OVERVIEW ã…¡ Pneumonia is an inflammatory condition of the pulmonary parenchyma caused by an infection. The symptoms, treatment, and morbidity associated with the infection vary by the setting in which it is acquired. A classification system for pneumonia has been adopted by the Infectious Disease Society of America (IDSA) and the American Thoracic Society (ATS) as below (see Table 1)...
| Table (1). Classification of pneumonia | |
|---|---|
| TYPE | COMMENT |
| Community-acquired pneumonia (CAP) | Acquired as an outpatient, without any risk factors for HCAP, as below. |
| Hospital-acquired pneumonia (HAP) | Acquired 48 hours or more after admission if not incubating at admission. |
| Health care-associated pneumonia (HCAP) | Acquired in patients who were hospitalized in acute care hospitals for ≥2 days within 90 days of onset of infection, reside in a nursing home or long-term care facility, attended a hospital-based or hemodialysis clinic, or received recent wound care, chemotherapy, or intravenous IV antibiotics. |
| Ventilator-associated pneumonia (VAP) | Pneumonia occurring in patients more than 48-72 hours after intubation. |
PATHOPHYSIOLOGY
ETIOLOGY ã…¡ The etiology of pneumonia in a particular patient depends on a variety of factors, including host immune status and comorbidities including chronic respiratory disease and chronic liver disease and infection status of contacts.
Viral pneumonias, such as influenza pneumonia, spread between hosts through multiple mechanisms including direct exposure of host mucosa with virus-inoculated bodily fluids of an infected contact, airborne inhalation of virus-inoculated droplets, and hand-to-mouth exposure of virus-inoculated secretions via direct contact or fomites. Bacterial pneumonias typically began as micro- or macroaspirations of nasopharyngeal or oropharyngeal bacteria. Rarely, bacteria can be transmitted through airborne droplets and lead to pneumonia after inhalation.
After inoculation of alveoli with the causative agent of pneumonia, an inflammatory cascade is activated with subsequent chemotaxis and cytokine release. This process leads to symptoms typical of pneumonia including cough, fatigue, fever, dyspnea, and chest pain.
DIAGNOSIS
HISTORY ã…¡ The initial presentation of patients with pneumonia can vary widely based on causative agent, comorbid conditions, and severity of infection. Symptoms typical of pneumonia include cough, dyspnea and increased sputum production, pleuritic chest pain, fevers, chills, anorexia, nausea and vomiting and mental status changes, particularly in the elderly.
PHYSICAL EXAMINATION ã…¡ The physical examination for pneumonia should involve prompt evaluation of vital signs and stability of respiratory status. Findings typical of pneumonia can include rales, rhonchi, or evidence of consolidation with egophony and dullness to percussion.
DIAGNOSTIC TESTING ã…¡ Initial diagnostic evaluation of suspected pneumonia in an acute care setting or hospital-based clinic should include chest radiograph and laboratory evaluation including sputum Gram stain and culture and blood Gram stain and culture (positive in 10-20% of pneumonias) prior to antibiotic administration if feasible. Legionella pneumophila urine antigen and S. pneumoniae urine antigen tests if these infections as suspected and especially in the setting of critical illness, complete blood cell count (CBC) and lactic acid level if sepsis syndrome criteria are met. Procalcitonin level may be used to help differentiate between viral and bacterial etiologies of pneumonia and guide duration of antibiotic therapy.
If a significant pleural effusion is present (> 1 cm of fluid layers on a lateral decubitus), consider a diagnostic thoracentesis to rule out an empyema. In intubated patients, tracheal aspirate Gram stain and culture have been shown to correlate well with invasive quantitative cultures, with some loss of specificity. Nasopharyngeal respiratory viral pathogen multiplex polymerase chain reaction (PCR) and influenza virus PCR may help rapidly detect common respiratory viruses as causative or contributory agents in pneumonia.
MANAGEMENT
ADMISSION DECISION ã…¡ The decision to admit a patient with CAP is complex. Multiple scoring systems have been established to aid risk stratification in this cohort of patients. The most frequently used prediction rules include the Pneumonia Severity Index (complex, but best supported by evidence), the CURB-65 score (easy to implement), and the severe CAP score (helpful in stratifying which patients may be best suited in an intensive care unit setting).
