Skip to Content

What triggers chest infection?

Chest infections, also known as lower respiratory tract infections, are common illnesses that affect the lungs and airways. They can range from mild to severe and are typically triggered by viruses, bacteria, or other microorganisms invading the respiratory system.

What Causes Chest Infections?

The most common causes of chest infections include:

  • Viruses – Viruses like influenza, respiratory syncytial virus (RSV), rhinovirus, adenovirus, and coronavirus often cause chest infections. The flu virus is a frequent culprit during flu season.
  • Bacteria – Bacterial chest infections are commonly caused by Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and Moraxella catarrhalis bacteria.
  • Fungi – Fungal infections like histoplasmosis and coccidioidomycosis can sometimes infect the lungs and lead to pneumonia.
  • Mycoplasma – Mycoplasma pneumonia is an atypical bacterial lung infection caused by Mycoplasma pneumoniae.

In most cases, viruses are the initial cause of chest infections, but secondary bacterial infections can sometimes occur at the same time or following the viral illness. Fungal and mycoplasma pneumonia are less common causes.

Risk Factors

Certain people are at higher risk of developing chest infections or having more severe illness. Risk factors include:

  • Age – Young children and older adults over 65 years old.
  • Smoking – Current or past tobacco smoking damage lungs.
  • Asthma & COPD – Chronic lung diseases impact airway defenses.
  • Immune deficiencies – Conditions like HIV/AIDS, cancer, organ transplant, and steroid medications impair immunity.
  • Chronic diseases – Heart disease, kidney failure, and diabetes increase susceptibility.
  • Obesity – Excess weight impairs lung function.
  • Air pollution – Pollutants can irritate and damage airways.


There are various triggers that can set off a chest infection in high-risk individuals:

Infectious Microbes

Exposure to viruses, bacteria, or fungi through contact with an infected person or contaminated surfaces can transmit the infection to others and cause illness. Outbreaks of respiratory infections are more common in fall and winter.


Allergens like pollen, pet dander, dust mites, and mold spores can trigger allergic reactions and asthma flare-ups that irritate the airways and lungs, increasing vulnerability to infections.

Air Pollution

Breathing in polluted outdoor air or irritating indoor air containing smoke, fumes, or chemicals can inflame and damage the airways, making it easier for infections to take hold.


Smoking introduces toxins into the lungs that paralyze and kill cilia (tiny hair-like structures) in the airways that normally trap and expel mucus and microbes. This impairs the lungs’ self-cleaning ability.


Sudden chilling of the body from cold temperatures, wet clothes, or air conditioning may also compromise respiratory defenses. Breathing in cold air can reduce cilia function.

How Infections Start and Spread in Lungs

When infectious particles first enter the respiratory tract through the mouth or nose, they land on and adhere to cells lining the sinuses, throat, and airways. Viruses then invade these cells and use them to replicate, while bacteria release toxins that damage cells.

This initial invasion triggers inflammation and swelling of the respiratory tract lining as the immune system activates to fight the infection. Fluid and immune cells flood to the site of infection, causing congestion, mucus production, coughing, and sneezing.

As inflammation spreads deeper into the smaller bronchial tubes and air sacs, it can obstruct airflow and cause breathing difficulty. Bacteria may also spill into the bloodstream and provoke body-wide symptoms like fever, chills, and muscle aches.

Secondary Infections

Viral respiratory infections damage and weaken lung defenses, increasing vulnerability to secondary bacterial infections. Bacteria like S. pneumoniae, H. influenzae, and S. aureus often take advantage of this opportunity, invading on the heels of a primary viral illness.

Atypical Pathogens

Less common atypical bacteria like Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila have different mechanisms of causing pneumonia independent of other infections.


Chest infection symptoms may include:

  • Cough (usually with mucus)
  • Shortness of breath, rapid breathing
  • Wheezing
  • Chest pain or tightness
  • Fever, chills
  • Fatigue
  • Sore throat, runny nose
  • Muscle aches
  • Nausea, vomiting, diarrhea
  • Headache

Severe cases may progress to respiratory distress and sepsis. Symptoms tend to last around 1-3 weeks but can persist longer with complications.


Doctors use a combination of methods to diagnose chest infections:

  • Physical exam – Listening to lungs with a stethoscope
  • Medical history questions
  • Chest X-ray
  • Sputum and nasal swab samples
  • Pulse oximetry – Measures blood oxygen saturation
  • Blood tests

These help determine if there is an infection, where it is located, and whether a virus or bacteria is the cause. Pneumonia visible on an X-ray confirms the diagnosis.


Steps to help prevent chest infections include:

  • Get recommended vaccines like the flu shot and pneumococcal vaccines
  • Wash hands frequently and practice good hygiene
  • Avoid contact with sick people
  • Don’t smoke and avoid secondhand smoke
  • Control chronic conditions like asthma, COPD, and diabetes
  • Eat a healthy diet and exercise regularly
  • Avoid and reduce exposure to allergens and air pollution when possible


Mild chest infections may resolve without treatment or with OTC medications to manage symptoms. More severe cases often require:

  • Antibiotics – Used for bacterial chest infections to speed recovery. Common options include amoxicillin, azithromycin, doxycycline.
  • Antivirals – Antiviral drugs like oseltamivir (Tamiflu) can be used for influenza.
  • Cough medicine – Helps control coughing.
  • Fever reducers – Like acetaminophen and ibuprofen.
  • Increased fluids – Helps thin mucus.
  • Oxygen therapy – May be needed with low oxygen levels.
  • Hospitalization – For very severe cases with complications like respiratory failure.

Most healthy people recover fully within 2-3 weeks with proper treatment. But hospitalization for supportive care may be necessary in up to 20% of pneumonia cases.


Potential complications of chest infections include:

  • Pleurisy – Inflammation of lining around lungs.
  • Lung abscess – Necrotic cavity in lung tissue.
  • Respiratory failure – Life-threatening low oxygen levels.
  • Sepsis – Body-wide infection spreading via bloodstream.
  • Empyema – Pus collecting around lungs in pleural space.
  • Bronchiectasis – Permanent lung damage and scarring.

Those over 65, smokers, people with chronic diseases or weak immune systems are at higher risk of complications. Seeking prompt medical treatment can prevent more serious progression.


Chest infections are commonly caused by viral or bacterial pathogens invading the lungs and airways. Many different microbes can be responsible, but the flu, RSV, S. pneumoniae, and S. aureus are among the most frequent culprits.

Exposure to these infectious microbes, often coupled with impairment of the body’s immune defenses from allergens, chilling, smoking, or chronic disease, allows the infections to take hold and spread in the respiratory system.

Symptoms like cough, fever, and shortness of breath typically signal the onset of a chest infection, while diagnostic tests help confirm the cause and severity. Treatment focuses on the use of antibiotics or antivirals along with symptom relief. Good prevention comes down to practicing healthy habits to keep the respiratory system strong.