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Community-Acquired Pneumonia


Sanjay Sethi

, MD, University at Buffalo SUNY

Last full review/revision Dec 2020| Content last modified Dec 2020

Community-acquired pneumonia is defined as pneumonia that is acquired outside the hospital. The most commonly identified pathogens are Streptococcus pneumoniae, Haemophilus influenzae, atypical bacteria (ie, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella species), and viruses. Symptoms and signs are fever, cough, sputum production, pleuritic chest pain, dyspnea, tachypnea, and tachycardia. Diagnosis is based on clinical presentation and chest x-ray. Treatment is with empirically chosen antibiotics. Prognosis is excellent for relatively young or healthy patients, but many pneumonias, especially when caused by S. pneumoniae, Legionella, Staphylococcus aureus, or influenza virus, are serious or even fatal in older, sicker patients.

(See also Overview of Pneumonia.)

Etiology of Community-Acquired Pneumonia

Many organisms cause community-acquired pneumonia, including bacteria, viruses, and fungi. Pathogens vary by patient age and other factors (see table Community-Acquired Pneumonia in Adults), but the relative importance of each as a cause of community-acquired pneumonia is uncertain because most patients do not undergo thorough testing, and because even with testing, specific agents are identified in < 50% of cases.

Bacterial causes

The most common bacterial causes are

Pneumonias caused by chlamydia and mycoplasma are often clinically indistinguishable from other pneumonias.

C. pneumoniae accounts for 2 to 5% of community-acquired pneumonia and is the 2nd most common cause of lung infections in healthy people aged 5 to 35 years. C. pneumoniae is commonly responsible for outbreaks of respiratory infection within families, in college dormitories, and in military training camps. It causes a relatively benign form of pneumonia that infrequently requires hospitalization. Chlamydia psittaci pneumonia (psittacosis) is rare and occurs in patients who own or are often exposed to psittacine birds (ie, parrots, parakeets, macaws).

Since the year 2000, the incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections has increased markedly. This pathogen can rarely cause severe, cavitating pneumonia and tends to affect young adults.

S. pneumoniae and MRSA can cause necrotizing pneumonia.

P. aeruginosa is an especially common cause of pneumonia in patients with cystic fibrosis, neutropenia, advanced acquired immunodeficiency syndrome (AIDS), and/or bronchiectasis. Another risk factor for P. aeruginosa pneumonia is hospitalization with receipt of IV antibiotics within the previous 3 months

A host of other organisms causes lung infection in immunocompetent patients.

Q fever, tularemia, anthrax, and plague are uncommon bacterial syndromes in which pneumonia may be a prominent feature. Tularemia, anthrax, and plague should raise the suspicion of bioterrorism.

Viral causes

Bacterial superinfection can make distinguishing viral from bacterial infection difficult.

Common viral causes include

Adenoviruses, Epstein-Barr virus, and coxsackievirus are common viruses that rarely cause pneumonia. Seasonal influenza can rarely cause a direct viral pneumonia but often predisposes to the development of a serious secondary bacterial pneumonia. Varicella virus and hantavirus cause lung infection as part of adult chickenpox and hantavirus pulmonary syndrome. Coronaviruses cause severe acute respiratory syndrome (SARS), the Middle East respiratory syndrome (MERS), and COVID-19.

Other causes

Common fungal pathogens include Histoplasma capsulatum (histoplasmosis) and Coccidioides immitis (coccidioidomycosis). Less common fungal pathogens include Blastomyces dermatitidis (blastomycosis) and Paracoccidioides braziliensis (paracoccidioidomycosis). Pneumocystis jirovecii commonly causes pneumonia in patients who have human immunodeficiency virus (HIV) infection or are immunosuppressed (see Pneumonia in Immunocompromised Patients).

Parasites causing lung infection in developed countries include Toxocara canis or T. catis (toxocariasis), Dirofilaria immitis (dirofilariasis), and Paragonimus westermani (paragonimiasis).

Pulmonary tuberculosis and nontuberculous mycobacterial infections are discussed elsewhere.

Pneumonia in children

In children, the most common causes of pneumonia depend on age:

  • < 5 years: Most often viruses; among bacteria, S. pneumoniae, S. aureus, and S. pyogenes, are common
  • ≥ 5 years: Most often the bacteria S. pneumoniae, M. pneumoniae, or Chlamydia pneumoniae

Pneumonia in neonates is discussed elsewhere.

