For a quick reference guide, please see our COVID-19 summary article.

COVID-19 (coronavirus disease 2019) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), previously known as 2019 novel coronavirus (2019-nCoV), a strain of coronavirus. The first cases were seen in Wuhan, China in December 2019 before spreading globally 1,2,10. The current outbreak was recognized as a pandemic on 11 March 2020 44.

The non-specific imaging findings are most commonly of atypical or organizing pneumonia, often with a bilateral, peripheral, and basal predominant distribution 32. No effective treatment or vaccine exists currently (March 2020) 20.

The World Health Organization (WHO) originally called this illness "novel coronavirus-infected pneumonia (NCIP)" and the virus itself had been named "2019 novel coronavirus (2019-nCoV)" 1.

On 11 February 2020, the WHO officially renamed the clinical condition COVID-19 (a shortening of COronaVIrus Disease-19) 15. Coincidentally, on the same day, the Coronavirus Study Group (CSG) of the International Committee on Taxonomy of Viruses renamed the virus "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2) 16,22,46. The names of both the disease and the virus should be fully capitalized, except for the 'o' in the viral name, which is in lowercase 16,22,41

The official virus name is similar to SARS-CoV, the virus strain that caused epidemic severe acute respiratory syndrome (SARS) in 2002-2004, potentially causing confusion 38. The WHO has stated it will use "COVID-19 virus" or the "virus that causes COVID-19" instead of its official name, SARS-CoV-2, in dealings with the public 45.

As of 27 March 2020, over 535,000 cases of COVID-19 have been confirmed worldwide, having been diagnosed in 172 territories, in six continents according to an online virus tracker created by the medical journal, The Lancet, and hosted by Johns Hopkins University 5,13. There are nine countries with >10,000 confirmed cases and 27 countries with between 1000 and 10,000 confirmed cases. On 27 March 2020, the USA surpassed China as the country with the most confirmed cases 5

NB: Surveillance methods and capacity vary dramatically between countries, and there is reason to suspect that there may be a significant number of carriers in some countries not diagnosed.

The R0 (basic reproduction number) of SARS-CoV-2 has been estimated between 2.2 and 3.28 12,33, that is each infected individual, on average, causes between 2-3 new infections. 

The incubation period for COVID-19 was initially calculated to be ~5 days, which was based on 10 patients only 12. An American group performed an epidemiological analysis of 181 cases, for which days of exposure and symptom onset could be estimated accurately. They calculated a median incubation period of 5.1 days, that 97.5% became symptomatic within 11.5 days (CI, 8.2 to 15.6 days) of being infected, and that extending the cohort to the 99th percentile results in almost all cases developing symptoms in 14 days after exposure to SARS-CoV-2 92.

The number of deaths from COVID-19 is over 24,000 (27 March), with a case fatality rate of 2-3% 5,93. It is speculated that the true case fatality rate is lower than this, because many mild cases are not being tested which thus skews the apparent death rate upwards 93.

A paper published by the Chinese Center for Disease Control and Prevention (CCDC) analyzed all 44,672 cases diagnosed up to 11 February 2020. Of these, 1.2% were asymptomatic and 80.9% were classed as "mild" 25

Another study looked at clinical characteristics in COVID-19 positively tested closed contacts of COVID-19 patients 81. Approximately 30% of those COVID-19 positive close contacts never developed any symptoms or changes on chest CT scans. The remainder showed changes on CT but ~20% reportedly developed symptoms during their hospital course, none of them developed severe disease 81. This suggests that a high percentage of COVID-19 carriers are asymptomatic.

In the Chinese population, 55-60%% of COVID-19 patients were male and the median age has been reported between 47 and 59 years 12,93.

Children seem to be relatively unaffected by this virus, or indeed other closely-related coronaviruses 31,47,90 with large cohort studies reporting that 1-2% of COVID-19 patients are children 59,90,91. However, there have been cases of critically-ill children with infants under 12 months likely to be more seriously affected 59. A very low number of pediatric deaths have been reported 90,91. In children, male gender does not seem to be a risk factor 59. The incubation period has been reported to shorter than adults, at about two days 90.

