Pneumonia: Causes, Symptoms, Treatment and Prevention

Pneumonia is an infection that affects one or both lungs.

Inside healthy lungs are millions of tiny air sacs called alveoli. Normally, these sacs fill with air when we breathe.

When a person develops pneumonia, inflammation caused by infection can make the alveoli fill with fluid or pus. This can make breathing difficult and reduce the amount of oxygen reaching the bloodstream.

Pneumonia ranges from relatively mild illness that can be treated at home to severe, life-threatening disease requiring hospitalization, oxygen therapy or intensive care.

People of any age can develop pneumonia, but babies, young children, older adults and people with certain underlying medical conditions have a greater risk of severe disease.

What Causes Pneumonia?

Many different microorganisms can cause pneumonia.

The major categories include:

• bacteria,
• viruses,
• fungi,
• and, less commonly, parasites.

Healthcare professionals are not always able to identify the exact organism responsible.

The likely cause can also vary depending on a person's age, health, geographic location and whether the infection developed in the community or in a healthcare setting.

Bacterial Pneumonia

Different bacteria can cause pneumonia.

One important cause is Streptococcus pneumoniae, also called pneumococcus.

Other bacterial causes include:

• Mycoplasma pneumoniae,
• Haemophilus influenzae,
• Chlamydia pneumoniae,
• Legionella species,
• and other bacteria.

Bacterial pneumonia can develop independently or sometimes after a viral respiratory infection such as influenza.

What Is “Walking Pneumonia”?

“Walking pneumonia” is an informal term often used for relatively mild pneumonia, particularly illness caused by Mycoplasma pneumoniae.

A person may feel well enough to continue some everyday activities despite having pneumonia.

However, the term does not mean the infection should be ignored.

Symptoms that are worsening or persistent still require appropriate medical assessment.

Viral Pneumonia

Viruses are another important cause of pneumonia.

Viruses capable of causing pneumonia include:

• influenza viruses,
• respiratory syncytial virus (RSV),
• SARS-CoV-2, which causes COVID-19,
• human metapneumovirus,
• parainfluenza viruses,
• rhinoviruses,
• and others.

Some viral infections can also make it easier for a secondary bacterial infection to develop.

Fungal Pneumonia

Fungi can cause pneumonia, although fungal pneumonia is generally less common than bacterial or viral pneumonia.

The risk varies considerably according to:

• geographic location,
• environmental exposure,
• and immune-system function.

Examples include infections associated with organisms such as:

• Histoplasma,
• Coccidioides,
• and Pneumocystis jirovecii.

People with significantly weakened immune systems can be particularly vulnerable to some fungal pneumonias.

What Is Aspiration Pneumonia?

Aspiration pneumonia can occur when material from the mouth or stomach enters the lungs instead of being swallowed normally.

This may include:

• saliva,
• food,
• liquid,
• or vomit.

The risk is higher in people who have difficulty swallowing or reduced consciousness.

Risk factors can include:

• stroke,
• neurological disorders,
• swallowing problems,
• severe intoxication,
• sedation,
• and certain medical conditions.

This corrects an important problem in the old article: aspiration pneumonia does not simply mean pneumonia caused by chemicals or smoke.

Inhaling irritating chemicals can injure the lungs, but this is a different process and may cause chemical pneumonitis.

Community-Acquired Pneumonia

Community-acquired pneumonia means pneumonia that develops outside a hospital or other healthcare setting.

It can be caused by various bacteria and viruses.

A person does not have to be severely ill or hospitalized to develop pneumonia.

Healthcare-Associated and Hospital-Acquired Pneumonia

Pneumonia can also develop during or following healthcare exposure.

Hospital-acquired pneumonia develops during a hospital stay and can involve organisms different from those commonly causing community-acquired infection.

Ventilator-associated pneumonia can develop in people receiving mechanical ventilation.

These infections can be particularly serious and may involve bacteria resistant to multiple antibiotics.

What Are the Symptoms of Pneumonia?

Symptoms vary according to:

• the organism responsible,
• age,
• overall health,
• and severity of infection.

Common symptoms include:

• cough,
• fever,
• chills,
• shortness of breath,
• fatigue,
• and chest pain, particularly when breathing deeply or coughing.

A cough may be:

• dry,
• or accompanied by mucus.

