Influenza

What is Influenza?

Influenza, commonly known as the flu, is a contagious virus that affects the breathing system. It’s caused by a range of flu viruses which can infect humans and some specific to certain animals. The virus spreads through tiny droplets from the mouth or nose when a person coughs, talks, or sneezes. You can also get the flu by touching objects with the virus on them and then touching your nose or eyes.

Important to note is that a person with the flu can spread the virus even before they start showing symptoms and up to 5 – 7 days after getting infected. Although most healthy people can recover from the flu within a few days, it can become serious and lead to complications like pneumonia, or even death, especially in high-risk groups such as young children, older people, people with weakened immune systems, and pregnant women. Flu symptoms commonly include a runny nose, a high fever, a cough, and a sore throat.

Flu viruses spread quickly and lead to seasonal flu epidemics. These happen each fall and winter in regions with mild climates and can affect many adults and children. However, the impact and severity of the flu can differ between age groups and seasons.

In the past few decades, new, more deadly flu viruses have emerged that can infect both humans and animals. Doctors need to know that quick tests for detecting flu can sometimes give false negatives. The most reliable ways to diagnose flu are the PCR test or culturing throat secretions, but these tests can take a few days to give results. The best way to reduce complications from the flu is to get vaccinated.

What Causes Influenza?

There are four kinds of influenza, or flu, viruses: A, B, C, and D. Types A and B are the ones that typically make people sick each year during flu season. Influenza A viruses are further broken down into subtypes based on two proteins on the surface of the virus, which are known as hemagglutinin (H) and neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. Influenza A viruses are often named after their H and N types, like H1N1 and H3N2.

Influenza B viruses, on the other hand, are sorted into different lineages and strains. The influenza B viruses that have been common in recent flu seasons belong to two lineages: influenza B Yamagata and influenza B Victoria.

Flu viruses also have unique features that make them specific to certain species. However, animal flu viruses can sometimes infect humans if the virus changes enough. When this occurs, it’s usually hard for the virus to spread from one person to another. Still, if the virus changes in a way that allows it to spread easily between people, it could potentially cause a flu pandemic — a worldwide outbreak that can be very dangerous. For example, the flu pandemics in 1918 and 2009 occurred in this manner.

One type of flu virus that can affect both animals and humans is avian influenza, or bird flu. This is a disease in birds caused by certain types of influenza A viruses, such as A(H5N1), A(H5N8), and H7N9. These viruses are a concern because they can change and gain the ability to spread from person to person, which could start a severe pandemic. For instance, the 2009 pandemic was likely caused by an animal flu virus that started in South America and then changed to be able to spread from person to person across the globe.

Risk Factors and Frequency for Influenza

Influenza A was first discovered in 1933 and seven years later, Influenza B was found. Every year during the winter seasons, in certain regions of the world, there is an increase in influenza cases, known as an influenza epidemic. The impact of the epidemic can vary greatly in terms of severity, duration, age groups most affected, and rates of hospitalization and deaths. For example, seasons when the H3N2 virus is most common, often result in more severe effects, particularly for children and the elderly.

The World Health Organization (WHO) conducts global surveillance of the influenza virus and has found that the virus can be found in humans in a particular geographic region every month. In areas with temperate climates, there is a peak in influenza activity during the winter months. For the Northern Hemisphere, influenza outbreaks and epidemics typically occur from October to March. Meanwhile, in the Southern Hemisphere, influenza activity usually happens between April and August. But in the tropical belt, influenza is present all throughout the year.

Signs and Symptoms of Influenza

Influenza, also known as the flu, can present differently in various people based on their age, overall health, whether they’ve been vaccinated, and their natural immunity to the virus. Individuals who have received the seasonal flu vaccine usually have less severe symptoms and are less likely to experience complications.

The symptoms of the flu, particularly in mild cases, may include the following:

• Cough
• Fever
• Sore throat
• Muscle aches (myalgia)
• Headache
• Runny nose
• Congested eyes
• Headache felt in the front or behind the eyes accompanied by increased light sensitivity (photophobia) and eye pain

These symptoms are caused by the flu virus, which can affect different types of cells in our body. Severe flu cases can worsen rapidly, leading to shortness of breath, fast heart rate (tachycardia), low blood pressure (hypotension), and the need for breathing assistance, sometimes in as short as 48 hours.

Testing for Influenza

It’s usually possible to diagnose influenza, also known as the flu, through ordinary medical checks, particularly during flu season. Most people recover from the flu without treatment and don’t need a lab test for diagnosis. However, for high-risk patients, treatment should begin immediately and shouldn’t wait for test results.

