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It was first identified in December 2019 in Wuhan, China, and has resulted in an ongoing pandemic. The first confirmed case has been traced back to 17th November 2019. Traces of the virus have been found in December-2019 wastewater that was collected from Milan and Turin. As of 21 June 2020, more than 8.75 million cases have been reported across 188 countries and territories, resulting in more than 463,000 deaths. More than 4.33 million people have recovered. 
Common symptoms include fever, cough, fatigue, shortness of breath, and loss of smell and taste. While the majority of cases result in mild symptoms, some progress to acute respiratory distress syndrome (ARDS) possibly precipitated by cytokine storm, multi-organ failure, septic shock, and blood clots. The time from exposure to onset of symptoms is typically around five days, but may range from two to fourteen days. 
The virus is primarily spread between people during close contact, most often via small droplets produced by coughing, sneezing, and talking. The droplets usually fall to the ground or onto surfaces rather than travelling through air over long distances. However, research as of June 2020 has shown that speech-generated droplets may remain airborne for tens of minutes. Less commonly, people may become infected by touching a contaminated surface and then touching their face. It is most contagious during the first three days after the onset of symptoms, although spread is possible before symptoms appear, and from people who do not show symptoms. The standard method of diagnosis is by real-time reverse transcription polymerase chain reaction (rRT-PCR) from a nasopharyngeal swab. Chest CT imaging may also be helpful for diagnosis in individuals where there is a high suspicion of infection based on symptoms and risk factors; however, guidelines do not recommend using CT imaging for routine screening. 
Recommended measures to prevent infection include frequent hand washing, maintaining physical distance from others (especially from those with symptoms), quarantine (especially for those with symptoms), covering coughs, and keeping unwashed hands away from the face. The use of cloth face coverings such as a scarf or a bandana has been recommended by health officials in public settings to minimise the risk of transmissions, with some authorities requiring their use. Health officials also stated that medical-grade face masks, such as N95 masks, should only be used by healthcare workers, first responders, and those who directly care for infected individuals.
According to the World Health Organization (WHO), there are no vaccines nor specific antiviral treatments for COVID-19. Management involves the treatment of symptoms, supportive care, isolation, and experimental measures. The World Health Organization (WHO) declared the COVID 19 outbreak a public health emergency of international concern (PHEIC) on 30 January 2020 and a pandemic on 11 March 2020. Local transmission of the disease has occurred in most countries across all six WHO regions. 
Preventive measures to reduce the chances of infection include staying at home, avoiding crowded places, keeping distance from others, washing hands with soap and water often and for at least 20 seconds, practising good respiratory hygiene, and avoiding touching the eyes, nose, or mouth with unwashed hands. The U.S. Centers for Disease Control and Prevention (CDC) recommends covering the mouth and nose with a tissue when coughing or sneezing and recommends using the inside of the elbow if no tissue is available. Proper hand hygiene after any cough or sneeze is encouraged. The CDC has recommended cloth face coverings in public settings where other social distancing measures are difficult to maintain, in part to limit transmission by asymptomatic individuals. The U.S. National Institutes of Health guidelines do not recommend any medication for prevention of COVID 19, before or after exposure to the SARS-CoV-2 virus, outside the setting of a clinical trial. 
Social distancing strategies aim to reduce contact of infected persons with large groups by closing schools and workplaces, restricting travel, and cancelling large public gatherings. Distancing guidelines also include that people stay at least 6 feet (1.8 m) apart. There is no medication known to be effective at preventing COVID 19. After the implementation of social distancing and stay-at-home orders, many regions have been able to sustain an effective transmission rate ("Rt") of less than one, meaning the disease is in remission in those areas. 
As a COVID-19 vaccine is not expected until 2021 at the earliest, a key part of managing COVID 19 is trying to decrease and delay the epidemic peak, known as "flattening the curve".This is done by slowing the infection rate to decrease the risk of health services being overwhelmed, allowing for better treatment of current cases, and delaying additional cases until effective treatments or a vaccine become available. 
Several countries have recommended that healthy individuals wear face masks or cloth face coverings (like scarves or bandanas) at least in certain public settings, including China, Hong Kong, Spain, Italy, Russia, and the United States. This recommendation is meant to reduce the spread of the disease by asymptomatic and pre-symtomatic individuals and is a complementary measure to established preventive measures such as social distancing. Face coverings minimise the excretion of respiratory droplets by infected individuals while breathing, talking and coughing. Non-medical cloth face coverings such as a scarf or a bandana are recommended for the general public in places where social distancing is difficult to maintain. Medical grade facemasks such as N95 masks should be reserved and prioritised for healthcare workers and first responders. 
