Scientists have made an advancement in identifying the likely order in which COVID-19 symptoms make their appearance. This latest step forward, many say, will enable clinicians to rule other diseases out of the context and assist patients to seek care or make an early decision for self-isolation. As per a study published in the journal Frontiers in Public Health, the likely order of COVID-19 symptoms in patients starts with fever, followed by cough, muscle pain, and then nausea, and/or vomiting, and diarrhea.

Peter Kuhn, a professor of medicine and biomedical engineering at the University of Southern California (USC) in the US provided an explanation in the study saying, "This order is especially important to know when we have overlapping cycles of illnesses like the flu that coincide with infections of COVID-19,". He added that the new information will help doctors determine the steps necessary for taking care of the patients, and prevent their condition from turning worse. Researchers state the identification of patients in the earlier stages will reduce hospitalisation, considering there are better ways now for treating coronavirus in comparison to when the pandemic had struck first.

The study adds that the scientists had made the prediction on the order of symptoms based on the data on the rates of symptom incidence of more than 55,000 confirmed coronavirus cases in China, which were all collected by the World Health Organization (WHO) between February 16 to 24. They also went on to study a dataset of nearly 1,100 cases collected from December 11, 2019 to January 29, 2020, which was provided by the China Medical Treatment Expert Group via the National Health Commission of China (NHC). Scientists drew comparisons of the COVID-19 symptoms to that of influenza by examining flu data from 2,470 cases in North America, Europe and the Southern Hemisphere, reported between 1994 and 1998. 

Joseph Larsen, study lead author from USC said, "The order of the symptoms matter. 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,".

Although fever and cough were the basic symptoms associated with a variety of respiratory illnesses, including Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS) which caused the 2002-03 pandemic, researchers stated that the timing and symptoms in the upper and lower gastrointestinal tract set COVID-19 apart.

The scientists wrote, "The first two symptoms of COVID-19, SARS, and MERS are fever and cough. However, the upper GI tract (nausea/vomiting) seems to be affected before the lower GI tract (diarrhea) in COVID-19, which is the opposite from MERS and SARS,". 

As per research, only a small percentage of patients experienced diarrhea as an initial symptom. "This report suggests that diarrhea as an early symptom indicates a more aggressive disease, because each patient in this dataset that initially experienced diarrhea had pneumonia or respiratory failure eventually," the scientists added. They also noted saying, "The highest reported symptom is fever, followed by cough or dyspnea, and then finally, a small percent of patients reported diarrhea. This order confirms the most likely paths that we have determined,".