Symptoms and Signs of Community-Acquired Pneumonia

Symptoms include malaise, chills, rigor, fever, cough, dyspnea, and chest pain. Cough typically is productive in older children and adults and dry in infants, young children, and older adults. Dyspnea usually is mild and exertional and is rarely present at rest. Chest pain is pleuritic and is adjacent to the infected area. Pneumonia may manifest as upper abdominal pain when lower lobe infection irritates the diaphragm. Gastrointestinal symptoms (nausea, vomiting, diarrhea) are also common. Symptoms become variable at the extremes of age. Infection in infants may manifest as nonspecific irritability and restlessness; in older patients, manifestation may be as confusion and obtundation.

Signs include fever, tachypnea, tachycardia, crackles, bronchial breath sounds, egophony (E to A change—said to occur when, during auscultation, a patient says the letter “E” and through the stethoscope the examiner hears the letter “A”), and dullness to percussion. Signs of pleural effusion may also be present. Nasal flaring, use of accessory muscles, and cyanosis are common among infants. Fever is frequently absent in older patients.

Symptoms and signs were previously thought to differ by type of pathogen. For example, factors thought to suggest viral pneumonia included gradual onset, preceding symptoms of an upper respiratory infection (URI), diffuse findings on auscultation, and absence of a toxic appearance. Atypical pathogens were considered more likely when onset was less acute and are more likely during known community outbreaks. However, manifestations in patients with typical and atypical pathogens overlap considerably. In addition, no single symptom or sign is sensitive or specific enough to predict the organism. Symptoms and signs are even similar for other noninfective inflammatory lung diseases such as hypersensitivity pneumonitis and cryptogenic organizing pneumonia.

Diagnosis of Community-Acquired Pneumonia

  • Chest x-ray
  • Consideration of alternative diagnoses (eg, heart failure, pulmonary embolism)
  • Sometimes identification of pathogen
  • Evaluation of severity and risk stratification

Diagnosis of pneumonia is suspected on the basis of clinical presentation and infiltrate seen on chest x-ray. When there is high clinical suspicion of pneumonia and the chest x-ray does not reveal an infiltrate, doing computed tomography (CT) or repeating the chest x-ray in 24 to 48 hours is recommended. Severity of the pneumonia is estimated using a variety of clinical and laboratory factors (see Risk Stratification) which are sometimes organized using quantitative scoring systems. Typically, testing includes oxygen saturation, complete blood count, and blood urea nitrogen (BUN) level.

Differential diagnosis in patients presenting with pneumonia-like symptoms includes acute bronchitis and exacerbation of chronic obstructive pulmonary disease (COPD), which can be distinguished from pneumonia by the absence of infiltrates on chest x-ray. Other disorders should be considered, particularly when findings are inconsistent or not typical, such as heart failure, organizing pneumonia, and hypersensitivity pneumonitis. The most serious common misdiagnosis is pulmonary embolism, which may be more likely in patients with acute onset of dyspnea, minimal sputum production, no accompanying upper respiratory infection or systemic symptoms, and risk factors for thromboembolism (see table Risk Factors for Deep Venous Thrombosis); thus, testing for pulmonary embolism should be considered in patients with such symptoms and risk factors.

Quantitative cultures of bronchoscopic or suctioned specimens, if they are obtained before antibiotic administration, can help distinguish between bacterial colonization (ie, presence of microorganisms at levels that provoke neither symptoms nor an immune response) and infection. However, bronchoscopy is usually done only in patients receiving mechanical ventilation or for those with other risk factors for unusual microorganisms or complicated pneumonia (eg, immunocompromise, failure of empiric therapy).

Distinguishing between bacterial and viral pneumonias is challenging. Many studies have investigated the utility of clinical, imaging, and routine blood tests, but no test is reliable enough to make this differentiation. Even identification of a virus does not preclude concomitant infection with a bacteria; therefore, antibiotics are indicated in almost all patients with a community-acquired pneumonia.

