What is the 1st symptom of COVID-19 versus flu?

A new study, which gives the order of COVID-19 symptom progression, may make it easier to recognize an infection with the dreaded virus.

With a laundry list of symptoms that seem to vary wildly from person to person, COVID-19 can be easily confused with allergies, the flu or a stomach bug. And that means it can be hard to know if it’s time to get tested and to self-isolate. A new study, which gives the order of COVID-19 symptom progression, may make it easier to recognize an infection of the dreaded virus.

How do COVID-19 symptoms progress?

University of Southern California researchers used a computer model to analyze data on COVID-19, SARS (severe acute respiratory syndrome), MERS (Middle East respiratory syndrome) and the flu. Their study, published last week in Frontiers in Public Health, determined that fever was most likely to be the first symptom experienced by those infected by the coronavirus, followed by cough, nausea and/or vomiting, and then lower gastrointestinal symptoms, such as diarrhea.

“Where I think this can really help is in understanding how cautious do I need to be if I only have a cough or I only have diarrhea,” said study co-author Peter Kuhn, a professor of biological sciences, medicine and engineering at the University of Southern California. “If it starts with a fever then I would be more cautious and maybe I would get tested and try harder to not be around others until I got the results.”

To try to distinguish between the diseases, Kuhn and his colleagues used a computer model and data from several sources: more than 55,000 confirmed cases from China in February, 2,470 confirmed cases of the flu in Michigan, 245 MERS cases and 357 SARS cases collected worldwide.

Symptoms of COVID-19 versus flu

The analysis showed that the first symptom of the flu was most likely to be a cough. For the three coronaviruses, SARS, MERS and COVID-19, the first symptom was a fever.

What differentiated COVID-19 from SARS and MERS was the order of digestive symptoms. With COVID-19 upper gastrointestinal tract symptoms — nausea and vomiting — came before lower GI tract symptoms, such as diarrhea. The order was reversed with SARS and MERS.

Dr. David Thomas, a professor of medicine and director of the division of infectious diseases at Johns Hopkins Medicine in Baltimore who was not involved in the study, welcomed the new research.

“We should be as smart as we can be about which virus is which and that will be even more important when the flu breaks,” said Thomas. “It is good to know how those virus infections differ. But for now we will most likely want to test anyone with new symptoms no matter what the order and just be sure the testing includes influenza, COVID-19, as well as the other common respiratory viruses.”

Thomas sees fever as the telling symptom.

“If I had a fever I would get tested, even if I had another symptom first!” Thomas said in an email.

A cough as the first symptom is a very common sign of flu, said Dr. Richard Zimmerman, a professor of family medicine and public health at the University of Pittsburgh, who was not involved in the study.

The study did not address two commonly reported symptoms of COVID-19: a loss of smell or taste, Zimmerman said. The Centers for Disease Control and Prevention also includes the following symptoms: chills, fatigue, sore throat, headache, congestion, runny nose and difficulty breathing. The data the study analyzed was gathered in February, before the list of symptoms of the coronavirus had been expanded by the CDC.

Call your physician to see if your symptoms warrant being tested for COVID-19. Zimmerman stressed that shortness of breath and low oxygen levels indicate the illness “most likely will lead to admission to the hospital.”