A contagious respiratory illness, influenza, is caused by a variety of viruses. It may cause mild to severe symptoms, including fever, cough, sore throat, muscle aches, headache, and fatigue. Complications of the flu include pneumonia, ear infections, sinus infections, dehydration, and worsening of chronic conditions. Some people are at higher risk of serious illness from the flu, such as young children, older adults, pregnant women, and people with weakened immune systems.
A flu virus is one of four main groups of influenza viruses: A, B, C, and D. Influenza A and B viruses cause most human infections and seasonal epidemics. Influenza C viruses are not considered a major public health concern and cause mild respiratory infections. Humans are not known to be infected by influenza D viruses, which mainly affect cattle.
Antigenic drift and antigenic shift are the main ways influenza viruses change and evolve, making it difficult to prevent and treat them. Virus surface proteins change gradually and minorly, allowing the virus to evade the immune system and infect new hosts, which is known as antigenic drift. The term "antigenic shift" refers to the sudden and major change in the surface protein of a virus caused by the mixing of genes from different viruses. This can result in the emergence of a new, novel virus that can cause a pandemic, which is a global outbreak of a new and severe disease.
Some possible risk factors for getting the flu include:
Exposure to someone who has the flu or is contagious
Traveling to areas where the flu is circulating or prevalent
Having a weak or compromised immune system
Having a chronic medical condition, such as asthma, diabetes, heart disease, or kidney disease
Being under stress or having poor sleep quality
Having a low or inadequate vaccination status
The symptoms of the flu usually start one to four days after exposure to the virus and last for about a week. Some common symptoms include:
Fever or feeling feverish
Cough
Sore throat
Runny or stuffy nose
Muscle or body aches
Headache
Fatigue or tiredness
Chills or sweats
Some people may also experience:
Nausea or vomiting
Diarrhea
Loss of appetite
Loss of taste or smell
There are a variety of symptoms associated with the flu, and they vary from person to person and from season to season. Some people may have mild symptoms, while others may have severe or life-threatening symptoms. Flu symptoms can also be similar to those associated with other respiratory infections like the common cold, COVID-19, or pneumonia. If your symptoms are severe, persistent, or worsening, or if you notice complications, such as:
Difficulty breathing or shortness of breath
Chest pain or pressure
Confusion or altered mental status
Severe or persistent vomiting or diarrhea
Dehydration or signs of shock
Bluish lips or face
Seizures or convulsions
Ear pain or discharge
Sinus pain or pressure
Symptoms, medical history, and a physical examination are usually used to diagnose flu. When the symptoms are severe, the patient is at a high risk of complications, or if the treatment depends on the type of virus, a laboratory test may be required to confirm the diagnosis. Several types of tests can be used to detect influenza virus presence or type, including:
Rapid influenza diagnostic tests (RIDTs), which are quick and easy tests that can provide results within 15 minutes, but are not very accurate or reliable
Rapid molecular assays, which are faster and more accurate tests that can provide results within 20 minutes, but are not widely available or affordable
Reverse transcription polymerase chain reaction (RT-PCR) tests, which are the most accurate and sensitive tests that can provide results within a few hours, but are more complex and expensive
Viral culture tests, which are the most definitive tests that can provide results within a few days, but are rarely used for routine diagnosis
The treatment of the flu depends on the severity of the symptoms, the risk of complications, and the type of virus. Treatments aim to relieve symptoms, prevent or treat complications, and decrease virus transmission. Some possible treatments include:
If taken within 48 hours of the onset of symptoms, antiviral medications such as oseltamivir (Tamiflu), zanamivir (Relenza), and baloxavir (Xofluza) can reduce the severity and duration of symptoms, as well as lower the risk of complications.
It is important to use symptomatic medications, such as acetaminophen (Tylenol), ibuprofen (Advil), or naproxen (Aleve), with caution and under medical supervision, especially in children, pregnant women, and people with chronic illnesses.
As coughing helps remove the virus and the secretions from the lungs, cough suppressants, such as dextromethorphan (Robitussin), or expectorants, such as guaifenesin (Mucinex), should only be used sparingly and only when necessary.
Decongestants, such as pseudoephedrine (Sudafed), or antihistamines, such as diphenhydramine (Benadryl), can relieve nasal congestion and runny nose, but should be taken with caution and only for a short period of time, as they can cause side effects, including dry mouth, drowsiness, or increased blood pressure.
Lozenges, sprays, and gargles, which can soothe a sore throat and reduce irritation, but should not be swallowed or overused as they may cause numbness, burning, or allergic reactions.
Home remedies, such as honey, lemon, ginger, garlic, or chicken soup, which can provide some relief and comfort, should not be used as a substitute for medical treatment and advice, and should be used in moderation and with caution, since they may have interactions, contraindications, or adverse effects.
You can prevent influenza infection and its complications by getting vaccinated every year before flu season begins, usually in the fall. The best way to prevent influenza is to get vaccinated every year before the flu season begins. In addition to reducing the risk of illness, hospitalization, and death, the flu vaccine protects against the most common and severe strains of the virus. The flu vaccine is safe and recommended for everyone who is 6 months of age or older, unless they have a medical reason not to get it, such as an allergy or a history of Guillain-Barré syndrome. Young children, older adults, pregnant women, people with chronic conditions or weakened immune systems, as well as those with chronic conditions or weakened immune systems, need the flu vaccine in particular.
Some other ways to prevent the flu include:
Practicing good hygiene, such as washing the hands frequently and thoroughly, covering the mouth and nose when coughing or sneezing, and disposing of the tissues properly
Avoiding close contact with people who are sick or have flu symptoms, and staying home if you are sick or have flu symptoms, until you are fever-free for at least 24 hours without the use of fever-reducing medications
Wearing a mask or a face covering when in public or crowded places, and maintaining a physical distance of at least 6 feet from others, especially during the COVID-19 pandemic
Cleaning and disinfecting the surfaces and objects that are frequently touched or shared, such as doorknobs, keyboards, phones, or toys
Boosting the immune system, such as eating a balanced and nutritious diet, drinking plenty of fluids, getting enough sleep and rest, exercising regularly, and managing stress
Seeking medical attention and treatment as soon as possible if you have flu symptoms or are exposed to someone who has the flu, and following the doctor’s advice and instructions regarding the use of antiviral medications, symptomatic medications, or home remedies
Influenza is a common and contagious respiratory illness that can cause mild to severe symptoms and complications. With proper diagnosis, treatment, and prevention, most cases of the flu can be resolved and avoided.
