Community-Acquired Pneumonia in Adults

Terminology

Clinical Clarification

• Community-acquired pneumonia in adults is acute infection of the pulmonary parenchyma not acquired in a hospital or other health care facility (patient neither hospitalized nor residing in a long-term care facility for at least 14 days before the onset of symptoms) ^[6]

Classification

• By cause ^[9]

  • Typical

    • Classically caused by Streptococcus pneumoniae, but other pyogenic organisms may cause a similar presentation

    • Characterized both by cough that produces purulent sputum and by lobar consolidation

  • Atypical

    • Caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella species, and respiratory viruses

    • Characterized by dry cough and patchy infiltrates

• By severity level (and site of care) ^[7]

  • Determined by severity of illness scores in combination with clinical judgment and an assessment of the patient’s social support

    • Pneumonia that can be managed in an outpatient setting

    • Pneumonia that should be managed with inpatient admission (general ward)

    • Pneumonia that is severe and should be managed in the ICU

  • Severe community-acquired pneumonia (either major criteria or 3 or more minor criteria) ^[7]

    • Major criteria

      • Need for mechanical ventilation

      • Septic shock with need for vasopressors

    • Minor criteria

      • Respiratory rate of 30 breaths per minute or more

      • Ratio of arterial PaO₂ (partial pressure of oxygen) to fraction of FiO₂ (inspired oxygen) 250 or less

      • Multilobar disease

      • Leukopenia (leukocyte count less than 4000 cells/μL)

      • Uremia (BUN level of 20 mg/dL or higher)

      • Confusion or disorientation

      • Hypothermia (core temperature lower than 36 °C)

      • Thrombocytopenia (platelet count less than 100,000 cells/μL)

      • Hypotension requiring aggressive fluid resuscitation

Diagnosis

Clinical Presentation

History

• Fever may be reported

• Chills, sweating, and/or shivering

• Chest pain with inspiration and coughing

• Cough (productive or nonproductive)

• Dyspnea

• Fatigue

• Myalgia

Physical examination

• General

  • Altered mental status may occur with severe pneumonia, especially in older patients

  • Fever (typically over 38.1 °C)

    • In COVID-19 pneumonia, although fever is typical, it may be low-grade or absent, even in hospitalized patients (especially if vaccinated) ^[10]

  • Signs of respiratory distress

    • Cyanosis, if hypoxemic

    • Tachypnea is a suggestive sign

    • Clinicians should be aware of the COVID-19–related phenomenon of silent (or "happy") hypoxemia: absence of signs of respiratory distress may be misleading

  • Tachycardia occurs with fever and with severe disease

  • Other symptoms that may suggest COVID-19 infection

    • Upper respiratory tract symptoms (eg, rhinorrhea, sneezing, sore throat) may be present in up to 20% of symptomatic infections ^[11]

    • Alteration in smell and/or taste is less common but highly suggestive ^[12]

    • Gastrointestinal symptoms (eg, abdominal pain, nausea, vomiting, diarrhea) are present in 10% to 20% of symptomatic infections ^[10][11]

• Pulmonary

  • Respiratory splinting

  • Palpable fremitus

  • Dullness to percussion

  • Bronchial breath sounds or rales ^[7]

  • Egophony

  • Whispered pectoriloquy

Causes and Risk Factors

Causes

• Common pathogens ^[13][14]

  • Streptococcus pneumoniae (pneumococcus)

  • Mycoplasma pneumoniae

  • Haemophilus influenzae

  • Chlamydia pneumoniae

  • Staphylococcus aureus

  • Legionella species

  • Gram-negative bacilli

  • MRSA

  • Pseudomonas aeruginosa

  • Respiratory viruses

    • SARS-CoV-2 ^[15][16]

    • Influenza A and B viruses

    • Parainfluenza virus

    • Respiratory syncytial virus

    • Adenoviruses

    • Rhinovirus

Risk factors and/or associations

Other risk factors/associations

• Hospitalization and treatment with parenteral antibiotics in the preceding 90 days

  • MRSA, Pseudomonas aeruginosa, resistant gram-negative bacilli

    • Documented history of infection with these organisms

    • Previously regarded as health care–associated pneumonia, infection due to these bacteria is now considered within the spectrum of community-acquired pneumonia ^[7]

• Chronic obstructive pulmonary disease

  • Streptococcus pneumoniae

  • Haemophilus influenzae

  • Moraxella (Branhamella) catarrhalis

  • Legionella species

• Bronchiectasis

  • Pseudomonas aeruginosa

  • Burkholderia cepacia

  • Staphylococcus aureus

• Cystic fibrosis

  • Pseudomonas aeruginosa

    • Most common organism in adults

• Diabetes

  • Staphylococcus aureus

  • Gram-negative organisms

• Renal disease

  • Streptococcus pneumoniae

• Early-stage HIV

  • Streptococcus pneumoniae

  • Haemophilus influenzae

  • Mycobacterium tuberculosis

• Late-stage HIV

  • Pneumocystis jiroveci

  • Cryptococcus species

  • Histoplasma species

• Medical conditions that result in aspiration of nasopharyngeal secretions, food, liquids, or gastric contents

• Alcohol use disorder

  • Streptococcus pneumoniae

  • Klebsiella pneumoniae

  • Anaerobic bacteria

• Asplenia

  • Encapsulated organisms

    • Streptococcus pneumoniae

    • Haemophilus influenzae

• Sickle cell disease

  • Streptococcus pneumonia

  • Haemophilus influenzae

• Poor dental hygiene

  • Anaerobic bacteria

• Smoking

  • Streptococcus pneumonia

  • Haemophilus influenzae

  • Moraxella (Branhamella) catarrhalis

  • Legionella species

• Travel history

  • Travel to area of known outbreak within 2 weeks before illness

    • Legionella species

  • Travel to the southwestern United States within 1 month before illness

    • Coccidioides species

• Exposure to animals

  • Exposure to bats or soil enriched with bird droppings

    • Histoplasma capsulatum

  • Exposure to birds

    • Chlamydia psittaci

  • Exposure to rabbits

    • Francisella tularensis

  • Exposure to farm animals or parturient cats

    • Coxiella burnetii

• Comorbid conditions that have been conclusively associated with increased risk for severe COVID-19 infection include the following (based on systematic review or meta-analysis): ^[17]