Those diagnosed with COVID 19 or who believe they may be infected are advised by the CDC to stay home except to get medical care, call ahead before visiting a healthcare provider, wear a face mask before entering the healthcare provider's office and when in any room or vehicle with another person, cover coughs and sneezes with a tissue, regularly wash hands with soap and water and avoid sharing personal household items. The CDC also recommends that individuals wash hands often with soap and water for at least 20 seconds, especially after going to the toilet or when hands are visibly dirty, before eating and after blowing one's nose, coughing or sneezing. It further recommends using an alcohol-based hand sanitiser with at least 60% alcohol, but only when soap and water are not readily available. 
For areas where commercial hand sanitisers are not readily available, the WHO provides two formulations for local production. In these formulations, the antimicrobial activity arises from ethanol or isopropanol. Hydrogen peroxide is used to help eliminate bacterial spores in the alcohol; it is "not an active substance for hand antisepsis". Glycerol is added as a humectant.
Fever is the most common symptom of COVID-19, but is highly variable in severity and presentation, with some older, immunocompromised, or critically ill people not having fever at all. In one study, only 44% of people had fever when they presented to the hospital, while 89% went on to develop fever at some point during their hospitalization. A lack of fever does not verify someone is disease free.
Other common symptoms include cough, loss of appetite, fatigue, shortness of breath, sputum production, and muscle and joint pains. Symptoms such as nausea, vomiting, and diarrhoea have been observed in varying percentages. Less common symptoms include sneezing, runny nose, sore throat, and skin lesions. Some cases in China initially presented with only chest tightness and palpitations. A decreased sense of smell or disturbances in taste may occur. Loss of smell was a presenting symptom in 30% of confirmed cases in South Korea. 
As is common with infections, there is a delay between the moment a person is first infected and the time he or she develops symptoms. This is called the incubation period. The typical incubation period for COVID 19 is five or six days, but it can range from one to fourteen days with approximately ten percent of cases taking longer. 
An early key to the diagnosis is the tempo of the illness. Early symptoms may include a wide variety of symptoms but infrequently involves shortness of breath. Shortness of breath usually develops several days after initial symptoms. Shortness of breath that begins immediately along with fever and cough is more likely to be anxiety than COVID-19. The most critical days of illness tend to be those following the development of shortness of breath. 
A minority of cases do not develop noticeable symptoms at any point in time. These asymptomatic carriers tend not to get tested, and their role in transmission is not fully known. Preliminary evidence suggested they may contribute to the spread of the disease. In June 2020, a spokeswoman of WHO said that asymptomatic transmission appears to be "rare," but the evidence for the claim was not released. The next day, WHO clarified that they had intended a narrow definition of "asymptomatic" that did not include pre-symptomatic or paucisymptomatic (weak symptoms) transmission and that up to 41% of transmission may be asymptomatic. Transmission without symptoms does occur. 
COVID-19 spreads primarily when people are in close contact and one person inhales small droplets produced by an infected person (symptomatic or not) coughing, sneezing, talking, or singing. The WHO recommends 1 metre (3 ft) of social distance; the U.S. CDC recommends 2 metres (6 ft). People can transmit the virus without showing symptoms, but it is unclear how often this happens. One estimate of the number of those infected who are asymptomatic is 40%.
People are most infectious when they show symptoms (even mild or non-specific symptoms), but may be infectious for up to two days before symptoms appear (pre-symptomatic transmission). They remain infectious an estimated seven to twelve days in moderate cases and an average of two weeks in severe cases. 
When the contaminated droplets fall to floors or surfaces they can, though less commonly, remain infectious if people touch contaminated surfaces and then their eyes, nose or mouth with unwashed hands. On surfaces the amount of active virus decreases over time until it can no longer cause infection, and surfaces are thought not to be the main way the virus spreads. It is unknown what amount of virus on surfaces is required to cause infection via this method, but it can be detected for up to four hours on copper, up to one day on cardboard, and up to three days on plastic (polypropylene) and stainless steel (AISI 304). Surfaces are easily decontaminated with household disinfectants which kill the virus outside the human body or on the hands. Disinfectants or bleach are not a treatment for COVID 19, and cause health problems when not used properly, such as when used inside the human body. 
The first case of coronavirus at Delhi was confirmed on 2nd March when a 45 years old person from East Delhi, with a history of travel from Italy, has been tested to be positive for COVID-19. Total 92 contacts of Delhi index case have been traced. Out of these 92 contacts 14 belong to Delhi and rest 74 contacts have been cross notified to respective states. Out of 14 contacts two were symptomatic and found negative for COVID-19. 
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. It has since spread worldwide, leading to an ongoing pandemic.

