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🌱 來自: Huppert’s Notes
Pulmonary Infections🚧 施工中
Pulmonary Infections
Community acquired pneumonia (CAP)
• Definition: An acute pulmonary infection that develops outside of the hospital or within the first 48 hours of admission
• Pathophysiology:
- Organisms that colonize the nasopharynx make their way to the lungs via microaspiration
- Once in the lung, poor mucociliary clearance and the organism’s virulence factors allow replication and establishment of infection
- The body’s immune response to the organisms creates the clinical features of pneumonia
• Clinical features: Cough, shortness of breath, fever. Patients who meet the following criteria can be classified as having severe CAP (relevant for some diagnostic tests, see Table 8.17)
• Pathogens:
- Typical bacteria:
• S. pneumoniae: Historically the most common cause of CAP; rates are decreasing due to use of the pneumococcal vaccines in the United States
• H. influenzae: Especially prominent in those with underlying lung disease
• M. catarrhalis
- Atypical bacteria:
• M. pneumoniae: Transmitted with high frequency via close contact
• C. pneumoniae and C. psittaci
• Legionella spp: Outbreaks are associated with exposure to aerosols, including those from air conditioners, showers, spas, and fountains; also associated with travel
- Other clinically relevant bacteria:
• S. aureus:
- CAP from S. aureus includes both MSSA and MRSA isolates
- Preceding influenza is a risk factor for S. aureus pneumonia
- CAP from MRSA often causes a severe pneumonia, and is most commonly seen in patients with:
• Necrotizing pneumonia or co-existing empyema
• Known colonization or prior infection with MRSA
• Recent broad-spectrum antibiotic use
• Post-influenza pneumonia, injection drug use, HIV/AIDS
• Gram-negative rods
- Pseudomonas aeruginosa: Relatively uncommon cause of CAP. Specific risk factors for community-acquired P. aeruginosa infections include:
• Structural lung disease (e.g., bronchiectasis or cystic fibrosis)
• Recent broad-spectrum antibiotic use
• Severe immunocompromise (e.g., HIV, solid organ of hematopoietic stem cell transplant, neutropenia, immunosuppressive therapy)
• Frequent COPD exacerbations requiring glucocorticoid and/or antibiotic use
- K. pneumoniae: Most common in patients with underlying lung disease or heavy alcohol use
- Viruses: There is increasing evidence to suggest viruses are a common cause of CAP, either as the sole pathogen or with a bacterial infection. Notable viruses include:
• Influenza A/B
• Respiratory syncytial virus (RSV)
• Parainfluenza viruses (especially in immunocompromised adults)
• Rhinovirus (frequently isolated, though there is conflicting evidence on whether it is a true pathogen or a bystander organism)
• Human metapneumovirus
• Coronavirus (including SARS-CoV-2 of the COVID-19 outbreak)
• Diagnosis:
- CXR and/or chest CT showing a focal consolidation with a compatible clinical syndrome suggesting pneumonia
- Obtain blood cultures, sputum Gram stain, and sputum culture in patients with severe CAP (see Table 8.17), immunocompromised hosts, patients being empirically treated for MRSA or P. aeruginosa
- Obtain a nasopharyngeal (NP) swab for influenza PCR testing in all patients with suspected CAP during influenza season
• In critically ill patients, obtain both upper and lower NP swab and do not stop empiric anti-viral therapy until the lower respiratory specimen is negative. This is because some patients may stop shedding influenza virus form the upper airways but not the lower airways, leading to a false-negative upper airway NP swab.
