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Influenza, also commonly known as flu, occurs due to a viral infection. The viruses involved in causing this disease are known as influenza viruses. It is a well-known disease that affects thousands of individuals across the globe every year. Despite the availability of vaccines for certain types of influenza viruses, these pathogenic organisms have a high ability to modify themselves and continue to cause this infection in most people. In most cases, the infection resolves on its own within two weeks, but in some cases might lead to serious complications.


The cause of influenza is the different types of influenza viruses belonging to the Orthomyxomiridae family. These viruses can affect human beings and certain animals (pigs, bats, poultry, ducks, etc.)


Influenza viruses are of three major types: Type A, Type B, and Type C.

Influenza A virus is the most common type that causes flu in most infected cases. This virus has many subtypes. Primarily it affects younger children, older adults, and those with a weakened immune system. It also frequently occurs in birds and can develop a widespread pandemic.
Influenza B virus is also relatively common, and it usually affects human beings only. Children are a prime target of this virus since they have comparatively less developed immune systems.
Influenza C virus is less common and causes only a mild infection in affected individuals.

Risk Factors And Epidemiology

Age is a primary risk factor for influenza because the viruses are predominant among younger children and adults over 65 years. Both have weakened immune systems compared to young adults, allowing the virus to propagate its copies. Doctors, nurses, and healthcare staff are also at high risk. Lessened immunity due to other infections, diseases, medications, or treatments is a significant risk factor for influenza. Systemic diseases that can increase the chance of developing this infection include asthma, kidney disorder, liver disorder, congestive heart failure, sickle cell anemia, etc. Pregnant women and morbidly obese individuals have also been included in the high-risk category
In recent years, it has been estimated by WHO that almost 3 to 5 million people worldwide have been reported to be infected by the influenza virus. This states that around 5 to 15% of the global population are affected yearly by these viruses. Native American people have been noticed to have a higher tendency to develop this infection. Overall, it can affect individuals of any gender and age, although children and elders are at a higher risk.

Signs And Symptoms

The onset of symptoms caused by the influenza virus are sudden, but they usually occur after an incubation period of one to four days. Predominant symptoms include fever, headache, chills, tiredness, and generalized body ache. These symptoms usually occur along with the upper respiratory tract symptoms, including sore throat, dry cough, runny nose, nasal congestion, etc. You may also experience nausea, vomiting, loss of appetite, and diarrhea. The majority of the cases are limited to these symptoms, but if the virus progresses along the respiratory tract, it may lead to pneumonia and other complications. 


The complications of influenza include pneumonia, sinus infections, middle ear infections, meningitis, bronchitis, and encephalitis.


The first step towards diagnosing the influenza virus is to record the history of symptoms, onset, and duration of the disease in the infected person. This is followed by thorough clinical examination, and vital signs are checked (temperature, blood pressure, pulse rate, and respiratory rate). Because the symptoms of influenza are similar to other respiratory tract diseases, your doctor may suggest a viral culture test, rapid antigen test, or PCR for a conformational diagnosis.

Differential Diagnosis

Influenza is typically confused with the common cold caused by adenoviruses. Other conditions with almost similar symptoms as the influenza virus include rhinovirus infection, parainfluenza virus infection, respiratory syncytial virus infection, herpes simplex virus infection, dengue, malaria, ebola, q fever, histoplasmosis, asthma, chronic obstructive bronchitis, emphysema, streptococcal pneumonia, etc.


In case of a mild or moderate infection from the influenza virus, only symptomatic care is recommended to relieve the symptoms and speed the recovery process. Antipyretics, analgesics, antihistamines, and cough suppressants are given depending on the patient’s age, severity, and duration of the symptoms. Supportive care at home is preferred, including intake of fluids, drinking warm soups or broths, gargling with warm saline water, using a nebulizer or humidifier (for the congested nose), and bed rest. In case of a severe infection, antiviral drugs are prescribed to reduce the risk of systemic complications. Smoking and alcohol use is inhibited during the recovery process of influenza.


Symptomatic care requires antipyretic drugs like paracetamol, analgesics such as naproxen, ibuprofen, etc., antihistamines such as loratadine, diphenhydramine, etc., and nasal or cough drops. Antiviral medication is only prescribed in severe cases. Commonly prescribed antiviral drugs for influenza include Oseltamivir and Zanamivir. These are to be taken in the dosage as prescribed by your doctor.


Individuals with a healthy immune system recover from this infection within one to two weeks with or without medication. Children, elders, or those with weak immunity are at risk of developing serious complications if the symptoms are not addressed on time and treated effectively. Cases of mortality have been reported in which the common cause is obstruction of the respiratory system.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on May 23, 2023.


Influenza (Seasonal) (who.int)


Influenza and antiviral resistance: an overview | SpringerLink



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