Community-Acquired Pneumonia
GENERAL PRINCIPLES
• Community-acquired pneumonia (CAP) is a significant cause of morbidity and mortality in the United States.
• CAP ranks highly among all causes of death. The exact mortality rate varies widely depending on the treatment setting (outpatient vs. inpatient vs. intensive care unit [ICU]), the presence or absence of associated comorbidities, and the age of the patient.
• It causes over 1 million hospitalizations annually.
• Administration of appropriate antimicrobials and management for severe pneumonia have a significant benefit on patient survival.
Nearly half of all cases do not have an identified etiologic agent.
Early empiric treatment is essential, and bacterial resistance must be considered.
• The most widely recognized guidelines for the treatment of CAP include those of the American Thoracic Society, the Infectious Diseases Society of America, and the Canadian Infectious Disease Society and Canadian Thoracic Society.
Definition
• CAP is a primary infection of lung parenchyma. Bacterial or viral invasion causes inflammation and alveolar infiltration that result in focal consolidation.
• CAP is distinctive from health care–associated pneumonia (HCAP) and hospital-acquired pneumonia (HAP) in that the infection is acquired in the community.
Classification
• Typical bacterial: Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Group A streptococci, Moraxella catarrhalis, mixed anaerobes (aspiration), and aerobic gram-negative organisms.
• Atypical bacterial: Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae.
• Viral: Influenza A and B, respiratory syncytial virus (RSV), adenovirus, rhinoviruses, rubeola, varicella.
Epidemiology
Pneumonia and influenza combine to be the eighth leading cause of death in the United States. In 2008, there were over 56,000 deaths due to pneumonia and influenza.1 The rate of deaths due to pneumonia is increasing. Pneumonia is more common in the winter months and elderly. Men and African-Americans are slightly more affected than women and Caucasians.
Etiology
• The most common etiology for CAP is S. pneumoniae.
• Frequently, pneumonia is preceded by an upper airway infection or viral illness.
Pathophysiology
• Lobar pneumonia is characterized by consolidation of a large portion of lung. Consolidation of airspaces is caused by host inflammatory infiltration in response to bacterial infection of lung tissue.
• Bronchopneumonia similarly involves acute inflammation, but the consolidated areas are patchy and often multilobar or bilateral. This pattern is more common to atypical viral pneumonias or mycoplasmal pneumonias.
Risk Factors
• Predisposing comorbid conditions: chronic obstructive pulmonary disease (COPD), heart failure, chronic renal disease, and chronic bronchitis.
• Host factors: advanced age, tobacco use, prior history of pneumonia, recent viral respiratory infection.
• Immunosuppressed states: HIV infection, chemotherapy, solid organ and stem cell transplant recipients.
• Mechanical: dysphagia, lung cancer, mechanical obstruction of bronchus, hiatal hernia, radiation esophagitis.
• Aspiration risk factors: alcoholism and drug intoxication, altered mental status, seizure disorder, stroke, procedural sedation, and anesthesia.
• Mucus clearance: cystic fibrosis, Kartagener syndrome, immotile cilia syndrome, Young syndrome.
Prevention
Prevention should include major risk factor modifications such as smoking cessation and vaccination against influenza and pneumococcus.
DIAGNOSIS
The gold standard for diagnosis of pneumonia is a posteroanterior and lateral CXR demonstrating new pulmonary infiltration. Clinical signs and symptoms should correlate with active infection and pulmonic consolidation.
Clinical Presentation
• Patients will typically complain of fever, chills, productive cough, shortness of breath, and chest pain.
• Physical examination findings include fever, tachypnea, tachycardia, abnormal breath sounds including rhonchi or crackles, increased tactile fremitus, dullness to percussion, and reduced chest movement.
Differential Diagnosis
• The differential diagnosis for pneumonia includes pathology that causes radiographic consolidations that can mimic pneumonia. This includes acute heart failure exacerbation and other causes of pulmonary edema, malignancy, pulmonary embolism (PE), septic embolism, and foreign body.
• Multiple different bacteria, viruses, and fungi can cause acute pneumonia.
Diagnostic Testing
The primary objective is to identify the causative agent. Other laboratory testing should be undertaken to assess the severity of illness. Typical studies include basic laboratory chemistries, blood cell counts, and cultures.