The colour of mucus alone cannot reliably tell you whether pneumonia is bacterial or viral.

Other Possible Symptoms

Some people also experience:

• headache,
• muscle aches,
• reduced appetite,
• nausea,
• vomiting,
• diarrhoea,
• weakness,
• rapid heartbeat,
• and generally feeling very unwell.

Not everyone experiences every symptom.

Does Pneumonia Always Cause Fever?

No.

Some people with pneumonia do not develop a high fever.

This is particularly important in:

• older adults,
• people with weakened immune systems,
• and people who are seriously ill.

An older person with pneumonia may even have a lower-than-normal body temperature.

Therefore, the absence of fever does not rule out pneumonia.

Pneumonia in Older Adults

Older adults may experience less typical symptoms.

Instead of obvious fever and severe coughing, an older person may develop:

• sudden confusion,
• weakness,
• unusual tiredness,
• reduced appetite,
• or worsening ability to carry out everyday activities.

New confusion in an older person should never automatically be dismissed as normal ageing.

It can be a sign of serious illness and requires medical assessment.

Pneumonia in Babies and Young Children

Babies and young children may also have symptoms different from adults.

Possible symptoms include:

• cough,
• fever,
• rapid breathing,
• difficulty breathing,
• reduced feeding,
• vomiting,
• irritability,
• tiredness,
• and reduced activity.

A baby with severe breathing difficulty may show:

• grunting,
• widening of the nostrils,
• chest indrawing or retractions,
• or abnormal colour around the lips or skin.

A baby or child struggling to breathe requires urgent medical attention.

Who Is at Higher Risk of Pneumonia?

Anyone can develop pneumonia, but some people are more vulnerable.

Higher-risk groups include:

• babies and young children,
• older adults,
• people with weakened immune systems,
• and people with certain chronic medical conditions.

Medical Conditions That Can Increase Risk

Risk may be increased by conditions such as:

• chronic lung disease,
• asthma,
• chronic obstructive pulmonary disease (COPD),
• heart disease,
• diabetes,
• chronic kidney disease,
• chronic liver disease,
• and conditions that weaken the immune system.

Some cancer treatments, immune-suppressing medicines and other therapies can also increase susceptibility to infection.

Smoking and Pneumonia

Smoking damages the respiratory system and interferes with mechanisms that help the lungs clear germs and particles.

Smoking can therefore increase the risk of respiratory infection, including pneumonia.

Avoiding tobacco smoke is an important part of protecting respiratory health.

Exposure to secondhand smoke is also harmful.

Alcohol and Pneumonia Risk

The old article simply told readers that alcohol intake should be “stopped.”

The relationship is more nuanced.

Heavy or harmful alcohol use can increase the risk of pneumonia and aspiration by:

• weakening immune defences,
• affecting consciousness,
• and increasing the chance of material entering the lungs.

People who drink alcohol should follow appropriate health guidance and avoid harmful consumption.

Indoor Air Pollution

Exposure to polluted indoor air can contribute to respiratory disease.

This is particularly important in households where cooking or heating produces substantial smoke from fuels such as:

• wood,
• charcoal,
• coal,
• crop waste,
• or animal dung

without adequate ventilation or clean-burning technology.

Reducing household air pollution can help protect respiratory health.

How Is Pneumonia Diagnosed?

A healthcare professional may begin by asking about:

• symptoms,
• when they started,
• medical conditions,
• medicines,
• recent infections,
• travel,
• and other risk factors.

They may then examine you and listen to your lungs.

Oxygen Level

A small device called a pulse oximeter may be placed on a finger to estimate the amount of oxygen in your blood.

Low oxygen levels can indicate more severe respiratory illness.

However, pulse oximeters have limitations and readings should be interpreted alongside symptoms and clinical assessment.

A normal home reading should not be used to dismiss severe breathing symptoms.

Chest X-Ray

A chest X-ray may be used to help diagnose pneumonia and determine which areas of the lungs are affected.

Not every mild respiratory infection requires an X-ray.

The decision depends on symptoms, examination findings, severity and local clinical practice.

Other Tests

Depending on the situation, testing may include:

• blood tests,
• sputum testing,
• viral testing,
• blood cultures,
• or other investigations.

More extensive testing is particularly likely when pneumonia is severe, unusual or requires hospitalization.

How Is Pneumonia Treated?