  • Chronic kidney disease

  • Chronic liver disease, specifically the following:

    • Cirrhosis

    • Non-alcoholic fatty liver disease

    • Alcoholic liver disease

    • Autoimmune hepatitis

  • Chronic lung disease, specifically the following:

    • Bronchiectasis

    • Chronic obstructive pulmonary disease

    • Interstitial lung disease

    • Pulmonary embolism

    • Pulmonary hypertension

  • Cerebrovascular disease

  • Diabetes type 1 and type 2

  • Malignancy, particularly hematologic malignancies

  • Corticosteroid or other immunosuppressive medication use

  • Cystic fibrosis

  • Tuberculosis

  • Solid organ or blood stem cell transplantation

  • Pregnancy and recent pregnancy

  • Primary immunodeficiencies

  • Obesity (BMI of 30 kg/m² or higher)

  • Cardiac conditions (eg, heart failure, coronary artery disease, cardiomyopathy)

  • Smoking, current and former

  • Mental health disorders (mood disorders and schizophrenia spectrum disorders)

  • Dementia

  • Physical inactivity

Diagnostic Procedures

Primary diagnostic tools

• History and physical examination alone may be sufficient to suggest the diagnosis ^[13]

• Chest radiography or other chest imaging demonstrating an infiltrate confirms the diagnosis ^[13]

• Testing to identify a causative agent is not routine for outpatients, except in certain circumstances ^[13]

• Testing to identify a causative agent (eg, polymerase chain reaction, blood cultures, sputum testing, pleural fluid testing, antigen testing, and/or cultures for fungi and tuberculosis, depending on history and clinical findings) is indicated if any of the following apply: ^[13]

  • Infection with SARS-CoV-2 is suspected or probable

  • Severe pneumonia

  • Pleural effusion and/or a cavitary infiltrate

  • Specific comorbidities (eg, alcohol use disorder, liver disease, leukopenia, chronic lung disease, asplenia)

  • Identification of a suspected pathogen would significantly alter antibiotic choice

  • Failure of outpatient treatment

  • Epidemiologic considerations (eg, outbreaks of public health importance)

• Pulse oximetry assesses hypoxemia ^[13]

• Other laboratory tests—including blood gases, CBC, C-reactive protein, and blood chemistries (including lactate)—may be useful in both determining degree of severity at presentation and managing hospitalized patients ^[13]

• For hospitalized patients, multiplex nucleic acid detection testing for influenza A and B and SARS-CoV-2 is recommended; collect 2 separate specimens if multiplex testing is unavailable ^[18]

  • RSV (respiratory syncytial virus) testing may be considered for selected patients (eg, older adults, patients with congenital cardiac disease, chronic lung disease, immunocompromise)

• Serum procalcitonin has been used to discriminate between infectious and noninfectious causes of pneumonia and between bacterial and viral causes. However, current guidelines do not recommend its use either to determine need for antibacterial therapy or to determine when to discontinue antibiotics ^[7][19]

Laboratory

• Blood gas tests are not routine but are indicated when there is respiratory distress and/or suspicion of carbon dioxide retention

  • PaO₂ or FiO₂ ratio less than 250 suggests the need for ICU admission and/or mechanical ventilation ^[20]

• CBC will reveal leukocytosis in most cases of community-acquired pneumonia

  • Leukopenia (WBC count less than 4000) suggests immunosuppression or severe infection and the need for hospitalization ^[20]

  • Thrombocytopenia (platelet count less than 100,000 cells/mm³) may be present and is associated with poor prognosis ^[13]

• Serum chemistry testing is indicated for hospitalized patients receiving IV fluids and to monitor renal function and glucose levels in patients with severe pneumonia. BUN level can be used as a criterion to determine a CURB-65 score, and lactate level can be used to identify and manage sepsis ^[22][21]

• C-reactive protein

  • C-reactive protein level greater than 30 mg/L, in addition to suggestive symptoms and signs, implies diagnosis of pneumonia ^[19]

• Etiologic testing

  • Blood cultures are indicated for patients with the following: ^[7]

    • Severe community-acquired pneumonia (patients admitted to ICU)

    • Patients being empirically treated for MRSA or Pseudomonas aeruginosa (or other resistant gram-negative bacilli)

    • Patients previously infected with MRSA or Pseudomonas aeruginosa (or other resistant gram-negative bacilli), especially those with history of respiratory tract infection

    • Patients who were hospitalized and received parenteral antibiotics, whether during the hospitalization event or not, in the last 90 days

  • Sputum Gram stain and culture are indicated for the following: ^[7]

    • All ICU patients (severe)

      • Use an endotracheal specimen in intubated patients

    • Patients being empirically treated for MRSA or Pseudomonas aeruginosa (or other resistant gram-negative bacilli)

    • Patients previously infected with MRSA or Pseudomonas aeruginosa (or other resistant gram-negative bacilli), especially those with prior respiratory tract infection

    • Patients who were hospitalized and received parenteral antibiotics, whether during the hospitalization event or not, within the last 90 days

• Pathogen-specific tests

  • SARS-CoV-2 polymerase chain reaction or antigen test

    • Polymerase chain reaction is regarded as the gold standard test for diagnosis ^[23][24]

    • In general, polymerase chain reaction is more sensitive than antigen testing, although specificity is nearly equivalent ^[25]

      • A negative antigen test result may warrant retesting (preferably within 2 days) with polymerase chain reaction if there is a high suspicion for infection based on clinical or epidemiologic indicators

    • Nasopharyngeal, deep nasal (midturbinate), anterior nare, oropharyngeal, or saliva specimens may be submitted for polymerase chain reaction testing; nasopharyngeal wash (or aspirate) or nasal aspirate specimens (using 1-1.5 mL of nonbacteriostatic saline) are also acceptable ^[26]

    • Bronchoalveolar lavage or tracheal aspirate are suitable lower respiratory tract specimens for polymerase chain reaction testing. A deep cough sputum specimen is also acceptable (sputum induction not advised) ^[26]

    • Antigen tests are validated only for use on certain specimens; check manufacturer's specifications