Laboratories
• Initial inpatient and outpatient studies should include blood cultures, complete blood count (CBC) with differential, basic metabolic profile (BMP), and liver function tests (LFT).
• Blood cultures are positive in 5–18% of hospitalized patients.2,3 Ideally blood cultures should be obtained before antibiotics are given, but this should not delay administration of early empiric treatment.
• HIV testing should be considered among patients age 15 years and older.
• Urine studies such as urine pneumococcal and Legionella antigen assays can assist in microbe identification.
• For patients with suspected influenza, nasopharyngeal viral culture and immunofluorescence, or polymerase chain reaction (PCR) should be obtained. For M. pneumonia, PCR or serology can aid in diagnosis.
• Gram stain and sputum culture have been commonly used in the evaluation of CAP. Due to limitations in Gram stain and culture of sputum, we no longer recommend it in the initial care of uncomplicated CAP. Sputum analysis should be considered in patients who fail initial treatment with antibiotics, require ICU-level care, have cavitary lesions on CXR, or have a history of alcoholism or immunosuppression.
Imaging
• Plain CXR is the imaging study of choice. Pneumonic infiltrates can “fluff up” after volume resuscitation in volume-depleted patients.
• CT and MRI are not required for the diagnosis of pneumonia.
• CT scan should be performed when clinical symptoms do not suggest infection as the cause of radiographic infiltrate (e.g., malignancy). CT can also be used to evaluate empyema, cavitary disease, interstitial lung disease, and in patients who fail to respond to antibiotics.
• MRI can provide additional information about mass lesions and lymphadenopathy.
Diagnostic Procedures
• Invasive diagnostic procedures such as bronchoscopy and bronchoalveolar lavage are rarely required or recommended but can be of use in nonresponders, critically ill patients, or immunocompromised hosts.
• Diagnostic thoracentesis should be performed for pleural effusions that layer >10 mm on a lateral decubitus radiograph. Sampling of fluid helps rule out empyema, which would require tube thoracostomy. Pleural fluid testing should include cell count and differential, protein, lactate dehydrogenase, pH, glucose, Gram stain, and culture.
• Tracheal aspiration should be performed on patients requiring intubation.
TREATMENT
• Care should be triaged to inpatient versus outpatient treatment. Patients should also be evaluated for severity of illness, for example, patient requiring ICU admission versus admission to a medical floor.
• CURB-65 criteria (0–1 points: outpatient; 2 points: medical floor admission; ≥3 points: ICU-level care)4
Confusion
Uremia (blood urea nitrogen [BUN] >20 mg/dL)
Respiratory rate (>30 breaths/min)
Blood pressure (systolic <90 mm Hg or diastolic <60 mm Hg)
Age ≥65 years
• Criteria for determining severity of CAP (ICU admit is recommended for patients with ≥1 major criteria or ≥3 minor criteria)5
Major criteria
Invasive mechanical ventilation
Septic shock with the need for vasopressors
Minor criteria
Respiratory rate ≥30 breaths/min
PaO2/FiO2 ratio ≤250
Multilobar infiltrates
Confusion/disorientation
Uremia (BUN >20 mg/dL)
Leukopenia (white blood cell [WBC] count <4000 cells/mm3)
Thrombocytopenia (platelet count <100,000 cells/mm3)
Hypothermia (core temperature <36°C)
Hypotension requiring aggressive fluid resuscitation
Medications
• Outpatient, previously healthy5
Macrolide (any of the following)
Azithromycin 500 mg PO × 1, then 250 mg PO daily × 4 days
Clarithromycin 500 mg PO bid or clarithromycin XL 1000 mg PO daily
Erythromycin 250–500 mg PO q6h
Doxycycline 100 mg PO bid
• Outpatient with comorbidities5 (e.g., heart/lung/liver/renal disease, diabetes, alcoholism, malignancy, asplenia, immunosuppressed, prior use of antibiotics)
Respiratory quinolone (any of the following)
Levofloxacin 750 mg PO daily
Moxifloxacin 400 mg PO daily
β-Lactam (any of the following) PLUS macrolide OR doxycycline
Amoxicillin 1 g PO tid
Amoxicillin-clavulanate 875 mg/125 mg PO bid
Cefpodoxime 200 mg PO bid
Cefuroxime 500 mg PO bid
• Inpatient therapy non-ICU5
Respiratory quinolone (any of the following)
Levofloxacin 750 mg IV daily
Moxifloxacin 400 mg IV daily
β-Lactam (any of the following) PLUS macrolide (e.g., azithromycin 500 mg IV daily) OR doxycycline 100–200 mg IV bid
Cefotaxime 1 g IV q8h
Ceftriaxone 1 g IV q24h
Ampicillin/sulbactam 3 g IV q6h
Ertapenem 1 g IV q24h
• Inpatient therapy ICU5
IV β-lactam PLUS
IV respiratory quinolone OR IV azithromycin
Other Nonpharmacologic Therapies
Pulmonary hygiene with cough assist devices or chest physiotherapy can aid in the medical management of pneumonia.
