Pneumonia is a lung infection caused by bacteria, viruses, or fungi, leading to inflammation and potentially fluid or pus accumulation in the lungs. The severity and treatment vary depending on the causative pathogen and the type of pneumonia, which is categorized by how and where it was acquired: community-acquired, hospital-acquired, or ventilator-associated.

  • Community-Acquired Pneumonia (CAP):
    • Bacterial causes: The most common is Streptococcus pneumoniae, leading to pneumococcal disease which can also cause other infections like sinusitis and meningitis. Mycoplasma pneumoniae often causes a milder form known as atypical pneumonia. Other bacteria include Haemophilus influenzae, Chlamydia pneumoniae, and Legionella pneumophila (causing Legionnaires’ disease).
    • Viral causes: Common cold viruses, influenza, COVID-19, and respiratory syncytial virus (RSV) can also lead to pneumonia.
    • Fungal causes: Less common, affecting mainly those with compromised immune systems, include Cryptococcus, Pneumocystis jirovecii, and Coccidioides.
    • Protozoa causes: Rare causes like Toxoplasma can lead to pneumonia.
  • Hospital-Acquired Pneumonia (HAP): Occurs in patients already hospitalized for other conditions, often caused by antibiotic-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA), making it more severe and harder to treat.
  • Healthcare-Associated Pneumonia (HCAP): Develops in long-term care facilities or during extended outpatient stays, usually involving antibiotic-resistant bacteria.
  • Ventilator-Associated Pneumonia (VAP): Occurs in patients using a ventilator, commonly in an ICU setting, where the causative agents can be similar to those of CAP, including drug-resistant strains.
  • Aspiration Pneumonia: Results from inhaling food, liquids, or vomit into the lungs, leading to infection if not expelled.

Pneumonia’s impact varies from mild to life-threatening, posing the highest risk to infants, young children, people over 65, and those with weakened immune systems or preexisting health conditions.


Pneumonia can manifest with varying degrees of signs and symptoms, ranging from mild to severe, contingent upon factors such as its cause, your age, and overall health. While mild manifestations persist longer, they are often mistaken for symptoms of the flu or a common cold.

  • Bacterial pneumonia signs and symptoms can appear gradually or abruptly. Among the indications are:
    • Chest pain when breathing or coughing.
    • Confusion or change in mental status.
    • Coughing with yellow, green or bloody mucus.
    • Cyanosis or bluish discoloration of skin, lips or nails.
    • Fast breathing.
    • Fever (up to 105 F or 40.55 C).
    • Loss of appetite.
    • Rapid heart rate.
    • Shortness of breath.
    • Sweating or chills.
    • Tiredness or fatigue.
  • Viral pneumonia signs and symptoms typically appear over a few days. In addition to symptoms resembling bacterial pneumonia, you may also have:
    • Dry cough.
    • Headache.
    • Muscle pain.
    • Severe tiredness or fatigue.
  • Pneumonia in babies and newborns may not cause any symptoms at all or may cause symptoms that differ from those in adults, such as:
    • Coughing.
    • Crying more than usual.
    • Difficult to feed.
    • Difficulty breathing or rapid breathing (tachypnea).
    • Fever or chills,
    • General discomfort
    • Lack of energy or restlessness.
    • Less urine in diapers.
    • Loss of appetite.
    • Noisy breathing or grunting sound.
    • Sweating, flushed skin, or pale skin.
    • Vomiting.

Pneumonia can rapidly turn into a life-threatening condition in certain elderly persons, those with heart failure, and those with persistent lung issues.
Consult your healthcare provider if you experience difficulty breathing, chest pain, a persistent fever (102 F or higher), or a chronic cough (particularly if you’re producing pus in your cough).


Pneumonia is classified based on the types of germs that cause it and the location where the infection was acquired:

  • Community-acquired pneumonia: This is the most common type and occurs outside of healthcare facilities.
    • Bacteria: Streptococcus pneumoniae is a common cause, often following a cold or flu. This can lead to lobar pneumonia, affecting a specific part of the lung.
    • Bacteria-like organisms: Mycoplasma pneumoniae, often causing milder symptoms, is referred to as “walking pneumonia.”
    • Fungi: Common among individuals with chronic health issues or weakened immune systems, this type is linked to organisms found in soil or bird droppings.
    • Viruses: This includes common respiratory viruses and COVID-19, which can lead to severe pneumonia, particularly in children under 5.
  • Hospital-acquired pneumonia: Occurs during a hospital stay, particularly among patients on ventilators in intensive care. This type can be more severe due to antibiotic-resistant bacteria.
  • Health care-acquired pneumonia: Affects individuals in long-term care or outpatient settings like dialysis centers, also caused by resistant bacteria.
  • Aspiration pneumonia: Results from inhaling food, drink, vomit, or saliva into the lungs, often exacerbated by impaired gag reflex due to factors like brain injuries or substance abuse.

Risk factors

Anyone can get pneumonia.  Although the bacteria and viruses that cause pneumonia are contiguous, pneumonia itself is not.

  • Age: Individuals who are 65 years of age or older, as well as children ages two and under, are more likely to contract pneumonia.
  • Hospitalization: If you’re in a hospital intensive care unit, you have an increased risk of pneumonia, particularly if you’re dependent on a ventilator for breathing assistance.
  • Tobacco usage: Smoking weakens the body’s defenses against the viruses and bacteria that cause pneumonia.
  • Other medical condition: Asthma, chronic obstructive pulmonary disease (COPD), and heart disease increase your risk of pneumonia.
    Individuals who are receiving chemotherapy or long-term steroids, have undergone an organ transplant, or have HIV/AIDS are at risk.