Symptoms of COVID-19 are variable, but often include fever, cough, fatigue, breathing difficulties, and loss of smell and taste. Symptoms begin one to fourteen days after exposure to the virus. Around one in five infected individuals do not develop any symptoms. While most people have mild symptoms, some people develop acute respiratory distress syndrome (ARDS). ARDS can be precipitated by cytokine storms,[10] multi-organ failure, septic shock, and blood clots. Longer-term damage to organs (in particular, the lungs and heart) has been observed. There is concern about a significant number of patients who have recovered from the acute phase of the disease but continue to experience a range of effects—known as long COVID—for months afterwards. These effects include severe fatigue, memory loss and other cognitive issues, low-grade fever, muscle weakness, and breathlessness.[11][12][13][14]

The virus that causes COVID-19 spreads mainly when an infected person is in close contact[a] with another person. 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. The exact route of transmission is rarely proven conclusively,[20] but infection mainly happens when people are near each other for long enough. It can spread as early as two days before infected persons show symptoms, and from individuals who never experience symptoms. People remain infectious for up to ten days in moderate cases, and two weeks in severe cases. Various testing methods have been developed to diagnose the disease. The standard diagnosis method is by real-time reverse transcription polymerase chain reaction (rRT-PCR) 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 various countries have initiated mass vaccination campaigns.

Although work is underway to develop drugs that inhibit the virus, the primary treatment is currently symptomatic. Management involves the treatment of symptoms, supportive care, isolation, and experimental measures.
Symptoms of COVID-19 are variable, ranging from mild symptoms to severe illness. Common symptoms include headache, loss of smell and taste, nasal congestion and rhinorrhea, cough, muscle pain, sore throat, fever and breathing difficulties.People with the same infection may have different symptoms, and their symptoms may change over time. In people without prior ears, nose, and throat disorders, loss of taste combined with loss of smell is associated with COVID-19 with a specificity of 95%.[25]

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).Around one in five people are infected with the virus but do not develop noticeable symptoms at any point in time. These asymptomatic carriers tend not to get tested, and they can spread the disease. Other infected people will develop symptoms later (called pre-symptomatic) or have very mild symptoms, and can also spread the virus.[31]

As is common with infections, there is a delay, known as the incubation period, between the moment a person first becomes infected and the appearance of the first symptoms. The median incubation period for COVID-19 is four to five days.Most symptomatic people experience symptoms within two to seven days after exposure, and almost all symptomatic people will experience one or more symptoms before day twelve.
COVID-19 is caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus strain.

 
COVID-19 spreads from person to person mainly through the respiratory route after an infected person coughs, sneezes, sings, talks or breathes. 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. During human-to-human transmission, an average 1000 infectious SARS-CoV-2 virions are thought to initiate a new infection.

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. The larger droplets may also evaporate into the aerosols (known as droplet nuclei). The relative importance of the larger droplets and the aerosols is not clear as of November 2020, however the virus is not known to transmit between rooms over long distances such as through air ducts. Airborne transmission is able to particularly occur indoors, in high risk locations, such as in restaurants, choirs, gyms, nightclubs, offices, and religious venues, often when they are crowded or less ventilated. It also occurs in healthcare settings, often when aerosol-generating medical procedures are performed on COVID-19 patients.

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.

