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Influenza (flu): Everything you need to know

Influenza (flu): Everything you need to know

A contagious, infectious disease caused by influenza viruses, flu shares several symptoms with other respiratory infections
flu, fever
Photo by Anantha Subramanyam K

Analysia G, a 21-year-old woman from the US, showed up at the ER (emergency room) of a hospital in May with symptoms of vomiting and fever with chills.

A throat swab confirmed that she had been infected with the influenza A virus, commonly known as the flu. Four months post the diagnosis, Analysia is still experiencing long-term symptoms of the flu, including dysphagia (a condition where it becomes difficult to swallow food and liquids), chest pains, ear pains and coughing up green or grey phlegm.

“It’s a struggle,” she tells Happiest Health. “Initially, when it first started, I had fever with chills and throwing up. When that calmed down, I started to experience intense respiratory symptoms that included wheezing, chest pain and weird-coloured phlegm. I had to get an inhaler prescribed to me for the first time in my life.”


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Talking about the long-term symptoms of the flu she is currently experiencing, Analysia says, “In June, food started to feel stuck in my throat, so I stayed on a liquid diet that I’m still on now. Now I experience throat itchiness also. My endoscopy and esophagram came back normal, so doctors don’t know what’s going on. It’s frustrating and very hard to deal with.”

According to the US Centre for Disease Control and Prevention (CDC), flu is a contagious respiratory illness caused by influenza viruses that affects the nose, throat and sometimes the lungs, causing mild to severe illness.

At a recent media briefing, officials of the World Health Organization (WHO) also warned people that with colder weather approaching in the Northern Hemisphere, the risk of “more intense transmission and hospitalization” for diseases including Covid-19 and influenza will increase in the coming months.

“We are already witnessing an increasing incidence of the flu virus,” says Dr Radha Balaji, pediatrician, Rajawadi Hospital, Mumbai.

Dr Swati Rajagopal, consultant, infectious disease and travel medicine, Aster CMI Hospital, Bengaluru, says flu spreads through the respiratory route through coughing or sneezing. “Surfaces contaminated with droplets from the infected individual could act as fomites (objects that have the potential to carry and spread infections) in transmission of infection,” she says.

According to the CDC, some of the common symptoms of influenza (flu) include:

  • Fever or feeling feverish or chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headaches
  • Fatigue (tiredness)

The CDC also points out that although fever is one of the symptoms commonly associated with influenza, not all people with the infection may show fever as one of the symptoms, especially those who are elderly and the immunosuppressed.

Dr Rajagopal says that there are four types of influenza viruses: influenza A, B, C and D. “Influenza virus A and B are responsible for human infection,” she says. “Influenza C causes mild infection. Influenza D causes infection in cattle. Influenza A is responsible for ‘flu’ pandemics. Influenza A – H1N1 subtype (responsible for H1N1 pandemic or swine flu) has continued to circulate in the community. The influenza viruses are named based on virus type, place of isolation of the virus, virus strain, year isolated and virus subtype.”

Dr Balaji says that doctors witness different flu viruses with each passing year because the strain of the influenza viruses keeps changing. “Every year, we have different flu viruses because they keep changing their strain and do not maintain the same pattern due to mutation,” she says. “Every year, usually, we have the Northern Hemisphere and the Southern Hemisphere strains.”

According to a 2017 study, ‘Evolution of Influenza A Virus by Mutation and Re-Assortment’, Influenza A virus being prone to rapid mutation has resulted in the loss of vaccine optimal efficacy and posed a challenge to the complete eradication of the virus.

The best way to prevent onset of flu and reduce the intensity of the infection, say doctors, is making sure one gets vaccinated before the flu season starts.

Talking about the vaccination schedule for children, Dr Balaji says, “Children are given two vaccines initially after six months of age. After that, they must get vaccinated every year at least up to the age of eight. Even children who are nine, ten or 11 years old are also being given the vaccination, especially given the picture of the Covid pandemic also being around.”

Who is at higher risk of getting infected with influenza?

Dr Meghana Reddy Sankepalli, consultant, interventional pulmonology and sleep medicine, Medicover Hospitals, Hitec City, Hyderabad, says that those at a higher risk of getting the flu include people older than 65 years, children younger than two years, people who suffer from asthma, neurologic and neurodevelopment conditions, blood disorders (such as sickle cell disease), chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic fibrosis), endocrine disorders (such as diabetes mellitus), heart diseases (such as congenital heart disease, congestive heart failure and coronary artery disease), kidney diseases, liver disorders, metabolic disorders and people who are obese with a body mass index of 40 or higher.

How is influenza diagnosed?

“Flu is diagnosed based on a clinical suspicion,” says Dr Rajagopal. “The confirmation is based on polymerase chain reaction (PCR) test using a throat or nasal swab for influenza A, B and H1N1 subtype.”

Dr Sankepalli says that flu has several overlapping symptoms with other viruses and is most commonly confused with common cold. “Flu is caused by influenza viruses only, whereas the common cold can be caused by a number of different viruses, including rhinoviruses, parainfluenza and seasonal coronaviruses,” she says. “In general, flu is worse than the common cold, and symptoms are typically more intense and begin more abruptly. Colds are usually milder than flu.”

Dr Balaji says throat swab helps differentiate between influenza A, influenza B and also H1N1 virus. 

How is influenza treated?

“I was recommended to just take over-the-counter cold or flu medicine, use a nasal spray, an albuterol inhaler, a humidifier and lots of warm tea with honey and soup when I was able to eat,” says Analysia.

For babies, meanwhile, Dr Balaji recommends that almost every parent approach a healthcare professional as soon as possible since they will become the first point of contact to help the parent understand if the child is stable or not.

Ninety per cent of home management involves managing the fever with antipyretics and sponging, she says, adding that adequate amounts of fluids should be administered.

“If the child is stable, the fever can be managed with antipyretics,” Dr Balaji says. “If the respiratory rate is within control, for instance (not above 60 for a six- to 12-month-old and less than 40 for a child older than 12 months), then the child can be managed at home. Anything above this, the child should be hospitalised and monitored there. If the child is vomiting or has any other symptoms, the child should be immediately taken to the hospital and should preferably be monitored for 24 to 48 hours.”

According to the CDC, the time period when people with flu are contagious and may be able to infect others ranges from one day before the symptoms develop to five to seven days after the onset of symptoms.

The CDC also recommends the following good-health habits to reduce the risk of seasonal flu:

  • Avoid close contact with people who are sick
  • Stay home when you are sick
  • Cover your mouth and nose
  • Clean your hands
  • Avoid touching your eyes, nose or mouth

“For precaution, I always wear a mask everywhere I go,” says Analysia. “I wash my hands constantly, especially when I come back home from somewhere. I also keep my distance from people now. I’m planning on getting the flu shot when I can.”

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