Community-acquired pneumonia causes

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2]

Overview

Community-acquired pneumonia can be caused by viral, bacterial, and fungal organisms. The etiology depends upon various factors like age, immune status, geographical area, and comorbid conditions.

Causes

• Newborn infants, children, and adults are at risk for different spectrums of disease causing microorganisms.
• In addition, adults with chronic illnesses, who live in certain parts of the world, who reside in nursing homes, who have recently been treated with antibiotics, or who are alcoholics are at risk for unique infections.

Infants

Source of Infection

• Aerosol

Newborn

• GBS causes at least 50% of cases of CAP in the first week of life.
• Other bacterial causes in the newborn period include Listeria monocytogenes and tuberculosis
• Viral causes like herpes simplex virus (most common) adenovirus, mumps, and enterovirus

Children

• For the most part, children older than one month are at risk for the same microorganisms as adults.
• However, children less than five years are much less likely to have pneumonia caused by mycoplasma pneumoniae, chlamydophila pneumoniae, or legionella pneumophila.
• In contrast, older children and teenagers are more likely to acquire mycoplasma pneumoniae and chlamydophila pneumoniae than adults.
• A unique cause of CAP in this group is chlamydia trachomatis, which is acquired during birth but does not cause pneumonia until 2-4 weeks later.
• Common viruses include respiratory syncytial virus (RSV), metapneumovirus, adenovirus, parainfluenza, influenza, and rhinovirus.
• RSV in particular is a common source of illness and hospitalization.
• Fungi and parasites are not typically encountered in otherwise healthy infants, though maternally-derived syphilis can be a cause of CAP in this age group.

Adults

Viruses

• Viruses cause 20% of CAP cases.
• Common viruses are influenza, parainfluenza, respiratory syncytial virus, metapneumovirus, and adenovirus.
• Less common viruses include chicken pox, SARS, avian flu, and hantavirus.

Atypical Organisms

• Mycoplasma pneumoniae, chlamydophila pneumoniae, and legionella pneumophila are often grouped as atypical pneumonia. Community acquired pneumonia caused by these agents present insidiously, with a non-productive cough and prominent extra-pulmonary complaints, such as myalgias and diarrhea (lack the typical pneumonia symptoms of fever, cough, and sputum).
• Mycoplasma pneumonia is often called is "walking pneumonia." It is transmitted via respiratory droplets and is common among healthy individuals in close contact with one another, such as dormitories or military barracks.
• Atypical organisms are more difficult to grow, respond to different antibiotics, and were discovered more recently than the typical bacteria discovered in the early twentieth century.

Streptococcus Pneumoniae

• Streptococcus pneumoniae is the most common cause of community acquired pneumonia.
• Aspiration pneumonia is most commonly caused by anaerobic organisms.
• Prior to the development of antibiotics and vaccination, it was a leading cause of death.
• Traditionally, it was highly sensitive to penicillin, but during the 1970s resistance to multiple antibiotics began to develop.
• Current strains of "drug resistant Streptococcus pneumoniae" or DRSP are common, accounting for twenty percent of all streptococcus pneumoniae infections.
• Adults with risk factors for DRSP including being older than 65, having exposure to children in day care, alcoholism, other severe underlying disease, or recent treatment with antibiotics should initially be treated with antibiotics effective against DRSP.

Hemophilus Influenzae

• Another common bacterial cause of CAP.
• First discovered in 1892, it was initially believed to be the cause of influenza because it commonly causes CAP in people who have suffered recent lung damage from viral pneumonia.

Enteric Gram Negative Bacteria

• Involve colonic bacteria E.coli and K.pneumonia
• Adults with risk factors for infection, which include living in a nursing home, serious heart and lung disease, and recent antibiotic use should initially be treated with antibiotics effective against Enteric Gram negative bacteria.

Pseudomonas Aeruginosa

• Uncommon cause of CAP, but it is a particularly difficult bacteria to treat.
• Individuals who are malnourished, have bronchiectasis, are on corticosteroids, or have recently had strong antibiotics for a week or more, should initially be treated with antibiotics effective against Pseudomonas aeruginosa.

