Influenza is a common, contagious respiratory illness caused by a group of viruses known as influenza viruses. It can cause mild (usually)to severe disease, and at times can lead to death. The best way to prevent influenza is to get vaccinated. Influenza can occur and spread worldwide (pandemic)

How does one contract the flu?

The respiratory route spreads the flu virus. When a patient with the flu sneezes, coughs, or even talks, droplets of respiratory secretions are released into the air. These also carry the flu virus and can be inhaled by other people. The flu virus then settles in the respiratory tract and, given the right conditions, could cause influenza infection. A much less common route of transmission is by touch. When a person comes in contact with a surface on which droplets of respiratory secretions of a patient infected with the flu have been deposited, they may then carry this infected material when he comes into contact with the upper respiratory tract, say by touching his nose.

A person can infect others from one day before getting symptoms to five days after getting sick.

What are the symptoms that a patient with the flu experiences?

After a person contracts the infection, it takes around two days for the symptoms to manifest. The most common symptoms are:

• Fever – Usually high (however, it is essential to emphasize that some patients will not have fever).
• A cough that is usually dry
• Sore throat
• Runny nose
• Headache
• Myalgia (muscle pain)
• Arthralgia (joint pain)
• Malaise – feeling of being unwell
• Vomiting and diarrhea – especially in children

What is the subsequent course?

In most people, the symptoms subside within a week and do not require medical attention. However, people with risk factors can progress to a significant illness that may lead to considerable morbidity and, rarely, even mortality. Persistence of symptoms like weakness and easy fatigability (post-influenza asthenia) may last for several weeks in older children. One needs to be very careful if:

• Extremes of age: Adults who are > 65 years of age and Children who are < 5 years of age, especially those who are < 2 years.
• Pregnant women.
• People suffering from underlying medical conditions:
  • Asthma – even if they are well controlled with medications
  • Pre-existing chronic lung diseases like chronic obstructive pulmonary disease or cystic fibrosis
  • Heart disease – congenital heart disease, congestive heart failure, and coronary artery disease
  • Diabetes and other endocrine disorders
  • Pre-existing liver disease
  • Pre-existing kidney disease
  • Children who have inherited disorders of metabolism
  • Immunodeficient – either due to disease (like HIV), drugs (steroids), or malignancy
  • < 19 years and on chronic aspirin therapy
  • People who are morbidly obese (BMI > 40)

What can one do to prevent the spread of the flu and protect oneself against the flu?

• General health and hygiene measures.
• Vaccinating oneself against the flu by taking flu shots once a year.
• Any person suffering from a flu-like illness should stay at home until 24 hours after their fever has resolved without taking fever medications.
• Pre-exposure prophylaxis (This is usually indicated for high-risk groups who cannot be vaccinated for some reason).
• Post-exposure prophylaxis (Again indicated in high-risk groups who have been exposed to a patient suffering from the flu and who either cannot be vaccinated or who have been vaccinated < 2 weeks before exposure).

How do you diagnose the flu?

In most cases, the flu is diagnosed by the typical symptoms that the patient experiences. In most people, we do not order specific tests to diagnose the flu, preferring to prescribe standard treatment. However, there are times when the symptoms may not match up to the typical presentation, and then the tests may be ordered. Tests are also ordered when the flu is suspected in pregnant women and in any person whose immunological status is compromised.

The most common tests used to diagnose the flu are the rapid tests that can diagnose the illness in about 30 minutes. However, these tests have a wide variability in their ability to give an accurate diagnosis depending on the number of factors, such as which viruses are causing this particular attack of flu, etc. More specific tests are only done in special labs and involve taking a swab from the back of the throat or nose and then sending it to a specialized lab (in our country, the National Institute of Virology, Pune, is the standard lab).

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