COVID-19

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Coronavirus disease 2019
(COVID-19)
Other namesCOVID, (the) coronavirus
Symptomatic and supportive
Frequency774,834,237[4] confirmed cases (true case count is expected to be much higher[5])
Deaths
  • 7,037,007[4] (reported)
  • 18.2–33.5 million[6]
(estimated)

Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the virus SARS-CoV-2. The first known case was identified in Wuhan, China, in December 2019.[7] The disease quickly spread worldwide, resulting in the COVID-19 pandemic.

The

hypoxia, or more than 50% lung involvement on imaging), and 5% develop critical symptoms (respiratory failure, shock, or multiorgan dysfunction).[15] Older people are at a higher risk of developing severe symptoms. Some people continue to experience a range of effects (long COVID) for months or years after infection, and damage to organs has been observed.[16] Multi-year studies are underway to further investigate the long-term effects of the disease.[17]

COVID‑19 transmits when infectious particles are breathed in or come into contact with the eyes, nose, or mouth. The risk is highest when people are in close proximity, but small airborne particles containing the virus can remain suspended in the air and travel over longer distances, particularly indoors. Transmission can also occur when people touch their eyes, nose or mouth after touching surfaces or objects that have been contaminated by the virus. People remain contagious for up to 20 days and can spread the virus even if they do not develop symptoms.[18]

reverse transcription loop-mediated isothermal amplification (RT‑LAMP)[19][20] from a nasopharyngeal swab.[22]

Several COVID-19 vaccines have been approved and distributed in various countries, which have initiated mass vaccination campaigns. Other preventive measures include physical or social distancing, quarantining, ventilation of indoor spaces, use of face masks or coverings in public, covering coughs and sneezes, hand washing, and keeping unwashed hands away from the face. While work is underway to develop drugs that inhibit the virus, the primary treatment is symptomatic. Management involves the treatment of symptoms through supportive care, isolation, and experimental measures.

Nomenclature

During the initial outbreak in

Middle East respiratory syndrome, and Zika virus.[29] In January 2020, the World Health Organization (WHO) recommended 2019-nCoV[30] and 2019-nCoV acute respiratory disease[31] as interim names for the virus and disease per 2015 guidance and international guidelines against using geographical locations or groups of people in disease and virus names to prevent social stigma.[32][33][34] The official names COVID‑19 and SARS-CoV-2 were issued by the WHO on 11 February 2020 with COVID-19 being shorthand for "coronavirus disease 2019".[35][36] The WHO additionally uses "the COVID‑19 virus" and "the virus responsible for COVID‑19" in public communications.[35][37]

Symptoms and signs

Symptoms of COVID-19

The

breathing difficulties.[42] People with the COVID-19 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; and a cluster of digestive symptoms with abdominal pain, vomiting, and diarrhea.[42] In people without prior ear, nose, or throat disorders, loss of taste combined with loss of smell is associated with COVID-19 and is reported in as many as 88% of symptomatic cases.[43][44][45]

Of people who show symptoms, 81% develop only mild to moderate symptoms (up to mild

hypoxia, or more than 50% lung involvement on imaging) that require hospitalization, and 5% of patients develop critical symptoms (respiratory failure, septic shock, or multiorgan dysfunction) requiring ICU admission.[46][needs update
]

Proportion of asymptomatic SARS-CoV-2 infection by age. About 44% of those infected with SARS-CoV-2 remained asymptomatic throughout the infection.[47]

At least a third of the people who are infected with the virus do not develop noticeable symptoms at any point in time.[47][48][49] These asymptomatic carriers tend not to get tested and can still spread the disease.[49][50][51][52] Other infected people will develop symptoms later (called "pre-symptomatic") or have very mild symptoms and can also spread the virus.[52]

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[53] possibly being infectious on 1-4 of those days.[54] Most symptomatic people experience symptoms within two to seven days after exposure, and almost all will experience at least one symptom within 12 days.[53][55]

Most people recover from the acute phase of the disease. However, some people continue to experience a range of effects, such as fatigue, for months, even after recovery.[56] This is the result of a condition called long COVID, which can be described as a range of persistent symptoms that continue for weeks or months at a time.[57] Long-term damage to organs has also been observed after the onset of COVID-19. Multi-year studies are underway to further investigate the potential long-term effects of the disease.[58]

The Omicron variant became dominant in the U.S. in December 2021. Symptoms with the Omicron variant are less severe than they are with other variants.[59]

Complications

Mechanisms of SARS-CoV-2 cytokine storm and complications

Complications may include

venous thromboembolism.[64][65][66][67][68][69] Approximately 20–30% of people who present with COVID‑19 have elevated liver enzymes, reflecting liver injury.[70][71]

Neurologic manifestations include

paediatric multisystem inflammatory syndrome, which has symptoms similar to Kawasaki disease, which can be fatal.[74][75] In very rare cases, acute encephalopathy can occur, and it can be considered in those who have been diagnosed with COVID‑19 and have an altered mental status.[76]

According to the US

Fungal infections such as aspergillosis, candidiasis, cryptococcosis and mucormycosis have been recorded in patients recovering from COVID‑19.[78][79]

Cause

COVID‑19 is caused by infection with a strain of coronavirus known as "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2).[80]

Transmission

Transmission
of COVID‑19

COVID-19 is mainly transmitted when people breathe in air contaminated by droplets/aerosols and small airborne particles containing the virus. Infected people exhale those particles as they breathe, talk, cough, sneeze, or sing.[81][82][83][84] Transmission is more likely the closer people are. However, infection can occur over longer distances, particularly indoors.[81][85]

The transmission of the virus is carried out through virus-laden fluid particles, or droplets, which are created in the respiratory tract, and they are expelled by the mouth and the nose. There are three types of transmission: “droplet” and “contact”, which are associated with large droplets, and “airborne”, which is associated with small droplets.

contaminate surfaces surrounding them.[86] Droplets that are below a certain critical size, evaporate faster than they settle; due to that fact, they form nuclei that remain airborne for a long period of time over extensive distances.[86]

upper respiratory tract samples occurs close to the time of symptom onset and declines after the first week after symptoms begin.[88] Current evidence suggests a duration of viral shedding and the period of infectiousness of up to ten days following symptom onset for people with mild to moderate COVID-19, and up to 20 days for persons with severe COVID-19, including immunocompromised people.[89][88]

Infectious particles range in size from
aerosols that remain suspended in the air for long periods of time to larger droplets that remain airborne briefly or fall to the ground.[90][91][92][93] Additionally, COVID-19 research has redefined the traditional understanding of how respiratory viruses are transmitted.[93][94] The largest droplets of respiratory fluid do not travel far, but can be inhaled or land on mucous membranes on the eyes, nose, or mouth to infect.[92] Aerosols are highest in concentration when people are in close proximity, which leads to easier viral transmission when people are physically close,[92][93][94] but airborne transmission can occur at longer distances, mainly in locations that are poorly ventilated;[92] in those conditions small particles can remain suspended in the air for minutes to hours.[92][95]

Virology