Researchers at the University of Southern California (USC) have identified the likely order that Covid-19 symptoms first appear, which they hope will help doctors to identify patients sooner and give appropriate treatment.
One of the more difficult challenges of the Covid-19 pandemic has been identifying who has contracted the disease and isolating them in order to contain further spread. Governments around the world have set up test, track and trace systems in order to do just this. However, if we were to identify likely cases earlier, we could reduce the numbers and size of case clusters, the researchers write in the journal Frontiers in Public Health.
With that end in mind, biologists from USC set out to identify the order of Covid-19 symptoms so that medical practitioners and members of the public alike will know what to look out for, particularly during the early stages of the disease. They also identified how the order of symptoms differs from similar viruses like influenza and other coronaviruses, to aid in quicker identification.
To do this they looked at data from 55,924 cases of Covid-19 from the World Health Organization (WHO) and China from February 16-24, 2020, as well as 1,100 cases between December 11, 2019 and January 29, 2020, collated by the China Medical Treatment Expert Group. They focused on symptoms that were easily discernable or objective, in comparison to other reported symptoms such as neurological effects including loss of smell.
"A person infected with Covid-19 is most likely to experience symptoms in the order of fever, cough, nausea/vomiting, then diarrhea," the authors revealed. "The least likely path starts at diarrhea and nausea/vomiting and is followed by cough, and finally fever."
Distinguishing Covid-19 from influenza could be particularly challenging as we head into flu season. To help with this, they compared the Covid-19 order of symptoms with 2,500 influenza cases from health authorities in the US and Europe from 1994 to 1998 and the two known coronavirus diseases Middle East respiratory syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).
Their model found that influenza usually begins with a cough, whereas Covid-19, like other coronavirus-related diseases, starts with a fever. However, the timing and symptoms in the upper and lower gastrointestinal tract set Covid-19 apart from SARS and MERS.
"This order is especially important to know when we have overlapping cycles of illnesses like the flu that coincide with infections of Covid-19," Professor Peter Kuhn from USC said in a statement.
Though this is just the most likely order of symptoms and some patients will differ (for example, a very small number of patients experienced diarrhea as an initial symptom), the team believes that this supports the idea that "fever should be used to screen for entry into facilities as regions begin to reopen after the outbreak of Spring 2020." As new treatments are created and improved upon, they hope that knowing the likely order of symptoms will save lives as people seek and are given treatments at an earlier stage of the illness.
Though confident in their results, the team says the overall accuracy could be improved if physicians were to record the order of occurrence of symptoms; something which, somewhat surprisingly, is not yet standard practice.
"Our findings suggest that good clinical practice should involve recording the order of symptom occurrence in COVID-19 and other diseases," the paper concludes. "If such a systemic clinical practice had been standard since ancient diseases, perhaps the transition from local outbreak to pandemic could have been avoided."