The number of people generally infected by one infected person varies; as of September 2020 it was estimated that one infected person will, on 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.
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. All features of the novel SARS-CoV-2 virus occur in related coronaviruses in nature.

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

SARS-CoV-2 is closely related to the original SARS-CoV. 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). 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 98.6% similar to the M protein of bat SARS-CoV, maintains 98.2% homology with pangolin SARS-CoV, and has 90% homology with the M protein of SARS-CoV; whereas, the similarity is only 38% with the M protein of MERS-CoV. In silico analyses showed that the M protein of SARS-CoV-2 has a triple helix bundle, forms a single 3-transmembrane domain, and is homologous to the prokaryotic sugar transport protein SemiSWEET.[44]

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

Several notable variants of SARS-CoV-2 emerged in the fall of 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.
COVID-19 can affect the upper respiratory tract (sinuses, nose, and throat) and the lower respiratory tract (windpipe and lungs).[49] The lungs are the organs most affected by COVID-19 because the virus accesses host cells via the enzyme angiotensin-converting enzyme 2 (ACE2), which is most abundant in type II alveolar cells of the lungs.[50] The virus uses a special surface glycoprotein called a "spike" (peplomer) to connect to ACE2 and enter the host cell.The density of ACE2 in each tissue correlates with the severity of the disease in that tissue and some have suggested decreasing ACE2 activity might be protective,[52] though another view is that increasing ACE2 using angiotensin II receptor blocker medications could be protective.[53] As the alveolar disease progresses, respiratory failure might develop and death may follow.[54]

Whether SARS-CoV-2 is able to invade the nervous system remains unknown. The virus is not detected in the CNS of the majority of COVID-19 patients with neurological issues. However, SARS-CoV-2 has been detected at low levels in the brains of patients who died from COVID-19, but these results need to be confirmed. SARS-CoV-2 may cause respiratory failure through affecting the brain stem as other coronaviruses have been found to invade the CNS. While virus has been detected in cerebrospinal fluid of autopsies, the exact mechanism by which it invades the CNS remains unclear and may first involve invasion of peripheral nerves given the low levels of ACE2 in the brain.[56][57][58] The virus may also enter the bloodstream from the lungs and cross the blood-brain barrier to gain access to the CNS, possibly within an infected white blood cell by a "Trojan horse" mechanism.

The virus also affects gastrointestinal organs as ACE2 is abundantly expressed in the glandular cells of gastric, duodenal and rectal epithelium[59] as well as endothelial cells and enterocytes of the small intestine.

The virus can cause acute myocardial injury and chronic damage to the cardiovascular system.An acute cardiac injury was found in 12% of infected people admitted to the hospital in Wuhan, China, and is more frequent in severe disease. Rates of cardiovascular symptoms are high, owing to the systemic inflammatory response and immune system disorders during disease progression, but acute myocardial injuries may also be related to ACE2 receptors in the heart. ACE2 receptors are highly expressed in the heart and are involved in heart function.A high incidence of thrombosis and venous thromboembolism have been found in intensive care unit (ICU)-transferred patients with COVID-19 infections, and may be related to poor prognosis. Blood vessel dysfunction and clot formation (as suggested by high D-dimer levels) are thought to play a significant role in mortality, incidences of clots leading to pulmonary embolisms, and ischaemic events within the brain have been noted as complications leading to death in patients infected with SARS-CoV-2. Infection appears to set off a chain of vasoconstrictive responses within the body, constriction of blood vessels within the pulmonary circulation has also been posited as a mechanism in which oxygenation decreases alongside the presentation of viral pneumonia.

Another common cause of death is complications related to the kidneys.Early reports show that up to 30% of hospitalized patients both in China and in New York have experienced some injury to their kidneys, including some persons with no previous kidney problems.

Autopsies of people who died of COVID-19 have found diffuse alveolar damage (DAD), and lymphocyte-containing inflammatory infiltrates within the lung.[68]


Although SARS-CoV-2 has a tropism for ACE2-expressing epithelial cells of the respiratory tract, patients with severe COVID-19 have symptoms of systemic hyperinflammation. Clinical laboratory findings of elevated IL-2, IL-7, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-γ inducible protein 10 (IP-10), monocyte chemoattractant protein 1 (MCP-1), Macrophage inflammatory protein 1-α (MIP-1α), and tumour necrosis factor-α (TNF-α) indicative of cytokine release syndrome (CRS) suggest an underlying immunopathology.

