Pneumonia

Summary

Pneumonia is a respiratory infection characterized by inflammation of the alveolar space and/or

the interstitial tissue of the lungs. In industrialized nations, it is the leading infectious cause of
death. Pneumonia is most commonly transmitted via aspiration of airborne pathogens (primarily
bacteria, but also viruses and fungi) but may also result from the aspiration of stomach contents.
The most likely causal pathogens can be narrowed down based on patient age, immune status,
and where the infection was acquired (community-acquired or hospital-acquired). Pneumonia is
classified based on clinical features as either typical and atypical; each type has its own spectrum
of commonly associated pathogens. Typical pneumonia manifests with sudden onset
of malaise, fever, and a productive cough. On auscultation, crackles and bronchial breath sounds
are audible. Atypical pneumonia manifests with gradual onset of unproductive cough, dyspnea,
and extrapulmonary manifestations. Auscultation is usually unremarkable. Some patients may
present with elements of both types. Diagnostics include blood tests for inflammatory
parameters and pathogen detection in blood, urine, or sputum samples. Chest x-ray in cases
of typical pneumonia shows opacity restricted to one lobe, while x-ray in atypical
pneumonia may show diffuse, often subtle infiltrates. Together with the characteristic clinical
features, newly developed pulmonary infiltrate on chest x-ray confirms the diagnosis.
Management consists of empiric antibiotic treatment and supportive measures (e.g., oxygen
administration, antipyretics).

For specific information on the diagnosis and management of pneumonia in pediatric patients,

see “Pneumonia in children.”

Etiology
Pathogens

Pneumonia pathogens according to the source of infection

Type of
Common pathogens
pneumonia

 Typical pneumonia

o Streptococcus pneumoniae (most common) 

 Also the most common pathogen in nursing home residents

 Most common cause of pneumonia in persons who inject drugs [1]

o Haemophilus influenzae 

o Moraxella catarrhalis

o Klebsiella pneumoniae 

o Staphylococcus aureus 

 Atypical pneumonia

o Bacteria

Community-  Mycoplasma pneumoniae (most common in the ambulatory setting)

acquired
pneumonia  Chlamydophila pneumoniae 

 Chlamydophila psittaci

 Legionella pneumophila → legionellosis

 Coxiella burnetii → Q fever

 Francisella tularensis → tularemia

o Viruses

 RSV

 Influenza viruses, Parainfluenza viruses

 CMV

 Adenovirus

 Coronaviridae (e.g., SARS-CoV-2)

Hospital-
acquired  Gram-negative pathogens
pneumonia 
o Pseudomonas aeruginosa

o Enterobacteriaceae

o Acinetobacter spp

 Staphylococci (Staphylococcus aureus) 
 Pneumonia pathogens according to the source of infection

Type of
Common pathogens
pneumonia

 Streptococcus pneumoniae

For atypical pneumonia bacterial causes, remember the mnemonic: Atypically, Legions of Clams Mind their P's and Q's!

• Legionella pneumophila

• Chlamydophila pneumoniae

• Mycoplasma pneumoniae

• Psittacosis (Chlamydophila psittaci)

• Q fever (Coxiella burnetii)

Pneumonia pathogens according to location

Type of pneumonia Common pathogens

 Most common: S. pneumoniae

 Less common

Lobar pneumonia o Legionella

o Klebsiella

o H. influenzae

 S. pneumoniae

 S. aureus
Bronchopneumonia
 H. influenzae

 Klebsiella

Interstitial pneumonia
 Atypical pathogens

o Mycoplasma pneumoniae

o Chlamydophila pneumoniae

o Chlamydophila psittaci (primarily transmitted by parrots)

 Pneumonia pathogens according to location

Type of pneumonia Common pathogens

o Legionella

o Viruses (e.g., RSV, CMV, influenza, adenovirus)

o Coxiella burnetii

Cryptogenic organizing  Noninfectious

pneumonia

Pneumonia pathogens according to affected population

Type of pneumonia Common pathogens

 Encapsulated bacteria 

 Pneumocystis jirovecii → Pneumocystis jirovecii pneumonia

 Aspergillus fumigatus → aspergillosis

 Histoplasma capsulatum

Pneumonia  Coccidioides immitis

in immunocompromised patients
 Candida species → candidiasis

 Cytomegalovirus (CMV) → CMV pneumonia

 S. aureus

 Gram-negative bacteria

 Escherichia coli

 Streptococcus agalactiae (Group B streptococcus)

Pneumonia in newborns
 Streptococcus pneumoniae

 Haemophilus influenzae

 C. trachomatis (in infants) [2][3]

 C. pneumoniae (in young children and adolescents) [4]

 S. pneumoniae
Pneumonia in children (4 weeks –18 years)
 Respiratory syncytial virus (RSV)

 Mycoplasma

 See also “Pneumonia in children.”