Treatment depends on:

• the cause,
• severity,
• age,
• underlying medical conditions,
• and risk of complications.

Mild pneumonia may sometimes be treated at home.

Severe pneumonia may require hospitalization.

Antibiotics for Bacterial Pneumonia

Bacterial pneumonia is treated with antibiotics.

The appropriate antibiotic depends on factors including:

• likely bacteria,
• local antibiotic-resistance patterns,
• allergies,
• age,
• pregnancy,
• other medical conditions,
• and severity.

Do not use leftover antibiotics or another person's prescription.

If antibiotics are prescribed, take them exactly as directed by your healthcare professional.

Antibiotics Do Not Treat Viral Pneumonia

Antibiotics kill or inhibit bacteria.

They do not treat viruses.

Therefore, antibiotics should not automatically be used for every case of pneumonia.

Certain viral pneumonias may be treated with specific antiviral medicines when clinically appropriate.

Antifungal medicines may be required for fungal pneumonia.

Why Unnecessary Antibiotics Are a Problem

Using antibiotics when they are not needed can:

• cause side effects,
• disrupt normal bacteria in the body,
• contribute to antibiotic resistance,
• and make future bacterial infections more difficult to treat.

The decision to prescribe antibiotics should be based on professional medical assessment.

Supportive Treatment

Depending on the individual, supportive treatment can include:

• adequate rest,
• appropriate fluid intake,
• fever or pain relief,
• and monitoring symptoms.

People with conditions affecting fluid balance, including significant heart or kidney disease, may need individualized advice about fluid intake.

Do not assume that drinking very large amounts of water is appropriate for everyone.

Hospital Treatment

Severe pneumonia may require treatment in hospital.

Hospital treatment can include:

• oxygen therapy,
• intravenous fluids when appropriate,
• intravenous medicines,
• close monitoring,
• and respiratory support.

People with very severe respiratory failure may require intensive care and mechanical ventilation.

How Long Does Pneumonia Last?

There is no single recovery time that applies to everyone.

Some symptoms may begin improving within several days of appropriate treatment, while cough and tiredness can persist for weeks.

Recovery may take longer in:

• older adults,
• people with severe pneumonia,
• people with underlying medical conditions,
• and people who develop complications.

The old article's statement that pneumonia generally lasts two to three weeks is therefore too rigid.

Recovery depends on the cause and severity of illness and the person's health.

Possible Complications of Pneumonia

Pneumonia can cause serious complications.

These may include:

Respiratory failure

The lungs may become unable to provide the body with enough oxygen.

Sepsis

An infection can trigger a dangerous whole-body response that causes organ dysfunction.

Sepsis is a medical emergency.

Pleural effusion

Fluid can accumulate between the layers of tissue surrounding the lungs.

Empyema

Infected fluid or pus can collect in the space surrounding the lung.

Lung abscess

A pocket of pus may form within lung tissue.

These complications require professional medical treatment.

Can Pneumonia Be Prevented?

Not every case can be prevented, but several measures can reduce risk.

One of the most important is vaccination.

Pneumococcal Vaccination

Pneumococcal vaccines help protect against disease caused by Streptococcus pneumoniae.

Pneumococcal vaccination is particularly important for certain:

• children,
• older adults,
• and people with particular health conditions or other risk factors.

Vaccination schedules differ between countries and can change over time.

Follow the immunization programme where you live or ask a healthcare professional which pneumococcal vaccine recommendations apply to you.

Other Vaccines Can Help Prevent Pneumonia

Pneumonia can occur as a complication of several vaccine-preventable infections.

Depending on age, health status and national immunization recommendations, vaccines that may reduce pneumonia risk include those protecting against:

• influenza,
• COVID-19,
• pertussis,
• measles,
• Haemophilus influenzae type b (Hib),
• and other infections.

Follow your country's current vaccination recommendations.

Hand Hygiene

Wash your hands properly with soap and water, particularly:

• after coughing or blowing your nose,
• after using the toilet,
• before preparing food,
• before eating,
• and when caring for someone who is ill.

When soap and water are unavailable, an appropriate alcohol-based hand sanitizer can help in many situations.

Cover Coughs and Sneezes

Cover your mouth and nose when coughing or sneezing.

Use a tissue when available and dispose of it appropriately.