Special Situations

• Coccidioides are common in southwestern US.
• Anaerobic infection is common in alcoholics. Pneumococcal pneumonia remains the most common cause of CAP in alcoholics too.
• Psittacosis (due to Chlamydophila psittaci) should be considered in the patient with exposure to birds or bird droppings.
• Anaerobes are common in patients with poor dental hygiene, and a suspected large volume of aspiration.
• Streptococcus pneumoniae, H.influenza, moraxella catarrhalis, and legionella species are the common causes of community acquired pneumonia in chronic obstructive pulmonary disorders and smokers.
• S. pneumonia, gram negative bacilli, H.influenza, staphylococcus aureus, anaerobes, and chlamydiae pneumonia are more common in nursing home residents.
• S. pneumonia, H.influenza, and mycobacterium tuberculosis are common pathogens in early stages of HIV, whereas, P.jiroveci, histoplasma, and cryptococcus are commonly seen in late stages HIV.
• In patients with structural lung disease such as bronchiectasis and cystic fibrosis, pseudomonas aeruginosa, Burkholderia cepacia (pseudomonas), and staphylococcus aureus are the common pathogens involved.

Aspiration Pneumonia Causes

• Incompetent swallowing mechanism, such as in neurological disease (a common cause being strokes) or while a person is intoxicated.
• Iatrogenic causes such as general anaesthesia for an operation. Patients are therefore instructed to be nil per os (NPO) for at least four hours before surgery.
• Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy.

Infectious Diseases Society of America/American Thoracic Society consensus statement on common etiologies of community-acquired pneumonia in adults. (DO NOT EDIT)

Outpatient

• Streptococcus pneumoniae
• Mycoplasma pneumoniae
• Haemophilus influenzae
• Chlamydophila pneumoniae
• Respiratory viruses

Inpatient (non-ICU)

• S. pneumoniae
• M. pneumoniae
• C. pneumoniae
• H. influenzae
• Legionella species
• Aspiration
• Respiratory viruses
• Yersinia enterocolitica

Inpatient (ICU)

• S. pneumoniae
• Staphylococcus aureus
• Legionella species
• Gram-negative bacilli
• H. influenzae
• Acinetobacter baumannii

Causes by Organ System

Cardiovascular	No underlying causes
Chemical/Poisoning	No underlying cause
Dental	No underlying causes
Dermatologic	No underlying causes
Drug Side Effect	No underlying cause
Ear Nose Throat	No underlying causes
Endocrine	No underlying causes
Environmental	No underlying cause
Gastroenterologic	No underlying cause
Genetic	No underlying cause
Hematologic	No underlying causes
Iatrogenic	No underlying cause
Infectious Disease	Acinetobacter baumann, Acinetobacter spp, Actinomycosis, Adenovirus serotypes (1, 2, 3, 4, 5, 7, 14, 21, and 35, Adenovirus, Aids-related opportunistic infections, Aspergillosis , Aspiration, Bacillus anthracis, Bird flu (avian influenza) , BlastomycosisBurkholderia cepacia, Burkholderia pseudomallei , C. pneumoniae, Chicken pox, Chlamydia pneumoniae , Chlamydophila pneumoniae,Coccidioides immitis, Coronaviruses, Cryptococcus neoformans, Cytomegalovirus, Cytomegalovirus, E.coli, Enterovirus 71 ,Enterovirus, Francisella tularenis infection, Gram-negative bacilli, Group b streptococcal infections , H. influenzae, H1n1 flu , Haemophilus influenzae, Hantavirus , Herpes simplex virus, Histoplasma capsulatum, Histoplasmosis, Human bocavirus,Human parechovirus types 1, 2, and 3, Influenza, K.pneumonia, Klebsiella sp, Legionella pneumophila, [Legionella species]], Legionnaires' disease, Listeria monocytogenes, M. pneumoniae, Measles, Melioidosis, Metapneumovirus, Middle east respiratory syndrome coronavirusMoraxella catarrhalis, Mumps, Mycobacterium avium-intracellulare, Mycobacterium haemophilum , Mycobacterium kansasii, Mycoplasma pneumoniae, Neisseria meningitidis, New haven coronavirus, Nocardia, Paragonimiasis , Parainfluenza , Parainfluenza virus type 1 , Parainfluenza virus type 2, Parainfluenza virus type 3 , Parainfluenza virus type 4 .., Parainfluenza, Pittsburgh pneumonia, Pneumococcal pneumonia , Pneumococcus, Pneumocystis jiroveci, Pneumonic plague , Proteus, Pseudomonas aeruginosa, Pseudomonas pseudomallei , Psittacosis , Psittacosis, Q fever , Q fever, Rat-bite fever, Respiratory syncytial virus, Respiratory viruses, Rhinovirus,Rhodococcus equi, S. pneumoniae, Sars ., Sars, Serratia , Severe acute respiratory syndrome, Sporotrichosis Staphylococcus aureus, Streptococcus agalactiae, Streptococcus group a, Streptococcus pneumoniae, Swine flu, Toxocariasis ,Toxoplasma gondii, Trichosporon , Trypanosomiasis , Type a influenza , Type a influenza subtype h1 , Type a influenza subtype h10n71,Type a influenza subtype h1n1, Type a influenza subtype h1n2 1, Type a influenza subtype h2n2 , Type a influenza subtype h3n2, Type a influenza subtype h5 , Type a influenza subtype h5n1 , Type a influenza subtype h7 , Type a influenza subtype h7n2 , Type a influenza subtype h7n3 ,Type a influenza subtype h7n7 , Type a influenza subtype h9 , Type a influenza subtype h9n2, Type b influenza , Type c influenza ,Typhus, Varicella-zoster virus, Yersinia enterocolitica, Yersinia pestis, Zygomycosis,
Musculoskeletal/Orthopedic	No underlying causes
Neurologic	No underlying causes
Nutritional/Metabolic	No underlying cause
Obstetric/Gynecologic	No underlying causes
Oncologic	No underlying cause
Ophthalmologic	No underlying causes
Overdose/Toxicity	No underlying cause
Psychiatric	No underlying causes
Pulmonary	No underlying causes
Renal/Electrolyte	No underlying causes
Rheumatology/Immunology/Allergy	No underlying cause
Sexual	No underlying causes
Trauma	No underlying causes
Urologic	No underlying causes
Miscellaneous	No underlying cause

