Medical conditionCoronirus disease 2019(COVID-19)Other namesCOVID, (the) coronirusTransmission and life-cycle of SARS-CoV-2, which causes COVID-19Pronunciation/kəˈroʊnəvaɪrəs//ˌkoʊvɪdnaɪnˈtiːn, ˌkɒvɪd-/[1] SpecialtyInfectious diseaseSymptomsFever, cough, fatigue, shortness of breath, vomiting, loss of taste or smell; some cases asymptomatic[2][3]ComplicationsPneumonia, sepsis, ARDS, kidney failure, respiratory failure, pulmonary fibrosis, CKS, MIS-C, long COVID, brain damageUsual onset2–14 days (typically 5)after infectionDuration5 days to chronicCausesSARS-CoV-2Diagnostic methodRT‑PCR testing, CT scan, rapid antigen testPreventionVaccination, face coverings, quarantine, social distancing, ventilation, hand washingTreatmentSymptomatic and supportiveFrequency778,852,659[4] confirmed cases (true case count is expected to be much higher[5])Deaths7,102,566[4] (reported)18.2–33.5 million[6] (estimated)
Coronirus disease 2019 (COVID-19) is a contagious disease caused by the coronirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic.
The symptoms of COVID‑19 can vary but often include fever,[7] fatigue, cough, breathing difficulties, loss of smell, and loss of taste.[8][9][10] Symptoms may begin one to 14 days after exposure to the virus. At least a third of people who are infected do not develop noticeable symptoms.[11][12] Of those who develop symptoms noticeable enough to be classified as patients, 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% develop critical symptoms (respiratory failure, shock, or multiorgan dysfunction).[13] Older people he a higher risk of developing severe symptoms. Some complications result in death. Some people continue to experience a range of effects (long COVID) for months or years after infection, and damage to organs has been observed.[14] Multi-year studies on the long-term effects are ongoing.[15]
COVID‑19 transmission occurs 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 trel over longer distances, particularly indoors. Transmission can also occur when people touch their eyes, nose, or mouth after touching surfaces or objects that he 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.[16]
Testing methods for COVID-19 to detect the virus's nucleic acid include real-time reverse transcription polymerase chain reaction (RT‑PCR),[17][18] transcription-mediated amplification,[17][18][19] and reverse transcription loop-mediated isothermal amplification (RT‑LAMP)[17][18] from a nasopharyngeal swab.[20]
Several COVID-19 vaccines he been approved and distributed in various countries, many of which he 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 drugs he been developed to inhibit the virus, the primary treatment is still symptomatic, managing the disease through supportive care, isolation, and experimental measures.
The first known case was identified in Wuhan, China, in December 2019.[21] Most scientists believe that the SARS-CoV-2 virus entered into human populations through natural zoonosis, similar to the SARS-CoV-1 and MERS-CoV outbreaks, and consistent with other pandemics in human history.[22][23] Social and environmental factors including climate change, natural ecosystem destruction and wildlife trade increased the likelihood of such zoonotic spillover.[24][25][26][27]
Nomenclature Main article: COVID-19 namingDuring the initial outbreak in Wuhan, the virus was commonly called "coronirus" and "Wuhan coronirus",[28][29][30] and the disease was referred to by the same terms and sometimes as "Wuhan pneumonia".[31][32] In the past, many diseases he been named after geographical locations, such as the Spanish flu,[33] Middle East respiratory syndrome, and Zika virus.[34] In January 2020, the World Health Organization (WHO) recommended 2019-nCoV[35] and 2019-nCoV acute respiratory disease[36] 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.[37][38][39] The official names COVID‑19 and SARS-CoV-2 were issued by the WHO on 11 February 2020 with COVID-19 being shorthand for "coronirus disease 2019".[40][41] The WHO additionally uses "the COVID‑19 virus" and "the virus responsible for COVID‑19" in public communications.[40][42]
Signs and symptoms Main article: Symptoms of COVID-19Symptoms of COVID-19
The symptoms of COVID-19 are variable depending on the type of variant contracted, ranging from mild symptoms to a potentially fatal illness.[43][44] Common symptoms include coughing, fever, loss of smell and taste, with less common ones including headaches, nasal congestion and runny nose, muscle pain, sore throat, diarrhea, eye irritation,[45] and toes swelling or turning purple,[46] and in moderate to severe cases, breathing difficulties.[47] People with the COVID-19 infection may he different symptoms, and their symptoms may change over time.