Duration of Therapy
• Minimum duration should be 5 days.
• Antibiotics should not be tapered until the patient has been afebrile for 48–72 hours, symptoms are improving, and the WBC count is decreasing.
• Patients may be switched to oral antibiotics once improvement is noted clinically and they are stable enough to take oral medicines.
Surgical Management
• If present, an empyema should be drained with thoracostomy tube placement.
• Drainage of lung abscess is controversial. Chest physiotherapy should be used to promote natural expectoration. Complications of percutaneous or surgical drainage can include bronchopleural fistula and pneumothorax.
MONITORING/FOLLOW-UP
• Infiltrate on CXR will persist longer than clinical symptoms of pneumonia.
• Routine follow-up CXR is not recommended. However, there is evidence to suggest that follow-upradiography in select groups (e.g., >50 years old, tobacco users) may reveal other diagnosesincluding malignancy.6,7
OUTCOME/PROGNOSIS
• Treatment failure
Occurs in 10–15% of cases, and mortality is increased nearly 5-fold in some studies.8
It is important to distinguish clinical deterioration from failure in symptomatic improvement.
• Clinical deterioration
Within 72 hours: typically resistant organisms, alternate diagnosis (consider PE, acute respiratory distress syndrome [ARDS], pulmonary vasculitis syndromes, polymicrobial infection due to aspiration), severe illness, and natural progression of disease to respiratory and/or multiorgan failure.
After 72 hours: nosocomial infections, severe comorbid conditions, PE, myocardial infarction (MI), renal failure.
• Failure in symptomatic improvement
Within 72 hours: typically normal response.
After 72 hours: resistant organisms or inappropriate antibiotic selection, local complications (parapneumonic effusion or empyema), alternate diagnosis (pulmonary edema, malignancy, vasculitis, PE), drug fevers.
• Overall mortality from pneumonia ranges based on severity of disease and host factors. In one meta-analysis ranged from 5.1% in hospitalized and ambulatory patients to 36.5% in patients requiring ICU care.9
REFERENCES
1. Miniño AM, Murphy SL, Xu J, et al. Deaths: final data for 2008. Natl Vital Stat Rep. 2011; 59(10):1–126.
2. Campbell SG, Marrie TJ, Anstey R, et al. The contribution of blood cultures to the clinical management of adult patients admitted to the hospital with community-acquired pneumonia: a prospective observational study. Chest. 2003;123:1142–50.
3. Waterer GW, Wunderink RG. The influence of the severity of community-acquired pneumonia on the usefulness of blood cultures. Respir Med. 2001;95:78–82.
4. Lim WS, van der Eerden MM, Laing R, et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax. 2003;58:377–82.
5. Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007;44(Suppl 2):S27–72.
6. Tang KL, Eurich DT, Minhas-Sandhu JK, et al. Incidence, correlates, and chest radiographic yield of new lung cancer diagnosis in 3398 patients with pneumonia. Arch Intern Med. 2011;171:1193–8.
7. Little BP, Gilman MD, Humphrey KL, et al. Outcome of recommendations for radiographic follow-up of pneumonia on outpatient chest radiography. AJR Am J Roentgenol. 2014;202:54–9.
8. Menendez R, Torres A. Treatment failure in community-acquired pneumonia. Chest. 2007; 132(4):1348–55.
9. Fine MJ, Smith MA, Carson CA. Prognosis and outcomes of patients with community acquired pneumonia: a meta-analysis. JAMA. 1996;275:134–41.
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