 Pneumonia pathogens according to location

Type of pneumonia Common pathogens

 Mycoplasma

 Influenza virus
Pneumonia in young adults (18–40 years)
 C. pneumoniae

 S. pneumoniae

 S. pneumoniae

 H. influenzae

Pneumonia in adults (40–65 years)  Mycoplasma

 Anaerobes

 Viruses

 S. pneumoniae [5]

 H. influenzae

Pneumonia in elderly individuals  Gram-negative bacteria

 Anaerobes [6]

 Influenza virus

 Uncommon organisms (e.g., Nocardia, Coxiella burnetii, Aspergillus, Pseudomonas

Recurrent pneumonia 
aeruginosa)

“Track my respiration: chlassic strep formation”: C. trachomatis, Mycoplasma, Respira

tory syncytial virus, Chlamydia pneumoniae, and Streptococcus pneumoniae are the most

common causative agents of pneumonia in children.

Risk factors [7]

 Old age and immobility of any cause 

 Chronic diseases
 o Preexisting cardiopulmonary
conditions (e.g., bronchial asthma, COPD, heart failure)
o Acquired or congenital abnormalities of
the airways (e.g., bronchiectasis, space-occupying lesions, cystic fibrosis)
 Immunosuppression
o HIV infection 
o Diabetes mellitus
o Cytostatic and immunosuppressive therapy
o Alcoholism
o Malnutrition
 Impaired airway protection 
o Alteration in consciousness (e.g., due to stroke, seizure,
anesthesia, drugs, alcohol)
o Dysphagia
o Smoking 
 Environmental factors
o Crowded living conditions (e.g., prisons, homeless shelters) 
o Toxins (e.g., solvents, gasoline)
o Endemic exposures (e.g., areas of
high Coccidioides and Histoplasma endemicity) 
o Contaminated water systems (e.g., in hotels, on cruise ships) 
o Zoonotic exposures (e.g., birds, farm animals) 
 Cryptogenic organizing pneumonia
o Specific medications (e.g., amiodarone, bleomycin) [8]
o Chronic inflammatory disorders (e.g., rheumatoid arthritis)
 Surgical procedures 
o Upper abdominal surgery
o Chest surgery

Bear in mind immune status and potential exposures when considering potential pathogens

in patients with suspected pneumonia.

 Consider aspiration pneumonia in patients with altered mental status or other risk factors

for aspiration.

Classification

Pneumonia can be classified according to etiology, location acquired, clinical features, and the
area of the lung affected by the pathology.

Etiology

 Primary pneumonia: no apparent preexisting conditions that may predispose to

pneumonia
 Secondary pneumonia
o Bronchial asthma, COPD, heart failure, cystic fibrosis
o Viral upper respiratory tract infections with bacterial superinfection
o Anatomical abnormalities such as tubercular caverns, bronchial tumors, or
stenosis (postobstructive pneumonia) [9]
o Aspiration pneumonia

Location acquired

 Community-acquired pneumonia (CAP): pneumonia that is acquired outside of a

healthcare establishment
 Hospital-acquired pneumonia (HAP): nosocomial pneumonia, with onset > 48
hours after admission
o Ventilator-associated pneumonia (VAP): pneumonia occurring in
patients who are on mechanical ventilation breathing machines in
hospitals (typically in the intensive care unit)
 Healthcare-associated pneumonia (HCAP): pneumonia that is acquired
in healthcare facilities (e.g., hospital, nursing homes, hemodialysis centers, and
 outpatient clinics); this terminology is no longer recommended but is included for
historical purposes.  [10][11]

Clinical features 

 Typical pneumonia
o Pneumonia featuring classic symptoms (typical findings
on auscultation and percussion)
o Manifests as lobar pneumonia or bronchopneumonia
 Atypical pneumonia
o Pneumonia with less distinct classical symptoms and often unremarkable
findings on auscultation and percussion
o Manifests as interstitial pneumonia

Area of lung affected by the pathology 

 Lobar pneumonia: pneumonia affecting one lobe of a lung

o Multilobar pneumonia refers to the involvement of multiple lobes in a
single lung or both lungs.
o Panlobar pneumonia involves all the lobes of a single lung.
 Bronchial pneumonia: pneumonia affecting the tissue around
the bronchi and/or bronchioles
 Interstitial pneumonia: pneumonia affecting the tissue between the alveoli
 Cryptogenic organizing pneumonia (formerly known as bronchiolitis obliterans
organizing pneumonia): a noninfectious pneumonia of unknown etiology
characterized by the involvement of the bronchioles, alveoli, and surrounding tissue

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Pathophysiology

Routes of infection

 Most common: microaspiration (droplet infection) of airborne pathogens or

oropharyngeal secretions 
 Aspiration of gastric acid (aspiration pneumonitis) , food, or liquids 
  Hematogenous dissemination (rare) 

Pathogenesis

1. Failure of protective pulmonary mechanisms (e.g., cough reflex, mucociliary

clearance , alveolar macrophages )

2. Infiltration of the pulmonary parenchyma by the pathogen → interstitial and

alveolar inflammation

3. Impaired alveolar ventilation → ventilation/perfusion (V/Q) mismatch with

intrapulmonary shunting (right to left) 

4. Hypoxia due to increased alveolar-arterial oxygen gradient 

o Hypoxia is worsened when the affected lung is in the dependent position,
as perfusion to the dependent lung is better compared to the
nondependent lung.
o In the case of a large unilateral pulmonary abscess, it may be helpful to
position the patient so that the affected lung is in the dependent
position in order to prevent the pus from filling the unaffected lung.