In outpatients with mild pneumonia, no further diagnostic testing is needed (see table Risk Stratification for Community-Acquired Pneumonia). In patients with moderate or severe pneumonia, a white blood cell count and measurement of electrolytes, blood urea nitrogen (BUN), and creatinine are useful to classify risk and hydration status. Pulse oximetry or arterial blood gas (ABG) testing should also be done to assess oxygenation. For patients with moderate or severe pneumonia who require hospitalization, 2 sets of blood cultures are obtained to assess for bacteremia and sepsis. The Infectious Diseases Society of America (IDSA) provides a guide to recommended testing based on patient demographic and risk factors (Infectious Diseases Society of America Clinical Guidelines on Community-Acquired Pneumonia).

Pathogen identification

Diagnosis of etiology can be difficult. A thorough history of exposures, travel, pets, hobbies, and other exposures is essential to raise suspicion of less common organisms.

Identification of the pathogen can be useful to direct therapy and verify bacterial susceptibilities to antibiotics. However, because of the limitations of current diagnostic tests and the success of empiric antibiotic treatment, experts recommend limiting attempts at microbiologic identification (eg, cultures, specific antigen testing) unless patients are at high risk or have complications (eg, severe pneumonia, immunocompromise, asplenia, failure to respond to empiric therapy). In general, the milder the pneumonia, the less such diagnostic testing is required. Critically ill patients require the most intensive testing, as do patients in whom a antibiotic-resistant or unusual organism is suspected (eg, Mycobacterium tuberculosis, P. jirovecii) and patients whose condition is deteriorating or who are not responding to treatment within 72 hours.

Chest x-ray findings generally cannot distinguish one type of infection from another, although the following findings are suggestive:

  • Multilobar infiltrates suggest S. pneumoniae or Legionella pneumophila infection.
  • Interstitial pneumonia (on chest x-ray, appearing as increased interstitial markings and subpleural reticular opacities that increase from the apex to the bases of the lungs) suggests viral or mycoplasmal etiology.
  • Cavitating pneumonia suggests S. aureus or a fungal or mycobacterial etiology.
Chest X-ray Findings in Pneumonia

Blood cultures, which are often obtained in patients hospitalized for pneumonia, can identify causative bacterial pathogens if bacteremia is present. About 12% of all patients hospitalized with pneumonia have bacteremia; S. pneumoniae accounts for two thirds of these cases.

Sputum testing can include Gram stain and culture for identification of the pathogen, but the value of these tests is uncertain because specimens often are contaminated with oral flora and overall diagnostic yield is low. Regardless, identification of a bacterial pathogen in sputum cultures allows for susceptibility testing. Obtaining sputum samples also allows for testing for viral pathogens via direct fluorescence antibody testing or polymerase chain reaction (PCR), but caution needs to be exercised in interpretation because 15% of healthy adults carry a respiratory virus or potential bacterial pathogen. In patients whose condition is deteriorating and in those unresponsive to broad-spectrum antibiotics, sputum should be tested with mycobacterial and fungal stains and cultures.

Sputum samples can be obtained noninvasively by simple expectoration or after hypertonic saline nebulization (induced sputum) for patients unable to produce sputum. Alternatively, patients can undergo bronchoscopy or endotracheal suctioning, either of which can be easily done through an endotracheal tube in mechanically ventilated patients. Otherwise, bronchoscopic sampling is usually done only for patients with other risk factors (eg, immunocompromise, failure of empiric therapy).

Urine testing for Legionella antigen and pneumococcal antigen is now widely available. These tests are simple and rapid and have higher sensitivity and specificity than sputum Gram stain and culture for these pathogens. Patients at risk of Legionella pneumonia (eg, severe illness, failure of outpatient antibiotic treatment, presence of pleural effusion, active alcohol abuse, recent travel) should undergo testing for urinary Legionella antigen, which remains present long after treatment is initiated, but the test detects only L. pneumophila serogroup 1 (70% of cases).

The pneumococcal antigen test is recommended for patients who are severely ill; have had unsuccessful outpatient antibiotic treatment; or who have pleural effusion, active alcohol abuse, severe liver disease, or asplenia. This test is especially useful if adequate sputum samples or blood cultures were not obtained before initiation of antibiotic therapy. A positive test can be used to tailor antibiotic therapy, though it does not provide antimicrobial susceptibility.

COVID-19 test using reverse transcriptase-polymerase chain reaction (RT-PCR) testing of respiratory secretions (nasopharyngeal specimen is preferred) is recommended in patients presenting with pneumonia during the current pandemic.