NB: it is important to appreciate that the known epidemiological parameters of any new disease are likely to change as larger cohorts of infected people are studied, although this will only to some extent reflect a true change in the underlying reality of disease activity (as a disease is studied and understood humans will be simultaneously changing their behaviors to alter transmission or prevalence patterns).

COVID-19 typically presents with systemic and/or respiratory manifestations 93. Some individuals infected with SARS-CoV-2 are asymptomatic and can act as carriers 70. Some also experience mild gastrointestinal or cardiovascular symptoms, although these are much less common 18,50

The full spectrum of clinical manifestation of COVID-19 remains to be determined 1,13. Symptoms and signs are non-specific 68:


  • fever  (85-90%)
  • cough (65-70%)
  • fatigue (35-40%)
  • sputum production (30-35%)
  • shortness of breath (15-20%)

Less common:


  • nausea, vomiting, nasal congestion (<10%), diarrhea (<5%) 93
  • palpitations, chest tightness 50

Anecdotal reports from ENT specialists in the UK suggest that COVID-19 sufferers have high rates of anosmia/hyposmia 79. However, no peer-reviewed studies currently support this.

In the main, the clinical presentation in children with COVID-19 is milder than in adults 59,90. Symptoms are similar to any acute chest infection, encompassing most commonly pyrexia, dry cough, sore throat, sneezing, myalgia and lethargy. Wheezing has also been noted 59,90. Other less common (<10%) symptoms in children included diarrhea, lethargy, rhinorrhea and vomiting 91.

The definitive test for SARS-CoV-2 is the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) test and is believed to be highly specific, but with sensitivity reported as low as 60-70% 32 and as high as 95-97% 56. Thus, false negatives are a real clinical problem and several negative tests might be required in a single case to be confident about excluding the disease.

Multiple radiological organizations have come forward to state that CT should not be relied upon as a primary diagnostic/screening tool for COVID-19 52,57,87,88. On 16 March 2020, an American-Singaporean panel published that CT findings were not part of the diagnostic criteria for COVID-19 56. However, CT findings have been used as a surrogate diagnostic test by some 2,32,89

The most common ancillary laboratory findings in a study of 138 hospitalized patients were the following 13,89:

Mild elevations of inflammatory markers (CRP 89 and ESR) and D-dimer are also seen.

In one of the largest studies of hospitalized patients, reviewing 1,099 individuals across China, the admission rate to the intensive care unit (ICU) was 5% 93. In this same study, 6% of all patients required ventilation, whether invasive or non-invasive. 

ICU patients tend to be older with more comorbidities 13,93. Common reported sequelae include the following:

In a small subgroup of severe ICU cases:

On 9 January 2020, the World Health Organization (WHO) confirmed that SARS-CoV-2 was the cause of COVID-19 (2019-nCoV was the name of the virus at that time) 14,37. It is a member of the Betacoronavirus genus, one of the genera of the Coronaviridae family of viruses. Coronaviruses are enveloped single-stranded RNA viruses that are found in humans, mammals and birds. These viruses are responsible for pulmonary, hepatic, CNS, and intestinal disease. 

As with many human infections, SARS-CoV-2 is zoonotic. The closest animal coronavirus by genetic sequence is a bat coronavirus, and this is the likely ultimate origin of the virus 11,19,26. The disease can also be transmitted by snakes 24.

Six coronaviruses are known to cause human disease.Two are zoonoses: the severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), both of which may sometimes be fatal. The remaining four viruses cause the common cold

The SARS-CoV-2 virus, like the closely-related MERS and SARS coronaviruses, effects its cellular entry via attachment of its virion spike protein (a.k.a. S protein) to the angiotensin-converting enzyme 2 (ACE 2) receptor. This receptor is commonly found on alveolar cells of the lung epithelium, underlying the development of respiratory symptoms as the commonest presentation of COVID-19 50. It is thought that the mediation of the less common cardiovascular effects is also via the same ACE-2 receptor which is also commonly expressed on the cells of the cardiovascular system 50.