Pattern of involvement

 Lobar pneumonia
o Classic (typical) pneumonia of an entire lobe; primarily caused
by pneumococci
o Characterized by inflammatory intra-alveolar exudate, resulting in
consolidation 
o Can involve the entire lobe or the whole lung

Stages of lobar pneumonia 

Macroscopic
Stages Microscopic findings
findings

Congest  Paren  Alveolar lumens

ion (day
1–2) chyma with
 Stages of lobar pneumonia 

Macroscopic
Stages Microscopic findings
findings

l parti
al
consol serous exudate,
idatio bacteria, and rare
n inflammatory cells
 Red-
purple

 Paren
chyma
l cons
olidati
on  Alveolar lumens
 Red- with exudate rich
brown in fibrin,
Red  Dry bacteria, erythrocy
hepatiza
tion (da and tes, and
y 3–4)
firm inflammatory cells
 Liver–  Alveolar walls
like c thickening 
onsist
ency
 Rever
sible

Gray
 Unifor  Alveolar lumens
hepatiza
tion (da mly with
y 5–7)
gray suppurative exudat
 Liver– e (neutrophils and 
like c macrophages)
 Stages of lobar pneumonia 

Macroscopic
Stages Microscopic findings
findings

 Erythrocytes and
most bacteria have
onsist
been degraded.
ency
 Alveolar walls
thickening 

 Gradu
al
 Enzymatic fibrinol
aerati
ysis
Resoluti on of
 Macrophages remo
on (day the
8 to wee ve the
k 4) affect
suppurative exudat
ed
e. 
segme
nt

 Bronchopneumonia: mostly commonly a descending infection that affects

the bronchioles and adjacent alveoli
o Primarily caused by pneumococci and/or other streptococci
o Characterized by acute inflammatory infiltrates that fill
the bronchioles and the adjacent alveoli (patchy distribution) 
o Usually involves the lower lobes or right middle lobe and affects ≥ 1 lobe
o Manifests as typical pneumonia
o Necrotizing bronchopneumonia and pneumatocele are caused
by Staphylococcus aureus and are often preceded by
an influenza infection. [12]
 Interstitial pneumonia: interstitial inflammation, typically caused
by Mycoplasma and viral infections
o Characterized by a diffuse patchy inflammation that mainly involves the
alveolar interstitial cells
 o Bilateral multifocal opacities are classically found on chest x-ray.
o Manifests as atypical pneumonia
o Often has an indolent course (walking pneumonia)
 Miliary pneumonia: multiple small infiltrations caused by hematogenous
dissemination (e.g., of tuberculosis)
 Cryptogenic organizing pneumonia: characterized by inflammation of
the bronchioles and surrounding structures

Clinical features

Typical pneumonia

Typical pneumonia is characterized by a sudden onset of symptoms caused by lobar infiltration.

 Severe malaise
 High fever and chills
 Productive cough with purulent sputum (yellow-greenish)
o Crackles and bronchial breath sounds on auscultation
o Decreased breath sounds
o Enhanced bronchophony, egophony, and tactile fremitus
o Dullness on percussion 
 Tachypnea and dyspnea (nasal flaring, thoracic retractions) 
 Pleuritic chest pain when breathing, often accompanying pleural effusion
 Pain that radiates to the abdomen and epigastric region (particularly in children; see
also “Pneumonia in children”)

Suspect bacterial pneumonia in immunocompromised patients with

acute high fever and pleural effusion.

Atypical pneumonia
Atypical pneumonia typically has an indolent course (slow onset) and commonly manifests with
extrapulmonary symptoms.
  Nonproductive, dry cough
 Dyspnea
 Auscultation often unremarkable
 Common extrapulmonary features include fatigue, headaches, sore throat, myalgias,
and malaise.

This classification does not have a major impact on patient management because it is not

always possible to clearly distinguish between typical and atypical pneumonia.

Diagnostics

Pneumonia is a clinical diagnosis based on history, physical examination, laboratory findings,

and CXR findings. Consider microbiological studies and advanced diagnostics based on patient
history, comorbidities, severity, and entity of pneumonia.  [13]

In ambulatory settings, the combination of normal vital signs and an unremarkable lung

examination indicates a very low likelihood of CAP. [14][15]

Laboratory studies

Routine

 CBC, inflammatory markers: ↑ CRP, ↑ ESR, leukocytosis 
 ↑ Serum procalcitonin (PCT): Procalcitonin is an acute phase reactant that can help to
diagnose bacterial lower respiratory tract infections.  [11]
o PCT can be used to guide antibiotic treatment but should not be used to
decide if antibiotic therapy is necessary on its own. [11][16][17]
o PCT levels ≥ 0.25 mcg/L correlate with an increased probability of a
bacterial infection.
o Low PCT level after 2–3 days of antibiotic therapy can help facilitate the
decision to discontinue antibiotics. [17]
 Decrease of PCT to ≤ 80% of peak level
 Decrease of PCT to < 0.25 mcg/L
 ABG: ↓ PaO2   [13]
  BMP, LFTs 