  • Legionella urinary antigen test

    • Indicated for patients with either of the following: ^[7]

      • Severe community-acquired pneumonia

      • In cases where indicated by epidemiologic factors (eg, association with a Legionella outbreak, recent travel)

  • Pneumococcal urinary antigen test (for diagnosis of Streptococcus pneumoniae)

    • Indicated only for patients with severe community-acquired pneumonia ^[7]

  • Influenza test ^[7]

    • Obtain nasal swab samples to test for influenza in patients with suspected viral pneumonia ^[27]

    • Testing for influenza with a rapid influenza molecular assay (ie, influenza nucleic acid amplification test) is preferred over a rapid influenza diagnostic test (ie, antigen test) ^[7]

    • Standard polymerase chain reaction may be used if rapid molecular test is not available. It detects influenza A and B viruses on sputum and endotracheal or bronchoalveolar lavage specimens and confirms positive nasal swab rapid test result in nonepidemic settings ^[28]

  • Respiratory syncytial virus

    • Consider testing for selected patients (eg, older adults, patients with congenital cardiac disease, chronic lung disease, immunocompromise)

    • Real-time reverse transcription-polymerase chain reaction is preferred test and may be performed on upper or lower respiratory tract specimens

  • Fungal culture and tuberculosis testing

    • Indicated for patients with the following:

      • Cavitary infiltrate on chest radiograph ^[13]

      • Persistent cough associated with weight loss, weakness, or night sweats ^[27]

      • Presence of risk factors for tuberculosis (eg, older adults, those who traveled to or reside in tuberculosis-endemic regions, those with low socioeconomic status) ^[27]

  • Serology and/or polymerase chain reaction test may be indicated to confirm the diagnosis of pathogens such as Chlamydia, Legionella, or Mycoplasma pneumoniae ^[27]

Imaging

• Chest radiography ^[13]

  • Routine investigation for evaluation of pneumonia in adults

  • Results may be negative, especially with dehydration

  • Lung infiltrate is the hallmark finding

  • May demonstrate alveolar filling with inflammatory exudate or interstitial thickening

  • Pleural effusion may be present

  • With COVID-19, usually shows bilateral involvement, varying from consolidation in more severely ill patients to ground-glass opacities in less severe cases

• Lung ultrasonography ^[29][30]

  • Accurate alternative to chest radiography that may be performed at bedside in emergency department setting or in critically ill patients ^[31][32]

  • May be used as adjunctive means of diagnosing pneumonia, especially in patients with baseline chest radiograph abnormalities

• CT ^[31]

  • More sensitive than plain radiographs for detecting pneumonia

  • Consider if clinical suspicion for pneumonia remains high despite negative chest radiography findings

  • Better at visualizing upper lobes and lingula, necrotizing infection, multilobar disease, interstitial infiltrates due to atypical pathogens, empyema, and pleural involvement

  • Useful for excluding tuberculosis or lung cancer

  • Can help differentiate COVID-19 pneumonia from other viral pneumonias ^[15]

Procedures

Diagnostic thoracentesis ^[13]

General explanation

• Insertion of a small-gauge needle between the ribs, through the thorax, and into the pleural space to access pleural fluid for diagnostic purposes

• Procedure can be performed with or without ultrasonographic guidance

Indication

• Pleural effusions greater than 5 cm high on a lateral view chest radiograph

Contraindications

• No absolute contraindications

• Relative

  • Uncorrected coagulopathy

  • Small effusion with secure clinical diagnosis

  • Mechanically ventilated patient

  • Perform bilateral thoracentesis only after ensuring absence of pneumothorax in the first side

Complications ^[33]

• Pain at puncture site

• Bleeding (eg, hematoma, hemothorax, hemoperitoneum)

• Pneumothorax

• Re-expansion pulmonary edema

• Infection (eg, empyema, soft tissue infection)

• Spleen or liver puncture

• Vasovagal events

• Retained intrapleural catheter fragments

Interpretation of results

• Pleural fluid analysis

  • Obtain pH, glucose, Gram stain, and aerobic and anaerobic cultures ^[34]

    • Parapneumonic effusion and empyema are exudative

      • Protein level higher than 3 g/dL

      • Ratio of pleural fluid protein to serum protein greater than 0.5

      • Lactate dehydrogenase level higher than 200 units/L

      • Ratio of pleural fluid lactate dehydrogenase to serum lactate dehydrogenase higher than 0.6

      • Glucose level lower than 60 mg/mL

    • pH is generally low

    • WBC count may exceed 50,000 cells/mm³ with neutrophils predominating

  • Fluid can be saved for further analysis based on initial results

  • Other pleural fluid testing (eg, cytology) based on clinical suspicion

Differential Diagnosis

Most common

• Bronchitis

  • Presents with fever, malaise, productive cough, hoarseness, chest pain, and muscle pain

  • Differentiated by chest radiography and physical examination

    • No radiographic evidence of pulmonary pathology

    • Signs of consolidation (eg, rales, egophony, fremitus) indicative of pneumonia will be absent

• Seasonal influenza

  • Sudden onset of high fever with chills, myalgia, or malaise

  • Dry cough, sneezing, sore throat, nasal discharge, and substernal soreness

  • History of contact with an infected person

  • Viral infection present in the winter season

  • Differentiated by history and laboratory testing

    • Antigen detection test using nasopharyngeal secretion will help in detecting type A and type B viral antigens

• Asthma

  • Patient may present with recurrent attacks of dyspnea with wheezing or accessory muscle use

  • Differentiated by history (absence of fever), chest radiography, spirometry or pulmonary function testing, and response to bronchodilators

• Chronic obstructive pulmonary disease

  • Patients present with dyspnea, pursed lip breathing, or use of accessory muscles for breathing

  • Other features include chronic productive cough, cyanosis, tachycardia, and tachypnea

  • Differentiated by history, chest radiography, and spirometry or pulmonary function testing

    • Spirometry shows abnormal diffusing capacity, fixed reduction in FEV1, and increased total lung capacity and/or residual volume in patients with chronic obstructive pulmonary disease

    • Chest radiography shows hyperinflation with flattened diaphragm, tenting of the diaphragm at the rib, and increased retrosternal chest space in patients with chronic obstructive pulmonary disease

