COVID-19 signs, symptoms and severity of disease: A clinician guide

Last updated: September 18, 2020

The information below is based on currently available scientific evidence and informed by expert opinion, and is subject to change as new information becomes available. The contents provide clinicians with interim information on what is presently known about the clinical features of COVID-19, including presentation, risk factors and the spectrum of disease severity. COVID-19 is the disease caused by SARS-CoV-2 coronavirus, a new virus that was first recognized in Wuhan, China, in December 2019. 

Signs and symptoms

COVID-19 presents with varied clinical features. Clinical presentation and symptoms of COVID-19 vary in frequency and severity. Common reported symptoms may be broadly categorized as “more frequent”, “less frequent” and “rare” (Table 1) Footnote 1Footnote 2Footnote 3Footnote 4Footnote 5Footnote 6Footnote 7Footnote 8Footnote 9Footnote 10Footnote 11Footnote 12Footnote 13Footnote 14. The true frequency of symptoms associated with COVID-19 is unknown. Published reports may over-represent individuals who have more bothersome or severe symptoms, and this may also differ across care settings. Symptoms absent at the onset of illness may develop over time with disease progression. To date, there is no list of symptoms that has been validated to have high specificity or sensitivity for COVID-19. Clinical diagnosis should therefore always be confirmed by laboratory testing, and patients should always be encouraged to seek medical consultation if experiencing new or worsening symptoms.

Table 1. Reported frequency of symptoms Footnote 1Footnote 2Footnote 3Footnote 4Footnote 5Footnote 6Footnote 7Footnote 8Footnote 9Footnote 10Footnote 11Footnote 12Footnote 13Footnote 14Footnote 15Footnote 16Footnote 17
More frequent (>50%) Less frequent (<50%) Rare (<10%)
  • Fever (44-91%)
  • Cough (57-74%)
  • Shortness of breath (31–63%)
  • Fatigue (31–70%)
  • Loss of appetite (39-84%)
  • Loss of smell and/or taste (54-88%)
  • Sputum production (28–33%)
  • Muscle aches (11–44%)
  • Chest pain (16-36%)
  • Diarrhea (5-24%)
  • Nausea/vomiting (5-19%)
  • Headache (6-70%)
  • Dizziness (9-17%)
  • Sore throat (11-13%)
  • Confusion
  • Runny nose
  • Fainting
  • Skin manifestations

Note: Symptoms among older adults (65 years of age and older) and those with underlying medical conditions may be atypical or subtle; for instance they may be more likely to present without fever or respiratory symptoms.


The frequency of fever varied among studies, ranging from 44-91%Footnote 1Footnote 2Footnote 3Footnote 4Footnote 5Footnote 6Footnote 7Footnote 8Footnote 9Footnote 10Footnote 11Footnote 12Footnote 13Footnote 14Footnote 15Footnote 16Footnote 17Footnote 18Footnote 19Footnote 20. In a large cohort study in Europe, fever was present in 45.4% of cases, while the two largest studies from China reported fever in more than 80% of patientsFootnote 29Footnote 40Footnote 41.

In many publications, fever was reported as body temperature of a minimum of 37.3 degrees Celsius and any temperature higher. In one study that reported symptoms in over 1,000 hospitalized patients, 44% of individuals were categorized as having fever on admission (22% had a body temperature between 37.6 and 38 oC, 18% between 38.1 and 39 oC, and 4% for temperatures between 38.2 - 39 oC) Footnote 1. Overall, while 89% of patients with COVID-19 in reported studies had increased body temperature during hospitalization, maximum body temperature of over 38 oC was measured in just half of the patients (38.1 - 39 oC in 47% and >39 oC in 2%) Footnote 1Footnote 2Footnote 3Footnote 4Footnote 5Footnote 6Footnote 7.

Cough, shortness of breath, fatigue, loss of appetite and loss of smell and/or taste

Other symptoms that have been commonly reported include cough, shortness of breath, fatigue, loss of appetite and loss of smell and/or taste.

Cough has been reported in many COVID-19 patientsFootnote 5Footnote 6Footnote 7Footnote 8Footnote 9Footnote 10Footnote 11Footnote 12Footnote 13Footnote 14Footnote 15Footnote 16Footnote 17Footnote 18Footnote 19Footnote 20Footnote 21Footnote 22Footnote 23Footnote 24Footnote 25Footnote 26Footnote 27Footnote 28Footnote 29Footnote 30Footnote 31Footnote 32Footnote 33Footnote 34Footnote 35Footnote 36Footnote 37Footnote 38Footnote 39. A large European study, found the frequency of cough to be 63%Footnote 2, while in two large studies from China cough was reported in 49%Footnote 20 and 66%Footnote 19of cases. In a systematic review of the literature, cough was found, on average, to be present in approximately two thirds of adult patients with non-severe diseaseFootnote 12Footnote 13. However, due to its variable frequency, cough should not be considered a sensitive indicator for COVID-19 disease.

