Introduction
Influenza ( also known as the flu) and bronchitis are both respiratory disorders which are caused by an infection caused by the influenza viruses. Both disorders share similar symptoms and are often misdiagnosed. What makes these disorders different and how can we differentiate them? This article aims to answer these questions. We will look into both disorders, understanding the causes, pathophysiology (abnormal physiology) and symptoms followed by a comparison.
Influenza
What is influenza?
Influenza, commonly referred to as the seasonal flu, is a virus-related respiratory disorder which can affect the nose, throat and lungs. It can vary in severity with some cases being mild and others being severe.
What causes influenza?
Influenza (the seasonal flu) is caused by a viral infection in the respiratory tract. Influenza viruses gain entry into the body through the epithelial cells that line the respiratory tract, as the influenza virus replicates, it causes damage to the tissue. This damage to the tissue induces inflammation which is responsible for the symptoms of influenza.1
Brief overview of the respiratory system
The respiratory system runs from your nose and mouth to the lungs. Its primary function is to act as an interface between the external environment and the heart. The lungs receive oxygen from the air we breathe, the air enters the lungs in air-filled sacs known as alveoli, whereby it diffuses in the bloodstream and is sent to the heart. The heart pumps this oxygenated blood around the body which meets the demands of all cells. Lungs also receive deoxygenated blood from the heart via the circulatory system containing carbon dioxide, which is pumped out of the body.
Brief overview of immune system response to infection
The immune system consists of many specialised cells which can recognise non-self cells (certain harmful bacteria and viruses or cancer cells). When the immune system is exposed to a pathogen it has not encountered before, an innate response is triggered. An innate response is a general non-specific chain of cellular events which aim to eliminate the pathogen (s). The adaptive immune response follows the innate response and is specifically tailored to the pathogen encountered.2
Seasonal flu
The population regularly requires vaccinations for seasonal flu and this is because influenza viruses can mutate (undergo structural changes). The mutations alter components (proteins) on their surface which are responsible for interacting with epithelial cells in the respiratory tract. We can use a lock and key as an example of how cells interact with molecules. For a key to work a lock, it must have the exact shape which will enable it to fit the lock. The same principle can be applied to how viruses interact with cell surface molecules (in this case respiratory cells), to interact, the molecule must have a shape that compliments and fits the cell component that it is interacting with.3 There are two main ways by which viruses undergo mutational changes:
Antigenic drift
Antigenic drift is where influenza viruses accumulate mutations over time, which leads to a different type of virus which is not recognised by the immune system.3
Antigenic shift
Antigenic shift is where animal viruses undergo sudden mutational changes which enable them to infect human hosts.3
Symptoms of influenza
Bronchitis
What is bronchitis?
Bronchitis is a respiratory disorder which is characterised by inflammation of the bronchial tubes leading to the lungs. The bronchioles are the airways that feed into the alveoli in the lungs and connect the trachea (windpipe) to the lungs. Inflammation of the bronchioles leads to a decreased lumen (inside space). The decreased lumen restricts oxygen flow to the lungs via the bronchioles. There are two types of bronchitis: acute and chronic. Acute bronchitis is the most common and typically develops from a cold or other respiratory infection. Chronic bronchitis on the other hand is less common and more serious, often a result of continuous irritation and inflammation to the lining of the bronchioles.
What causes bronchitis?
Acute bronchitis is typically caused by viruses, often the same viruses that cause cold and flu (influenza). Chronic bronchitis is usually caused by smoking or other irritants such as air pollution, dust or toxic gases.
Symptoms of bronchitis
Key differences between influenza and bronchitis
Onset and duration
The onset of influenza (time taken for symptoms to develop once the influenza virus has first infected) is typically 2 days, however, it can range anywhere from 1-4 days. Acute bronchitis is similar, it tends to develop after 3-4 days after a cold or flu. However, it lasts longer than influenza (flu), ranging from 2-3 weeks, with some cases lasting a month or over.
Complications
Complications of influenza (flu) include pneumonia, ear infection, sinus infection and worsening of pre-existing medical conditions. Bronchitis can also lead to pneumonia. It is important to note that cases vary and not all cases of pneumonia and bronchitis lead to these complications.
Treatment approaches
Influenza is best treated with rest and hydration. However, in some cases, antiviral medication can be prescribed which can help relieve symptoms and help prevent any further complications as a result of influenza.
Treatment for bronchitis is similar to influenza in the sense that rest and recovery will usually help the individual get over bronchitis. Medications that help relieve the symptoms of bronchitis can include cough medicine or an inhaler to help with breathing. In the case of chronic bronchitis, pulmonary rehabilitation can be prescribed which helps to use techniques which aid in breathing.
Diagnosis
Influenza diagnosis first involves a healthcare professional carrying out a physical examination and assessing you for flu-like symptoms. If it is thought to be influenza, an influenza test kit can be ordered. A common influenza test is the polymerase chain reaction (PCR) test.
Bronchitis diagnosis can initially involve a physical examination which uses a stethoscope to listen to the lungs during inhalation and exhalation. In some cases, doctors can suggest the following tests:
- Chest x-ray
- Sputum test
- Pulmonary function test
Prevention
The most effective way to prevent influenza is to get vaccinated. Other measures you can take to prevent influenza include washing hands, avoiding touching eyes or mouth and disposing of used tissues.
You can reduce the risk of bronchitis by avoiding smoking, getting vaccinated, and washing your hands.
When to see a doctor
If you are experiencing symptoms similar to influenza or bronchitis, you should consult with your doctor. Various tests can be carried out to help identify the cause of your symptoms.
Recap of key differences between influenza and bronchitis
| Feature | Influenza | Bronchitis |
| Cause | Influenza viruses (Types A, B, or rarely C) | Usually viral (e.g., rhinovirus) or bacterial (less common) |
| Symptoms | Fever, chills, muscle aches, fatigue, cough, sore throat, runny or stuffy nose | Persistent cough, often with mucus production, chest discomfort, fatigue, mild fever, sore throat, runny or stuffy nose (less common) |
| Onset | Sudden onset | Gradual onset |
| Duration | Typically 1-2 weeks | Acute bronchitis: 1-3 weeks; Chronic bronchitis: Several months to years |
| Complications | Pneumonia, sinus infections, worsening of chronic medical conditions | Pneumonia, worsening of chronic respiratory conditions, bronchial infections |
| Treatment | Antiviral medications (if started early), rest, fluids, over-the-counter pain relievers | Symptomatic relief (e.g., cough suppressants, bronchodilators), rest, fluids, and antibiotics if bacterial infection suspected |
| Prevention | Annual influenza vaccination, good hygiene practices (handwashing, covering coughs) | Avoiding tobacco smoke, avoiding close contact with sick individuals, good hand hygiene |
Summary
Both influenza and bronchitis are respiratory disorders affected by the influenza virus. Influenza affects the nose, throat and lungs, whereas bronchitis affects the bronchi which supply oxygen to the lungs. Respiratory-related symptoms such as difficulty breathing, fatigue and cold-like symptoms are similar between both disorders. What differs is their onset, period of recovery and treatment approaches. With research, a deeper understanding of the two disorders is enabling new diagnostic tools to be implemented that can help differentiate both disorders and improve diagnostic outcomes.
References
- Kalil AC, Thomas PG. Influenza virus-related critical illness: pathophysiology and epidemiology. Critical care. 2019 Jul 19;23(1):258.
- Thompson AE. The immune system. Jama. 2015 Apr 28;313(16):1686-.
- Petrova VN, Russell CA. The evolution of seasonal influenza viruses. Nature Reviews Microbiology. 2018 Jan;16(1):47-60.