• Congestive heart failure

  • Characterized by the following:

    • Dyspnea

    • Fatigue

    • Exercise intolerance

    • Fluid retention

  • Differentiated by the following:

    • Chest radiography showing the following:

      • Pulmonary edema

      • Pleural effusion

      • Pulmonary venous congestion

      • Chamber dilation

      • Kerley B lines

      • Cardiomegaly

    • Echocardiography showing abnormalities with cardiac structure and function

• Pneumothorax

  • Sudden onset of breathlessness and chest pain

  • Differentiated by history, physical examination, and chest radiography

    • Chest radiography will reveal air in the pleural space

• Pulmonary embolism

  • Blocking of pulmonary artery by thrombus

  • Patients present with dyspnea and pleuritic chest pain but usually do not have a fever or cough productive of purulent sputum

  • Calf tenderness and swelling may be present if embolism was caused by deep venous thrombosis

  • Differentiated by history, physical examination, and imaging

    • Chest CT shows filling defects in the pulmonary arteries

• Tuberculosis

  • Patients present with weight loss, night sweats, and cough

  • Travel to or residence in a tuberculosis-infected endemic area or advanced age (born early 20th century during worldwide endemicity)

  • Differentiated by history, laboratory testing, and imaging

    • Positive tuberculin test result

    • Chest radiography findings of reactivation disease (usually in older patients) showing upper-lobe predominance or cavity, and/or granuloma formation

    • Chest radiography of primary tuberculous pneumonia (usually in in younger patients) showing hilar adenopathy, and/or pleural effusion (sometimes massive)

Treatment

Goals

• Eradicate infection

• Relieve symptoms and provide supportive care as needed

• Prevent disease progression and complications

Disposition

Admission criteria

Use severity of illness scores combined with clinical judgment to determine if patient can be safely managed as outpatient or should be managed as inpatient. 2019 guidelines recommend Pneumonia Severity Index preferentially over CURB-65 criteria ^[7]

• Pneumonia Severity Index ^[35]

  • Uses a point system of several variables, including patient age, vital signs, mental status, and the presence of comorbid conditions (eg, neoplastic disease, liver disease, chronic heart failure, cerebrovascular disease, renal disease)

  • Classifies patients into a mortality risk level

    • Class I and II patients (fewer than 70 points) may be treated as outpatients

    • Class III patients should be treated in an observation unit or briefly hospitalized (71-90 points)

    • Class IV (91-130 points) and V (greater than 130 points) should be treated as inpatients

• CURB-65 criteria ^[1]

  • Patients receive 1 point for each of the following indicators:

    • Confusion (compared to baseline)

    • BUN greater than 19 mg/dL (urea greater than 7 mmol/l)

    • Respiratory rate at least 30 breaths per minute

    • Systolic blood pressure less than 90 mm Hg or diastolic blood pressure of 60 mm Hg or less

    • Age 65 years or older

  • Inpatient admission is recommended for patients with a score of 2 or more

  • Most patients with a score of 1 can be managed as outpatients; consider overnight observation for some patients

• Studies of specific biomarkers used to identify high-risk patients have not proven more accurate than these scoring systems ^[36]

For COVID-19 pneumonia

• Nonsevere pneumonia: admission criteria include radiographic evidence of pneumonia, progressive clinical illness, risk factors for severe disease, and inadequate care at home. CDC provides further guidance ^[37]

• More severe or critical respiratory tract disease requires ICU admission ^[38]

• Follow recommended infection prevention and control practices ^[39]

Consider inpatient admission for patients otherwise meeting criteria for outpatient treatment but who are unable to safely and reliably take medication orally or who have insufficient personal support ^[27]

Criteria for ICU admission

• Recommended with either major criteria or 3 or more minor criteria (severe community-acquired pneumonia) ^[7]

  • Major criteria

    • Need for mechanical ventilation

    • Septic shock with need for vasopressors

  • Minor criteria

    • Respiratory rate of 30 breaths per minute or more

    • Ratio of arterial PaO₂ to FiO₂ (fraction of inspired oxygen) of 250 or less

    • Multilobar disease

    • Leukopenia (leukocyte count less than 4000 cells/μL)

    • Uremia (BUN level of 20 mg/dL or higher)

    • Confusion or disorientation

    • Hypothermia (core temperature lower than 36 °C)

    • Thrombocytopenia (platelet count fewer than 100,000 cells/μL)

    • Hypotension requiring aggressive fluid resuscitation

• Pneumonia prognostic prediction tools have also been used in practice to determine level of in-hospital care; ICU is appropriate in the following patients: ^[31]

  • Pneumonia severity index: class V (greater than 130 points)

  • CURB-65 score of 4 or 5^[1]

• For severe COVID-19 pneumonia

  • Admit patients with severe or critical respiratory tract disease to an intensive care environment ^[38]

    • Tachypnea (respiratory rate greater than 30 breaths or less than 10 breaths per minute), severe respiratory distress, inadequate oxygenation (eg, SpO₂ less than 92%)

    • Presence of severe complications (eg, septic shock, acute respiratory distress syndrome)

Recommendations for specialist referral

• Refer to pulmonologist for the following:

  • Respiratory failure requiring noninvasive and positive pressure ventilation or intubation and mechanical ventilation

  • Worsening hypoxemia

  • Pleural effusion requiring chest tube drainage

  • Nonresolving pneumonia (characterized by persistent fever and absence of clinical improvement)

  • Bronchoscopic sampling, if necessary

• Refer to infectious disease specialist for assistance with identification of causative agent and antibiotic management of severe pneumonia or pneumonia that does not respond to empiric antibiotics

Treatment Options

Determine the optimal care setting using severity of illness scores and clinical judgment ^[7]

For COVID-19 pneumonia

• Until a diagnosis of COVID-19 is confirmed by polymerase chain reaction or antigen test, administer appropriate antimicrobial therapy for other viral pathogens (eg, influenza virus) or bacterial pathogens in accordance with severity of clinical disease, site of acquisition (hospital or community), epidemiologic risk factors, and local antimicrobial susceptibility patterns ^[18][23]