Although originating from animals, COVID-19 is not considered a direct zoonosis as its transmission is now primarily human-to-human. It is primarily transmitted in a similar way to the common cold, via contact with droplets of infected individuals' upper respiratory tract secretions, e.g. from sneezing or coughing 19.

A recent Bayesian regression model has found that aerosol and fomite transmission are plausible 58.

Orofecal spread was seen with the SARS epidemic, and although it remains unclear if SARS-CoV-2 can be transmitted in this way, there is some evidence for it 19,43.

A recently published cohort study (26 March 2020) could not rule out the possibility of vertical transmission with 9% of neonates (n=3/33) developing an early onset SARS-CoV-2 infection despite strict infection control measures during delivery 94. However, a retrospective study of nine pregnant patients infected by SARS-CoV-2 did not show any evidence of vertical/intrauterine infection 21. More recent published (20 March 2020) guidance from a joint American-Chinese consensus panel stated that it remains unclear if vertical transmission can occur 82.

Given that the staff in a medical imaging department are some of the first parties to be in contact with COVID-19 patients, clear infection control guidelines are imperative. At the time of writing (8 March 2020) droplet-type precautions are in place for COVID-19 patients, that is, medical mask, gown, gloves, and eye protection (aerosol-generating procedures require N95 masks and aprons) 39.

Patients requiring general radiography should receive it portably (to limit transporting patients) or in dedicated auxiliary units. Patients that require transport to departments must wear a mask to and from the unit. Machines, including any ancillary equipment used during examinations, should be cleaned after examinations 40. It is recommended that any imaging examinations have two radiographers in attendance using the 'one clean, one in contact with the patient' system to minimize cross-contamination 89. SARS-CoV-2 can exist on surfaces for up to 72 hours, reinforcing the need for protection of equipment with barriers such as covers and thorough cleaning of equipment between patients 58.

Please follow your departmental policies on personal protective equipment (PPE).

Both the American College of Radiology (ACR) and the Centers for Disease Control and Prevention (CDC) in the United States advise that non-urgent outpatient appointments should be rescheduled 83,84. The British Society of Skeletal Radiologists has advised that intra-articular, soft tissue and perineural steroid injections may reduce viral immunity and therefore should not be performed unless they are unavoidable 85.

Patients requiring CT should receive a non-contrast chest CT (unless iodinated contrast medium is indicated), with reconstructions of the volume at 0.625-mm to 1.5-mm slice thickness (gapless) 57. If iodinated contrast is indicated (for example a CT pulmonary angiogram), a non-contrast scan should be considered prior to contrast administration, as contrast may impact the interpretation of GGO patterns 89.

The primary findings of COVID-19 on chest radiograph and CT are those of atypical pneumonia 40 or organizing pneumonia 32,34.

Imaging has limited sensitivity for COVID-19, up to 18% demonstrate normal chest x-rays or CT when mild or early in the disease course but this decreases to 3% in severe disease 89,93. Bilateral and/or multilobar involvement is common 6,78.

  • may be normal in initial stages
  • asymmetric patchy or diffuse airspace opacities have been descibed 89

The primary findings on CT in adults have been reported 13,17,27,28,36:

The ground-glass and/or consolidative opacities are usually bilateral, peripheral, and basal in distribution 2,32.

A retrospective study of 112 patients found 54% of asymptomatic patients had pneumonic changes on CT 67.

Some papers suggest that CT has a sensitivity that could justify its use in the early imaging in the acute setting in select cases. Yet its use as a primary screening tool is currently discouraged, not least because these studies tended to suffer from selection bias 52,57,87,88. In a recent investigation, these chest CT findings had the highest discriminatory value (p<0.00151:

  • peripheral distribution
  • ground-glass opacity
  • bronchovascular thickening (in lesions)

These findings only seen in a small minority of patients should raise concern for superadded bacterial pneumonia or other diagnoses 2,32,89:

Four stages on CT have been described 17,24,32,86:

  • early/initial stage (0-4 days): normal CT or GGO only
    • up to half of patients have normal CT scans within 2 days of symptom onset
  • progressive stage (5-8 days): increased GGO and crazy paving appearance.
  • peak stage (9-13 days): consolidation
  • absorption stage (> 14 days): with an improvement in the disease course, "fibrous stripes" appear and the abnormalities resolve at 1 month and beyond

In a small study of five children that had been admitted to hospital with positive COVID-19 RT-PCR tests and who had CT chest performed, only three children had abnormalities. The main abnormality was bilateral patchy ground-glass opacities, similar to the appearances in adults, but less florid, and in all three cases the opacities resolved as they clinically recovered 48.

