COVID-19: Infection and symptoms
Current estimates suggest a median incubation period from five to six days for COVID-19, with a range from two to up to 14 days. Modelling studies suggest that the incubation period can be from 2.3 days (95% CI, 0.8–3.0 days) before symptom onset and up to 14 days, although incubation periods beyond 10 days are thought to be rare.
In terms of viral load profile, SARS-CoV-2 is similar to that of influenza, which peaks at around the time of symptom onset, but contrasts with that of SARS-CoV, which peaks at around 10 days after symptom onset, and that of MERS-CoV which peaks at the second week after symptom onset. Older age has also been associated with higher viral loads. The high viral load close to symptom onset suggests that SARS-CoV-2 can be easily transmissible at an early stage of infection.
A study from China that clearly and appropriately defined asymptomatic infections suggests that the proportion of infected people who never developed symptoms was 23%.
Presenting signs and symptoms of COVID-19 vary. Most people experience:
- fever (83–99%),
- cough (59–82%),
- fatigue (44–70%),
- anorexia (40–84%),
- shortness of breath (31–40%),
- myalgias (11–35%).
Other non-specific symptoms, such as sore throat, nasal congestion, headache, diarrhoea, nausea and vomiting, have also been reported. Loss of smell (anosmia) or loss of taste (ageusia) preceding the onset of respiratory symptoms has also been reported.
Older people and immunosuppressed patients in particular may present with atypical
symptoms such as fatigue, reduced alertness, reduced mobility, diarrhoea, loss of appetite,
delirium, and absence of fever.
Symptoms such as dyspnoea, fever, gastrointestinal symptoms or fatigue due to
physiologic adaptations in pregnant women, adverse pregnancy events, or other diseases
such as malaria, may overlap with symptoms of COVID-19.
COVID-19, like SARS and MERS, is observed less frequently in children, who tend to present with milder symptoms and have a better overall outcome than adults. The most commonly reported symptoms in children are fever and cough. Other symptoms include gastrointestinal symptoms, sore throat/pharyngitis, shortness of breath, myalgia, rhinorrhoea/nasal congestion and headache, with varying prevalence among different studies. Asymptomatic infections in children have been reported.
Severe or critical illness has been reported among 2.5% to 5% of paediatric cases from China. Pre-existing medical conditions have been suggested as a risk factor for severe disease and ICU admission in children and adolescents
Pregnant women and neonates
Clinical manifestations in pregnant women are predominantly mild, with few reports of severe disease and fatal outcomes.
Underlying health conditions among severe cases
Underlying health conditions reported among patients with COVID-19 and admitted to ICU include hypertension, diabetes, cardiovascular disease, chronic respiratory disease, immune compromised status, cancer and obesity.
Elderly residents of long-term care facilities and nursing homes
A high proportion of long-term care facilities (LTCF) and nursing homes across Europe and the world have been severely affected by COVID-19. High morbidity and mortality in residents as well as high rates of staff absence due to SARS-CoV-2 infections have been observed.
Healthcare workers (HCW) are at high risk of COVID-19 infection because of more frequent exposure to COVID-19 cases and may contribute to the spread of COVID-19 in healthcare institutions. A recent study in the United Kingdom and the US estimated that frontline healthcare workers had a 3.4-fold higher risk than people living in the general community for reporting a positive test, adjusting for the likelihood of receiving a test. In addition, exposure to higher virus concentrations, especially from severely ill patients, may influence disease severity.
- European Centre for Disease Prevention and Control. Coronavirus: Epidemiology of COVID-19.
- European Centre for Disease Prevention and Control. Coronavirus: Infection. Accessed 6 October 2020.
- Wang Y, Tong J, Qin Y, Xie T, Li J, Li J, et al. Characterization of an asymptomatic cohort of SARS-COV-2 infected individuals outside of Wuhan, China. Clin Infect Dis. 2020;ciaa629.
- World Health Organisation. Clinical management of COVID-19. May 2020. https://www.who.int/publications/i/item/clinical-management-of-covid-19
- Nguyen LH, Drew DA, Joshi AD, Guo C-G, Ma W, Mehta RS, et al. Risk of COVID-19 among frontline healthcare workers and the general community: a prospective cohort study. medRxiv. 2020:2020.04.29.20084111.