What causes pneumonia in adults

Overview

Pneumonia is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid or pus (purulent material), causing cough with phlegm or pus, fever, chills, and difficulty breathing. A variety of organisms, including bacteria, viruses, and fungi, can cause pneumonia. Community-acquired pneumonia (CAP) is the most common type and occurs outside of hospitals or other healthcare facilities. Healthcare-associated pneumonia (HAP) can develop in people who have received inpatient care for other conditions.

Causes of Pneumonia in Adults

Bacterial Pneumonia

Bacteria are the most common cause of pneumonia in adults. Several types of bacteria can cause pneumonia, but the most frequent culprit is Streptococcus pneumoniae (pneumococcus). Other bacteria that can cause pneumonia include:

• Haemophilus influenzae
• Mycoplasma pneumoniae (sometimes called "walking pneumonia")
• Chlamydia pneumoniae
• Legionella pneumophila (causes Legionnaires' disease)

Bacterial pneumonia often develops suddenly, with symptoms like high fever, chills, and shaking. The sputum (phlegm) may be greenish or rust-colored. Antibiotics are typically effective in treating bacterial pneumonia.

Viral Pneumonia

Viruses are another common cause of pneumonia, particularly in children and older adults. Viral pneumonia often causes milder symptoms than bacterial pneumonia, but it can be severe. Common viruses that can cause pneumonia include:

• Influenza viruses (flu)
• Respiratory syncytial virus (RSV)
• Rhinoviruses (common cold)
• Coronaviruses (including SARS-CoV-2, which causes COVID-19)
• Adenoviruses
• Parainfluenza viruses

Viral pneumonia symptoms often appear alongside other flu-like symptoms and may include dry cough, fever, and muscle aches. Antiviral medications may be prescribed for certain viral pneumonias, such as influenza and COVID-19, but often treatment focuses on supportive care to manage symptoms while the body fights the infection.

Fungal Pneumonia

Fungal pneumonia is less common in healthy individuals but can affect people with weakened immune systems, such as those with HIV/AIDS, undergoing chemotherapy, or taking immunosuppressant drugs. Fungi that can cause pneumonia include:

• Pneumocystis jirovecii (a common cause of pneumonia in people with weakened immune systems)
• Histoplasma capsulatum
• Coccidioides immitis
• Blastomyces dermatitidis

These fungi are often found in soil or bird droppings. Treatment involves antifungal medications.

Other Causes

In addition to infectious agents, other factors can lead to pneumonia:

• Aspiration Pneumonia: This occurs when foreign material, such as food, liquid, vomit, or saliva, is inhaled into the lungs. This can happen if you have difficulty swallowing, have a seizure, are under anesthesia, or have a problem with substance abuse. The inhaled material can irritate the lungs and lead to infection.
• Chemical Pneumonitis: Inhaling certain chemicals or irritants can cause inflammation in the lungs, which can sometimes lead to pneumonia.

Risk Factors

While anyone can develop pneumonia, certain factors increase your risk:

• Age: Adults aged 65 and older and children younger than 2 are at higher risk.
• Underlying Medical Conditions: Chronic illnesses such as asthma, COPD, heart disease, diabetes, and weakened immune systems (due to HIV/AIDS, chemotherapy, or organ transplant) increase susceptibility.
• Lifestyle Factors: Smoking damages your lungs' ability to fight infection. Excessive alcohol use can also weaken your immune system.
• Environment: Exposure to certain pollutants or working in environments where you are exposed to more germs can increase risk.

Prevention

Preventing pneumonia involves several strategies:

• Vaccinations: Vaccines against pneumococcal disease (pneumonia) and influenza can significantly reduce your risk.
• Good Hygiene: Frequent handwashing, covering coughs and sneezes, and avoiding close contact with sick people are crucial.
• Healthy Lifestyle: Not smoking, limiting alcohol intake, eating a balanced diet, and getting enough sleep support your immune system.
• Managing Chronic Conditions: Keeping chronic illnesses well-controlled can help maintain overall health.

Understanding the causes of pneumonia is the first step in prevention and seeking appropriate medical care if symptoms arise.