Do not rely on laboratory markers like CRP or procalcitonin to determine the need

for antibiotic therapy. [18][11]

Microbiological studies

Indication Microbiological studies to consider [11][10][13]

Any admitted patient  MRSA nares swab (PCR and/or culture)

Any patient being treated  Blood cultures (2 sets)

empirically for MRSA or P.
 Sputum culture and Gram stain 
aeruginosa 

 Blood cultures (2 sets)

Severe CAP  Sputum culture and Gram stain 

HAP  Pneumococcal urinary antigen

VAP  Legionella pneumophila urinary antigen 

 Consider Chlamydia pneumoniae respiratory PCR. 

 Influenza nasal swab (NAAT) 

Influenza season
 Consider respiratory virus panel nasal swab (NAAT). 

 Testing for specific pathogens: e.g., COVID-19

All patients
in pandemic or epidemic settings testing with SARS-CoV-2 PCR [19]

In pandemic or epidemic settings, rule out the prevalent

respiratory pathogen (e.g., COVID-19) in all patients with suspected pneumonia. [19]

Avoid routine blood cultures and sputum Gram stain in patients with CAP, except if severe

or there is concern for MRSA or Pseudomonas infection. [11]

Imaging

Chest x-ray (posteroanterior and lateral) 

 Indications: all patients suspected of having pneumonia

 X-ray findings in pneumonia
o Lobar pneumonia
 Opacity of one or more pulmonary lobes
 Presence of air bronchograms: appearance of
translucent bronchi inside opaque areas of alveolar
consolidation 
o Bronchopneumonia
 Poorly defined patchy infiltrates scattered throughout
the lungs
 Presence of air bronchograms
o Atypical or interstitial pneumonia
 Diffuse reticular opacity
 Absent (or minimal) consolidation
o Parapneumonic effusion

A new pulmonary infiltrate on chest x-ray in a patient with classic symptoms of pneumonia confirms the diagnosis.

Typical pneumonia usually appears as lobar pneumonia on x-ray, while atypical pneumonia tends to appear as interstitial pneumonia.

However, the underlying pathogen cannot be conclusively identified based on imaging results alone.

Consider chest CT or empiric treatment if clinical suspicion for CAP remains high despite a negative CXR, as the initial CXR may

be falsely negative. [20][21]

Chest CT (usually without contrast) 

 Indications
o Inconclusive chest x-ray
o Recurrent pneumonia 
o Poor response to treatment 
  Advantages: more reliable evaluation of circumscribed opacities, pleural empyema,
or sites of consolidation
 Findings:  [22]
o Localized areas of consolidation (hyperdense) 
o Air bronchograms 
o Ground-glass opacities
o Pleural effusion/empyema
 Hyperdense fluid collection
 Split pleura sign
o Nodules
 Large (e.g., in tuberculosis or fungal pneumonia)
 Peribronchial (e.g., bronchopneumonia)
 Disseminated (e.g., septic emboli or varicella-
zoster pneumonia)

CT is more sensitive and specific than CXR for the diagnosis of pneumonia.

Lung ultrasound in pneumonia

Point-of-care ultrasound (POCUS) has high sensitivity and specificity for the diagnosis of

pneumonia. [23][24]

 Indications
o Evaluation of suspected pneumonia
o Assessment of undifferentiated dyspnea  [25]
 Characteristic findings [26][27]
o Consolidation 
o Irregular and serrated lung margins
o Air bronchograms
o Unilateral B-lines
o Pleural effusion
 In the emergency department, consider POCUS to quickly confirm pneumonia and assess

for other causes of dyspnea.

Advanced diagnostics for pneumonia

Bronchoscopy

 Indications
o Suspected mass (e.g., recurrent pneumonia)
o Need for pathohistological diagnosis (e.g., biopsy of a central mass
discovered on CT)
o Inconclusive results on CT
o Poor response to treatment

Diagnostic thoracentesis

 Indications: consider if pleural effusion > 10 mm is present to evaluate for pleural

empyema [28][13]
 Findings: See “Diagnostics” and “Parapneumonic effusion” in “Pleural effusion”.
 Consider therapeutic thoracentesis in large effusions (≥ half of the hemithorax) or if
the effusion is suspected of causing dyspnea [28]
 Consider tube thoracostomy if pleural empyema (e.g., echogenic debris
on lung ultrasound) or complicated effusion (e.g.,pH < 7.20, glucose < 60
mg/dL, LDH above three times the upper limit of serum LDH, positive culture) is
suspected  [28]

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Treatment

Approach
  Evaluate all patients for hypoxemia and/or sepsis and manage as indicated.
 Assess the need for hospitalization with the CURB-65 score or the pneumonia
severity index (PSI/PORT score). 
 Determine the appropriate level of care using clinical judgment and the IDSA/ATS
criteria for severe CAP. 
 Begin empiric antibiotic therapy based on severity and patient risk
factors (e.g., VAP vs. CAP).
 Provide supportive care.
 Re-evaluate therapy after 48 hours (earlier if the patient's condition deteriorates or
new information becomes available).