Prognosis for Community-Acquired Pneumonia

Short-term mortality is related to severity of illness. Mortality is < 1% in patients who are candidates for outpatient treatment. Mortality in hospitalized patients is 8%. Death may be caused by pneumonia itself, progression to sepsis syndrome, or exacerbation of coexisting conditions. In patients hospitalized for pneumonia, risk of death is increased during the year after hospital discharge.

Mortality varies to some extent by pathogen. Mortality rates are highest with gram-negative bacteria and CA-MRSA. However, because these pathogens are relatively infrequent causes of community-acquired pneumonia, S. pneumoniae remains the most common cause of death in patients with community-acquired pneumonia. Atypical pathogens such as Mycoplasma have a good prognosis. Mortality is higher in patients who do not respond to initial empiric antibiotics and in those whose treatment regimen does not conform with guidelines.

Treatment of Community-Acquired Pneumonia

  • Risk stratification for determination of site of care
  • Antibiotics
  • Antivirals for influenza or varicella
  • Supportive measures

Risk stratification

Risk stratification via risk prediction rules may be used to estimate mortality risk and thus help guide decisions regarding hospitalization. These rules have been used to identify patients who can be safely treated as outpatients and those who require hospitalization because of high risk of complications (see table Risk Stratification for Community-Acquired Pneumonia). However, these rules should supplement, not replace, clinical judgment because many unrepresented factors, such as likelihood of adherence, ability to care for self, ability to maintain oral intake, should also influence triage decisions.

Intensive care unit (ICU) admission is required for patients who

  • Need mechanical ventilation
  • Have hypotension (systolic blood pressure ≤ 90 mm Hg) that is unresponsive to volume resuscitation

Other criteria, especially if ≥ 3 are present, that should lead to consideration of ICU admission include

  • Hypotension requiring fluid support
  • Respiratory rate >30/minute
  • PaO2/fraction of inspired oxygen (FIO2) < 250
  • Multilobar pneumonia
  • Confusion
  • Blood urea nitrogen (BUN) > 19.6 mg/dL (> 7 mmol/L)
  • Leukocyte count < 4000 cells/microL (< 4 × 109/L)
  • Platelet count < 100,000/microL (< 100 × 109/L)
  • Temperature < 36° C

The Pneumonia Severity Index (PSI) is the most studied and validated prediction rule. However, because the PSI is complex and requires several laboratory assessments, simpler rules such as CURB-65 are usually recommended for clinical use. Use of these prediction rules has led to a reduction in unnecessary hospitalizations for patients who have milder illness.

In CURB-65, 1 point is allotted for each of the following risk factors:

  • Confusion
  • Uremia (BUN ≥19 mg/dL [6.8 mmol/L])
  • Respiratory rate > 30 breaths/minute
  • Systolic Blood pressure < 90 mm Hg or diastolic blood pressure ≤ 60 mm Hg
  • Age ≥ 65 years

Scores can be used as follows:

  • 0 or 1 points: Risk of death is < 3%. Outpatient therapy is usually appropriate.
  • 2 points: Risk of death is 9%. Hospitalization should be considered.
  • ≥ 3 points: Risk of death is 15 to 40%. Hospitalization is indicated, and, particularly with 4 or 5 points, ICU admission should be considered.

Risk Stratification for Community-Acquired Pneumonia (the Pneumonia Severity Index)



Patient demographics

  • Men

Age (in years)

  • Women

Age (in years) −10

Nursing home resident


Coexisting illness



Liver disease


Heart failure


Cerebrovascular disease


Renal disease


Physical examination

Altered mental status


Respiratory rate ≥ 30 breaths/minute


Systolic blood pressure < 90 mm Hg


Temperature ≥ 40° C or <35°C


Heart rate ≥ 125 beats/minute


Test results

Arterial pH < 7.35


Blood urea nitrogen ≥ 30 mg/dL (11 mmol/L)


Sodium < 130 mmol/L


Glucose ≥ 250 mg/dL (14 mmol/L)


Hematocrit < 30%


PaO2< 60 mm Hg or

Oxygen saturation < 90%*


Pleural effusion






< 1%

Outpatient treatment†



Outpatient treatment†







* Many consider hypoxemia an absolute indication for admission.

† Acute care admission, subacute care admission, observation period, home IV antibiotics, or home nursing visits should be considered for patients who are frail, isolated, or living in unstable environments.