Additionally, people with COVID-19 and acute respiratory distress syndrome (ARDS) have classical serum biomarkers of CRS, including elevated C-reactive protein (CRP), lactate dehydrogenase (LDH), D-dimer, and ferritin.

Systemic inflammation results in vasodilation, allowing inflammatory lymphocytic and monocytic infiltration of the lung and the heart. In particular, pathogenic GM-CSF-secreting T-cells were shown to correlate with the recruitment of inflammatory IL-6-secreting monocytes and severe lung pathology in COVID-19 patients. Lymphocytic infiltrates have also been reported at autopsy.
COVID-19 can provisionally be diagnosed on the basis of symptoms and confirmed using reverse transcription polymerase chain reaction (RT-PCR) testing of infected secretions.[72][73] Along with laboratory testing, chest CT scans may be helpful to diagnose COVID-19 in individuals with a high clinical suspicion of infection.Detection of prior infection is possible with serological tests, which detect antibodies produced by the body in response to infection.



The standard method of testing for presence of SARS-CoV-2 is real-time reverse transcription polymerase chain reaction (rRT-PCR),which detects the presence of viral RNA fragments. As this test detects RNA but not infectious virus, its "ability to determine duration of infectivity of patients is limited." The test is typically done on respiratory samples obtained by a nasopharyngeal swab; however, a nasal swab or sputum sample may also be used.Results are generally available within a few hours to two days.[81][82] Blood tests can be used, but these require two blood samples taken two weeks apart, and the results have little immediate value.[83] The WHO has published several testing protocols for the disease.

A number of laboratories and companies have developed serological tests, which detect antibodies produced by the body in response to infection. Several have been evaluated by Public Health England and approved for use in the UK.

On 22 June 2020, UK health secretary Matt Hancock announced the country would conduct a new "spit test" for COVID-19 on 14,000 key workers and their families in Southampton, having them spit in a pot, which was collected by Southampton University, with results expected within 48 hours. Hancock said the test was easier than using swabs and could enable people to conduct it at home.

The University of Oxford's CEBM has pointed to mounting evidence that "a good proportion of 'new' mild cases and people re-testing positives after quarantine or discharge from hospital are not infectious, but are simply clearing harmless virus particles which their immune system has efficiently dealt with" and have called for "an international effort to standardize and periodically calibrate testing" On 7 September, the UK government issued "guidance for procedures to be implemented in laboratories to provide assurance of positive SARS-CoV-2 RNA results during periods of low prevalence, when there is a reduction in the predictive value of positive test results."

Chinese scientists were able to isolate a strain of the coronavirus and publish the genetic sequence so laboratories across the world could independently develop polymerase chain reaction (PCR) tests to detect infection by the virus. As of 4 April 2020, antibody tests (which may detect active infections and whether a person had been infected in the past) were in development, but not yet widely used. Antibody tests may be most accurate 2-3 weeks after a person's symptoms start. The Chinese experience with testing has shown the accuracy is only 60 to 70%.[98] The US Food and Drug Administration (FDA) approved the first point-of-care test on 21 March 2020 for use at the end of that month. The absence or presence of COVID-19 signs and symptoms alone is not reliable enough for an accurate diagnosis.[100] Different clinical scores were created based on symptoms, laboratory parameters and imaging to determine patients with probable SARS-CoV-2 infection or more severe stages of COVID-19.

A study asked hospitalised COVID-19 patients to cough into a sterile container, thus producing a saliva sample, and detected the virus in eleven of twelve patients using RT-PCR. This technique has the potential of being quicker than a swab and involving less risk to health care workers (collection at home or in the car).


In November 2020, research showed that breath analysis could make the "rapid identification" in seconds for coronavirus possible.



