Coronavirus disease 2019

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Coronavirus disease 2019 (COVID‑19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It was first identified in December 2019 in Wuhan, Hubei, China, and has resulted in an ongoing pandemic. As of 19 September 2020, more than 30.3 million cases have been reported across 188 countries and territories with more than 950,000 deaths; more than 20.6 million people have recovered.

Common symptoms include fever, cough, fatigue, shortness of breath or breathing difficulties, and loss of smell and taste. While most people have mild symptoms, some people develop acute respiratory distress syndrome (ARDS) possibly precipitated by cytokine storm, multi-organ failure, septic shock, and blood clots. The incubation period may range from one to fourteen days.

The disease mainly spreads between people when they are in close proximity.[a] It spreads very easily and sustainably, primarily via contaminated droplets produced during breathing, coughing, sneezing, talking and singing. Many larger droplets rapidly fall to the ground, however some can be suspended in air as aerosols, especially in indoor spaces. It may also be transmitted via contaminated surfaces, although this has not been conclusively demonstrated. It can spread for up to two days prior to symptom onset, and from people who are asymptomatic. People remain infectious in moderate cases for 7–12 days, and up to two weeks in severe cases. 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 it for routine screening.

Recommended measures to prevent infection include frequent hand washing, social distancing, quarantine, covering coughs, and keeping unwashed hands away from the face.[8] 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 be used only by healthcare workers, first responders, and those who directly care for infected individuals.

There are no proven vaccines or specific treatments for COVID-19 yet, though several are in development. 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.

Longer-term damage to organs (in particular lungs and heart) has been observed, and 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 including severe fatigue, memory loss and other cognitive issues, low grade fever, muscle weakness, breathlessness and other symptoms for months afterwards.


Signs and symptoms

Symptoms of COVID-19 are variable, but usually include fever and a cough.[27][6] People with the same infection may have different symptoms, and their symptoms may change over time. For example, one person may have a high fever, a cough, and fatigue, and another person may have a low fever at the start of the disease and develop difficulty breathing a week later. All of the symptoms of COVID-19 are non-specific, which means that they are also seen in some other diseases.

Fever is the most common symptom of COVID‑19.[27] The fever may be high or low. Most people with COVID-19 develop a fever at some point.[27] Most people with COVID-19 also have a cough, which could be either dry or a productive cough.[27]

Other typical symptoms include fatigue, shortness of breath and muscle and joint pains.[27][6] Some symptoms, such as difficulty breathing, are more common in patients who need hospital care.[6] Shortness of breath tends to develop later in the illness.

About 40% of people temporarily lose their sense of smell (called anosmia), experience changes in how food tastes (dysgeusia), or have other disturbances to their normal abilities to smell or taste.[6][28] This symptom, if it is present at all, often appears early in the illness.[28] A disturbance in smell or taste is more commonly found in younger people, and perhaps because of this, it is associated with a lower risk of medical complications.[28] Although most people with COVID-19 do not experience these symptoms, it is an unusual symptom for other respiratory diseases, so it is used for symptom-based screening.[28]

Other symptoms are less common among people with COVID-19. Some people experience gastrointestinal symptoms such as loss of appetite, diarrhoea, or nausea.[6][29] Some people have a sore throat, headache, vertigo, or other symptoms.[27][6]

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.[30] 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.[30][31] Some symptoms usually appear sooner than others. In August 2020, scientists at the University of Southern California reported the “likely” order of initial symptoms of the COVID-19 disease as a fever followed by a cough and muscle pain, and that nausea and vomiting usually appear before diarrhoea.[32] This contrasts with the most common path for influenza where it is common to develop a cough first and fever later.[32]

Some people are infected with the virus but do not develop noticeable symptoms at any point in time.[33] These asymptomatic carriers tend not to get tested, and they can spread the disease.[34][35][33] Other infected people will develop symptoms later (called pre-symptomatic) or have very mild symptoms (called paucisymptomatic), and can also spread the virus.


Without pandemic containment measures—such as social distancing, vaccination, and use of face masks—pathogens can spread exponentially. This graphic shows how early adoption of containment measures tends to protect wider swaths of the population.

Without pandemic containment measures—such as social distancing, vaccination, and use of face masks—pathogens can spread exponentially.[105] This graphic shows how early adoption of containment measures tends to protect wider swaths of the population.