If a tissue is unavailable, cough or sneeze into your elbow rather than your hands.

Then clean your hands.

These habits help reduce the spread of respiratory infections.

Avoid Smoking

Not smoking is one of the most important steps you can take to protect your lungs.

Avoiding secondhand tobacco smoke is also beneficial.

If you smoke, professional support can improve your chances of quitting successfully.

Nutrition and Children's Pneumonia Risk

Adequate nutrition helps support children's natural defences against infection.

WHO particularly emphasizes exclusive breastfeeding during the first six months of life, where appropriate, as part of protecting infants from pneumonia and other infections.

Children should also receive adequate complementary nutrition as they grow.

Can Pneumonia Spread From Person to Person?

Pneumonia itself describes an infection in the lungs, but many of the organisms that cause pneumonia can spread between people.

Viruses and bacteria may spread through respiratory droplets, aerosols, direct contact or contaminated hands and surfaces, depending on the organism.

However, being exposed to someone who has pneumonia does not mean you will necessarily develop pneumonia.

You may:

• remain well,
• develop a milder respiratory infection,
• or develop pneumonia depending on the organism and your individual risk factors.

When Should You Seek Medical Care?

Seek medical advice if you have symptoms suggestive of pneumonia, particularly:

• persistent or worsening cough,
• shortness of breath,
• chest pain when breathing,
• persistent fever,
• significant weakness,
• or symptoms that worsen rather than improve.

People at higher risk of complications should seek medical advice sooner.

This includes:

• babies and young children,
• older adults,
• people with weakened immune systems,
• and people with significant chronic illnesses.

When Is Pneumonia an Emergency?

Seek urgent medical care if someone develops:

• severe difficulty breathing,
• rapidly worsening breathlessness,
• blue, grey or unusually pale lips or skin,
• severe chest pain,
• confusion or markedly reduced alertness,
• fainting,
• inability to stay awake,
• signs of shock,
• or other signs of severe illness.

For babies and children, urgent warning signs include:

• severe difficulty breathing,
• grunting,
• pronounced chest indrawing,
• inability to drink or feed,
• unusual drowsiness or difficulty waking,
• convulsions,
• or abnormal blue or grey colour around the lips or skin.

Contact your local emergency medical service if the person's condition appears life-threatening.

The Bottom Line

Pneumonia is an infection of the lungs, not simply chronic lung inflammation.

It can be caused by bacteria, viruses, fungi and, less commonly, other organisms.

Common symptoms include:

• cough,
• fever or chills,
• shortness of breath,
• fatigue,
• and chest pain when breathing or coughing.

Symptoms can be less typical in babies and older adults.

Treatment depends on the cause and severity. Bacterial pneumonia may require antibiotics, while antibiotics do not treat viral pneumonia.

Vaccination, good hand and respiratory hygiene, avoiding smoking and reducing exposure to harmful indoor air pollution can help lower the risk.

Most importantly:

Severe breathing difficulty, blue or grey lips or skin, confusion, fainting or rapidly worsening illness requires urgent medical attention.

Medical Disclaimer

This article provides general health information for an international audience and is not a substitute for diagnosis or treatment by a qualified healthcare professional. Pneumonia can become serious rapidly, particularly in babies, young children, older adults and people with weakened immune systems or chronic medical conditions. Vaccine recommendations and treatment protocols vary between countries. Seek urgent medical care for severe breathing difficulty, abnormal blue or grey skin or lips, confusion, fainting or other signs of severe illness.

Sources and Further Reading

World Health Organization — Pneumonia

https://www.who.int/health-topics/pneumonia

World Health Organization — Pneumonia in Children

https://www.who.int/news-room/fact-sheets/detail/pneumonia

Centers for Disease Control and Prevention — About Pneumonia

https://www.cdc.gov/pneumonia/about/index.html

Centers for Disease Control and Prevention — Pneumonia Prevention and Control

https://www.cdc.gov/pneumonia/prevention/index.html

Centers for Disease Control and Prevention — Risk Factors for Pneumonia

https://www.cdc.gov/pneumonia/risk-factors/index.html

National Heart, Lung, and Blood Institute — Pneumonia

https://www.nhlbi.nih.gov/health/pneumonia

National Heart, Lung, and Blood Institute — Pneumonia Treatment

https://www.nhlbi.nih.gov/health/pneumonia/treatment