A new study on the global pandemic has found those who contract COVID-19 may exhibit a predictable sequence of symptoms, and the order differs from what we experience with flu and other coronaviruses.
So far, evidence indicates the most likely order of initial COVID-19 symptoms tends to start with a fever and then progress to a cough and muscle pain, followed by nausea and/or vomiting, and lastly, diarrhea.
While the symptoms themselves are not particularly unique, the order in which they arrive is different to other respiratory viruses, and the authors think their model could help to distinguish new cases, thus helping us to limit the spread of the disease.
Using World Health Organisation (WHO) data from more than 55,000 confirmed cases in China, the authors compared COVID-19's order of symptoms to thousands of influenza cases collected by the University of Michigan, nearly 150 severe acute respiratory syndrome (SARS) cases in the Toronto area, and a handful of Middle East respiratory syndrome (MERS) cases reported in Korea.
An influenza infection was found to begin with a cough and then a fever. And while MERS and SARS might start similarly to COVID-19, the lower gastrointestinal tract is usually impacted first, leading to diarrhea before nausea and vomiting.
"The order of the symptoms matters," says Joseph Larsen who researches computational biology and bioinformatics at the University of Southern California.
"Knowing that each illness progresses differently means that doctors can identify sooner whether someone likely has COVID-19, or another illness, which can help them make better treatment decisions."
When the researchers simulated the symptoms of COVID-19 for 500,000 patients, they found "a most common order of discernible symptoms… that is also different from other prominent respiratory diseases."
Even when the authors included other symptoms like sore throat, headache and fatigue, the order of the four most likely initial symptoms remained the same.
Since fever appears to usually come first, taking someone's temperature could be a valid screening mechanism.
The United States Centres for Disease Control and Prevention (CDC) already advises that people take their temperature before leaving isolation to make sure it's safe, and this new research backs that up.
"We are not proposing initial symptoms as a diagnostic test, but instead as a possible sign to get tested," the authors write.
COVID-19 is more contagious than influenza and it tends to break out in clusters. If we can better inform the public on its order of symptoms, this might help us faster identify and quarantine cases before they spread further.
Bob Lahita, a rheumatologist not affiliated with the study, told CBS news that the new model of symptoms was "a good guide".
Even if the disease doesn't present exactly the same in everyone, paying close attention to initial symptoms of respiratory infections could allow us to tease apart typical cycles of sickness from the current global pandemic.
The study was published in Frontiers in Public Health.