• WHO , NIH , and Surviving Sepsis Campaign provide specific guidance for management of COVID-19^{[23][18][40][41]}

• Current standard treatment options include infection control measures, routine supportive care, and medications including antivirals, monoclonal antibodies, immunomodulators, corticosteroids, and, for selected patients, therapeutic or prophylactic anticoagulation ^[40]

• Antivirals and monoclonal antibodies directed at viral components are most effective when used early in the course of infection (to prevent cell entry and viral replication); antiinflammatory drugs (eg, dexamethasone) and immunomodulators are of most benefit during the hyperinflammatory response in later phases of severe disease

For non–COVID-19 pneumonias: begin empiric therapy based on treatment setting; in patients admitted to the hospital, give first antimicrobial dose before patient leaves emergency department

• Outpatient treatment

  • First line therapy for patients without comorbidities or risk factors for antibiotic-resistant pathogens includes amoxicillin or doxycycline or a macrolide (only in areas with pneumococcal resistance to macrolides less than 25%) ^[7]

  • For outpatient adults with the following comorbidities, antibiotic options include combination therapy or monotherapy ^[7]

    • Comorbidities include: ^[7]

      • Chronic heart, lung, liver, or renal disease

      • Diabetes

      • Alcohol use disorder

      • Active malignancy

      • Asplenia

    • Combination therapy ^[7]

      • Amoxicillin-clavulanate or a cephalosporin (eg, cefpodoxime, cefuroxime), and

      • Macrolide or doxycycline

    • Monotherapy ^[7]

      • Respiratory fluoroquinolone

  • Start treatment with oral oseltamivir in patients with suspected or confirmed influenza as soon as possible, independent of duration of illness before diagnosis ^[7][42]

• General ward inpatient treatment (nonsevere community-acquired pneumonia without risk factors for MRSA, Pseudomonas aeruginosa, or resistant gram-negative bacilli) ^[7]

  • Monotherapy with an appropriate respiratory fluoroquinolone, or ^[7][43]

  • A β-lactam plus a macrolide may be used ^[7][43]

    • Doxycycline may be used in place of a macrolide ^[7]

  • A systematic review showed either monotherapy with a respiratory quinolone or combination therapy with a β-lactam plus a macrolide to be superior to β-lactam monotherapy in patients requiring hospitalization ^[44]

  • Start treatment with oral or enterically administered oseltamivir for hospitalized patients with suspected or confirmed influenza as soon as possible, independent of duration of illness before diagnosis; because patients with influenza often have concurrent bacterial infection, administer recommended antibacterial antibiotics, pending culture results ^[7][42]

  • 2019 guidelines recommend clinicians only cover empirically for MRSA or Pseudomonas aeruginosa in adults with community-acquired pneumonia if locally validated risk factors for either pathogen are present. Infectious Diseases Society of America guidelines do not recommend empiric coverage (pending culture results) for these organisms based on individual risk factors in patients with nonsevere pneumonia ^[7]

    • Empiric treatment options for MRSA include vancomycin or linezolid ^[7]

    • Empiric treatment options for Pseudomonas aeruginosa include piperacillin-tazobactam, cefepime, ceftazidime, aztreonam, meropenem, or imipenem ^[7]

• ICU inpatient treatment (severe community-acquired pneumonia without risk factors for MRSA or Pseudomonas aeruginosa) ^[7]

  • β-Lactam plus a macrolide ^[7]

  • Alternatively, a β-lactam plus a respiratory fluoroquinolone may be used ^[7]

  • Start treatment with oral or enterically administered oseltamivir for patients with suspected or confirmed influenza, independent of duration of illness before diagnosis; because concurrent bacterial infection is common with influenza, administer recommended antibacterial antibiotics, pending culture results ^[7]

  • 2019 American Thoracic Society and Infectious Diseases Society of America guidelines recommend clinicians only cover empirically for MRSA or Pseudomonas aeruginosa in adults with community-acquired pneumonia if locally validated risk factors for either pathogen are present. Absent these, clinicians may treat patients with severe pneumonia empirically for these pathogens if history of recent (90 days) hospitalization and parenteral antibiotic treatment or documented past infection with these pathogens. De-escalate antibiotics if indicated by culture results ^[7]

    • Empiric treatment options for MRSA include vancomycin or linezolid ^[7]

    • Empiric treatment options for Pseudomonas aeruginosa include: ^[7]

      • Piperacillin-tazobactam

      • Cefepime

      • Ceftazidime

      • Aztreonam

      • Meropenem

      • Imipenem

General considerations

• 2019 guidelines recommend that duration of antibiotic therapy be guided by a validated measure of clinical stability. Continue antibiotic therapy until patient achieves stability and for at least 5 days ^[7]

  • Indicators of clinical stability ^[45]

    • Temperature of 37.8 °C or lower

    • Heart rate of 100 beats per minute or fewer

    • Respiratory rate of 24 breaths per minute or fewer

    • Systolic blood pressure of 90 mm Hg or higher

    • Arterial oxygen saturation of 90% or higher or PO₂ of 60 mm Hg or higher on room air

    • Ability to maintain oral intake

    • Normal mental status

• Most patients will achieve clinical stability within the first 48 to 72 hours; thus, a total duration of therapy of 5 days should be appropriate for most patients ^[7][46]

  • 2019 guidelines suggest duration of therapy for community-acquired pneumonia due to suspected or proven MRSA or Pseudomonas aeruginosa should be 7 days ^[7]

  • Other pathogens or clinical circumstances may require a longer duration:

    • Initial therapy is not effective against identified pathogen ^[7]

    • Staphylococcus aureus lobar pneumonia (2 weeks) ^[31]

    • Staphylococcus aureus bacteremia (4 weeks, IV) ^[31]

    • Mycoplasma pneumoniae or Chlamydia pneumoniae (10-14 days) ^[31]

    • Legionella (14-21 days) ^[31]

    • Complications caused by extrapulmonary infections (eg, meningitis, endocarditis) ^[7]

• If there is no improvement within 72 hours of initiation of the empiric treatment, there may be drug resistance, an unsuspected pathogen, or unrecognized complications (eg, endobronchial obstruction, empyema)

• When culture and antibiotic susceptibility results are available, adjust antibiotics to specific, narrow-spectrum therapy ^[7]