Initial stabilization [29][30]

 Identification and management of sepsis

 Fluid resuscitation and management of septic shock as needed
 Respiratory support as needed
o Supplemental oxygen for hypoxia
o HFNC oxygen therapy, NIPPV, or intubation for respiratory failure

Criteria for hospitalization [11][18]

Every patient should be assessed individually and clinical judgment is the most important factor.
The pneumonia severity index (PSI) and the CURB-65 score are tools that can help to determine
whether to admit a patient. 

 CURB-65 score [31]
o Confusion (disorientation, impaired consciousness)
o Serum Urea > 7 mmol/L (20 mg/dL)
o Respiratory rate ≥ 30/min
o Blood pressure: systolic BP ≤ 90 mm Hg or diastolic BP ≤ 60 mm Hg
o Age ≥ 65 years
o Interpretation
 Each finding is assigned 1 point.
 CURB-65 score 0 or 1: The patient may be treated as an
outpatient.
 CURB-65 score ≥ 2: Hospitalization is indicated.
 CURB-65 score ≥ 3: Consider ICU level of care. 
 o CRB-65 score (if serum urea is not known or unavailable)
CRB-65 score of 0: The patient may be treated as an

outpatient.
 CRB-65 score of ≥ 1: Hospitalization is recommended.
 Pneumonia severity index (PSI/PORT score) [32]
o Patients are assigned to one of five risk classes based on a more complex
point system than in CURB-65.
o Points are distributed based on patient age, comorbidities, and lab results.

The CURB-65 score and PSI are tools for evaluating the risk of mortality. They have not

been validated for determining the necessity for ICU admission.

Criteria for ICU admission [11][18]

 The decision of whether to admit a patient to the ICU should be based on clinical

judgment.
 The IDSA/ATS criteria for severe CAP can be used to help triage patients
with CAP and guide empiric antibiotic treatment decisions. [11] 

IDSA/ATS criteria for severe CAP  [11]

 Septic shock/need for vasopressors

Major
criteria  Mechanical ventilation

Minor
 Confusion
criteria
 Body temperature < 36°C
 Hypotension requiring fluid resuscitation
 Respiratory rate ≥ 30/min
 PaO2/FiO2 ≤ 250
 Leukopenia (WBC < 4,000/mm3) 
 Thrombocytopenia (platelet count <
 IDSA/ATS criteria for severe CAP  [11]

100,000/mm3)
 BUN ≥ 20 mg/dL
 Multilobar infiltrates

Interpretation

 Severe CAP: one major criterion or ≥ 3 minor criteria

Empiric antibiotic therapy for community-acquired pneumonia [33][11]

Outpatient

Empiric antibiotic therapy for community-acquired

pneumonia in an outpatient setting

Patient
Recommended empiric antibiotic regimen [11]
profile

 Monotherapy with one of the

following:
Previous o Amoxicillin DOSAGE
ly
healthy o Doxycycline DOSAGE
patients o A macrolide (only in areas
without
comorbi with
dities
a pneumococcal macrolide 
or risk
factors f resistance < 25%) 
or
 Azithromyci
resistant
pathogen n DOSAGE
s
 Clarithromy
cin DOSAGE

Patients  Combination therapy

with
o An antipneumococcal β-
comorbi
dities lactam:
 Empiric antibiotic therapy for community-acquired
pneumonia in an outpatient setting

Patient
Recommended empiric antibiotic regimen [11]
profile

 Amoxicillin-
clavulanate 
DOSAGE

 Cefuroxime 
DOSAGE

 Cefpodoxim
e DOSAGE
o PLUS one of the
following:
 A macrolide
or risk
factors f 
or Azi
resistant
pathogen
s  
Cla

 Doxycycline 
DOSAGE

 Monotherapy: with a respiratory
fluoroquinolone 
o Gemifloxacin DOSAGE
o Moxifloxacin DOSAGE
o Levofloxacin DOSAGE

 Duration of treatment
o 5 days of therapy is usually sufficient for CAP that is treated in the
outpatient setting.
o Any patient being treated in a primary care setting should be re-
examined after 48–72 hours to evaluate the efficacy of the
prescribed antibiotic.
  Additional considerations: Knowing local resistance patterns of S.
pneumoniae to macrolides is critical when deciding on an empiric antibiotic regimen.