TABLE 8.17 • Criteria to Define Severe Community Acquired Pneumonia (CAP)
• Treatment:
- CAP that can be managed in the outpatient setting:
• No recent antibiotics/comorbidities: PO amoxicillin, doxycycline, or azithromycin
• If recent antibiotics, more severe case, and/or notable medical comorbidities (e.g., chronic lung disease, CKD, chronic liver disease, alcohol use disorder, cardiac disease):
- [PO amoxicillin/clavulanate or cefpodoxime or cefuroxime] AND [PO doxycycline or azithromycin]
OR
- A respiratory fluoroquinolone (e.g., PO levofloxacin or moxifloxacin)
- CAP requiring hospital admission to the general medical floor: ceftriaxone + [azithromycin or clarithromycin] + empiric oseltamivir during flu season until influenza testing returns
- Severe CAP, requiring ICU admission: vancomycin + [ceftriaxone or cefepime (if P. aeruginosa coverage needed)] + azithromycin + empiric oseltamivir during flu season until influenza testing returns
• When empiric MRSA coverage is started (e.g., vancomycin) can use a negative MRSA swab to narrow antibiotics. A negative MRSA nasal swab has a ~95% negative predictive value for MRSA pneumonia
- Duration of therapy:
• Five days of antibiotics is appropriate for most patients
• Treatment duration can be extended in those with a delayed response to therapy
• Patients with S. aureus or Pseudomonas should be treated for at least 7 days
Hospital-acquired pneumonia (HAP) & ventilator-acquired pneumonia (VAP)
• Definitions:
- Hospital-acquired pneumonia (HAP): Pneumonia diagnosed >48 hrs after hospital admission and not present at hospital admission
- Ventilator-associated pneumonia (VAP): Pneumonia diagnosed >48 hrs after intubation
• Pathogens:
- Gram-negative rods: P. aeruginosa, Klebsiella spp., E. coli, Enterobacter spp. There is an increased risk for multidrug-resistant Gram-negative rods, as well (e.g., ESBL-producing organisms)
- Gram-positive cocci: S. aureus
• Clinical Features: Similar to CAP, the clinical features of HAP/VAP include the presence of new systemic signs of infection (e.g., fever, leukocytosis) + suggestion of a new pulmonary process (including a new lung infiltrate on chest imaging, purulent sputum production, and new or worsening hypoxemia)
• Diagnosis: Obtain the following for any patient suspected for HAP/VAP:
- Sputum cultures from either produced sputum or endotracheal or endobronchial sampling, such as a tracheal aspirate
- Peripheral blood cultures
- MRSA nasal swab
- Chest imaging (CXR or CT chest)
• Treatment:
- Empiric therapy for HAP/VAP should include:
• Coverage of MRSA, such as with vancomycin
• Coverage of P. aeruginosa and Gram-negative rods, such as with piperacillin-tazobactam or cefepime
• Consider whether ESBL coverage and/or a second agent for Gram-negative organisms (e.g., ciprofloxacin) is needed for critically-ill patients
- Duration of therapy:
• Seven days is an effective duration of therapy for most patients
• Complications such as bacteremia, lung abscess or complicated pleural effusions may warrant longer courses
Parapneumonic effusions
• Definition: Pleural effusions that develop in the setting of and adjacent to pneumonia, representing a common complication of pneumonia
• Pathogens: Pyogenic bacterial infections with Gram-positive organisms are most common, including:
- S. pneumoniae
- Viridians streptococci, including members of the S. anginosus group
- S. aureus (most common cause of hospital-acquired parapneumonic effusions)
- Anaerobic oral flora, such as Fusobacterium spp., Prevotella spp., Peptostreptococcus spp., and Bacteroides spp.
• Clinical features: Similar to pneumonia. Dullness to percussion on exam may increase suspicion
• Diagnosis:
- Parapneumonic effusions are often found on imaging (CXR, CT, bedside ultrasound)
- Characterization of a parapneumonic effusion relies on pleural fluid analysis: See Table 8.18
TABLE 8.18 • Parapneumonic Effusions: Diagnosis and Management
• Treatment: See Table 8.18
Pneumocystis jirovecii pneumonia (PJP, aka PCP)
• Risk factors:
- HIV (CD4 <200 cells/µL)
- Cancer, solid organ transplant, or bone marrow transplant
- Rheumatologic disease (granulomatosis with polyangiitis [GPA] has intrinsic risk)
- Patients on chronic steroids (prednisone ≥20 mg for 20+ days, or the equivalent)
• Clinical features:
- In HIV-infected patients, there is often a gradual onset of fever, cough, and dyspnea over days to weeks
- In non-HIV-infected patients, symptoms may be more aggressive and abrupt in onset
• Diagnosis:
- Bronchoscopy is gold standard. Can also check beta-D glucan, LDH. Test characteristics differ in patients with HIV versus non-HIV infected patients
- Can often perform testing on induced sputum samples that can make the diagnosis if positive. If negative, bronchoscopy should be performed
- Treat empirically while awaiting bronchoscopy, as organisms will be present for up to 2 weeks on BAL microscopy
• Treatment:
- High-dose trimethoprim-sulfamethoxazole: 15–20 mg/kg of trimethoprim divided in 3–4 daily doses for 21 days