• Treatment can be switched from IV to oral once hemodynamic stability and clinical improvement are seen ^[7]

• Use of adjunctive corticosteroids remains controversial and clinical studies have produced conflicting reports. They may be considered in some cases of severe pneumonia, particularly with septic shock ^[7][31][43]

  • 2019 Infectious Diseases Society of America guidelines recommend not routinely using corticosteroids in adults with nonsevere community-acquired pneumonia and suggest not routinely using corticosteroids in adults with severe community-acquired pneumonia or severe influenza pneumonia ^[7]

  • 2019 Infectious Diseases Society of America guidelines endorse the Surviving Sepsis Campaign recommendations on the use of steroids in patients with septic shock refractory to adequate fluid resuscitation and vasopressor support ^[47][7]

Drug therapy

• Antibiotics ^[14]

  • Macrolides

    • First line therapy for outpatient treatment; used in combination with other antibiotics in the inpatient setting

    • Azithromycin

      • Azithromycin Oral tablet; Outpatient Adults: 500 mg PO on day 1, followed by 250 mg PO once daily for at least 5 days.

      • Azithromycin Oral tablet; Hospitalized Adults: 500 mg PO once daily for at least 5 days.

      • Azithromycin Solution for injection; Adults: 500 mg IV once daily for at least 5 days.

    • Clarithromycin

      • Clarithromycin Oral tablet; Adults: 500 mg PO every 12 hours for at least 5 days.

  • Tetracyclines

    • Acceptable alternative to macrolides

    • Doxycycline

      • Doxycycline Hyclate Oral tablet; Adults: 100 mg PO every 12 hours for at least 5 days.

      • Doxycycline Hyclate Solution for injection; Adults: 100 mg IV every 12 hours for at least 5 days.

  • Quinolones

    • Respiratory quinolones (ie, gemifloxacin, moxifloxacin, levofloxacin, delafloxacin) are first line outpatient therapy for patients with community-acquired pneumonia who are at risk for multidrug-resistant Streptococcus pneumoniae

    • Gemifloxacin

      • Gemifloxacin Oral tablet; Adults: 320 mg PO once daily for at least 5 days.

    • Moxifloxacin

      • Moxifloxacin Hydrochloride Oral tablet; Adults: 400 mg PO once daily for at least 5 days.

      • Moxifloxacin Hydrochloride Solution for injection; Adults: 400 mg IV once daily for at least 5 days.

    • Levofloxacin

      • Levofloxacin Oral tablet; Adults: 750 mg PO every 24 hours for at least 5 days.

      • Levofloxacin Solution for injection; Adults: 750 mg IV every 24 hours for at least 5 days.

    • Delafloxacin

      • Delafloxacin Oral tablet; Adults: 450 mg PO every 12 hours for 5 to 10 days.

      • Delafloxacin Solution for injection; Adults: 300 mg IV every 12 hours for 5 to 10 days.

  • Penicillins

    • Frequently used in combination regimens in both outpatient and inpatient settings

    • Amoxicillin

      • Amoxicillin Trihydrate Oral tablet; Adults: 1 g PO every 8 hours for at least 5 days.

    • Amoxicillin-clavulanate

      • Amoxicillin Trihydrate, Clavulanate Potassium Oral tablet; Adults: 875 mg amoxicillin with 125 mg clavulanate PO every 12 hours or 500 mg amoxicillin with 125 mg clavulanate PO every 8 hours for at least 5 days.

      • Amoxicillin Trihydrate, Clavulanate Potassium Oral tablet, extended-release; Adults: 2,000 mg amoxicillin with 125 mg clavulanate PO every 12 hours for at least 5 days.

    • Ampicillin-sulbactam

      • Ampicillin Sodium, Sulbactam Sodium Solution for injection; Adults: 1.5 g (1 g ampicillin and 0.5 g sulbactam) or 3 g (2 g ampicillin and 1 g sulbactam) IV every 6 hours for at least 5 days.

    • Piperacillin-tazobactam

      • Piperacillin Sodium, Tazobactam Sodium Solution for injection; Adults: 4.5 g (4 g piperacillin and 0.5 g tazobactam) IV every 6 hours for at least 7 days.

  • Cephalosporins

    • Frequently used in combination regimens in both outpatient and inpatient settings

    • Cefuroxime

      • Cefuroxime Axetil Oral tablet; Adults: 500 mg PO every 12 hours for at least 5 days.

    • Cefpodoxime

      • Cefpodoxime Proxetil Oral tablet; Adults: 200 mg PO every 12 hours for at least 5 days.

    • Ceftriaxone

      • Ceftriaxone Sodium Solution for injection; Adults: 1 to 2 g IV every 24 hours for at least 5 days.

    • Cefotaxime

      • Cefotaxime Sodium Solution for injection; Adults: 1 to 2 g IV every 8 hours for at least 5 days.

    • Ceftaroline

      • Ceftaroline fosamil Solution for injection; Adults: 600 mg IV every 12 hours for at least 5 days.

    • Cefepime

      • Cefepime Hydrochloride Solution for injection; Adults: 2 g IV every 8 hours for at least 7 days.

    • Ceftazidime

      • Ceftazidime Sodium Solution for injection; Adults: 2 g IV every 8 hours for at least 7 days.

  • Carbapenems

    • Used in combination regimens in inpatient and ICU settings to manage seriously ill patients with community-acquired pneumonia; imipenem-cilastatin and meropenem also provide coverage for suspected Pseudomonas infection

    • Imipenem-cilastatin

      • Imipenem, Cilastatin Sodium Solution for injection; Adults: 500 mg IV every 6 hours for at least 7 days.

    • Meropenem

      • Meropenem Solution for injection; Adults: 1 g IV every 8 hours for at least 7 days.

  • Monobactams

    • Used in combination regimens in inpatient and ICU settings to manage seriously ill patients with community-acquired pneumonia who are allergic to penicillin

    • Aztreonam

      • Aztreonam Solution for injection; Adults: 2 g IV every 8 hours for at least 7 days.