On 18 March 2020, the details of a much larger cohort of 171 children with confirmed COVID-19, and evaluated in a hospital setting was published as a letter in the New England Journal of Medicine. Ground-glass opacities were seen in one-third of the total, whereas almost 16% of children had no imaging features of pneumonia 91.

Initial work on patients in China suggests that lung ultrasound may be useful in the evaluation of critically ill COVID-19 patients 55. The following patterns have been observed, tending to have a bilateral and posterobasal predominance:

  • multiple B-lines
    • ranging from focal to diffuse with spared areas 64
    • representative of thickened subpleural interlobular septa
  • irregular, thickened pleural line with scattered discontinuities 63
  • subpleural consolidations
    • can be associated with a discrete, localized pleural effusion
    • relatively avascular with color flow Doppler interrogation
    • pneumonic consolidation typically associated with preservation of flow or hyperemia 65
  • alveolar consolidation
    • tissue-like appearance with dynamic and static air bronchograms
    • associated with severe, progressive disease 
  • restitution of aeration during recovery

An initial small case series published on 22 February 2020 demonstrated that FDG uptake is increased in ground-glass opacities in those with presumed COVID-19 42. A commentary in the same issue of the journal as this paper suggested that those with higher SUVs in lung lesions take longer to heal 77. A further single case detailed in a letter to Radiology corroborated the FDG avidity of COVID lung lesions 75.

No specific treatment or vaccine exists for COVID-19 (March 2020). Therefore resources have been concentrated on public health measures to prevent further interhuman transmission of the virus. This has required a multipronged approach and for individuals includes meticulous personal hygiene, the avoidance of large crowds/crowded environments and where necessary, self-isolation 11.

In healthcare facilities, concerted efforts are required to effect rapid diagnosis, quarantine infected cases and provide effective supportive therapies. This will encompass empirical treatments with antibiotics, antivirals, and supportive measures. Mechanical ventilation and extracorporeal membrane oxygenation (ECMO) have also been used where clinically necessary. 

Whilst specific antiviral therapies for SARS-2-CoV do not currently exist, the combination of the protease inhibitors, ritonavir, and lopinavir, or a triple combination of these antiviral agents with the addition of ribavirin, showed some success in the treatment of SARS 20, and early reports suggested similar efficacy in the treatment of COVID-19 23. However, a more recent randomized, controlled open-label trial failed to demonstrate any added benefit of lopinavir-ritonavir combination therapy 66.

Remdesivir, a drug originally developed to treat Ebola virus and shown to be effective against MERS-CoV and SARS-CoV, showed promising in vitro results against SARS-CoV-2 29 and is undergoing phase III trials 30. Other antivirals in phase III trials include oseltamivir, ASC09F (HIV protease inhibitor), lopinavir, ritonavir, darunavir, and cobicistat 80.

Early reports demonstrated that treatment with two antimalarial drugs, chloroquine, and its close chemical derivative, hydroxychloroquine, have a beneficial effect on the clinical outcome, and it was also shown that they demonstrate anti-SARS-2-CoV activity in vitro. This was further corroborated by a recent open-label, randomized clinical trial, which demonstrated a significant reduction of viral carriage, and a lower average carrying duration in patients treated with hydroxychloroquine. Furthermore, a combination with the antibiotic azithromycin resulted in a synergistic effect 69

The primary target in developing coronavirus vaccines has been the spike protein (S protein) which is on the surface of the virion particle, and in vivo is the most important antigen for triggering an immune response 75

Vaccines for the coronaviruses have been under development since the SARS outbreak, but none are yet available for humans 11,26. A phase I trial in humans of a potential vaccine against MERS-CoV has already been performed in the UK 26.

