Types of pneumonia

Pneumonia in the lungs. BruceBlaus, CC4.0 license

Pneumonia is a breathing disorder caused by infection and subsequent abscess formation in the lungs. The condition affects millions of people in the U.S. each year and can be caused by various pathogens. The type of pneumonia a patient has is based on the cause of the infection. According to the National Heart Lung and Blood Institute (NHLBI), community-acquired pneumonia is the most common type of pneumonia.

Community-acquired pneumonia (CAP)

Community-acquired diseases occur outside of hospitals or health care centers, i.e. in the community. CAP is transmitted by breathing in the pathogens expelled by infected individuals from their respiratory system. CAP is most common during the winter, and approximately 20 percent of infected individuals end up being treated in the hospital according to NHLBI. The condition is sometimes referred to as bronchopneumonia and is most often caused by a bacterium called pneumococcus (Streptococcus pneumoniae). Viral forms of CAP also occur, sometimes in children as a complication of respiratory syncytial virus (RSV).

Walking pneumonia

Also known as atypical pneumonia, this type of lung infection is a CAP caused by non-pneumococcus bacteria. Bacterial strains include Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae. It is transmitted from person to person like pneumococus pneumonia.

Hospital-acquired pneumonia (HAP)

Hospital-acquired, or nosocomial, diseases occur when a patient in a hospital is exposed to and infected by an infectious agent during their treatment for an unrelated illness. Health care-acquired pneumonia is similar, but it occurs in other health care facilities, such as nursing homes. HAP tends to be related to ventilator use (ventilator-associated pneumonia) and is a more serious infection than community-acquired infection, often due to the already weak health of the patient prior to infection. HAP is caused by hospital-associated bacterial strains, including Streptococcus aureus and Gram-negative bacteria.

Aspiration pneumonia

Aspiration occurs when food, drink, or digestive secretions (i.e. vomit or saliva) are inhaled into the lungs. Disruption of the swallow and gag reflex (for example, due to excessive alcohol use, brain injury, medication use, or anatomical dysfunction in the throat) can allow particles to enter the airway and form a cavity in the lung tissue. The immune system reacts to the presence of the foreign particles and causes inflammation, leading to abscess formation and pneumonia.

Fungal pneumonia

Fungal infections that occur in humans tend to be either endemic or opportunistic. Endemic fungal strains that cause pneumonia include Coccidioides and Histoplasma. Opportunistic fungal strains that cause pneumonia include Candida, Aspergillis, Mucor, and Cryptococcus neoformans. However, Cryptococcus gattii is a new strain in the Pacific Northwest of the U.S. and Canada in the past decade (endemic strain). Individuals with a suppressed immune system, such as AIDS patients, sometimes have pneumonia caused by Pneumocystis jiroveci (formerly known as Pneumocystis carinii pneumonia, PCP), a type of CAP.

Thus, pneumonia type can be based on infectious agent or mode of transmission. For example, viral pneumonia vs. bacterial pneumonia is important for determining treatment, but CAP vs. HAP can aid in preventing further cases. However, all types of pneumonia are based on breathing difficulties that stem from inflammation of the lungs, which requires treatment.