  • Glycopeptides

    • Used for the treatment of MRSA and penicillin-resistant pneumococci

    • Vancomycin

      • Vancomycin Hydrochloride Solution for injection; Adults: 20 to 35 mg/kg/dose (Max: 3,000 mg/dose) IV loading dose, followed by 15 to 20 mg/kg/dose IV every 8 to 12 hours for at least 7 days; adjust dose based on target PK/PD parameter. Consider loading dose in critically ill patients.

  • Oxazolidinones

    • Used for treatment of infections due to aerobic gram-positive bacteria, including MRSA and penicillin-resistant pneumococci

    • Linezolid

      • Linezolid Oral tablet; Adults: 600 mg PO every 12 hours for at least 7 days.

      • Linezolid Solution for injection; Adults: 600 mg IV every 12 hours for at least 7 days.

  • Pleuromutilin

    • Lefamulin ^[48]

      • First-in-class antibiotic approved to treat community-acquired pneumonia

      • Lefamulin Oral tablet; Adults: 600 mg PO every 12 hours for 5 days.

      • Lefamulin Solution for injection; Adults: 150 mg IV every 12 hours for 5 to 7 days.

• Antiviral agent ^[14][42]

  • Antiviral agents are recommended for patients with confirmed or suspected influenza who have severe, complicated, or progressive illness; who are hospitalized; or who are at high risk for complications, regardless of time since symptom onset. Can be considered for previously healthy, symptomatic outpatients not at high risk for influenza complications if initiated within 48 hours of onset of symptoms

  • Neuraminidase inhibitors

    • Oseltamivir

      • Oseltamivir Phosphate Oral capsule; Adults: 75 mg PO twice daily for 5 days.

Nondrug and supportive care

Supplemental oxygen or mechanical ventilation ^[49]

• May be required in patients with severe pneumonia or underlying cardiopulmonary disease

• Maintain oxygen saturation within 94% to 98% in patients with hypoxemia ^[43]

Respiratory therapy

• Postural drainage facilitated by chest percussion may be helpful in patients who have difficulty mobilizing respiratory secretions

Breathing exercises

• Strengthen the chest wall muscles; beneficial particularly to sedentary patients

• Help patients mobilize secretions to improve expectoration

Venous thromboembolism prophylaxis ^[43]

• Low-molecular-weight heparin is recommended in patients at high risk

• Early ambulation is recommended

Smoking cessation ^[50]

• Advise patients to quit smoking, using counseling and pharmacologic approaches recommended in tobacco cessation guidelines and reviews ^[50][51]

Procedures

Therapeutic thoracentesis

General explanation

• Drainage of pleural fluid for therapeutic (versus diagnostic) purposes

  • Relieves dyspnea caused by a large parapneumonic effusion

  • Evacuation of purulent fluid is essential for treatment of empyema

Indication

• Parapneumonic pleural effusion ^[13]

  • Fluid more than 5 cm high on lateral view of an upright chest radiograph or more than 10 mm of fluid on lateral decubitus view

• Pleural fluid drainage by chest tube is recommended in cases of empyema ^[52]

  • Pleural fluid pH is less than 7.28

  • Pleural fluid glucose level is less than 40 mg/dL

  • Ratio of pleural fluid to serum glucose is less than 0.5

  • Pleural fluid lactate dehydrogenase level is greater than 1000 units/L

Contraindications

• No absolute contraindications

• Relative

  • Uncorrected coagulopathy

  • Mechanically ventilated patient

  • Perform bilateral thoracentesis only after ensuring absence of pneumothorax in the first side

Complications ^[33]

• Pain at puncture site

• Bleeding (eg, hematoma, hemothorax, hemoperitoneum)

• Pneumothorax

• Re-expansion pulmonary edema

• Infection (eg, empyema, soft tissue infection)

• Spleen or liver puncture

• Vasovagal events

• Retained intrapleural catheter fragments

Comorbidities

• Patients with comorbid disorders such as neoplastic disease, liver disease, congestive heart failure, cerebrovascular disease, or renal disease are likely to require hospital admission and IV antibiotics, at least initially

• Immunocompromised patients

  • Prone to multiorganism pneumonia, including unusual pathogens such as cytomegalovirus, Pneumocystis jiroveci, and fungal infection

  • Microbiologic diagnosis may require bronchoscopy with biopsy, immunohistology, and quantitative molecular assays

  • Begin empiric therapy as soon as possible based on epidemiologic history, sputum Gram stain, previous courses of antimicrobial agents, and historical microbiologic data

• Pneumonia caused by SARS-CoV-2 is a prominent feature of COVID-19; clinicians must consider whether treatment for additional potential causes of community-acquired pneumonia is appropriate ^[16]

Special populations

• Older patients

  • Classic signs and symptoms may be absent or altered in older patients

    • Presentation may include nonspecific symptoms such as confusion ^[27]

  • May recover more slowly compared with younger patients

  • Aspiration is an important risk factor for community-acquired pneumonia in older patients

• Pregnant patients

  • Prone to preterm labor and delivery

  • Prone to pulmonary edema

  • Acidosis and hypoxic state are poorly tolerated by the fetus

  • High risk for severe influenza

  • Treat with pregnancy-safe antibiotics

    • Azithromycin or erythromycin with or without ceftriaxone, depending on severity of illness; antiviral neuraminidase inhibitor for influenza

    • Antibiotics to be avoided in pregnancy include doxycycline, fluoroquinolones, and clarithromycin

    • Lefamulin may cause fetal harm when administered during pregnancy; effective contraception use is recommended for patients of reproductive potential

Monitoring

• 2019 guidelines recommend against routinely obtaining follow-up chest imaging in adults with community-acquired pneumonia whose symptoms have resolved within 5 to 7 days ^[7]

• In hospitalized patients with confirmed COVID-19, repeated testing may be done to document clearance of virus, defined as 2 consecutive negative results on polymerase chain reaction at least 24 hours apart ^[39]

Complications and Prognosis

Complications

• Reduction in breathing capacity requiring mechanical ventilation

• Empyema or lung abscess secondary to inadequately treated pleural effusion

• Systemic complications (eg, sepsis, meningitis, bacteremia, endocarditis)

• Pneumonia may recur in recently treated patients, particularly in high-risk groups (eg, older patients, patients who smoke, patients who have alcohol use disorder, immunosuppressed patients, patients with bronchopulmonary anatomic abnormalities)