Adapted from Pneumonia: New prediction model proves promising (AHCPR Publication No. 97-R031).


Antibiotic therapy is the mainstay of treatment for community-acquired pneumonia. Appropriate treatment involves starting empiric antibiotics as soon as possible, preferably ≤4 hours after presentation. Because pathogen identification is difficult and takes time, the empiric antibiotic regimen is selected based on likely pathogens and severity of illness. Consensus guidelines have been developed by many professional organizations; one widely used set is detailed in the table Community-Acquired Pneumonia in Adults (see also Infectious Diseases Society of America Clinical Guideline on Community-Acquired Pneumonia). Guidelines should be adapted to local susceptibility patterns, drug formularies, and individual patient circumstances. If a pathogen is subsequently identified, the results of antibiotic susceptibility testing can help guide any changes in antibiotic therapy.

For children, treatment depends on age, previous vaccinations, and whether treatment is outpatient or inpatient.

For children treated as outpatients, treatments are dictated by age:

  • < 5 years: Amoxicillin or amoxicillin/clavulanate is usually the drug of choice. If epidemiology suggests an atypical pathogen as the cause and clinical findings are compatible, a macrolide (eg, azithromycin, clarithromycin) can be used instead. Some experts suggest not using antibiotics if clinical features strongly suggest viral pneumonia.
  • ≥ 5 years: Amoxicillin or (particularly if an atypical pathogen cannot be excluded) amoxicillin plus a macrolide. Amoxicillin/clavulanate is an alternative. If the cause appears to be an atypical pathogen, a macrolide alone can be used.

For children treated as inpatients, antibiotic therapy tends to be more broad-spectrum and depends on the child's previous vaccinations:

  • Fully immunized (against S. pneumoniae and H. influenzae type b): Ampicillin or penicillin G (alternatives are ceftriaxone or cefotaxime). If MRSA is suspected, vancomycin or clindamycin is added. If an atypical pathogen cannot be excluded, a macrolide is added.
  • Not fully immunized: Ceftriaxone or cefotaxime (alternative is levofloxacin). If MRSA is suspected, vancomycin or clindamycin is added. If an atypical pathogen cannot be excluded, a macrolide is added.

Full details are described in the Clinical Practice Guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America.

With empiric treatment, 90% of patients with bacterial pneumonia improve. Improvement is manifested by decreased cough and dyspnea, defervescence, relief of chest pain, and decline in white blood cell count. Failure to improve should trigger suspicion of

  • An unusual organism
  • Resistance to the antimicrobial used for treatment
  • Empyema
  • Coinfection or superinfection with a 2nd infectious agent
  • An obstructive endobronchial lesion
  • Immunosuppression
  • Metastatic focus of infection with reseeding (in the case of pneumococcal infection)
  • Nonadherence to treatment (in the case of outpatients)
  • Wrong diagnosis (ie, a noninfectious cause of the illness such as acute hypersensitivity pneumonitis)

When usual therapy has failed, consultation with a pulmonary and/or infectious disease specialist is indicated.

Antiviral therapy may be indicated for select viral pneumonias. Ribavirin is not used routinely for respiratory syncytial virus pneumonia in children or adults but may be used occasionally in high-risk children age < 24 months.

For influenza, oseltamivir 75 mg orally twice a day or zanamivir 10 mg inhaled twice a day started within 48 hours of symptom onset and given for 5 days reduce the duration and severity of symptoms in patients who develop influenza infection. Alternatively, baloxavir started within 48 hours of symptom onset can be given in a single dose of 40 mg for patients 40 to 80 kg; 80 mg is used for patients ≥ 80 kg. In patients hospitalized with confirmed influenza infection, observational studies suggest benefit even 48 hours after symptom onset.

Acyclovir 5 to 10 mg/kg IV every 8 hours for adults or 250 to 500 mg/m2 body surface area IV every 8 hours for children is recommended for varicella lung infections. Though pure viral pneumonia does occur, superimposed bacterial infections are common and require antibiotics directed against S. pneumoniae, H. influenzae, and S. aureus.

Follow-up x-rays are generally not recommended in patients whose pneumonia resolves clinically as expected. Resolution of radiographic abnormalities can lag behind clinical resolution by several weeks. Chest x-ray should be considered in patients with pneumonia symptoms that do not resolve or that worsen over time.

