COVID-19: What are the symptoms?
More than a year after COVID-19 emerged, we are still learning about it. Every day we learn more, thanks to ongoing research, and this knowledge is essential to confronting and overcoming it. This disease affects people in different ways; most who become infected experience mild or moderate symptoms and recover without hospitalization, while for others it can be severe and even fatal.
An article published in the Journal of Infection highlights the importance of recognizing the symptoms of this disease. Although the World Health Organization (WHO) states that the most common symptoms of COVID-19 are fever, dry cough, and tiredness, this publication indicates that there are other symptoms that should also be taken into account.
On average, people who become infected begin to show symptoms within 5 to 6 days of becoming infected, but it can take up to 14 days for them to appear; older adults and people with serious underlying conditions, such as heart disease, lung disease or diabetes, seem to experience more serious complications from this disease.
Fever, cough, and loss of smell is the so-called "classic triad of coronavirus symptoms," which indicates that a person is very likely to be infected and should get tested. However, the new study suggests that a third of those infected with coronavirus did not experience any of the three classic symptoms in the first few days of infection.
The analysis, conducted on 122,000 adults in the UK through the ZOE COVID Symptom Study app, showed that limiting detection to cough, fever, and anosmia (total or partial loss of the sense of smell) only identifies 69% of cases, while expanding the symptom list to seven would detect 96%. The symptoms the study highlights as requiring attention are: in addition to the classic triad; fatigue, headache, sore throat, and diarrhea. These symptoms had already been identified as being associated with SARS-CoV-2, but due to their rarity, they were not considered significant.
The research has revealed that some of these symptoms appear first. Headache and diarrhea occur within the first three days of infection, while fever appears around the seventh day. Furthermore, 31% of people with Covid did not experience fever, cough, or anosmia in the early stages of infection, when the virus is most transmissible.
Researchers created a model to determine the proportion of positive cases detected with each symptom in the early days of infection. When symptoms are limited to cough and breathing difficulties, 46% of positive cases are identified; adding fever raises the proportion to 60%, and anosmia increases to 69%. However, when fatigue and headache are included, the percentage of positive cases rises to 92%.
The researchers acknowledge that these last two symptoms occur in many other diseases, but they have called for them to be considered in screening models, in combination with others. In addition to this research, other studies have revealed less common symptoms, such as chills, loss of appetite, and muscle aches.
While PCR swab testing is the most reliable way to determine if someone is infected with the SARS-CoV-2 coronavirus that causes COVID-19, the analysis suggests that the limited list of three symptoms used to screen suspected cases does not detect all positive cases. Consequently, these findings could be valuable in situations where testing capacity is limited. The researchers suggest a variety of optimal symptom combinations that could be used in vaccine efficacy trials or in public health settings, after assessing financial and logistical resources.
Ramona Avila Núñez, PhD
References
- Antonelli, J. Capdevila, A. Chaudhari, LS Canas, MS Graham, K. Klaser, M. Modat, et al. Optimal symptom combinations to aid COVID-19 case identification: Analysis from a community-based, prospective, observational cohort. Journal of Infection. (2021). Article in press. DOI: https://doi.org/10.1016/j.jinf.2021.02.015