Lab tests for influenza might be necessary in situations where they would inform medical decisions or provide important public health information. For example, during an outbreak, knowing the exact type of flu virus can help with treatment and prevention strategies.

Various lab tests can be used to diagnose the flu. These include rapid antigen tests, rapid molecular tests that detect viral nucleic acid, traditional molecular tests that uses PCR to detect nucleic acid, direct and indirect immunofluorescence tests that detect the antigen, and viral cultures.

Rapid or conventional molecular tests are the favored choices as both are highly reliable and can tell the difference between flu viruses A and B. Regular molecular tests can even differentiate between A subtypes, and they typically have results ready in one to eight hours. Rapid molecular tests have results ready in 15 to 30 minutes.

Results from rapid antigen tests, which have a strong specificity but only moderate to low sensitivity, are ready within 15 minutes. The most reliable test, the viral culture, can take a couple of days to yield results. For this reason, it’s not the best choice for quick diagnosis and treatment of the flu.

Lastly, if a patient is experiencing lung symptoms, they should have a chest x-ray to rule out bacterial pneumonia.

Treatment Options for Influenza

Flu usually gets better on its own and is mild in most healthy people who don’t have other health concerns. In such cases, antiviral treatment isn’t needed. However, antiviral medications can be used to treat or prevent the flu, especially when there’s an outbreak in places like hospitals or care homes.

Oseltamivir, zanamivir and peramivir are a certain type of antiviral medication known as neuraminidase inhibitors, and they can be used for flu types A and B. Another type of antiviral medication, known as adamantanes, includes amantadine and rimantadine. These are effective against influenza A but won’t work on influenza B. Recently, influenza A has shown high rates of resistance to adamantanes, so these aren’t recommended to treat or prevent it.

While resistance to neuraminidase inhibitors has been low in recent flu seasons, the flu virus can change at any time and become resistant. Sometimes, resistance can develop in some patients after treatment, especially those with weaker immune systems. Oseltamivir can be used to prevent flu in people one year and older in cases of outbreaks and exposure in high-risk groups. However, oseltamivir does have side effects, like severe skin reactions and occasional temporary mental health issues, which makes it difficult to use with older adults and those at risk of these side effects. The only reason a person shouldn’t be given zanamivir is if they’re allergic to eggs.

Getting a flu vaccine is strongly recommended at the start of winter. The recommendations for the flu vaccine include:

* Everyone aged six months and older should get the vaccine
* Those with an egg allergy who only get hives should also get the vaccine
* There should always be lifesaving equipment in the same room when giving the vaccine and the patient should be watched for 10-15 minutes afterwards
* In recent years, the nasal flu vaccine hasn’t been very effective, so the injection is preferable
* Pregnant women can get the flu vaccine
* The normal vaccine often doesn’t work as well in people over 65, so they should receive high-dose versions of the flu vaccine.

What else can Influenza be?

When diagnosing certain medical conditions, doctors need to consider a variety of possible illnesses that could be causing the patient’s symptoms. These may include:

• Acute Respiratory Distress Syndrome (ARDS), a severe lung condition causing shortness of breath.
• Adenovirus, a common cause of colds, sore throat and bronchitis.
• Arenaviruses, a family of viruses that can cause diseases like Lassa fever and meningitis.
• Cytomegalovirus, a virus that can cause fever, sore throat, fatigue and swollen glands.
• Dengue, a mosquito-borne illness causing severe flu-like symptoms.
• Echovirus infection, a virus causing symptoms like fever, sore throat, and rash.
• Hantavirus pulmonary syndrome, a severe respiratory disease caused by a specific type of rodent-borne virus.
• HIV infections, which affect the body’s ability to fight off infections.
• Legionnaires disease, a form of pneumonia.
• Human Parainfluenza Virus (HPV), a virus that can cause colds, flu, bronchitis and pneumonia.

By considering these potential causes, doctors can then carry out tests and assessments to reach an accurate diagnosis.

What to expect with Influenza

The flu can greatly affect people’s health and daily routines. It often leads to missed days of work or school. Moreover, it can be especially severe in children and the elderly, even causing death in some cases. Those with existing lung disease and diabetes face higher risks. In general, the flu can seriously affect a person’s quality of life for one to two weeks every flu season.

Possible Complications When Diagnosed with Influenza

Some potential complications include:

• Secondary bacterial pneumonia: This type of pneumonia occurs as a complication to an already existing health condition.
• Acute respiratory distress syndrome: A severe lung condition causing shortness of breath.
• Myositis: Inflammation of your muscles, causing muscle weakness.
• Myocarditis: An inflammation of your heart muscle.
• Multiorgan failure: This happens when two or more organs stop functioning properly, which can lead to life-threatening situations.