Overview of coronaviruses

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Last reviewed: 21 Sep 2025

Last updated: 21 Oct 2025

This page compiles our content related to coronaviruses. For further information on diagnosis and treatment, follow the links below to our full BMJ Best Practice topics on the relevant conditions and symptoms.

Coronaviruses are a large family of viruses, some of which cause illness in people, and others that circulate among mammals and birds.[1] Rarely, animal coronaviruses can spread to humans, and then spread between people. Zoonotic coronaviruses have emerged in recent years to cause human outbreaks such as coronavirus disease 2019 (COVID-19), severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS).

Illness in humans mainly manifests as a respiratory infection, or sometimes gastrointestinal infection. The clinical spectrum of illness varies from no symptoms or mild respiratory symptoms to severe, rapidly progressive pneumonia, acute respiratory distress syndrome, septic shock, or multiorgan failure resulting in death.[2]

Condition	Description
Coronavirus disease 2019 (COVID-19)	go to our full topic on Coronavirus disease 2019 (COVID-19) An acute respiratory infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).[3] The clinical presentation is generally that of a respiratory infection with a symptom severity ranging from a mild common cold-like illness, to a severe viral pneumonia leading to acute respiratory distress syndrome that is potentially fatal. Symptoms may be persistent and continue for more than 12 weeks in some patients. It was first identified in Wuhan City, Hubei Province, China, on 31 December 2019. In May 2023, the World Health Organization declared that COVID-19 no longer constitutes a public health emergency of international concern.
Middle East respiratory syndrome (MERS)	go to our full topic on Middle East respiratory syndrome (MERS) An acute viral respiratory tract infection caused by the novel betacoronavirus MERS coronavirus (MERS-CoV). It was first identified in Saudi Arabia in 2012.[4] Cases have been limited to the Arabian Peninsula and its surrounding countries, and to travelers from the Middle East or their contacts. The case fatality rate globally is approximately 36%.[5] The majority of patients present with fever and respiratory symptoms (e.g., cough, dyspnea); however, some patients may present with gastrointestinal symptoms only (e.g., nausea, vomiting, diarrhea, abdominal pain). Epidemic potential is considered low at present unless the virus mutates.
Severe acute respiratory syndrome (SARS)	go to our full topic on Severe acute respiratory syndrome (SARS) A viral pneumonia that rapidly progresses to respiratory failure caused by SARS-CoV.[6] It was first identified in the Guangdong province of Southern China in 2002. The epidemic affected 26 countries and resulted in 8096 cases and 774 deaths in 2003.[7] There have been no reported cases since 2004. The typical febrile response may be absent in older patients, who may present with malaise, loss of appetite, delirium, or even an episode of a fall with an associated fracture.[8] Infants and children present with milder symptoms and associated rhinorrhea in 50% of cases. The case fatality rate is approximately 10% and death usually occurs due to severe respiratory failure.

Condition

Description

Coronavirus disease 2019 (COVID-19)

go to our full topic on Coronavirus disease 2019 (COVID-19)

An acute respiratory infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).[3] The clinical presentation is generally that of a respiratory infection with a symptom severity ranging from a mild common cold-like illness, to a severe viral pneumonia leading to acute respiratory distress syndrome that is potentially fatal. Symptoms may be persistent and continue for more than 12 weeks in some patients. It was first identified in Wuhan City, Hubei Province, China, on 31 December 2019. In May 2023, the World Health Organization declared that COVID-19 no longer constitutes a public health emergency of international concern.

Middle East respiratory syndrome (MERS)

go to our full topic on Middle East respiratory syndrome (MERS)

An acute viral respiratory tract infection caused by the novel betacoronavirus MERS coronavirus (MERS-CoV). It was first identified in Saudi Arabia in 2012.[4] Cases have been limited to the Arabian Peninsula and its surrounding countries, and to travelers from the Middle East or their contacts. The case fatality rate globally is approximately 36%.[5] The majority of patients present with fever and respiratory symptoms (e.g., cough, dyspnea); however, some patients may present with gastrointestinal symptoms only (e.g., nausea, vomiting, diarrhea, abdominal pain). Epidemic potential is considered low at present unless the virus mutates.

Severe acute respiratory syndrome (SARS)

go to our full topic on Severe acute respiratory syndrome (SARS)

A viral pneumonia that rapidly progresses to respiratory failure caused by SARS-CoV.[6] It was first identified in the Guangdong province of Southern China in 2002. The epidemic affected 26 countries and resulted in 8096 cases and 774 deaths in 2003.[7] There have been no reported cases since 2004. The typical febrile response may be absent in older patients, who may present with malaise, loss of appetite, delirium, or even an episode of a fall with an associated fracture.[8] Infants and children present with milder symptoms and associated rhinorrhea in 50% of cases. The case fatality rate is approximately 10% and death usually occurs due to severe respiratory failure.

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