- Add adjunctive glucocorticoids if: A-a gradient >35 mmHg or PaO2< 70 mmHg
- Steroids are not well studied for non-HIV-infected patients but are generally recommended
• Prophylaxis: Bactrim (alternatives include dapsone, atovaquone, inhaled pentamidine). Prophylaxis is indicated in the following scenarios:
- Patients with HIV and a CD4 count <200 cells/µL
- Individuals with another immunocompromising condition (e.g., autoimmune disease, hematologic malignancy, or another immunocompromising medication) treated with glucocorticoids at a dose >20 mg prednisone for 20 days or more (“20/20” rule)
- Patients with acute lymphocytic leukemia
- Allogenic stem cell transplant recipients and most autologous stem cell transplant recipients
- Solid organ transplant recipients
- Patients with certain primary immunodeficiencies (e.g., severe CVID, hyper IgM syndrome)
Influenza
• Virus: Influenza, commonly known as the flu, is caused by an influenza virus. Three of the four types of influenza viruses infect humans: A, B, and C
• Clinical features: Spread by respiratory droplet. Symptoms include fevers, chills, cough, and malaise. Can also be asymptomatic
• Diagnosis: CXR: Normal or alveolar pattern. Check influenza PCR
• Treatment: Oseltamivir, supportive care
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
• Virus:
- Coronaviruses are a family of viruses that can cause mild illnesses such as the common cold or more severe illness such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). In 2019, a new coronavirus was identified as the cause of a disease outbreak that originated in China and subsequently caused a global pandemic
- The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the name of the virus, which causes the disease known as coronavirus disease 2019 (COVID-19)
• Clinical features: Spread mainly by respiratory droplets. Causes cough, fever, shortness of breath, muscle aches, gastrointestinal symptoms, loss of smell, and leukopenia. Can be asymptomatic in ~40% of cases
• Diagnosis: Molecular tests are the main method of diagnosis, although rapid antigen tests may be used in certain situations
• Treatment:
- Supportive care is the mainstay of therapy
- Remdesivir in hospitalized patients with lower respiratory tract disease: 200 mg IV ×1 then 100 mg IV q24h for 4 additional days. May consider extending treatment to 10 days on a case-by-case basis (e.g., if the patient is intubated and not responding to the initial course).
- Dexamethasone 6 mg IV or PO for up to 10 days (or until hospital discharge, whichever comes first) can be given to patients undergoing mechanical ventilation, non-invasive ventilation, high-flow nasal cannula, or supplemental oxygen (e.g., ≥ 3–4 L of nasal cannula or whose trajectory suggests increasing severity of disease). Dexamethasone is not needed if patients are not hypoxic.
- Clinical trials are underway to determine the benefit of other therapeutic interventions
• Prevention: Several highly effective and safe vaccines are now available.
Mycobacterium tuberculosis (MTB)
• Subtypes: See Table 8.19
• Diagnosis:
- Screening for latent TB (LTBI): PPD (consider to be positive if >15mm and no risk factors, >10mm and medium risk factors, >5mm and high risk factors) or interferon gamma release assay (IGRA) for latent TB infection. The results of these tests are not useful to evaluate for active infection
- CXR or CT chest for pulmonary TB
- CT imaging of the suspected area for extra-pulmonary TB
- Core biopsy (or excisional if high suspicion and core biopsy negative) to diagnose TB lymphadenitis. Ultrasound of an infected lymph nodes may show necrotizing lymphadenopathy
- Sputum AFB cultures and TB PCR
• Treatment:
- Latent TB (LTBI): First rule out active TB, then treat with rifampin ×4 mo OR isoniazid/rifapentine ×3 mo OR isoniazid ×9 mo
- Active TB: RIPE therapy (rifampin, isoniazid (INH), pyrazinamide, ethambutol)
• All patients treated with isoniazid should also be treated with pyridoxine to prevent peripheral neuropathy
• If the patient is smear positive at the time of diagnosis, they are no longer infectious when all of the following conditions are met: 1) Adequate TB treatment ×2 wks, 2) Improvement of symptoms, 3) Three consecutive negative AFB smears
TABLE 8.19 • Subtypes of Tuberculosis
Non-tuberculous mycobacteria (NTM)
• Pathogens:
- M. avium (MAC): Most common NTM infection that often occurs in middle-age men with underlying lung disease OR female non-smokers. Patients present with subacute-chronic cough +/- weight loss
- M. kansasii: Second most common NTM infection. Risk factors for infection include COPD, HIV, and hematologic malignancy. Patients typically have symptoms similar to those with TB. CXR: May show a fibrocavitary lesion (thin-wall)
- M. abscessus, M. fortuitum, M. chelonae: Can cause disease in those with underlying lung disease and/or immunosuppression
• Diagnosis: CXR or chest CT, AFB cultures, PCRs
• Treatment: Regimens vary, see IDSA guidelines or others