Emerging expert opinion is that non-steroidal anti-inflammatory drugs (NSAIDs) are relatively contraindicated in those with COVID-19. This is based upon several strands of "evidence" 61:

  • since 2019 the French government National Agency for the Safety of Medicines and Health Products has advised against the routine use of NSAIDs as antipyretic
  • previous research has shown that NSAIDs may suppress the immune system 
  • anecdotal reports from France suggest that young patients on NSAIDs, otherwise previously fit and well, developed more severe COVID-19 symptoms

However, it is important to note that there is currently (March 2020) no published scientific evidence showing that NSAIDs increase the risk of developing COVID-19 or worsen established disease. Also, at least one report shows antiviral activity by indomethacin (an NSAID) against SARS-CoV (cause of SARS) 60.

Progressive deterioration of imaging changes despite medical treatment is thought to be associated with poor prognosis 27. There is an increased risk of death in men over the age of 60 years old 62. The mortality rate is estimated to be 3.6% 89.

Early reports show that in some well patients, the RT-PCR test remains falsely positive despite an apparent clinical recovery. This raises the concern that asymptomatic carriage may occur 35.

The first mention in the medical press about the emerging infection was in the British Medical Journal (BMJ) on 8 January 2020 in a news article, which reported "outbreak of pneumonia of unknown cause in Wuhan, China, has prompted authorities in neighboring Hong Kong, Macau, and Taiwan to step up border surveillance, amid fears that it could signal the emergence of a new and serious threat to public health" 54. The first scientific article about the new disease, initially termed 2019‐new coronavirus (2019‐nCoV) by the World Health Organization (WHO), was published in the Journal of Medical Virology on 16 January 2020 53.

On 13 January 2020, the first confirmed case outside China was diagnosed, a Chinese tourist in Thailand 10. On 20 January, the first infected person in the United States was confirmed to be a man who had recently returned from Wuhan 9. The infection was declared a Public Health Emergency of International Concern (PHEIC) on 30 January 2020 by the WHO 7. On 28 February 2020, the WHO increased the global risk assessment of COVID-19 to “very high” which is the highest level. On 11 March 2020, COVID-19 was declared a pandemic by the WHO 44.

The WHO originally called this illness "novel coronavirus-infected pneumonia (NCIP)" and the virus itself had been named "2019 novel coronavirus (2019-nCoV)" 1. On 11 February 2020, the WHO officially renamed the clinical condition COVID-19 (a shortening of COronaVIrus Disease-19) 15. On the same day, the Coronavirus Study Group (CSG) of the International Committee on Taxonomy of Viruses renamed the virus "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2) 16,22,46

These lists are in alphabetical order:

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Article information

rID: 73913
System: Chest
Synonyms or Alternate Spellings:
  • COVID-19 pneumonia
  • Novel COVID-19-infected pneumonia (NCIP)
  • Wuhan virus
  • HCoV-19
  • Human coronavirus 2019 (HCoV-19)
  • COVID 19 virus
  • COVID-19 virus
  • Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
  • SARS coronavirus 2
  • SARS CoV2
  • SARS-CoV2
  • SARS-CoV-2
  • Coronavirus disease-19
  • Severe acute respiratory syndrome coronavirus 2
  • Coronavirus disease 19
  • COVID 19
  • COVID19
  • NCIP
  • Wuhan coronavirus infection
  • Novel coronavirus pneumonia
  • Novel coronavirus infected pneumonia (NCIP)
  • 2019 nCoV
  • 2019 novel coronavirus
  • Novel coronavirus-infected pneumonia (NCIP)
  • 2019-nCoV

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  • Case 10: rapidly progressive ARDS
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  • Case 15: at day 13
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  • Case 16: radiological evolution over 2 weeks
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  • Case 17: COVID-19 pneumonia
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  • Case 18: COVID-19 with unilateral air space consolidation
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  • Case 19: bilateral and peripheral alveolar consolidations
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  • Case 20: COVID-19 pneumonia
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  • Case 21: exclusive gastrointestinal symptoms
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  • Case 26: on CT abdomen
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