The sudden onset of fever, cough without sputum, runny nose, sore throat, headache, muscle aching, and fatigue is the flu syndrome. During flu season in healthy adults the flu syndrome is due to the influenza virus in 80 to 9o% of cases. Other viruses as well as bacteria can cause this collection of symptoms which is also called influenza-like illness (ILI).
But the influenza virus kills more than 36,000 people every flu season. That is why everyone needs to get their flu shot. That is the most important fact about influenza management: get your flu shot every year to lessen your chance of dying from the flu.
When should you go to the doctor when you have flu symptoms? If you have sudden onset of cough, fever, muscle aching, and sore throat, there are two factors that need to be considered.
First, how sick are you–mildly, moderately, or severely ill? (I’ll define each below)
And second, do you have any risk factors that make getting the influenza virus more likely to lead to serious complications.
If you have risk factors you should go to the doctor’s office even if you have only mild symptoms of the flu.
The risk factors are: nursing home resident, age greater than 65 yrs old, age less than 5 years old, chronic illness (neurologic disease, heart disease, lung disease, liver disease, kidney disease, blood disease, or metabolic disease [diabetes]), pregnant women, patients from 6 months to 18 years who are receiving aspirin therapy, immunosuppresion (due to medicines, organ transplantation, malignancy, or HIV infection), or severe obesity (BMI greater than or equal to 40).
If you have any of the above risk factors you should see your doctor even if your flu symptoms (cough, fever, muscle aching, and/or sore throat) are mild.
A person with mild symptoms has no shortness of breath and no trouble drinking plenty of fluids. He doesn’t feel that sick. If he has none of the above risk factors, he should just stay home. He doesn’t need a test for influenza and doesn’t need an influeza virus medicine (oseltamavir or zanamivir).
If your symptoms are moderate, you feel pretty bad—maybe you have a little shortness of breath, you have to force yourself to drink fluids—then you should see your doctor right away for testing for influeza (nasopharyngeal swap for PCR test for influenza) and treatment.
Patients with severe symptoms (severe trouble breathing, dizziness, weakness) should immediately go to the emergency department for evaluation.
Because pregnant women, especially those in the third trimester, are at high risk for complications from influenza, they should be evaluated in the emergency department even if they have only mild symptoms or moderate symptoms and their own physician is not immediately available.
But the big key is—get your flu shot. Everyone who is 6 months old or older needs a yearly flu shot.
Grace C, Influenza, Critical Care Secrets, 5th edition, 2013, pp 271-276.
Influenza tests available at http://www.cdc.gov/flu/professionals/diagnosis/rapidlab.htm.