Pneumonia is a type of lung infection that causes cough, fever, and difficulty breathing. Pneumonia may affect one or both lungs, and can cause serious illness in young children, people over age 65, and people with other health problems.
People can get pneumonia from bacteria, viruses, and fungi.
Typical bacteria that cause pneumonia include:
- S. pneumoniae (most common bacterial cause)
- Staphylococcus aureus
- Group A streptococci
- Haemophilus influenzae
- Moraxella catarrhalis
- Aerobic gram-negative bacteria (e.g., Enterobacteriaceae such as Klebsiella spp or Escherichia coli)
- Microaerophilic bacteria and anaerobes (associated with aspiration)
Atypical bacteria that cause pneumonia include:
- Mycoplasma pneumoniae
- Legionella spp
- Chlamydia pneumoniae
- Chlamydia psittaci
- Coxiella burnetii
Respiratory viruses that cause pneumonia include:
- Influenza (“flu”) A and B viruses
- Parainfluenza viruses
- Coronaviruses (e.g., Middle East respiratory syndrome coronavirus, COVID-19)
- Rhinoviruses
- Adenoviruses
- Respiratory syncytial virus (RSV)
- Human metapneumovirus
- Human bocaviruses
What Are Symptoms of Pneumonia?
Common symptoms of pneumonia include:
- Cough: cough may produce phlegm or mucus that may be greenish, yellow, or bloody
- Difficulty breathing/shortness of breath
- Sharp pain on inhalation or when coughing
- Fever
- Chills and shaking
- Sweating
- Fast heartbeat
- Loss of appetite
- Lack of energy
- Fatigue
- Nausea and vomiting, especially in small children
- Confusion, especially in older people
How Is Pneumonia Diagnosed?
Pneumonia is diagnosed with a patient history and physical examination, in which a doctor will check the lungs with a stethoscope to listen for crackling, bubbling, and rumbling sounds on inhalation.
Tests to confirm pneumonia include:
- Blood tests
- Polymerase chain reaction (PCR)
- Influenza
- COVID-19
- Sputum test on a sample of mucus (sputum) taken after a deep cough
- Chest X-ray
- Pulse oximetry to measure blood oxygen levels
- Arterial blood gas test
- Urinary antigen testing for S. pneumoniae
- Computerized tomography (CT) scan of the chest
- Pleural fluid culture: a small amount of fluid is removed from tissues surrounding the lung
- Bronchoscopy: a tube with a light on the end is used to look into the airways
What Is the Treatment for Pneumonia?
Treatment for pneumonia depends on the type of pneumonia, how sick the patient is, the patient’s age, and if there are other underlying medical conditions.
Medications used to treat pneumonia include:
- Antibiotics, if the cause is bacterial
- Antivirals, if the cause is viral
Often, managing symptoms and rest are sufficient to treat mild cases of pneumonia. Home care for pneumonia may include:
- Getting a lot of rest
- Drinking plenty of fluids
- Fever reducers
- Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil, Motrin) or naproxen (Aleve)
- Acetaminophen (Tylenol)
- Aspirin (do not give aspirin to children due to the risk of a serious condition called Reye’s syndrome)
- Steamy baths or showers or use of a humidifier can help open airways
- Don’t smoke and avoid secondhand smoke or any other lung irritants
- Check with your doctor before taking ant cough medicines because coughing helps the body work rid itself of infection
In severe cases, hospitalization may be needed, and treatment may include:
- Intravenous (IV) fluids
- Intravenous antibiotics
- Oxygen therapy
- Breathing treatments
From 
https://www.uptodate.com/contents/overview-of-community-acquired-pneumonia-in-adults?search=pneumonia%20causes&source=search_result&selectedTitle=3~150&usage_type=default&display_rank=3#H3873548286
https://www.lung.org/lung-health-diseases/lung-disease-lookup/pneumonia?referrer=https://www.google.com/