Pneumonia: Causes, Symptoms, and Treatment Options

Pneumonia, also known as pneumonitis, is a significant respiratory infection that affects the lungs. It occurs when the alveoli—the tiny air sacs in the lungs—become filled with fluid or pus, which hinders the body's ability to oxygenate blood effectively.

This condition can range from mild to life-threatening and affects millions of people worldwide. Every year, approximately 450 million people (about 7% of the global population) contract pneumonia, resulting in roughly 4 million deaths annually.

A schematic diagram of the human lungs with an empty circle on the left representing a normal alveolus and one on the right showing an alveolus full of fluid as in pneumonia — Pneumonia fills the lung's alveoli with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia.

Key Facts

Annual Incidence: 450 million cases worldwide.
Annual Mortality: Approximately 4 million deaths.
Primary Causes: Bacteria, viruses, fungi, parasites, and aspiration.
Common Symptoms: Cough, fatigue, fever, and shortness of breath.
Prevention: Vaccines, regular handwashing, and smoking cessation.

Signs and Symptoms

Pneumonia typically manifests over a few weeks. While symptoms can vary depending on the cause and the patient's overall health, certain signs are highly frequent across most cases.

The most common symptoms include:

Cough: Reported in 79–91% of cases.
Fatigue: Reported in 90% of cases.
Fever: Reported in 71–75% of cases.
Shortness of breath: Reported in 67–75% of cases.
Sputum production: Reported in 60–65% of cases.
Chest pain: Reported in 39–49% of cases.

A diagram of the human body outlining the key symptoms of pneumonia — Main symptoms of infectious pneumonia

Causes and Mechanisms

Pneumonia is classified based on the pathogen that triggers the infection or the environment in which it was acquired.

Infectious Causes

Bacteria: A common cause is Streptococcus pneumoniae. Bacterial pneumonia often presents as lobar pneumonia, where a specific lobe of the lung is consolidated.
Viruses: Viral pneumonia can be caused by various agents, including the SARS virus.
Fungi and Parasites: Less common but significant causes, particularly in immunocompromised individuals.

Three lone round objects in a black background — The bacterium Streptococcus pneumoniae, a common cause of pneumonia, imaged by an electron microscope

Noninfectious Causes

Aspiration pneumonia occurs when foreign materials, such as food, stomach acid, or saliva, are inhaled into the lungs, causing inflammation and potential infection.

Diagnosis and Clinical Evaluation

Medical professionals use a combination of physical exams and imaging to diagnose pneumonia and differentiate it from other conditions like COPD (Chronic Obstructive Pulmonary Disease), asthma, pulmonary edema, or pulmonary embolism.

Imaging Techniques

Chest X-ray: The primary tool for identifying airspace consolidation (fluid in the lungs).
CT Scan: Used for more detailed views, such as identifying cavitating pneumonia (holes in the lung tissue) often associated with MRSA.
Ultrasound: An emerging tool for diagnosing pneumonia in both adults and children.

A chest X-ray showing a very prominent wedge-shaped area of airspace consolidation in the right lung characteristic of acute bacterial lobar pneumonia

A black-and-white image shows the internal organs in cross-section as generated by CT. Where one would expect black on the left, one sees a whiter area with black sticks through it. — CT of the chest demonstrating right-sided pneumonia (left side of the image)

Cavitating pneumonia due to MRSA as seen on a CT scan

A chest x-ray of a patient with severe viral pneumonia due to SARS

Severity Assessment: The CURB-65 Score

To determine if a patient requires hospitalization, clinicians often use the CURB-65 score. Each of the following criteria earns one point:

Confusion
Urea > 7 mmol/L
Respiratory rate > 30 breaths per minute
Blood pressure (Systolic < 90mmHg or Diastolic < 60mmHg)
Age ≥ 65

Treatment and Management

Treatment depends on the underlying cause of the pneumonia and the severity of the symptoms.

Medications and Therapy

Antibiotics: Used to treat bacterial infections.
Antivirals: Used to treat viral infections.
Oxygen Therapy: Provided to patients with low blood oxygen levels to support respiratory function.

Complications

In severe cases, pneumonia can lead to pleural effusion (fluid buildup around the lung), empyema (pus in the pleural cavity), lung abscesses, or total respiratory and circulatory failure.

An X-ray showing a chest lying horizontally. The lower black area, which is the right lung, is smaller with a whiter area below it of a pulmonary effusion. Red arrows indicate size. — A pleural effusion: as seen on chest X-ray. The A arrow indicates fluid layering in the right chest. The B arrow indicates the width of the right lung. The volume of the lung is reduced because of the collection of fluid around the lung.

Prevention

Preventing pneumonia involves reducing risk factors and strengthening the immune system:

Vaccination: Pneumococcal vaccines are highly effective in preventing bacterial pneumonia.
Hygiene: Frequent handwashing reduces the spread of viruses and bacteria.
Lifestyle: Not smoking helps maintain the lungs' natural defense mechanisms.

A poster with a shark in the middle of it, which reads "Pneumonia Strikes Like a Man-Eating Shark Led by its Pilot Fish the Common Cold" — WPA poster, 1936/1937

Summary Table

Pneumonia Overview Summary
Category	Details
Common Symptoms	Cough, Fatigue, Fever, Shortness of Breath
Primary Pathogens	Bacteria (e.g., S. pneumoniae), Viruses, Fungi, Parasites
Diagnostic Tools	Chest X-ray, CT Scan, Ultrasound, Physical Exam
Treatment	Antibiotics, Antivirals, Oxygen Therapy
Prevention	Vaccines, Handwashing, Smoking Cessation

Pneumonia death rates in children under 5

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Frequently Asked Questions

What is the difference between pneumonia and a cold?

While a cold is a viral infection of the upper respiratory tract, pneumonia is an infection that reaches the alveoli of the lungs, causing them to fill with fluid, which makes breathing significantly more difficult.

How is pneumonia diagnosed?

Diagnosis is typically based on a combination of the patient's symptoms, a physical examination, and imaging tests, most commonly a chest X-ray.

Can pneumonia be prevented?

Yes, pneumonia can be prevented through vaccinations, maintaining good hand hygiene, and avoiding smoking, which damages the lungs' ability to clear pathogens.

What is the CURB-65 score used for?

The CURB-65 score is a clinical prediction rule used by doctors to assess the severity of community-acquired pneumonia and decide whether a patient can be treated at home or requires hospital admission.

What is aspiration pneumonia?

Aspiration pneumonia occurs when food, drink, or vomit is accidentally inhaled into the lungs instead of being swallowed into the esophagus, leading to inflammation and infection.