Seasonal influenza
Seasonal influenza, commonly known as the flu, is a viral infection primarily affecting the respiratory system, which can range from mild to severe illness and can occasionally result in death. The flu is caused by the influenza virus, which spreads globally during the winter months, with different strains emerging each year. Vaccination is the most effective preventive measure, and the Centers for Disease Control and Prevention (CDC) recommends annual flu shots, especially for high-risk groups like young children, the elderly, and individuals with certain health conditions.
Symptoms of the flu, which can begin abruptly, include fever, chills, body aches, fatigue, cough, sore throat, and gastrointestinal issues, particularly in children. The illness can be contagious even before symptoms appear, making it easy to spread in crowded environments such as schools and nursing homes. Treatment typically involves antiviral medications, which are most effective when taken soon after symptom onset, alongside supportive care like rest and hydration.
To minimize the risk of contracting the flu, individuals are advised to practice good hygiene, such as frequent hand washing, avoiding close contact with sick individuals, and maintaining clean surfaces. Understanding these factors can help individuals take proactive measures to protect themselves and others during flu season.
Seasonal influenza
- ANATOMY OR SYSTEM AFFECTED: Eyes, gastrointestinal system, lungs, nose, respiratory system, stomach, throat
- ALSO KNOWN AS: The flu
Definition
Seasonal influenza (the flu) is a viral infection that affects the respiratory system. It can cause mild to severe illness and sometimes death. To avoid getting the flu, one should get vaccinated every year.
Causes
The flu is caused by the influenza virus. Each winter, the virus spreads around the world. The strains usually differ from one year to the next. The two main kinds of influenza virus are type A and type B.
A person who is infected with the virus may sneeze or cough, releasing droplets into the air. If another person breathes in infected droplets, they can become infected. A person can also become infected by touching a contaminated surface, which risks the transfer of the virus from one’s hand to one’s mouth or nose.
Risk Factors
Factors that increase the chance of getting the flu include living or working in crowded group conditions, such as nursing homes, schools, daycare centers, and the military. Factors that increase the risk of developing complications from flu include being pregnant; having recently given birth; having diabetes or chronic lung, heart, kidney, liver, nerve, or blood conditions; and being in a chronic care facility. Other persons at risk are those with a weakened immune system, such as people infected with the human immunodeficiency virus and people taking immunosuppressive drugs.
Also at higher risk are children younger than five years of age, and especially under two years of age, adults ages sixty-five years and older, and people younger than the age of nineteen years who are on a long-term aspirin regimen.
Between the years 2010 and 2020, the Centers for Disease Control and Prevention (CDC) estimated a wide range of illnesses related to the flu. During the years, the flu resulted in between 9 million and 41 million illnesses, between 140,000 and 710,000 hospitalizations, and between 12,000 and 52,000 deaths. Precautions taken during the COVID-19 pandemic, such as wearing masks and social distancing, caused a drastic drop in flu-related illnesses in 2020 and 2021. During the 2023 through 2024 flu season, the CDC estimated between 34 million and 75 million illnesses, between 380,000 and 900,000 hospitalizations, and between 17,000 and 100,000 deaths showing a rebound in flu-related illness.
Symptoms
A person with the flu is infectious beginning one day before their own symptoms start and continuing up to five days (sometimes more) after becoming sick. This means that a person with the flu could infect others before knowing they are sick.
Symptoms usually start abruptly and include a high fever and chills; severe muscle aches; severe fatigue; a headache; decreased appetite or other gastrointestinal symptoms, such as nausea, vomiting, and diarrhea (more common in children than in adults); a runny nose and nasal congestion; sneezing; watery eyes or conjunctivitis; a sore throat; a cough (that lasts for two or more weeks); and swollen lymph nodes in the neck. The ill person might start to feel better in seven to ten days but may still have a cough and feel tired.
Screening and Diagnosis
A doctor will ask about symptoms and medical history to determine a person’s diagnosis of the flu. In some cases, the doctor may take samples from the person’s nose or throat to confirm the diagnosis.