The virus is thought to be natural and has an animal origin, through spillover infection. The first known human infections were in Wuhan, Hubei, China. A study of the first 41 cases of confirmed COVID-19, published in January 2020 in The Lancet, reported the earliest date of onset of symptoms as 1 December 2019. Official publications from the WHO reported the earliest onset of symptoms as 8 December 2019. Human-to-human transmission was confirmed by the WHO and Chinese authorities by 20 January 2020. According to official Chinese sources, these were mostly linked to the Huanan Seafood Wholesale Market, which also sold live animals. In May 2020, George Gao, the director of the Chinese Center for Disease Control and Prevention, said animal samples collected from the seafood market had tested negative for the virus, indicating that the market was the site of an early superspreading event, but it was not the site of the initial outbreak. Traces of the virus have been found in wastewater that was collected from Milan and Turin, Italy, on 18 December 2019.

There are several theories about where the first case (the so-called patient zero) originated. Phylogenetics estimates that SARS-CoV-2 arose in October or November 2019. Evidence suggests that it descends from a coronavirus that infects wild bats and spread to humans through an intermediary wildlife host. By December 2019, the spread of infection was almost entirely driven by human-to-human transmission.The number of coronavirus cases in Hubei gradually increased, reaching 60 by 20 December and at least 266 by 31 December.[370] On 24 December, Wuhan Central Hospital sent a bronchoalveolar lavage fluid (BAL) sample from an unresolved clinical case to sequencing company Vision Medicals. On 27 and 28 December, Vision Medicals informed the Wuhan Central Hospital and the Chinese CDC of the results of the test, showing a new coronavirus. A pneumonia cluster of unknown cause was observed on 26 December and treated by the doctor Zhang Jixian in Hubei Provincial Hospital, who informed the Wuhan Jianghan CDC on 27 December. On 30 December, a test report addressed to Wuhan Central Hospital, from company CapitalBio Medlab, stated an erroneous positive result for SARS, causing a group of doctors at Wuhan Central Hospital to alert their colleagues and relevant hospital authorities of the result. That evening, the Wuhan Municipal Health Commission issued a notice to various medical institutions on "the treatment of pneumonia of unknown cause". Eight of these doctors, including Li Wenliang (punished on 3 January), were later admonished by the police for spreading false rumours, and another, Ai Fen, was reprimanded by her superiors for raising the alarm.

The Wuhan Municipal Health Commission made the first public announcement of a pneumonia outbreak of unknown cause on 31 December, confirming 27 cases -enough to trigger an investigation.

During the early stages of the outbreak, the number of cases doubled approximately every seven and a half days. In early and mid-January 2020, the virus spread to other Chinese provinces, helped by the Chinese New Year migration and Wuhan being a transport hub and major rail interchange. On 20 January, China reported nearly 140 new cases in one day, including two people in Beijing and one in Shenzhen. Later official data shows 6,174 people had already developed symptoms by then, and more may have been infected. A report in The Lancet on 24 January indicated human transmission, strongly recommended personal protective equipment for health workers, and said testing for the virus was essential due to its "pandemic potential". On 30 January, the WHO declared the coronavirus a Public Health Emergency of International Concern.[383] By this time, the outbreak spread by a factor of 100 to 200 times.

On 31 January 2020, Italy had its first confirmed cases, two tourists from China. As of 13 March 2020, the World Health Organization (WHO) considered Europe the active centre of the pandemic. On 19 March 2020, Italy overtook China as the country with the most deaths. By 26 March, the United States had overtaken China and Italy with the highest number of confirmed cases in the world. Research on coronavirus genomes indicates the majority of COVID-19 cases in New York came from European travellers, rather than directly from China or any other Asian country. Retesting of prior samples found a person in France who had the virus on 27 December 2019 and a person in the United States who died from the disease on 6 February 2020.

On 11 June 2020, after 55 days without a locally transmitted case,[394] Beijing reported the first COVID-19 case, followed by two more cases on 12 June. By 15 June 79 cases were officially confirmed. Most of these patients went to Xinfadi Wholesale Market.

RT-PCR testing of untreated wastewater samples from Brazil and Italy have suggested detection of SARS-CoV-2 as early as November and December 2019, respectively, but the methods of such sewage studies have not been optimised, many have not been peer reviewed, details are often missing, and there is a risk of false positives due to contamination or if only one gene target is detected. A September 2020 review journal article said, "The possibility that the COVID-19 infection had already spread to Europe at the end of last year is now indicated by abundant, even if partially circumstantial, evidence", including pneumonia case numbers and radiology in France and Italy in November and December.