Prognosis

• Outcomes are improved through early diagnosis and timely administration of antibiotics ^[8][53]

  • Treatment within 4 to 6 hours of hospital arrival reduces mortality

• Patients with a CURB-65 score of 0 to 1 or a Pneumonia Severity Index risk class of I and II are at low risk of mortality. Mortality rate is higher in patients with higher scores or risk class^[1]

• Infections due to Staphylococcus aureus or gram-negative bacilli and aspiration pneumonia are associated with high mortality rates for all populations

• Incorrect diagnosis, comorbidities, inappropriate medication dose or route of administration, presence of an unusual or unanticipated pathogen, adverse drug reactions, or complications negatively affect prognosis

• With COVID-19 pneumonia, patients who require hospital admission often require prolonged inpatient stay (more than 20 days) and experience significant deconditioning. Infection fatality ratio (proportion of deaths among all who are infected, including confirmed cases, undiagnosed cases, and unreported cases) varies across global locations but has been estimated as 0.15% ^[10][11][54]

Screening and Prevention

Prevention

• Tobacco use

  • Smoking cessation is important for preventing pneumonia, especially in older patients ^[55]

• Immunization

  • Pneumococcal vaccine

    • In the United States, 2 formulations have historically been available: PCV13 (13-valent pneumococcal conjugate vaccine) and PPSV23 (pneumococcal polysaccharide vaccine); in 2021, PCV20 (20-valent pneumococcal conjugate vaccine) and PCV15 (15-valent pneumococcal conjugate vaccine) were licensed by FDA for adults aged 18 years or older; in 2024, the ACIP recommended PCV21 (21-valent pneumococcal conjugate vaccine) as an option for adults aged 19 years or older who are currently recommended to receive PCV15 or PCV20 ^[56][57]

    • ACIP recommends PCV15, PCV20, or PCV21 for adults aged 50 years or older who have not received pneumococcal conjugate vaccine and for adults aged 19 to 49 years with certain underlying conditions ^[2][56][57]

      • Adults aged 50 years or older who have not previously received pneumococcal conjugate vaccine or whose earlier vaccination history is unknown should receive 1 dose of pneumococcal conjugate vaccine (PCV21, PCV20, or PCV15) ^[2][56]

      • Adults aged 50 years or older who have an immunocompromising condition, cochlear implant, or cerebrospinal fluid leak should receive 1 dose of PCV15, PCV20, or PCV21 ^[2][56]

      • Adults aged 19 to 49 years with certain underlying medical conditions or other risk factors who have not previously received pneumococcal conjugate vaccine or whose earlier vaccination history is unknown should receive 1 dose of pneumococcal conjugate vaccine (PCV21, PCV20, or PCV15) ^[2][56]

      • For both age groups (19 years and older), if PCV15 is used, it should be followed by a dose of PPSV23 at least 1 year later (a minimum interval of 8 weeks can be considered for adults who have an immunocompromising condition, cochlear implant, or cerebrospinal fluid leak) ^[2][56]

      • For adults who have previously received only PPSV23, pneumococcal conjugate vaccine (PCV21, PCV20, or PCV15) may be administered at least 1 year after their last PPSV23 dose ^[2][56]

        • When PCV15 is used for those with the history of receiving PPSV23, it does not need to be followed by another dose of PPSV23 ^[57]

      • For adults who only received PCV13, administer single dose of PCV21 or PCV20 at least 1 year following PCV13 ^[2][56]

      • For adults who received PCV13 at any age and PPSV23 before age 65 years, administer PCV21 or PCV20 at least 5 years after the last pneumococcal vaccine ^[2][56]

      • For adults who received PCV13 at any age and PPSV23 at age 65 years or older, use shared decision-making to determine administration of PCV21 or PCV20 at least 5 years since the last pneumococcal vaccine ^[2][56]

      • For adults aged 19 to 49 years with immunocompromising condition, cochlear implant, or cerebrospinal fluid leak who received PCV13 and 1 dose of PPSV23, administer a single dose of PCV21 or PCV20 at least 5 years after the last pneumococcal vaccine ^[2][56]

      • For adults aged 19 to 49 years with immunocompromising condition, cochlear implant, or cerebrospinal fluid leak who received PCV13 and 2 doses of PPSV23, pneumococcal vaccination recommendations should be reviewed again at age 50 years; alternatively, a single dose of either PCV21 or PCV20 can be administered at least 5 years after the last pneumococcal vaccine ^[2]

      • For adults aged 19 to 49 years with chronic medical conditions who received PCV13 and 1 dose of PPSV23, pneumococcal vaccination recommendations should be reviewed again at age 50 years ^[2]

    • ACIP considers the following to be underlying medical conditions or risk factors for adults in the 19- to 49-year age group: ^[2]

      • Alcoholism; chronic heart, liver, or lung disease; chronic renal failure; cigarette smoking; cochlear implant; congenital or acquired asplenia; cerebrospinal fluid leak; diabetes mellitus; generalized malignancy; HIV; Hodgkin disease; immunodeficiency; iatrogenic immunosuppression; leukemia, lymphoma, or multiple myeloma; nephrotic syndrome; solid organ transplant; sickle cell disease; or other hemoglobinopathies ^[2]

  • Influenza vaccination

    • Annual seasonal influenza vaccination is recommended for all adults without contraindications ^[3]

  • COVID-19

    • CDC recommends vaccination with updated (2024–2025 formula) COVID-19 vaccine for all adults; refer to published administration schedules ^[4]

  • RSV vaccine

    • 3 vaccines have been approved for prevention of RSV-associated lower respiratory tract disease in adults aged 60 years or older: an adjuvanted recombinant stabilized prefusion F protein vaccine (Arexvy), a recombinant stabilized prefusion F protein vaccine (Abrysvo), and an mRNA vaccine (mResvia) ^[5]

    • ACIP recommends a single dose of FDA-approved RSV vaccine for all adults aged 75 years or older, and for adults 60 to 74 years of age with increased risk of severe RSV disease ^[5]

• Dental hygiene

  • Lack of good dental hygiene is a risk factor for community-acquired pneumonia; periodic dental hygiene checks are recommended