Shortness of breath was more frequently reported in hospitalized patientsFootnote 5Footnote 6Footnote 7Footnote 8Footnote 11Footnote 19Footnote 22Footnote 26Footnote 28Footnote 29Footnote 30Footnote 31Footnote 32Footnote 33. A recent systematic review and meta-analysis, found shortness of breath present among 44% of people with severe and 6% of people with non-severe diseaseFootnote 36. Two large studies, reported shortness of breath to range from 1-8 % of mild cases, compared to 33% of severe casesFootnote 2Footnote 5.

Loss of smell and/or taste has been commonly reported (54-88%)Footnote 20Footnote 34. These symptoms may occur earlier than other symptoms, and in some cases these were the only reported manifestation of COVID-19 infection Footnote 1Footnote 2Footnote 3.

Reporting of frequency of loss of appetite (39-84%) and fatigue (31-70%) ranged widely amongst studiesFootnote 2Footnote 3Footnote 5Footnote 10Footnote 18Footnote 20Footnote 25Footnote 26Footnote 27Footnote 28Footnote 29Footnote 31Footnote 32Footnote 33Footnote 34Footnote 38Footnote 41

Other less frequent symptoms

Reports of gastrointestinal symptoms in COVID-19 patients, such as diarrhea and nausea, have ranged from 5-24% Footnote 8Footnote 9Footnote 10Footnote 11Footnote 12Footnote 13Footnote 15Footnote 39. In one publication, 19% of individuals reported these symptoms prior to the development of fever or signs of lower respiratory tract infectionFootnote 7. Other symptoms that have been less frequently reported include confusion, runny nose, fainting and skin manifestationsFootnote 10Footnote 11Footnote 12Footnote 13Footnote 14Footnote 15.

Symptoms in children

In children, the reported signs and symptoms have been similar to those observed in adults, though they may often be less severe or altogether absent. See this link for general advice on how to care for a child with COVID-19.

Reports have found fever (children 56% vs. adults 71%), cough (children 46% vs. adults 80%), and shortness of breath (children 13% vs. adults 43%) at a lower frequency in childrenFootnote 36Footnote 37Footnote 38Footnote 39Footnote 40Footnote 41. Gastrointestinal symptoms are often predominant in clinical presentation, including abdominal pain, diarrhea, nausea, and vomiting Footnote 42Footnote 43.

Clinicians should be aware of very rare complications that have been associated with COVID-19 infection. A severe multisystem inflammatory syndrome in children (MIS-C) has been reported to share features of typical or atypical Kawasaki disease or toxic shock syndromeFootnote 24Footnote 25.

The WHO preliminary case definition for MIS-C states that cases should be suspected in children and adolescents 0-19 years of age with fever for ≥ 3 days and two of the following signs or symptoms:




Clinicians should have a high index of suspicion to obtain bloodwork for children and adolescents who present with the symptoms mentioned above.

Allergies, colds, flu and asthma during COVID-19

The most frequently reported COVID-19 symptoms (fever, cough, fatigue, loss of appetite, shortness of breath) are not specific to COVID-19 and are commonly reported in a large number of respiratory and other illnesses (e.g. common colds, influenza, asthma, and allergies). This may present increased challenges with diagnosing COVID-19 during allergy season, or when there is circulating influenza or other respiratory viruses within Canada.

Asymptomatic, pre-symptomatic and pauci-symptomatic infection

An asymptomatic person is someone with a positive SARS-CoV-2 test who never develops any symptoms, whereas a pre-symptomatic person is someone who has contracted COVID-19 and may have detectable virus, but is not yet showing symptoms. Pauci-symptomatic individuals will have a positive SARS-CoV-2 test in the presence of very limited symptomatology. Asymptomatic, pre-symptomatic and pauci-symptomatic COVID-19 cases and their exact roles in transmission is still undetermined.