Causes in Alphabetical Order

• Acinetobacter baumann
• Acinetobacter spp
• Actinomycosis
• Adenovirus serotypes (1, 2, 3, 4, 5, 7, 14, 21, and 35)
• Adenovirus
• Aids-related opportunistic infections
• Aspergillosis
• Aspiration
• Bacillus anthracis
• Bird flu (avian influenza)
• Blastomycosis
• Burkholderia cepacia
• Burkholderia pseudomallei
• C. pneumoniae
• Chicken pox
• Chlamydia pneumoniae
• Chlamydophila pneumoniae
• Coccidioides immitis
• Coronaviruses
• Cryptococcus neoformans
• Cytomegalovirus
• Cytomegalovirus
• E.coli
• Enterovirus 71
• Enterovirus
• Francisella tularenis infection
• Gram-negative bacilli
• Group b streptococcal infections
• H. influenzae
• H1n1 flu
• Haemophilus influenzae
• Hantavirus
• Herpes simplex virus
• Histoplasma capsulatum
• Histoplasmosis
• Human bocavirus
• Human parechovirus types 1, 2, and 3
• Influenza
• K.pneumonia
• Klebsiella sp
• Legionella pneumophila
• Legionella species
• Legionnaires' disease
• Listeria monocytogenes
• M. pneumoniae
• Measles
• Measles
• Melioidosis
• Metapneumovirus
• Middle east respiratory syndrome coronavirus
• Moraxella catarrhalis
• Mumps
• Mycobacterium avium-intracellulare
• Mycobacterium haemophilum
• Mycobacterium kansasii
• Mycoplasma pneumoniae
• Neisseria meningitidis
• New haven coronavirus
• Nocardia
• Paragonimiasis
• Parainfluenza
• Parainfluenza virus type 1
• Parainfluenza virus type 2
• Parainfluenza virus type 3
• Parainfluenza virus type 4
• Parainfluenza
• Pittsburgh pneumonia
• Pneumococcal pneumonia
• Pneumococcus
• Pneumocystis jiroveci
• Pneumonic plague
• Proteus
• Pseudomonas aeruginosa
• Pseudomonas pseudomallei
• Psittacosis
• Psittacosis
• Q fever
• Q fever
• Rat-bite fever
• Respiratory syncytial virus
• Respiratory viruses
• Rhinovirus
• Rhodococcus equi
• S. pneumoniae
• Sars
• Serratia
• Severe acute respiratory syndrome
• Sporotrichosis
• Staphylococcus aureus
• Streptococcus agalactiae
• Streptococcus group a
• Streptococcus pneumoniae
• Swine flu
• Toxocariasis
• Toxoplasma gondii
• Trichosporon
• Trypanosomiasis
• Type a influenza
• Type a influenza subtype h1
• Type a influenza subtype h10n71
• Type a influenza subtype h1n1
• Type a influenza subtype h1n2 1
• Type a influenza subtype h2n2
• Type a influenza subtype h3n2
• Type a influenza subtype h5
• Type a influenza subtype h5n1
• Type a influenza subtype h7
• Type a influenza subtype h7n2
• Type a influenza subtype h7n3
• Type a influenza subtype h7n7
• Type a influenza subtype h9
• Type a influenza subtype h9n2
• Type b influenza
• Type c influenza
• Typhus
• Varicella-zoster virus
• Yersinia enterocolitica
• Yersinia pestis
• Zygomycosis