Influenza (Flu)

Overview

Influenza, commonly known as the flu, is a respiratory system infection affecting the nose, throat, and lungs. It is caused by the influenza virus. Flu symptoms encompass fever, body and head aches, sore throat, as well as respiratory problems.

Influenza, often referred to as the flu, differs from stomach “flu” viruses, which cause symptoms such as diarrhea and vomiting. 

Many individuals who contract the flu typically recover without medical intervention. However, influenza and its associated complications can prove fatal in certain cases. Some specific demographics have an elevated susceptibility to flu–related complications. These include infants under 12 months old, pregnant individuals or those who have recently given birth during the flu season, adults aged 65 and older, as well as individuals residing or working in crowded facilities, such as nursing homes, military barracks, and hospitals.

Additional groups at a heightened risk for complications resulting from the flu encompass individuals with weakened immune systems, a body mass index (BMI) of 40 or higher, and nervous system disorders that alter cognitive processing are among those at an elevated risk of flu complications. 

Additionally, certain medical conditions increase the likelihood of experiencing flu complications, including chronic illnesses like asthma, heart disease, kidney disease, liver disease, and diabetes, as well as a history of strokes and young individuals under 20 years of age who are on long–term aspirin therapy.

While the annual influenza vaccine is not guaranteed to provide complete protection, it significantly reduces the likelihood of severe flu complications, particularly among those who are at a higher risk for such complications.

Symptoms

Typical signs and symptoms of the flu frequently include a fever, muscle aches, chills, and sweating. 

Flu symptoms typically manifest quickly, contrary to a cold which appears gradually. Despite the discomfort of a cold, the flu tends to bring a more severe set of symptoms, resulting in a generally more pronounced sense of illness. 

Flu symptoms may include:

• Headache
• Sore throat
• Dry cough
• Breathing difficulty
• Stuffy or congested nose
• Frequent sneezing
• Weakness and fatigue
• Pain in the eyes

Diarrhea and vomiting are also flu symptoms. However, children are more likely than adults to have them. It is important to note that not everyone may experience all of these symptoms. 

If one suspects flu, or if any of the signs and symptoms persist, consult a healthcare provider for proper diagnosis and treatment. Prompt testing is crucial for the optimal effectiveness of prescribed antiviral medications and avoid more serious complications. 

Immediate medical assistance may be necessary in certain cases, such as: 

• Symptoms persist for more than seven to 10 days without improvement or fever lasting more than three days. 
• Experiencing flu symptoms while having an underlying condition that increases the risk of severe illness.
• Pregnant and exhibit a fever or other flu–related symptoms 

For adults, emergency symptoms include difficulty breathing or shortness of breath, chest pain, persistent dizziness, seizures, deterioration of existing medical conditions, and severe weakness or muscle pain. Emergency symptoms in children encompass the symptoms observed in adults and may include discoloration of the lips or nail beds to gray or blue and signs of dehydration.

Causes

Flu, caused by the influenza virus. The most prevalent types infecting individuals are Influenza A, B, and C. Influenza A and B, prevalent during the winter season, are associated with more severe symptoms. In contrast, Influenza C, which is not seasonal, tends to result in milder symptoms, and the incidence remains relatively steady throughout the year. 

Influenza viruses are transmitted through the air in droplets when an infected individual coughs, sneezes, or speaks. These droplets can be inhaled directly or transferred to you by touching contaminated surfaces. Infected individuals are contagious from a day before symptoms to 5–7 days after they start, and this period might be a bit longer in children and those with weakened immune systems.

New strains of influenza viruses frequently emerge, and the virus itself is always evolving. If you’ve been previously infected with influenza, your body has already produced antibodies tailored to combat that particular strain of the virus. If future influenza viruses resemble the ones you’ve encountered before, either through prior illness or vaccination, these antibodies can potentially thwart infection or reduce its intensity. Antibodies generated in response to previous influenza viruses may not offer protection against new influenza strains, as these new strains can differ significantly from those you’ve encountered in the past.

Risk factors

Several factors may contribute to one’s risk of having flu and developing complications, such as:

• Age: In young children, particularly those aged 12 months or younger, seasonal influenza often results in more severe outcomes. Adults aged 65 and older tend to experience worse consequences that comes with flu. 
• Poor immune system: Weakened immune system results from cancer therapies, immunosuppressive medications, chronic steroid usage, organ transplants, blood cancer, or HIV/AIDS. It may raise the risk of problems and make it easier to get the flu virus. 
• Chronic health conditions: Certain health conditions increase the risk of severe infection, potentially leading to life–threatening complications necessitating hospitalization. Individuals with conditions such as asthma, COPD, or other chronic lung diseases, as well as those with a history of kidney, liver, neurological, heart, blood diseases, or previous history of stroke, are at a higher risk of experiencing serious complications from the flu.
• Residential or occupational environment: People who are hospitalized are more likely to acquire flu. Individuals residing or working in crowded facilities like nursing homes or long–term care facilities, have an increased risk of contracting the flu.
• Ethnicity: Non–Hispanic Black individuals, non–Hispanic American Indians, Alaska Native individuals, and Hispanic or Latino individuals experience more severe cases of flu compared to non–Hispanic White individuals and non–Hispanic Asian individuals.
• Taking aspirin under age 20: Individuals under the age of 20 who are undergoing prolonged aspirin therapy face a heightened risk of developing Reye’s syndrome if they contract the influenza virus. 
• Being pregnant: Pregnant individuals are at higher risk for influenza complications, especially in the second and third trimesters, extending up to two weeks after birth.
• Being overweight: Flu complications are more common in people with a body mass index (BMI) of 40 or higher.