Three common clusters of symptoms he been identified: a 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.[47] 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.[48][49][50]
Published data on the neuropathological changes related with COVID-19 he been limited and contentious, with neuropathological descriptions ranging from moderate to severe hemorrhagic and hypoxia phenotypes, thrombotic consequences, changes in acute disseminated encephalomyelitis (ADEM-type), encephalitis and meningitis. Many COVID-19 patients with co-morbidities he hypoxia and he been in intensive care for varying lengths of time, confounding interpretation of the data.[51]
Of those who show symptoms, 81% develop only mild to moderate symptoms (up to mild pneumonia), while 14% develop severe symptoms (dyspnea, 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.[52][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.[53]At least a third of the people who are infected with the virus do not develop noticeable symptoms at any point in time.[53][54][55] These asymptomatic carriers tend not to get tested and can still spread the disease.[55][56][57][58] Other infected people will develop symptoms later (called "pre-symptomatic") or he very mild symptoms and can also spread the virus.[58]
As is common with infections, there is a delay, or incubation period, 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[59] possibly being infectious on 1–4 of those days.[60] Most symptomatic people experience symptoms within two to seven days after exposure, and almost all will experience at least one symptom within 12 days.[59][61]
Most people recover from the acute phase of the disease. However, some people continue to experience a range of effects, such as fatigue, for prolonged periods after an initial COVID-19 infection.[62] This is the result of a condition called long COVID, which can be described as a range of persistent symptoms that continue for months or years.[62] Long-term damage to organs has been observed after the onset of COVID-19. Multi-year studies are underway to further investigate the protracted effects of long COVID.[62] Reducing the risk of long COVID includes staying up to date on the most recent COVID-19 vaccine, practicing good hygiene, maintaining clean indoor air, and physical distancing from people infected with a respiratory virus.[62]
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.[63] Complications Mechanisms of SARS-CoV-2 cytokine storm and complicationsComplications may include pneumonia, acute respiratory distress syndrome (ARDS), multi-organ failure, septic shock, and death.[64][65][66][67] Cardiovascular complications may include heart failure, arrhythmias (including atrial fibrillation), heart inflammation, thrombosis, particularly venous thromboembolism,[68][69][70][71][72][73] and endothelial cell injury and dysfunction.[74] Approximately 20–30% of people who present with COVID‑19 he elevated liver enzymes, reflecting liver injury.[75][76]
Neurologic manifestations include seizure, stroke, encephalitis, and Guillain–Barré syndrome (which includes loss of motor functions).[77][78] Following the infection, children may develop paediatric multisystem inflammatory syndrome, which has symptoms similar to Kawasaki disease, which can be fatal.[79][80] In very rare cases, acute encephalopathy can occur, and it can be considered in those who he been diagnosed with COVID‑19 and he an altered mental status.[81]
According to the US Centers for Disease Control and Prevention, pregnant women are at increased risk of becoming seriously ill from COVID‑19.[82] This is because pregnant women with COVID‑19 appear to be more likely to develop respiratory and obstetric complications that can lead to miscarriage, premature delivery and intrauterine growth restriction.[82]
Fungal infections such as aspergillosis, candidiasis, cryptococcosis and mucormycosis he been recorded in people recovering from COVID‑19.[83][84]
CauseCOVID‑19 is caused by infection with a strain of coronirus known as "severe acute respiratory syndrome coronirus 2" (SARS-CoV-2).[85]
Transmission Main article: Transmission of COVID-19 Transmission of COVID‑19
COVID-19 is mainly transmitted from person to person through inhaling 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.[86][87][88][89] Transmission is most likely at closer range but, can also occur can occur over longer distances, particularly indoors.[86][90]
The virus spreads 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.[91] If the droplets are above a certain critical size, they settle faster than they evaporate, and therefore they contaminate surfaces surrounding them.[91] Droplets that are below a certain critical size, generally thought to be