Progressively stronger mitigation efforts to reduce the number of active cases at any given time—”flattening the curve”—allows healthcare services to better manage the same volume of patients. Likewise, progressively greater increases in healthcare capacity—called raising the line—such as by increasing bed count, personnel, and equipment, helps to meet increased demand.

Mitigation attempts that are inadequate in strictness or duration—such as premature relaxation of distancing rules or stay-at-home orders—can allow a resurgence after the initial surge and mitigation.

A COVID-19 vaccine is not expected until 2021 at the earliest.[111] The US 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.[112][113] Without a vaccine, other prophylactic measures, or effective treatments, a key part of managing COVID‑19 is trying to decrease and delay the epidemic peak, known as “flattening the curve”.[107] 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.[107][110]

Preventive measures to reduce the chances of infection include staying at home, wearing a mask in public, 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.[114][115][116][117] 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.[118][119]

Personal protective equipment
For health care professionals who may come into contact with COVID‑19 positive bodily fluids, using personal protective coverings on exposed body parts improves protection from the virus.[120] Breathable personal protective equipment improves user-satisfaction and may offer a similar level of protection from the virus.[120] In addition, adding tabs and other modifications to the protective equipment may reduce the risk of contamination during donning and doffing (putting on and taking off the equipment).[120] Implementing an evidence-based donning and doffing protocol such as a one-step glove and gown removal technique, giving oral instructions while donning and doffing, double gloving, and the use of glove disinfection may also improve protection for health care professionals.[120]

Face masks
The World Health Organization (WHO) and most government health agencies (such as the US Centers for Disease Control and Prevention (CDC), the UK National Health Service (NHS), or the New Zealand Ministry of Health) recommend individuals wear non-medical face coverings in public settings where there is an increased risk of transmission and where social distancing measures are difficult to maintain.[121][122][123][124][125] This recommendation is meant to reduce the spread of the disease by asymptomatic and pre-symtomatic individuals and is complementary to established preventive measures such as social distancing.[122][126] Face coverings limit the volume and travel distance of expiratory droplets dispersed when talking, breathing, and coughing.[122][126] Many countries and local jurisdictions encourage or mandate the use of face masks or cloth face coverings by members of the public to limit the spread of the virus.

Masks are also strongly recommended for those who may have been infected and those taking care of someone who may have the disease.[131]

Social distancing
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.[132] Distancing guidelines also include that people stay at least 2 metres (6.6 ft) apart.[133] 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.[134]

Hand-washing and hygiene
When not wearing a mask, the CDC, WHO, and NHS 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.[115][124][135] Proper hand hygiene after any cough or sneeze is encouraged.[115][124] The WHO 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.[135] The CDC recommends using an alcohol-based hand sanitiser with at least 60% alcohol, but only when soap and water are not readily available.[124] 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.

Sanitizing of frequently touched surfaces is also recommended or required by regulation for businesses and public facilities; the United States Environmental Protection Agency maintains a list of products expected to be effective.

Case fatality rate by country and number of cases

The number of deaths vs total cases by country and approximate case fatality rate


The severity of COVID‑19 varies. The disease may take a mild course with few or no symptoms, resembling other common upper respiratory diseases such as the common cold. Mild cases typically recover within two weeks, while those with severe or critical diseases may take three to six weeks to recover. Among those who have died, the time from symptom onset to death has ranged from two to eight weeks.[55]

Children make up a small proportion of reported cases, with about 1% of cases being under 10 years and 4% aged 10–19 years. They are likely to have milder symptoms and a lower chance of severe disease than adults. In those younger than 50 years the risk of death is less than 0.5%, while in those older than 70 it is more than 8%. Pregnant women may be at higher risk of severe COVID‑19 infection based on data from other similar viruses, like severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), but data for COVID‑19 is lacking.[157][158] According to scientific reviews smokers are more likely to require intensive care or die compared to non-smokers, air pollution is similarly associated with risk factors,[160] and obesity contributes to an increased health risk of COVID‑19.

A European multinational study of hospitalized children published in The Lancet on 25 June 2020 found that about 8% of children admitted to a hospital needed intensive care. Four of those 582 children (0.7%) died, but the actual mortality rate could be “substantially lower” since milder cases that did not seek medical help were not included in the study.

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