Community-Acquired Pneumonia in Adults


Likely Organisms

Empiric Treatment

I. Outpatients—no modifying factors present†

Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydia pneumoniae, Haemophilus influenzae, respiratory viruses, miscellaneous organisms (eg, Legionella species, Mycobacterium tuberculosis, endemic fungi)

Amoxicillin 1 g orally three times a day


Macrolide (azithromycin 500 mg orally once, then 250 mg once a day; clarithromycin 250 to 500 mg orally twice a day; or extended-release clarithromycin 1 g orally once a day)


Doxycycline 100 mg orally twice a day (if allergic to macrolide)

II. Outpatients—modifying factors present†

S. pneumoniae, including antibiotic-resistant forms; M. pneumoniae; C. pneumoniae; mixed infection (bacteria + atypical pathogen or virus); H. influenzae; enteric gram-negative organisms; respiratory viruses; miscellaneous organisms (eg, Moraxella catarrhalis, Legionella species, anaerobes [aspiration], M. tuberculosis, endemic fungi)

Beta-lactam (cefpodoxime 200 mg orally every 12 hours; cefuroxime 500 mg orally every 12 hours; amoxicillin 1 g orally every 8 hours; amoxicillin/clavulanate 875/125 mg orally every 12 hours)


Macrolide orally


Antipneumococcal fluoroquinolone orally or IV (alone; eg, moxifloxacin [400 mg orally/IV every 24 hours], gemifloxacin [320 mg orally/IV every 24 hours], levofloxacin [750 mg orally/IV every 24 hours] )

III. Inpatient—not in intensive care unit (ICU)

S. pneumoniae, H. influenzae; M. pneumoniae; C. pneumoniae; mixed infection (bacteria + atypical pathogen or virus); respiratory viruses; Legionella species, miscellaneous organisms (eg, M. tuberculosis, endemic fungi, Pneumocystis jirovecii)

Azithromycin 500 mg IV every 24 hours


Beta-lactam IV (cefotaxime 1 to 2 g every 8 to 12 hours; ceftriaxone 1 g every 24 hours)


Antipneumococcal fluoroquinolone orally or intravenously (alone)

IVA. ICU patient—no Pseudomonas risk factors

S. pneumoniae, including antibiotic-resistant forms; Legionella species; H. influenzae; enteric gram-negative organisms,;Staphylococcus aureus; M. pneumoniae; respiratory viruses miscellaneous organisms (eg, C. pneumoniae, M. tuberculosis, endemic fungi)

Beta-lactam IV (cefotaxime 1 to 2 g IV every 8 to 12 hours; ceftriaxone 1 g IV every 24 hours)

plus either

Antipneumococcal fluoroquinolone IV


Azithromycin 500 mg IV every 24 hours

IVB. ICU patient—Pseudomonas risk factors present

Same as those for category IVA (above) plus Pseudomonas species

Antipseudomonal beta-lactam‡ or aztreonam (if allergic to or intolerant of beta-lactams) 1 to 2 g every 8 hours

plus either

Ciprofloxacin 400 mg IV every 12 hours or levofloxacin 750 mg orally or IV every 24 hours


Antipseudomonal beta-lactam‡


An aminoglycoside

plus either

Ciprofloxacin 400 mg IV every 12 hours or levofloxacin 750 mg po or IV every 24 hours

* These guidelines do not apply to patients with immunosuppression, influenza, aspiration pneumonia.

† Modifying factors:

  • Increased risk of antibiotic-resistant organisms: Age > 65, alcoholism, antibiotic within 3 months, exposure to child in day care center, multiple coexisting illnesses
  • Increased risk of enteric gram-negative organisms: Antibiotic use within 3 months, cardiopulmonary disease (including chronic obstructive pulmonary disease [COPD] or heart failure), multiple coexisting illnesses
  • Increased risk of Pseudomonas aeruginosa: Broad-spectrum antibiotics > 7 days in past month, corticosteroid use, undernutrition, structural pulmonary disease

‡ Antipseudomonal beta-lactams = cefepime 1 to 2 g IV every 12 hours, imipenem 500 mg IV every 6 hours, meropenem 500 mg to 1 g IV every 8 hours, piperacillin/tazobactam 3.375 g IV every 4 hours.

Data from Metlay JP, Waterer GW, Long AC, et al: Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med 200(7): e45–e67, 2019.

