Considering that the flu can spread like wildfire among unvaccinated communities, it’s tempting to worry that every cough, muscle ache, and hint of a fever is a sign you caught the flu.
That’s understandable, given that there are a ton of other illnesses that bring on copycat flu-like symptoms, like fever, cough, runny nose, and headaches, among others, per the Centers for Disease Control and Prevention.
“Any overwhelming infection that stimulates our immune system can [produce] some of the same symptoms,” explains Cindy Weston, DNP, RN, FNP-BC, assistant professor at the Texas A&M College of Nursing. In other words, “most flu just feels like a regular cold,” Joseph Khabbaza, MD, a pulmonologist at Cleveland Clinic, tells Health.
The only way to know for sure you have the flu is to get tested–but there are subtle clues to help you distinguish between influenza and something else. Here are a few of the many conditions that can cause flu-like symptoms, but aren’t the flu.
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Both colds and influenza are viral illnesses, they both tend to occur in the same seasons, and they have many overlapping symptoms, like a sore throat and a stuffy nose.
The main difference is how quickly the symptoms come on. “A cold typically gradually progresses symptom by symptom over [several] days,” says Keri Peterson, MD, an internist at Lenox Hill Hospital in New York City. “With the flu, the constellation of symptoms of high fever, cough, muscle ache, and severe lethargy comes on in 24 to 48 hours.”
And even though so many symptoms overlap, colds typically don’t come with chest pain or body aches, which are more characteristic of the flu, adds Dr. Peterson.
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The flu and strep throat share many symptoms, but there are two you may find in the flu but never in strep: cough and nasal congestion.
Strep throat may also bring swollen lymph nodes, swollen tonsils, a skin rash, or white blotches on the tonsils. None of these is typical of the flu.
If your doctor suspects strep, he or she will probably swab your throat and test for the bacteria. If the test comes back positive, you’ll likely get antibiotics, which can usually clear up the symptoms quickly.
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Pneumonia can come separately from the flu or it can be a secondary complication of getting sick. You may even look like you’re over the flu and then bang–you’re stricken with another infection. “People are getting the flu and maybe even riding it out, and a week or so later, they’re coming in with pneumonia,” Weston says.
Normally, pneumonia that comes with or after the flu is caused by bacteria and can be treated by antibiotics. With this type of pneumonia, “the cough is pretty persistent and unrelenting and often associated with chest pain,” Weston says. “The fever could be low grade or higher. A lot of times there’s no appetite with pneumonia, and there can be some body aches.” A pneumonia cough also has mucus in it.
Pneumonia that’s not related to the flu is often viral; viral pneumonia is also typically milder than the bacterial kind. You may also have some congestion, coughing, and fatigue, all of which could point to the flu–but in this case, they’re simply flu-like symptoms.
Doctors can listen for telltale signs of pneumonia by putting a stethoscope to your chest, says Dr. Peterson.
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Mono is also called the “kissing disease” because it can be passed through saliva (along with coughing, sneezing, and sharing utensils).
Mono is usually caused by the Epstein-Barr virus. It tends to hit teens and young adults more than other age groups.
Symptoms often come on slowly, but they can mimic the flu; you might feel really, really tired, spike a fever, or have a sore throat and body aches. But other symptoms can help differentiate mononucleosis from the flu, including a swollen liver or spleen.
Mono also drags on longer than the flu, often lasting two to four weeks–but sometimes six months or longer.
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Meningitis is inflammation of the membranes (meninges) that cover the brain and spinal cord.
Like pneumonia, meningitis can be caused by either a viral or a bacterial infection. Viral meningitis is more common and milder, but the symptoms of both are similar and look a lot like the flu: headache, fever, and fatigue. Meningitis, though, also comes with a stiff neck and sensitivity to bright light.
Viral meningitis is like colds and the flu in that most people recover on their own in a week or so. Bacterial meningitis, however, can cause brain damage and even death if it’s not treated promptly with antibiotics.
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Acute bronchitis not only has cold- and flu-like symptoms, it’s even caused by many of the same viruses.
“Bronchitis has a lot of overlap–productive cough with mucus, lethargy, and a sore throat,” says Dr. Peterson. The main difference is that bronchitis doesn’t come with a high fever. Bronchitis symptoms also tend to center on your chest and throat, instead of the full-body aches common with the flu, she adds. The nagging cough of bronchitis can last up to three weeks, longer than a cough from the flu.
There’s no test for bronchitis like there is for the flu, so doctors usually diagnose it by asking about symptoms and examining you. Bronchitis treatment consists of rest, drinking lots of fluids, and taking meds that can relieve symptoms.
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Respiratory syncytial virus
Respiratory syncytial virus or RSV has symptoms that can also be mistaken for the flu (or a cold). “It can cause runny nose and cough,” says Afif El-Hasan, MD, a spokesperson for the American Lung Association and a pediatrician with Kaiser Permanente.
Unlike the flu, though, RSV symptoms usually appear gradually. They typically go away on their own as well–you just need to drink plenty of fluids and rest.
Similar symptoms come from infection with what are called parainfluenza viruses. “They are like the flu, but they’re not as bad,” says Dr. El-Hasan.
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When should you contact your doctor?
“If you suspect you have the flu, then you should see the doctor within 48 hours because [antiviral] medicine has to be taken very quickly,” Dr. Peterson says. “Err on the side of caution.”
Dr. Khabbaza says that if you’re unable to go about your normal routine, you should consider heading to the doctor. Also, if certain symptoms escalate, this could be an indication of flu, not just a chest cold, and you, again, should consider getting checked out ASAP. (For example, if body aches progress “to the point you can barely move around,” or if your symptoms are causing difficulty breathing, it’s definitely time to head to the doctor, says Dr. Khabbaza.)
Most viral infections, including the flu, tend to go away on their own. But be on the alert for signs of trouble such as shortness of breath, chest or abdominal pain, dizziness, or dehydration. If you’re experiencing any of these in addition to your flu-like symptoms, call your doctor or head to an emergency room.
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