in healthcare settings, often when aerosol-generating medical procedures are performed on COVID-19 patients.[57]

Although it is considered possible there is no direct evidence of the virus being transmitted by skin to skin contact.[58] A person could get COVID-19 indirectly by touching a contaminated surface or object before touching their own mouth, nose, or eyes, though this is not thought to be the main way the virus spreads.[58] 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). It very rarely transmits from mother to baby during pregnancy.[58]

Social distancing and the wearing of cloth face masks, surgical masks, respirators, or other face coverings are controls for droplet transmission. Transmission may be decreased indoors with well maintained heating and ventilation systems to maintain good air circulation and increase the use of outdoor air.[59]

The number of people generally infected by one infected person varies.[58] Coronavirus disease 2019 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.[60] There is a major role of "super-spreading events", where many people are infected by one person.[58][61]

A person who is infected can transmit the virus to others up to two days before they themselves show symptoms, and even if symptoms never appear.[62] People remain infectious in moderate cases for 7–12 days, and two weeks or more in severe cases.[62] In October 2020, medical scientists reported evidence of reinfection in one person.[63][64]


Illustration of SARSr-CoV virion

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel severe acute respiratory syndrome coronavirus. It was first isolated from three people with pneumonia connected to the cluster of acute respiratory illness cases in Wuhan.[65] All structural features of the novel SARS-CoV-2 virus particle occur in related coronaviruses in nature.[66]

Outside the human body, the virus is destroyed by household soap, which bursts its protective bubble.[67]

SARS-CoV-2 is closely related to the original SARS-CoV.[68] It is thought to have an animal (zoonotic) origin. Genetic analysis has revealed that the coronavirus genetically clusters with the genus Betacoronavirus, in subgenus Sarbecovirus (lineage B) together with two bat-derived strains. It is 96% identical at the whole genome level to other bat coronavirus samples (BatCov RaTG13).[69][70] The structural proteins of SARS-CoV-2 include membrane glycoprotein (M), envelope protein (E), nucleocapsid protein (N), and the spike protein (S). The M protein of SARS-CoV-2 is about 98% similar to the M protein of bat SARS-CoV, maintains around 98% homology with pangolin SARS-CoV, and has 90% homology with the M protein of SARS-CoV; whereas, the similarity is only around 38% with the M protein of MERS-CoV. The structure of the M protein resembles the sugar transporter SemiSWEET.[71]

The many thousands of SARS-CoV-2 variants are grouped into clades.[72] Several different clade nomenclatures have been proposed. Nextstrain divides the variants into five clades (19A, 19B, 20A, 20B, and 20C), while GISAID divides them into seven (L, O, V, S, G, GH, and GR).[73]

Several notable variants of SARS-CoV-2 emerged in late 2020. Cluster 5 emerged among minks and mink farmers in Denmark. After strict quarantines and a mink euthanasia campaign, it is believed to have been eradicated. The Variant of Concern 202012/01 (VOC 202012/01) is believed to have emerged in the United Kingdom in September. The 501Y.V2 Variant, which has the same N501Y mutation, arose independently in South Africa.[74][75]

SARS-CoV-2 variants

Three known variants of SARS-CoV-2 are spreading among global populations As of January 2021, including the UK Variant (referred to as B.1.1.7) first found in London and Kent, a variant discovered in South Africa (referred to as 1.351), and a variant discovered in Brazil (referred to as P.1).[76]

Using Whole Genome Sequencing, epidemiology and modelling suggest the new UK variant ‘VUI – 202012/01’ (the first Variant Under Investigation in December 2020) transmits more easily than other strains.[77]

COVID-19 Cause articles: 36