Inpatient 

Empiric antibiotic therapy for community-acquired

pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

Nonsevere CAP  Combination therapy

/non-ICU treat
o An antipneumococ
ment
cal β-lactam:
 Ampi
cillin
-
sulba
ctam 
DOSA

GE

 Cefta
rolin
e DO
SAGE

 Ceftr
iaxon
e DO
SAGE

 Cefot
axim
e DO
SAGE

o PLUS one of the

following:
 A ma
croli
 Empiric antibiotic therapy for community-acquired
pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

de

A


C

 Doxy
cycli
ne D
OSA

GE  

 Monotherapy:
with a respiratory
fluoroquinolone 
o Gemifloxacin DOS
AGE

o Moxifloxacin DOS
AGE

o Levofloxacin DOS
AGE

Severe CAP/  Combination therapy

ICU treatment
o An antipneumococ
cal β-lactam:
 Ampi
cillin
-
sulba
ctam 
 Empiric antibiotic therapy for community-acquired
pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

DOSA

GE

 Cefta
rolin
e DO
SAGE

 Ceftr
iaxon
e DO
SAGE

 Cefot
axim
e DO
SAGE

o PLUS one of the

following:
 A ma
croli
de

A


C

 Doxy
cycli
ne D
OSA

GE  
 Empiric antibiotic therapy for community-acquired
pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

 A res
pirat
ory
fluor
oquin
olone 

M


L

 Alternative for patients with

a penicillin allergy:
o Aztreonam DOSAG
E

o PLUS a respiratory
fluoroquinolone
 Moxi
floxa
cin D
OSA

GE

 Levo
floxa
cin D
OSA

GE )

Risk  Combination therapy

 Empiric antibiotic therapy for community-acquired
pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

factors for Pseu o An antipneumococ
domonas
aeruginosa cal,
antipseudomonal β
-lactam: 
 Piper
acilli
n-
tazob
acta
m DO
SAGE

 Cefe
pime 
DOSA

GE

 Cefta
zidim
e DO
SAGE

 Mero
pene
m DO
SAGE

 Imip
enem
-
cilast
atin D
OSA

GE
 Empiric antibiotic therapy for community-acquired
pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

o PLUS one of the

following:
 A ma
croli
de

A


C

 Doxy
cycli
ne D
OSA

GE  

 A
respir
atory 
fluor
oquin
olone

L


M

 Alternative for patients with

a penicillin allergy:
 Empiric antibiotic therapy for community-acquired
pneumonia in an inpatient setting

Recommended empiric
Patient profile
antibiotic regimen [11]

o Aztreonam DOSAG
E

o PLUS a respiratory
fluoroquinolone
 Moxi
floxa
cin D
OSA

GE

 Levo
floxa
cin D
OSA

GE

 Addition of one of the

following antibiotics with MRS
A activity
Risk factors for
MRSA o Vancomycin DOSA
GE

o Linezolid DOSAGE

 Duration of therapy
o 5–7 days is usually sufficient.
o Consider longer courses in patients with one of the following:
 Patient not responding to treatment
 Suspected or concern for MRSA or P. aeruginosa infection
 Concurrent meningitis
 Unusual pathogens (e.g., Burkholderia pseudomallei, fungal

infection)
 Additional considerations
o If aztreonam is used instead of a β-lactam antibiotic (e.g.,
for penicillin allergy), the addition of MSSA coverage (e.g.,
a fluoroquinolone) is necessary.
o Anaerobic coverage is not routinely recommended for
suspected aspiration pneumonia (unless lung abscess or empyema is
suspected). [11]
o Corticosteroids are not routinely recommended as adjunct therapy. [11]

If aztreonam is used as an alternative to other β-lactam antibiotics, additional coverage

for MSSA must be included (e.g., a fluoroquinolone).

Empiric antibiotic therapy for hospital-acquired pneumonia [10]

Empiric antibiotic therapy for hospital-acquired pneumonia

Patient profile Recommended empiric antibiotic regimen [10]

Patients not at  Monotherapy

high risk for
o An antipneumococca
mortality and
without risk l,
factors for
MRSA antipseudomonal β-
infection lactam
 Imipen
em DO
SAGE

 Merop
enem D
OSAGE

 Cefepi
me DO
SAGE

 Piperac
Empiric antibiotic therapy for hospital-acquired pneumonia

Patient profile Recommended empiric antibiotic regimen [10]

illin-
tazobac
tam DO
SAGE

o OR levofloxacin DOS
AGE

Patients not at  Combination therapy

high risk for
o One of the
mortality but
with risk following antibiotics 
factors for
MRSA with MRSA activity
infection  :
 Linezol
id DOS
AGE

 Vanco
mycin 
DOSAG

o PLUS one of the
following:
 An anti
pneum
ococcal
,
antipse
udomo
nal β-
lactam

P
Empiric antibiotic therapy for hospital-acquired pneumonia

Patient profile Recommended empiric antibiotic regimen [10]


C


C


M


I

 A fluor
oquinol
one

L


C

 Aztreo
nam D
OSAGE

Patients at  Combination therapy

high risk for
o One of the
mortality 
Patients with following antibiotics 
structural lun with MRSA activity
g disease
(e.g., cystic :
Empiric antibiotic therapy for hospital-acquired pneumonia

