For those who get sick during the fall and winter, the diagnosis could be a toss-up.
With the threat of the common cold, flu, COVID-19 and RSV in the mix, it can be tricky to determine the culprit.
Fox News medical contributor Dr. Marc Siegel shared with Fox News Digital that among the four conditions, there is "very much [an] overlap" in symptoms.
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So how can you spot the difference between a cold, the flu, COVID and RSV?
Here are a few indications.
Caused by viruses, a cold is marked by typical symptoms such as a runny or stuffy nose, sore throat, cough, sneezing, nasal congestion, headache, slight body aches and a low-grade fever, according to Mayo Clinic.
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Adults may catch a cold two or three times a year, while infants and young children can get them more often.
Most people recover from a cold in about a week, and medical care is generally unnecessary unless symptoms worsen.
Colds are most frequently caused by rhinoviruses, according to the Centers for Disease Control and Prevention (CDC).
They are spread through respiratory droplets released by coughing and sneezing, or through personal contact such as shaking hands or hugging.
The best way to protect yourself from catching a cold is by washing your hands often and avoiding others who are infected, per the CDC.
Influenza symptoms may be similar to those of the common cold, but the repercussions could be more severe.
The flu is caused by influenza viruses that impact the nose, throat and sometimes the lungs, according to the CDC, and can cause mild to severe illness.
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In some cases, the flu can be deadly.
The virus has resulted in anywhere from 12,000 to 52,000 deaths annually in the years 2010 to 2020, per CDC data.
Flu symptoms are usually sudden, Siegel said — and can include fever, chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and sometimes vomiting and diarrhea.
The CDC noted that it's "impossible" for people to tell if they have the flu based on symptoms alone, which is why diagnosis requires testing by a medical professional, most commonly with rapid influenza diagnostic tests (RIDTs).
The flu is spread by the same respiratory droplets as a cold, and can also be transmitted by touching infected surfaces and then touching your face.
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People with the flu are most contagious within the first three to four days of being sick.
Children are most likely to come down with the flu, according to a 2018 study published in Clinical Infectious Diseases; but the CDC still considers the illness to be very common.
The most effective way to avoid the flu, according to the CDC, is to get a flu vaccine every year, follow frequent handwashing protocol and maintain distance from sick people.
COVID-19 has all the same symptoms as cold and flu, including fever, chills, cough, body aches, sore throat, congestion, runny nose, fatigue and headache.
Siegel noted that some additional symptoms of COVID-19 are characterized by sore throat, loss of taste, brain fog and shortness of breath.
One of the reasons for running rapid COVID tests on patients with these symptoms is to distinguish the virus from the others, Siegel said.
COVID-19 can also be detected through more accurate PCR testing, which will deliver a result within three days.
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People should seek emergency medical attention if symptoms develop into breathing trouble, persistent chest pain or pressure, new confusion or an inability to stay awake, as well as pale, gray or blue-colored skin, lips or nail beds, according to the CDC.
Coronavirus prevention measures include staying up to date with vaccines, improving ventilation in indoor spaces, testing for COVID, staying home when symptoms arise, and avoiding contact with people who may be infected, the agency stated.
Other preventative measures include wearing masks or respirators, avoiding crowded areas and keeping distance from others.
RSV, or respiratory syncytial virus, can cause the same basic symptoms of runny nose, cough, sneezing and fever.
Other symptoms of the virus, such as wheezing and a decrease in appetite, could differentiate it from other conditions, according to the CDC.
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While infants are at the highest risk for RSV infection, they may have different symptoms, such as irritability, decreased activity and breathing difficulties.
As Siegel noted, RSV patients can become short of breath and may spike a "very high" fever, which could require an ER visit.
"It is particularly risky to the very young, where it clogs small airways, and the elderly, who lack the immune response to fight it off quickly," he said.
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Infants and older adults are at risk of more severe infection, which can develop into other conditions like bronchiolitis and pneumonia, the CDC states.
Hospitalization may also be necessary for infants and older adults who experience dehydration or trouble breathing.
Most RSV infections will improve within one week, according to the CDC, and can be treated with over-the-counter medications and at-home care.
While there are subtle differences between RSV and other conditions, protocols for transmission and prevention remain mostly the same, including distancing from people with symptoms and being careful when touching foreign surfaces.
Multiple RSV vaccines are available for all ages and are recommended by the CDC as prevention aids.
