Classification of Pneumonia
Multiple types of pneumonia exist and are defined by where they were contracted, the cause of the infection, the types of symptoms exhibited, and the extent of the infection. The most general classification of pneumonia uses differences in the method of acquiring the infection. Individuals contract community-acquired pneumonia (CAP), the most globally prevalent type, outside of a hospital or health care facility [3,6]. If an individual contracts pneumonia in a hospital or long term care facility, the infection is referred to as hospital-acquired or heath care-acquired pneumonia.
The type of germ responsible for causing the infection forms the categorical criterion that distinguishes types of community-acquired pneumonia [5]. Pneumonia can be caused by various types of infectious agents. The five main types of CAP are bacterial pneumonia, viral pneumonia, fungal pneumonia, mycoplasma pneumonia, and aspiration pneumonia [8].
Bacterial pneumonia, the most common type in adults, can develop due to an immune system compromised by HIV, malnutrition, a common cold, or the flu (especially in adults over 65), or can develop independently of previous health problems [9]. Bacteria, though some types are more common than others, cause the majority of pneumonia cases documented [6].Given the plethora of bacteria types capable of causing bacterial pneumonia, this category of pneumonia is subdivided further into either typical pneumonia or atypical bacterial pneumonia. The bacteria Streptococcus pneumonia causes the most common type of bacterial infection referred to as typical pneumonia [4,6], which exhibits the normal pneumonia symptoms described in the next section. Atypical pneumonia describes infections caused by atypical microorganisms such as Mycoplasma pneumonia (common in individuals younger than 40 exposed to a crowded setting [9]), Chlamydophila pneumonia (most common in individuals of age 65 to 79 years old [9]), and Legionella pneumophila as well as Chlamydophila Psittaci [4,9]. Atypical pneumonia often exhibits a slightly distinct set of symptoms, discussed below, in comparison to typical pneumonia.
Pneumonia can also be caused by Mycoplasma pneumonia [27] which are characterized by both bacterial and viral features and are responsible for about 15-50% of all adult cases of pneumonia [10]. The individuals most affected are adults living or working in crowded areas [27].
Viral pneumonia, caused by respiratory viruses, most commonly affects adults in the form of a flu virus [9]. Additional viruses that add to the cases of viral pneumonia are respiratory syncytial virus, rhinovirus, herpes simplex virus, and severe acute respiratory syndrome [9]. This form of pneumonia can vary widely in the severity of the infection and consequently the difficulty of recovery of individuals is affected.
Fungal pneumonia mostly affects individuals with compromised immune systems [9]. Three common fungi cause this type of pneumonia: coccidioidomycosis, histoplasmosis, and cryptococcus [9]. For individuals affected by HIV or cancer, Pneumocystis jiroveci is the most common cause of pneumocystic carinii pneumonia (PCP), a fungal pneumonia [1,2,9]. This type of fungal pneumonia is also found in individuals who have received a transplant due to a weakened immune system [9].
Pneumonia can also be classified as aspiration pneumonia, caused by inhalation of substances (solid or liquid) directly into an individual’s lungs [9], potentially forming lung abscesses. This form differs from the others as it is not caused by a microorganism.
In addition to the previously mentioned classifications, pneumonia can be classified based on the extent of the infection within an individual’s respiratory system. Lobar pneumonia describes an infection involving a large portion of one or more lobes of the lung. A more common form, known as bronchopneumonia indicates a more widespread infection distributed across the lungs and bronchi. Finally, double pneumonia indicates both the individual’s lungs contain infection [28].
The type of germ responsible for causing the infection forms the categorical criterion that distinguishes types of community-acquired pneumonia [5]. Pneumonia can be caused by various types of infectious agents. The five main types of CAP are bacterial pneumonia, viral pneumonia, fungal pneumonia, mycoplasma pneumonia, and aspiration pneumonia [8].
Bacterial pneumonia, the most common type in adults, can develop due to an immune system compromised by HIV, malnutrition, a common cold, or the flu (especially in adults over 65), or can develop independently of previous health problems [9]. Bacteria, though some types are more common than others, cause the majority of pneumonia cases documented [6].Given the plethora of bacteria types capable of causing bacterial pneumonia, this category of pneumonia is subdivided further into either typical pneumonia or atypical bacterial pneumonia. The bacteria Streptococcus pneumonia causes the most common type of bacterial infection referred to as typical pneumonia [4,6], which exhibits the normal pneumonia symptoms described in the next section. Atypical pneumonia describes infections caused by atypical microorganisms such as Mycoplasma pneumonia (common in individuals younger than 40 exposed to a crowded setting [9]), Chlamydophila pneumonia (most common in individuals of age 65 to 79 years old [9]), and Legionella pneumophila as well as Chlamydophila Psittaci [4,9]. Atypical pneumonia often exhibits a slightly distinct set of symptoms, discussed below, in comparison to typical pneumonia.
Pneumonia can also be caused by Mycoplasma pneumonia [27] which are characterized by both bacterial and viral features and are responsible for about 15-50% of all adult cases of pneumonia [10]. The individuals most affected are adults living or working in crowded areas [27].
Viral pneumonia, caused by respiratory viruses, most commonly affects adults in the form of a flu virus [9]. Additional viruses that add to the cases of viral pneumonia are respiratory syncytial virus, rhinovirus, herpes simplex virus, and severe acute respiratory syndrome [9]. This form of pneumonia can vary widely in the severity of the infection and consequently the difficulty of recovery of individuals is affected.
Fungal pneumonia mostly affects individuals with compromised immune systems [9]. Three common fungi cause this type of pneumonia: coccidioidomycosis, histoplasmosis, and cryptococcus [9]. For individuals affected by HIV or cancer, Pneumocystis jiroveci is the most common cause of pneumocystic carinii pneumonia (PCP), a fungal pneumonia [1,2,9]. This type of fungal pneumonia is also found in individuals who have received a transplant due to a weakened immune system [9].
Pneumonia can also be classified as aspiration pneumonia, caused by inhalation of substances (solid or liquid) directly into an individual’s lungs [9], potentially forming lung abscesses. This form differs from the others as it is not caused by a microorganism.
In addition to the previously mentioned classifications, pneumonia can be classified based on the extent of the infection within an individual’s respiratory system. Lobar pneumonia describes an infection involving a large portion of one or more lobes of the lung. A more common form, known as bronchopneumonia indicates a more widespread infection distributed across the lungs and bronchi. Finally, double pneumonia indicates both the individual’s lungs contain infection [28].