Patient profile Recommended empiric antibiotic regimen [10]

fibrosis, bronc  Vanco
hiectasis)
mycin 
DOSAG

 Linezol
id DOS
AGE

o PLUS any two of the

following (avoid
combining two β-
lactams):
 An anti
pneum
ococcal
,
antipse
udomo
nal β-
lactam

P


C


C


M


Empiric antibiotic therapy for hospital-acquired pneumonia

Patient profile Recommended empiric antibiotic regimen [10]

 A fluor
oquinol
one

L


C

 An ami
noglyc
oside

A


G


T

 Aztreo
nam D
OSAGE

 Duration of treatment
o Empiric antibiotic therapy should be narrowed and/or de-escalated as
soon as feasible.
o Seven days of therapy are usually sufficient. [10]
  Additional considerations: Resistance patterns can vary widely;
local antibiograms should be considered when starting empiric treatment.

Patients with structural lung disease and/or at high risk for mortality should receive double

antipseudomonal coverage!

Empiric antibiotic therapy for ventilator-associated pneumonia [10]

 Recommended combination therapy

o An antipneumococcal, antipseudomonal β-lactam
 Aztreonam DOSAGE
 Imipenem DOSAGE
 Meropenem DOSAGE
 Ceftazidime DOSAGE
 Cefepime DOSAGE
 Piperacillin-tazobactam DOSAGE
o PLUS one of the following antibiotics with MRSA activity:
Vancomycin DOSAGE
 Linezolid DOSAGE
o PLUS one of the following:
A fluoroquinolone
 Levofloxacin DOSAGE
 Ciprofloxacin DOSAGE
 An aminoglycoside
 Amikacin DOSAGE
 Gentamicin DOSAGE
 Tobramycin DOSAGE
 A polymyxin
 Colistin DOSAGE
 Polymyxin B DOSAGE
 Duration of treatment: Seven days of therapy are usually sufficient. [10]
 Additional considerations:
o Risk factors for multi-drug resistant organisms (e.g., presence of
structural lung disease, recent IV antibiotic therapy, local resistance
patterns) should be considered when deciding on an empiric regimen
 o Empiric antibiotic therapy for ventilator-associated tracheobronchitis is
not routinely recommended. [10]

Supportive therapy for pneumonia

 Sufficient rest (not absolute bed rest) and physical therapy 

 Hydration with PO or IV fluids, supplemental oxygen as needed
 Incentive spirometer 
 Antipyretics, analgesics as needed (e.g., acetaminophen DOSAGE ) 
 Expectorants and mucolytics  [34]
 Antitussives (e.g., codeine DOSAGE )

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Acute management checklist

 Calculate the CURB-65 score and/or PSI/PORT score to identify patients who would

benefit from admission.
 Assess severity of CAP with the IDSA/ATS criteria for severe CAP.
 Order microbiological workup as indicated by patient severity and risk factors.
 Community-acquired pneumonia: Start empiric antibiotics for CAP.
 Hospital-acquired pneumonia: Start empiric antibiotics for HAP.
 Ventilator-associated pneumonia: Start empiric antibiotics for VAP.
 Evaluate and treat sepsis if present (see sepsis).
 Administer supplemental O2 if patient is hypoxemic.
 Consider advanced diagnostic evaluation.  [33]
 Provide supportive care for pneumonia (e.g., antipyretics, , IV fluids).
 Continuous pulse oximetry
 Trend inflammatory markers, procalcitonin.
 Narrow antibiotic therapy as soon as feasible.

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Pathogen-specific pneumonia

Mycoplasma pneumonia [35]
  Epidemiology
o One of the most common causes of atypical pneumonia
o More common in school-aged children and adolescents
o Outbreaks most commonly occur in schools, colleges, prisons, and
military facilities.
 Clinical features
o Generalized papular rash
o Erythema multiforme 
o See “Atypical pneumonia”.
 Diagnostics
o Subclinical hemolytic anemia: associated with elevated cold
agglutinin titers (IgM)
o Interstitial pneumonia, often with a reticulonodular pattern on chest x-ray
o Chest x-ray can show extensive pulmonary involvement in patients with
mild pneumonia.
 Treatment
o A macrolide, doxycycline, or fluoroquinolones
o Beta-lactam antibiotics are not effective 
o See “Empiric antibiotics for CAP” for dosages and duration of treatment.

Other types of pathogen-specific pneumonia

 Legionnaire disease
 Pneumocystis pneumonia
 Pseudomonas aeruginosa: causes VAP 
 Tuberculosis
 Primary influenza pneumonia
 Various viral infections (e.g., respiratory syncytial
virus, hantavirus, adenovirus, CMV, SARS-CoV, SARS-CoV-2)
 Ornithosis

Aspiration pneumonia
Definitions

 Aspiration
o The inhalation of foreign material into the respiratory tract
o Most commonly occurs after instrumentation of the
upper airways or esophagus (e.g., upper GI endoscopy) or secondary to
vomiting and regurgitation of gastric contents
 Aspiration pneumonia: a type of pneumonia that occurs as a result of oropharyngeal
secretions and/or gastric contents aspiration
 Aspiration pneumonitis
o Aspiration of gastric acid that initially causes tracheobronchitis, with
rapid progression to chemical pneumonitis
o May cause ARDS in extreme cases