Treatment and Therapy
Treatment for the flu includes antiviral prescription medicines. Most people with the flu do not need antiviral medicine, but those who do are in a high-risk group or have a severe illness (such as breathing problems). Antiviral medicines, which generally help relieve symptoms and shorten the time a person is sick, should be taken within forty-eight hours of the first symptoms. These medicines include zanamivir (Relenza), which may worsen a patient’s asthma or chronic obstructive pulmonary disease (COPD), and oseltamivir (Tamiflu). The CDC also recommends peramivir (Rapivab) and baloxavir marboxil (Xofluza). These medicines may have side effects, especially for children. One should monitor children closely for signs of unusual behavior.
Other forms of treatment include rest, which will help the body fight the flu; fluids, including water, juice, and caffeine-free tea; over-the-counter pain relievers, which are used to control fever and to treat aches and pains (adults can use acetaminophen or ibuprofen); and decongestants, which are available as pills or as nasal sprays. One should not use a nasal spray for more than three to five days. When stopping, the patient may experience an increase in congestion called a "rebound."
Prescription cough medicines and cough drops are also available, as are over-the-counter cough and cold medicines. These include decongestants, expectorants, antihistamines, and cough suppressants. However, these should not be used to treat infants or children less than two years of age. Rare but serious side effects have been reported, including death, convulsions, rapid heart rates, and decreased levels of consciousness. Serious side effects have also been reported in children between the ages of two and eleven years.
Herbal treatments, such as elderberry extract, may reduce flu symptoms. Researchers have found that products such as Sambucol and ViraBLOC, which contain elderberry, decrease symptoms in some studies. Herbal remedies, however, are not regulated by the government, so care should be taken using them. The herbal supplements may not have the same ingredients as those studied and may contain impurities.
Prevention and Outcomes
To prevent getting the flu, one should get vaccinated and do so each year because the virus changes every season. The best time to get vaccinated is between September and January (or later because the flu season can last longer). Two forms of the vaccine are available: a flu shot (injection) and a nasal spray (FluMist). The nasal spray is approved for healthy (and nonpregnant) people between the ages of two and forty-nine years.
People who care for others with severely weakened immune systems should not get the nasal spray; instead, they should get the flu shot. The flu shot is also effective against H1N1 flu.
Persons who want to reduce their risk of the flu should consider the vaccine. It takes about two weeks for the vaccination to protect against the flu. Those who should get a yearly flu vaccine include children ages six months to eighteen years; parents, babysitters, and caretakers of children less than six months of age (because these children are too young to be vaccinated); adults older than fifty years of age (because vaccination in this age group likely reduces hospitalizations and deaths); those living or working in nursing homes and long-term care facilities; those with chronic medical conditions such as asthma; those with diabetes, kidney problems, hemoglobin abnormalities, or immune system problems; women who are pregnant; health care workers; and those living with someone who is at high risk for complications from the flu.
People who should not be vaccinated are those severely allergic to chicken eggs, those who had a severe reaction to vaccination in the past, and children less than six months of age. Persons who are sick and have a fever should discuss vaccination with a medical provider.
There are general measures one can take to reduce the risk of getting the flu. These measures include washing one’s hands often, especially after contacting someone sick (rubbing alcohol-based cleaners on one’s hands is also helpful), and avoiding close contact with people who have respiratory infections. The flu can spread starting one day before and ending seven days after symptoms appear.
Other preventive measures are to cover one’s mouth and nose with a tissue when coughing or sneezing and then throw away the tissue after use; avoid spitting; avoid sharing drinks or personal items; avoid biting one’s nails; and avoid putting one’s hands near one’s eyes, mouth, or nose. Another measure is to keep surfaces clean by wiping them with a household disinfectant.
One should consult a doctor about lowering the risk of getting the flu (also about lowering the risk for children one year of age or older) with antiviral medications (such as zanamivir). Antiviral medications are helpful for persons at high risk for the flu and for those who were only recently vaccinated (within the past two weeks), especially if the flu is spreading in one’s community; for persons at high risk for the flu and who cannot have the vaccine; and for persons not vaccinated and who have repeated close contact with persons (such as family members) who are at high risk for the flu. Persons (such as older adults, infants, and persons with cancer) who are at risk for complications of the flu and who live with someone who has the flu should get antiviral medications.
Persons with the flu should take the following steps to avoid spreading the virus to others: Before returning to school or work, one’s fever should be gone for at least twenty-four hours without the help of fever-reducing medicine. This could take up to seven days after symptoms first appear. A sick person who cannot avoid close contact should cover their mouth and nose with a face mask.
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