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This story originally appeared on Business Insider
Is it COVID-19 or simply a cold?
It’s a question many Americans will likely be asking themselves come fall and winter, as coronavirus infections overlap with cases of the common cold and seasonal flu. The symptoms may be hard to distinguish, given that all three conditions can result in a cough.
But there are hallmarks of each illness.
A recent study from the University of Southern California identified a distinct order of symptoms among COVID-19 patients: Most symptomatic patients start with a fever, followed by a cough. For seasonal influenza, it’s typically the opposite — people generally develop a cough before a fever.
If you get a common cold, meanwhile, that’s more likely to start with a sore throat as the first symptom, according to the Centers for Disease Control and Prevention.
Here’s how to distinguish the novel coronavirus from the seasonal flu, allergies, and common cold.
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These symptom lists for each illness and the order in which they arrive aren’t foolproof, though: Some COVID-19 patients don’t develop a fever and some flu patients never come down with a cough.
That’s why it’s also helpful to consider how quickly symptoms appear and how long they last.
How COVID-19, flu, cold, and allergies manifest and progress
Coronavirus cases tend to develop gradually compared to the flu. While some people develop COVID-19 symptoms within two days of being infected, the disease’s symptoms can take up to two weeks to manifest. On average, people start to feel sick five days after they were infected.
People with the flu, on the other hand, usually feel sick one to four days after exposure. Most patients then fully recover within less than two weeks, often as quickly as a few days.
Some coronavirus patients may recover within two weeks as well, but a growing share of patients have reported symptoms that last for several months.
Common cold symptoms, by contrast, usually reach their peak within within two to three days of infection — but, like the coronavirus, they often develop gradually. And some symptoms last longer than others: Patients with a typical cold may have a sore throat for eight days, a headache for nine to 10 days, and congestion, a runny nose, or cough for more than two weeks.
Allergies tend to last longer — about two to three weeks per allergen — and won’t resolve until the allergen leaves the air. Seasonal allergies also tend to be more severe in the spring.
The most common symptoms of each illness
Coronavirus cases run the gamut from asymptomatic to mild to severe.
“I’ve never seen an infection with this broad range of manifestations,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told Facebook founder Mark Zuckerberg in July.
Some patients have even reported conditions that don’t appear on the official CDC list, like hair loss, hiccups, and purple, swollen toes.
Coronavirus testing in Jericho, New York on April 22, 2020.
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Many COVID-19 patients lose their sense of taste or smell — that may be the strongest predictor of a COVID-19 infection, according to a June study from scientists at Massachusetts General Hospital and King’s College London. A Spanish case study found that nearly 40% of patients with COVID-19 developed smell and/or taste disorders, compared to just 12% of patients with the flu.
Symptoms like a fever or headache could help rule out allergies or the common cold as well.
People with colds, meanwhile, are more likely to develop a runny or stuffy nose than COVID-19 patients. And cold symptoms are milder overall.
But one of the hallmarks of allergies — itchy eyes — isn’t associated with any of the other three illnesses.
Ultimately, the best way to know if you have COVID-19 is to get a diagnostic test. People who haven’t been tested should stay home if they’re feeling sick or if they were exposed to someone with the virus.
Everyone should also get a flu shot this fall in order to minimize the chance of overcrowding at hospitals as they treat both flu and COVID-19 patients.
“This will be, in my opinion, the most important flu season of our lifetimes,” US Surgeon General Jerome Adams said at a Senate hearing on Wednesday. “Less flu and fewer hospitalizations will help conserve precious healthcare resources.”