The CURB-65 criteria have been used to predict 30-day mortality. A score of 2 points out of 5 warrants consideration for short-stay unit admission or close outpatient monitoring, and a score of 3 or more suggests need for inpatient hospitalization and consideration for ICU admission.
If a patient is hospitalized, general supportive measures such as oxygen supplementation, pulmonary toilet, and prophylaxis for deep venous thrombosis should always be considered. Hospitalization also offers an opportunity to screen for pneumococcal infection and administer pneumococcal vaccine. Initial selection of antibiotic is discussed below. Pathogen-directed therapy is ideal if an organism is later obtained. Prompt initiation of antibiotics appears to improve outcomes.
EMPIRICAL ANTIBIOTIC ã…¡ Empiric recommendations for antibiotic therapy are guided by likely organisms and expected resistance patterns of these organisms.
Community-acquired pneumonia. β-lactam antibiotic plus a macrolide (e.g., ceftriaxone 1 g IV qday plus azithromycin 250 mg PO qday) OR a fluoroquinolone (e.g., moxifloxacin, 400 mg PO/IV qday). In those patients ill enough to require ICU placement, fluoroquinolone therapy should be combined with a β-lactam agent. A recent meta-analysis has shown that systemic corticosteroids in hospitalized patients with CAP may confer a modest mortality benefit and reduce hospital stay.
Hospital- or ventilator-acquired pneumonia. Early HAP without risk factors for MDR may be treated as CAP above. Late onset of health care-acquired pneumonia or any risk for multidrug-resistant pathogens should be treated with antipseudomonal cephalosporin (e.g., cefepime) OR antipseudomonal carbapenem (e.g., meropenem) OR β-lactam/β-lactamase inhibitor (piperacillin-tazobactam); aztreonam can be substituted for penicillin allergic patients PLUS Antipseudomonal fluoroquinolone OR aminoglycoside PLUS Vancomycin or linezolid. According to ATS/IDSA guidelines, treatment of nosocomial pneumonias such as VAP, HCAP, and HAP, you should avoid inadequate treatment given significant increase in mortality with undertreated health care infections tailor antibiotic therapy based on region, hospital, location within hospital, and time period and avoid antibiotic overuse by tailoring therapy based on culture results and treating for minimum effective time period.
DURATION OF ANTIBIOTIC THERAPY ã…¡ Patients will usually respond to appropriate treatment within 3-4 days, even if they are bacteremic. The IDSA and ATS recommend that CAP should be treated for a minimum of 5 days and until the patient is afebrile for 72 hours. Step-down to oral therapy and discharge from the hospital can occur when there is no more than one marker of clinical instability: Temperature < 37.8°C, Pulse < 100 bpm, Respiratory rate < 24/min, O2 saturation > 90%, Maintaining oral intake and Normal mental status. Duration of therapy for nosocomial pneumonias is uncertain, but shorter duration (8 vs. 15 days) has been shown to be as effective and to lead to less resistance. Pseudomonas and Staphylococcus species warrant 14-day courses. Negative growth in sputum or tracheal aspirate allows stopping treatment for Staphylococcus.
REFERENCES
ATS/IDSA Joint Statement. Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia. Am J Respir Care Med 2005;171: 388-416. Available at: https://pubmed.ncbi.nlm.nih.gov/15699079
Iregui M, Ward S, Sherman G, et al. Clinical importance of delays in the initiation of appropriate antibiotic treatment for ventilator-associated pneumonia. Chest 2002;122:262-8. Available at: https://pubmed.ncbi.nlm.nih.gov/12114368
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. Available at: https://pubmed.ncbi.nlm.nih.gov/17278083
Chastre J, Wolff M, Fagon JY, et al. Comparison of 8 vs 15 days of antibiotic therapy for ventilator-associated pneumonia in adults: a randomized trial. JAMA 2003;290:2588-98. Available at: https://jamanetwork.com/journals/jama/fullarticle/197644