Supportive care

Supportive care includes fluids, antipyretics, analgesics, and, for patients with hypoxemia, oxygen. Prophylaxis against thromboembolic disease and early mobilization improve outcomes for patients hospitalized with pneumonia. Cessation counseling should also be done for smokers.

Health Care-Associated Pneumonia

The category of health care-associated pneumonia was removed as a separate category of pneumonia in the 2016 Infectious Diseases Society of America guidelines for hospital-acquired pneumonia. Health care-associated pneumonia includes community based patients who have had recent contact with the health care system, such as those who reside in nursing homes or other long-term care facilities or visit dialysis centers and infusion centers. This category was created to help identify patients at increased risk for antibiotic-resistant bacteria. However, the 2016 IDSA guidelines found increasing evidence that many patients with health care-associated pneumonia were not infected with antibiotic-resistant bacteria. Rather, the risk for antibiotic-resistant bacteria in these patients can be based on validated risk factors described for patients with community-acquired pneumonia.

Prevention of Community-Acquired Pneumonia

Some forms of community-acquired pneumonia are preventable with vaccination. Two pneumococcal vaccines are available:

  • Pneumococcal conjugate vaccine (PCV13) is recommended for children age 2 months to 2 years and for adults ≥ 19 years with certain comorbid (including immunocompromising) conditions and for adults ≥ 65 years based on shared decision-making between clinician and patient.
  • Pneumococcal polysaccharide vaccine (PPSV23) is given to all adults ≥ 65 years and to any patient ≥ 2 years who has risk factors for pneumococcal infections, including but not limited to those with underlying heart, lung, or immune system disorders and those who smoke.

The full list of indications for both pneumococcal vaccines can be found at the CDC website. Recommendations for other vaccines, such as H. influenzae type b (Hib) vaccine (for patients < 2 years), varicella vaccine (for patients < 18 months and a later booster vaccine), and influenza vaccine (annually for everyone ≥ 6 months and especially for those at higher risk of developing serious flu-related complications), can also be found at the CDC website. This higher risk group includes people ≥ 65 years and people of any age with certain chronic medical conditions (such as diabetes, asthma, or heart disease), pregnant women, and young children.

In high-risk patients who are not vaccinated against influenza and household contacts of patients with influenza, oseltamivir 75 mg orally once/day or zanamivir 10 orally mg once/day can be given for 2 weeks. If started within 48 hours of exposure, these antivirals may prevent influenza (although resistance has been described for oseltamivir).

Smoking cessation can reduce the risk of developing pneumonia.

Key Points

  • Community-acquired pneumonia is a leading cause of death in the United States and around the world.
  • Common symptoms and signs include cough, fever, chills, fatigue, dyspnea, rigors, sputum production, and pleuritic chest pain.
  • Treat patients with mild or moderate risk pneumonia with empiric antibiotics without testing designed to identify the underlying pathogen.
  • Hospitalize patients with multiple risk factors, as delineated by risk assessment tools.
  • Consider alternate diagnoses, including pulmonary embolism, particularly if pneumonia-like signs and symptoms are not typical.

More Information

The following are English-language resources that may be useful. Please note that The Manual is not responsible for the content of these resources.

  • Clinical Practice Guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America
  • Infectious Diseases Society of America Clinical Guideline on Community-Acquired Pneumonia
  • Management of Adults With Hospital-acquired and Ventilator-associated Pneumonia: 2016 Clinical Practice Guidelines by the Infectious Diseases Society of America and the American Thoracic Society
  • Pneumococcal ACIP Vaccine Recommendations

Drugs Mentioned In This Article

Drug Name Select Trade
piperacillin/tazobactam ZOSYN
clarithromycin BIAXIN
Ciprofloxacin CILOXAN, CIPRO
gemifloxacin FACTIVE
azithromycin ZITHROMAX
moxifloxacin AVELOX
Amoxicillin AMOXIL
ceftriaxone ROCEPHIN
clindamycin CLEOCIN
oseltamivir TAMIFLU
cefpodoxime No US brand name
cefuroxime CEFTIN, ZINACEF
cefotaxime CLAFORAN
vancomycin VANCOCIN
aztreonam AZACTAM
meropenem MERREM
Ribavirin VIRAZOLE
Acyclovir ZOVIRAX
zanamivir RELENZA
cefepime MAXIPIME

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