Differential Diagnosis of Flu

Differential Diagnosis for Flu

Common Cold: Cold, Flu, or Allergy?

Know the Difference for Best Treatment

Colds and flu are caused by different viruses. “As a rule of thumb, the symptoms associated with the flu are more severe,” says Hauguel. Both illnesses can lead to a runny, stuffy nose; congestion; cough; and sore throat. But the flu can also cause high fever that lasts for 3-4 days, along with a headache, fatigue, and general aches and pain. These symptoms are less common when you have a cold.

Source: NIH News in Health (NIH)1

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Back to: « Flu

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Airborne Allergies: “Allergies are a little different, because they aren’t caused by a virus,” Hauguel explains. “Instead, it’s your body’s immune system reacting to a trigger, or allergen, which is something you’re allergic to.” If you have allergies and breathe in things like pollen or pet dander, the immune cells in your nose and airways may overreact to these harmless substances. Your delicate respiratory tissues may then swell, and your nose may become stuffed up or runny.

Allergies can also cause itchy, watery eyes, which you don’t normally have with a cold or flu,” Hauguel adds.

Allergy symptoms usually last as long as you’re exposed to the allergen, which may be about 6 weeks during pollen seasons in the spring, summer, or fall. Colds and flu rarely last beyond 2 weeks.

Source: NIH News in Health (NIH)2

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Common Cold, Allergies: Cold, Flu, or Allergy?

Treatment depends on which you have. A health professional can help you choose the best therapy.

Common Cold

Seasonal Flu

Airborne Allergy

Source: NIH News in Health (NIH)3

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Food Poisoning: A sick feeling washes over you: nausea, stomach cramps, headache and fever. Vomiting and diarrhea may soon follow. The symptoms are familiar to anyone who’s had the flu, but there may be another culprit—food that’s gone bad.

Source: NIH News in Health (NIH)4

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Toxoplasmosis: Symptoms may include influenzalike symptoms or a mononucleosis syndrome with prolonged fever

Source: CDC Yellow Book 20165

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Fungal Pneumonia: Fungal diseases in the lungs are often similar to other illnesses such as the flu or tuberculosis.

Source: CDC6

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Toxoplasmosis: Some people who have toxoplasmosis may feel as if they have the "flu" with swollen lymph glands or muscle aches and pains that last for a month or more.

Source: CDC Parasites7

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Trichinellosis: Many mild cases of trichinellosis are never specifically diagnosed because they are assumed to be the flu or other common illnesses.

Source: CDC Parasites8

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Common Cold: Flu is not the same as a common cold, and can be a serious illness. For some people, such as the elderly and those with underlying medical conditions, the flu can cause serious complications which require hospitalisation. It can sometimes lead to death.

Source: Queensland Health9

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Meningococcal disease: Other serious conditions can also look like the flu, including meningococcal disease.

Source: New Zealand Health10

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Common cold: Telling the difference between cold and flu

Cold and flu symptoms are similar but flu tends to be more severe.

Cold -- Flu

Appears gradually -- Appears quickly within a few hours

Affects mainly your nose and throat -- Affects more than just your nose and throat

Makes you feel unwell but you’re okay to carry on as normal - for example, go to work -- Makes you feel exhausted and too unwell to carry on as normal

Source: NHS Choices UK11

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Japanese encephalitis: Most people infected by the Japanese encephalitis virus have either no symptoms, or mild, short-lived symptoms, which are often mistaken for flu.

Source: NHS Choices UK12

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Lyme disease: Not everyone with Lyme disease gets the rash. Some people also have flu-like symptoms in the early stages.

Source: NHS Choices UK13

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Tick-borne encephalitis: Initial symptoms of TBE are similar to flu and can include:

Source: NHS Choices UK14

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Swine influenza: It causes similar symptoms to a seasonal flu. It is not usually a life-threatening illness.

Source: GOV.UK15

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Chronic carbon monoxide poisoning: Exposure to lower levels can result in symptoms that resemble flu, viral infections or food poisoning.

Source: GOV.UK16

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  1. Source: NIH News in Health (NIH): newsinhealth.nih.gov/ issue/ oct2014/ feature2
  2. ibid.
  3. ibid.
  4. Source: NIH News in Health (NIH): newsinhealth.nih.gov/ 2007/ February/ docs/ 01features_02.htm
  5. Source: CDC Yellow Book 2016: cdc.gov/ travel/ yellowbook/ 2016/ infectious-diseases-related-to-travel/ toxoplasmosis
  6. Source: CDC: cdc.gov/ fungal/ index.html
  7. Source: CDC Parasites: cdc.gov/ parasites/ toxoplasmosis/ gen_info/ faqs.html
  8. Source: CDC Parasites: cdc.gov/ parasites/ trichinellosis/ disease.html
  9. Source: Queensland Health: conditions.health.qld.gov.au/ HealthCondition/ condition/ 8/ 118/ 82/ influenza-the-flu
  10. Source: New Zealand Health: health.govt.nz/ your-health/ conditions-and-treatments/ diseases-and-illnesses/ influenza
  11. Source: NHS Choices UK: nhs.uk/ conditions/ common-cold/ 
  12. Source: NHS Choices UK: nhs.uk/ conditions/ japanese-encephalitis/ 
  13. Source: NHS Choices UK: nhs.uk/ conditions/ Lyme-disease/ 
  14. Source: NHS Choices UK: nhs.uk/ conditions/ tick-borne-encephalitis/ 
  15. Source: GOV.UK: gov.uk/ guidance/ swine-influenza
  16. Source: GOV.UK: gov.uk/ government/ collections/ carbon-monoxide-co

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.