COVID-19 Symptoms May Follow a Specific Order, Study Finds

The order in which COVID-19 symptoms appear may help medical providers distinguish the disease from other illnesses such as the flu, according to a new study from the University of Southern California.

After examining symptom data from over 57,000 patients with confirmed COVID-19, researchers determined COVD-19 symptoms are most likely to follow this trajectory:

1. Fever
2. Cough
3. Nausea/vomiting
4. Diarrhea

In their research article, published on August 13 in Frontiers in Public Health, the authors suggest that a predictable course of symptom progression can help both healthcare providers and patients decide how early to seek treatment or self-isolate. But physicians say COVID-19 is anything but predictable.

"I’ve seen a lot of variability," Mitchell Li, MD, a board-certified emergency physician and medical director at Thrive Direct Care, tells Verywell. "I see a lot of patients in the Emergency Department presenting with fatigue or GI symptoms only, plus or minus fever, with no cough at all."

COVID-19 Symptoms vs. Flu Symptoms

To conduct their study, researchers first analyzed COVID-19 datasets collected by the World Health Organization and the National Health Commission of China between December 2019 and February 2020. They then compared this information to previously-collected data from over 3,000 patients with either influenza, Middle East Respiratory Syndrome (MERS), or Severe Acute Respiratory Syndrome (SARS).

According to their model, which predicted "discernible" symptoms of fever, cough, nausea/vomiting, and diarrhea, researchers found COVID-19 is more likely to begin with a fever, while influenza is more likely to begin with a cough.

After incorporating additional symptoms of sore throat, myalgia (body aches), and headache into their analysis, researchers were able to differentiate COVID-19 symptom progression from flu symptom progression even further.

Researchers found that COVID-19 patients who did not follow the typical symptom progression and exhibited diarrhea first tended to have more severe cases of COVID-19. They also had an increased likelihood of developing pneumonia or respiratory failure.

COVID-19 vs. Other Respiratory Illnesses

Researchers predicted both MERS and SARS are most likely to begin with fever, just like COVID-19.

It's important to remember that these are just predictions of what symptom progression may look like. COVID-19, in particular, can present very differently from other illnesses, and there is still much that remains unknown about the disease.

Daniel B. Fagbuyi, MD, Obama Administration Public Health/Biodefense Appointee and emergency physician, tells Verywell that over 82% of symptomatic COVID-19 patients will experience fever and approximately 70% will experience cough, but that other respiratory conditions will look similar.

"We’re still learning—COVID-19 is keeping us all humble," he says. "It’s not like the flu or other viral illness we see."

Why Early Testing Is Important

According to Fagbuyi, around 50% to 80% of patients who test positive for COVID-19 have no symptoms or develop only mild, subtle symptoms. So symptoms are not the only indictor of whether or not you should get tested.

The Centers for Disease Control and Prevention (CDC) says that in addition to people with symptoms, the following groups should be tested for COVID-19:

• People who have had close contact (within 6 feet of an infected person for at least 15 minutes) with someone with confirmed COVID-19
• People who have been referred by their healthcare provider or state ​health department

“We are missing a good number of patients. That’s why we need testing to be at top-notch. We are way behind,” Fagbuyi says. “[It's] going to be even trickier as we go into the fall flu season if our testing is already lacking."

Li also emphasizes the importance of early testing when possible, because COVID-19 patients may not experience shortness of breath until their oxygen levels are already dangerously low. This phenomenon is known as silent hypoxia.

If you suspect COVID-19, do not delay testing, regardless of the order in which your symptoms appear. Early identification aids in containing the spread of the virus.

“If you start having lots of GI symptoms and a fever, and you have a cough, calling your doctor is useful, and getting tested is useful,” Li says.

Fagbuyi adds that your primary care provider or local health department should be your first point of contact.

“If you have a doctor or access to a local health department, you can call or reach out to them online," he says. "Not every case requires a trip to the emergency department."

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.