You are still contagious with the flu from around day one of the flu before the flu symptoms start and you're also still contagious with the flu until 5 days to 7 days after the symptoms of the flu start.
Although you're most contagious with the flu in the first 3 days to 4 days of the flu and you're also likely in the clear of being contagious once you're fever is gone 24 hours without any medicine.
Although some people, especially kids or those with weakened immunity can spread the flu longer.
To stop the spread of the flu, wash your hands often, cover coughs, stay home and cover sneezes and avoid close contact.
The best indication that you're less contagious with the flu is when you have been fever free for at least 24 hours without using fever reducing medication like Advil or Tylenol.
To confirm you have the flu you can do an at home flu test, which you can buy online or in store and it can help determine if you have the flu or not.
Or you can see a doctor and have them test you for the flu and they can also diagnose you based on your symptoms and using better test kits.
You can also test negative for flu and still have it, especially when using rapid tests which often do produce false negatives, which means that the flu tests miss the flu virus even when it's present to low sensitivity or testing too early or too late in the flu.
Although a doctor may still diagnose you with the flu, based on your symptoms and high flu activity in the community or they may recommend a test that is more accurate like the molecular PCR tests.
Rapid antigen tests detect virus parts or antigens but they are not as good as molecular tests at finding the virus.
Viruses like adenovirus, mono, gastroenteritis and bacterial infections like pneumonia, strep, tick borne illnesses like Lyme disease and even early hepatitis and HIV can mimic flu like symptoms.
Even COVID can mimic flu like symptoms.
COVID-19 shares symptoms of the flu like fever, cough, body aches and sore throat.
RSV (Respiratory Syncytial Virus) causes cold-like symptoms, potentially severe.
Mononucleosis (Mono) causes extreme fatigue, fever, sore throat, swollen glands.
Common Cold/Adenovirus causes mild, but can sometimes feel more intense.
Viral Gastroenteritis causes stomach flu with fever, aches, vomiting/diarrhea.
HIV (Acute) causes flu-like illness can be the first sign of infection.
Strep Throat causes sore throat, fever, fatigue, headache but less cough.
Pneumonia causes cough, fever, chills, shortness of breath and Lyme disease causes fever, headache, fatigue and muscle aches after a tick bite.
There's also a new strain of flu going around right now which is the H3N2 flu strain and it's making some people feel worse than the other flu viruses.
The new strain of the flu virus is currently more aggressive than the older flu viruses.
The new flu strain is showing typical influenza symptoms which include sudden fever, cough, sore throat, runny/stuffy nose, body aches, headache, and fatigue, with some experiencing vomiting/diarrhea (more common in kids).
Key indicators of the flu including the new flu strain are abrupt onset and intense fatigue/aches, but symptoms overlap with COVID-19, so testing helps differentiate, with emergency signs including trouble breathing or confusion.
COVID-19 and the flu also feel very similar, and share many of the same symptoms like fever, cough, fatigue, sore throat, and body aches, making them hard to tell apart just by how you feel, though COVID-19 is more known for taste/smell loss and sometimes diarrhea, while flu often hits suddenly with deep exhaustion and joint pain.
Respiratory adenovirus infections typically also cause mild cold or flu-like symptoms, although they can also cause acute bronchitis, pneumonia, conjunctivitis (pink eye), and acute gastroenteritis (inflammation of the stomach or intestines causing diarrhea, vomiting, nausea, and stomach pain).