Several studies have documented SARS-CoV-2 infections in patients who never develop symptoms (i.e. asymptomatic) and in patients who are not yet symptomatic (i.e. pre-symptomatic)Footnote 19Footnote 20Footnote 36Footnote 41Footnote 44Footnote 45Footnote 46Footnote 47Footnote 48Footnote 49Footnote 50Footnote 51Footnote 52. Since asymptomatic persons are not routinely tested, the prevalence of asymptomatic infection and pre-symptomatic infection are not well known. Some studies have estimated the frequency of pauci-symptomatic or asymptomatic individuals to be as high as 50% Footnote 53. It has also been shown that some presymptomatic individuals may have laboratory and radiological abnormalities prior to the onset of symptoms Footnote 20,Footnote 44,Footnote 54.

Incubation period

The incubation period for COVID-19 has been estimated to range from 1 to 14 days, with a median being 5-6 days from exposure to symptom onsetFootnote 1Footnote 26Footnote 27. Most individuals (97.5%) develop symptoms within 11.5 days of exposureFootnote 1Footnote 18Footnote 26Footnote 27.


Person-to-person spread via respiratory droplets is the main mode of transmission for COVID-19. With droplet transmission, infection occurs when the virus contained in the respiratory secretions of an infected person (through coughing or sneezing) reach the mucous membrane of a healthy individual. Infection can also occur if a person touches an infected surface and then touches their eyes, nose, or mouth. The contribution of surfaces or objects (also called fomites) in COVID-19 transmission is not completely understood.

The time period in which an individual with COVID-19 is infectious remains uncertain. Evidence has shown that an individual may be infectious for up to 3 days prior to any presentation of symptomsFootnote 28, which is referred to as pre-symptomatic infectiousness. The levels of viral RNA from posterior oropharyngeal saliva/sputum samples, upper respiratory specimens, and stool samples appear to be highest soon after symptom onsetFootnote 29Footnote 30Footnote 31, with some evidence that infectiousness may peak on or even before symptom onset Footnote 31Footnote 32.

Viral shedding may occur through the course of illness and the exact degree of SARS-CoV-2 viral shedding that confers risk of transmission is still unknown. A German study Footnote 35 comparing the viral loads between patients of different age groups found that viral loads in children do not differ significantly from those of adults, suggesting that children may be as infectious as adults. A Canadian study found that the SARS-CoV-2 potential to infect Vero cells under laboratory conditions was only observed at an interval between symptom onset to test of under 8 daysFootnote 55. Infectivity of patients with symptoms of ≥ 8 days is likely very low. The duration of viral shedding in severely ill patients, such as those in intensive care units or with immune suppression, is unknown but may be prolonged.

The clinical criteria for non-infectiousness, including 14 days from symptom onset or being symptoms free for 72 hours (whichever is longer) are being used in some jurisdictions. Laboratory criteria based on two negative Nasopharyngeal (NP) RT-PCR results 48 hours apart (after 14 days of symptom onset) were initially used, and are still being used in some circumstances.

Disease severity and risk factors for severe disease

There is a spectrum of COVID-19 disease severity, ranging from asymptomatic or mild, to moderate, severe and critical disease Footnote 56Footnote 57.

The largest cohort of >44,000 adults with COVID-19 from China showed that the greatest number of cases fell into the mild-moderate category at 81%, with severe (14%) and critical (5%) disease more rare. The overall case fatality rate (CFR) that was reported in this study was 2.3%, and there was a CFR of 49% among those patients with critical diseaseFootnote 52. Among children in China, disease severity was lower with 94% having asymptomatic, mild or moderate disease, 5% having severe disease, and <1% having critical disease Footnote 21.

The Canadian Epidemiological report on June 4, 2020 estimated that 16% of Canadians diagnosed with COVID-19 have been hospitalized. Among hospitalized individuals, 20% have been admitted to the Intensive Care Unit (ICU), and 19% required mechanical ventilation. These numbers are similar to those reported by the U.S., in which the proportion of persons who were hospitalized was 19% Footnote 36.

Data have consistently shown that older adults and those with some underlying medical conditions are at highest risk for severe disease. In Canada, among hospitalized cases for whom clinical presentation was reported, 74% reported one or more pre-existing conditions. Individuals aged ≥ 60 years comprise: 68% of hospital admissions, 64% of ICU admissions and 96% of deaths. Canadian data are similar to what is seen in other countries. A summary of the most common comorbidities found in persons with COVID-19 in the literature is found in Table 2, with cardiovascular disease, hypertension and diabetes being the most common. The frequency of underlying comorbid conditions amongst severe cases of COVID-19 is much higher than that amongst non-severe COVID-19 casesFootnote 1Footnote 2Footnote 3Footnote 8Footnote 9Footnote 10Footnote 12Footnote 13Footnote 14Footnote 36Footnote 40.