Patients may develop aspiration pneumonitis without pneumonia, aspiration

pneumonia without pneumonitis, or aspiration pneumonitis complicated by pneumonia. [36]

Etiology

 Pathogens [36][11]
o Gram-positive and gram-negative aerobic bacteria predominate
in community-acquired infections (e.g., S. pneumonia, S.
aureus, H. influenza, Enterobacteriaceae).
o Gram-negative bacilli predominate in hospital-acquired infections (e.g., P.
aeruginosa, Klebsiella spp.).
o Mixed infections with anaerobic organisms may occur
(e.g., Fusobacterium, Peptostreptococcus, Bacteroides).
 Risk factors for aspiration (predispose individuals to reduced epiglottic gag
reflex and dysphagia)
o Altered consciousness: alcohol, sedation, general anesthesia, stroke
o Apoplexy and neurodegenerative conditions 
o Gastroesophageal reflux disease, esophageal motility disorders
o Congenital defects (e.g., tracheoesophageal fistula)
o Use of a nasogastric feeding tube
 Aspiration pneumonitis and pneumonia are unusual following aspiration of tube feeds or

blood, which are typically high-pH and sterile. [36]

Clinical features [36][37]

 Aspiration pneumonitis
o Immediate symptoms: bronchospasms , dyspnea, wheezing
and/or crackles, hypoxemia
o Late symptoms: fever, shortness of breath, cough
 Aspiration pneumonia
o Immediate symptoms: often none 
o Late symptoms: fever, shortness of breath, cough with foul-
smelling sputum

Diagnostics
Clinical diagnosis supported by characteristic laboratory and imaging findings

 Laboratory and microbiological studies: same as for the diagnosis of pneumonia.

 ABG: e.g., ↓ PaO2
 Imaging: The lung region in which the infiltrates are seen depends on the patient's
position on aspiration.    [38][39]
o Supine position: superior segment of the right lower lobe (most common
site of aspiration)
o Standing/sitting: posterior basal segment of the right lower lobe
o Right lateral decubitus position: posterior segment of the right upper lobe
or right middle lobe

The initial CXR may be negative in early aspiration pneumonia. [36]

Treatment [36]

 Acute aspiration: airway management and respiratory support

o Immediate oropharyngeal suctioning 
 o Intubation if there is ongoing risk of aspiration (e.g., post-
extubation, ↓ LOC)
o O2 therapy and inhaled bronchodilators as needed
 Aspiration pneumonitis: typically requires supportive care only
o Antibiotics are usually not required  [11]
o Consider empiric antibiotics for patients with any of the following :
Respiratory failure or suspected septic shock

 Acid suppression medications
 Small bowel obstruction
 Aspiration pneumonia: antibiotic therapy following standard pneumonia
treatment regimens
o Choose agents based on site of acquisition, illness severity, and risk
factors for resistant organisms (see “Empiric antibiotics for CAP“ and
“Empiric antibiotics for HAP”).
o Consider coverage for anaerobic bacteria (e.g., with ampicillin-
sulbactam, moxifloxacin) in patients with severe periodontal disease, lung
abscess, or empyema. [11][36][40]
 All patients: supportive care for pneumonia, monitoring, consider serial imaging.

Aspiration pneumonia requires antibiotic therapy while aspiration pneumonitis typically

self-resolves within 24–48 hours with supportive care alone. [11][41]

Avoid routine anaerobic coverage for aspiration pneumonia without lung

abscess, empyema, or severe periodontal disease. [40]

Complications

 Acute respiratory failure, acute respiratory distress syndrome (ARDS)

 Abscess

Prevention [36]

 Treatment of underlying causes to reduce the risk of aspiration

 NPO status prior to elective procedures with general anesthesia 
  Formal swallowing evaluation when clinically appropriate 
 Aspiration precautions for patients with risk factors for aspiration
o Regular oral care
o Elevation of the head of the bed 
o Dysphagia-modified diet 
o One-on-one observation with meals
o Suctioning equipment at bedside

Complications

 Parapneumonic pleuritis
o Fibrinous pleuritis: inflammation → increased vessel permeability
→ fibrin-rich exudate deposited on the serosal surface of
the pleura → pleuritic chest pain and friction rub
o Analgesics can be used for the relief of symptoms.
 Parapneumonic pleural effusion (common)
 Pleural empyema
 Lung abscess
 ARDS
 Respiratory failure
 Sepsis

Prognosis

 Mortalityincreases with age.

 The mortality risk can be evaluated with the CURB-65 score. [42]
o Score 0: ∼ 1%
o Score 1–2: ∼ 10%
o Score 3: ∼ 14%
o Score 4: ∼ 40%
 HAP is associated with a mortality rate of > 20%.

Prevention

 Pneumococcal vaccination  [43]
 Influenza vaccination  [44]
  Smoking cessation

Tips and links Sources

last updated 02/16/2023