Table 2. Common comorbidities in COVID-19 cases Footnote 1Footnote 2Footnote 3Footnote 8Footnote 9Footnote 10Footnote 12Footnote 13Footnote 14Footnote 36Footnote 40
More frequent (>40%) Less frequent (10-39%) Infrequent (<10%)
  • Hypertension (17%-82%)
  • Cardiovascular disease
    including heart failure (5%-55%)
  • Diabetes (4%-40%)
  • Chronic respiratory disease (12%-22%)
  • Chronic renal disease (11%-14%)
  • Obesity (22-29%)
  • Asthma (11%)
  • Cancer (2%-7%)
  • Atrial fibrillation/arrhythmia (3%-6%)
  • Endocrine disorders (6%)
  • Gastrointestinal disease (5%)
  • Chronic liver disease (2%-3%)
  • Neurologic diseases, including dementia and stroke (8%-13%)


There is emerging evidence of human reinfection with SARS-CoV-2, as documented by individuals confirmed to have been infected by different strains of the virus (this has been demonstrated by different sequenced viral genomes from two infections).Footnote 67Footnote 68 There are too few cases to determine the clinical presentation in a second infection and how it may differ. To date, there has not been any evidence of antibody-dependent disease enhancement observed.

Following infection, the majority of individuals will develop IgM and IgG antibodies within days to weeks of symptom onset.Footnote 58Footnote 59Footnote 60 However, the relationship between antibody levels and the level of protection against reinfection remains undetermined, as well as the role of cellular immunity in preventing reinfection (including cross-protective immunity following exposure to common coronaviruses).Footnote 58Footnote 60Footnote 61Footnote 62Footnote 63Footnote 64Footnote 65

As serological testing for the detection of SARS-CoV-2 antibodies becomes more widely available, the results are expected to provide further insight into the questions on reinfection and the duration of immunity.

There is still more to learn about the SARS-CoV-2 virus, and it remains important that clinicians remind Canadians to remain steadfast in preventing the spread of COVID-19. This includes following appropriate public health precautions against infections such as physical distancing, observing regular hand hygiene, respiratory etiquette, mask wearing, environmental cleaning and disinfection and self-monitoring for symptoms compatible with COVID-19.


This document was prepared by: Dr. Marianna Ofner, Dr. Dara Petel, Yung-En Chung, Dr. Oliver Baclic, Dr. Marina Salvadori, Dr. Cheryl Volling, Dr. Peter Uhthoff, Mary Lou DeCou, Aidan Pucchio and Dr. James Brooks for the COVID-19 Clinical Issues Task Group, Public Health Agency of Canada.

COVID-19 Clinical Issues Task Group, Public Health Agency of Canada, Dr. Marina Salvadori. Dr. James Brooks, Dr. Marianna Ofner, Dr. Oliver Baclic, Yung-En Chung, Mary Lou DeCou, Dr. Peter Uhthoff and Dr. Cheryl Volling.

Additional Public Health Agency of Canada resources


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Footnote 60

To KK, Tsang OT, Leung WS, et al. Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect Dis. 2020;20(5):565-574. doi:10.1016/S1473-3099(20)30196-1.

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Footnote 63

He X, Lau EH, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. 2020. doi:10.1101/2020.03.15.20036707.

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Footnote 64

Grifoni A, Weiskopf D, Ramirez SI, et al. Targets of T Cell Responses to SARS-CoV-2 Coronavirus in Humans with COVID-19 Disease and Unexposed Individuals. Cell. 2020. doi:10.1016/j.cell.2020.05.015.

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Footnote 65

Soresina A, Moratto D, Chiarini M, et al. Two X‐linked agammaglobulinemia patients develop pneumonia as COVID‐19 manifestation but recover. Pediatric Allergy and Immunology. 2020. doi:10.1111/pai.13263.

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Footnote 66

Wu L-P , Wang N-C , Chang Y-H , et al. Duration of antibody responses after severe acute respiratory syndrome. Emerg Infect Dis. 2007;13(10):1562-1564. doi:10.3201/eid1310.070576.

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Footnote 67

Tillett, R., Sevinsky, J. Hartley P, et al. Genomic Evidence for a Case of Reinfection with SARS-CoV-2

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Footnote 68

Kelvin Kai-Wang To, K.KW., Hung, I.FN., Daniel J., et al COVID-19 re-infection by a phylogenetically distinct SARS-coronavirus-2 strain confirmed by whole genome sequencing Clinical Infectious Diseases, ciaa1275,

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