Community-Acquired Pneumonia: A Comprehensive Guide

Pneumonia is an inflammatory condition of the lung tissue (including alveoli, alveolar sacs, respiratory bronchioles, terminal bronchioles, and interstitial tissue) that can affect an entire lobe, alveoli adjacent to the bronchus, or interstitial tissue.

Classification:

• Acute pneumonia: Lasts less than 21 days.

• Community-acquired pneumonia: Not associated with a hospital environment.

• Pneumonia in immunocompetent individuals: Patients with a healthy immune system.

Special Cases:

• HIV Infection: Common pathogens include *Pneumocystis jirovecii, Mycobacterium tuberculosis, Cryptococcus, Histoplasmosis*.

• Organ Transplant Recipients: Common pathogens include fungi, *Nocardia* (soil infection), CMV.

• Neutropenia: Common pathogens include fungi, gram-negative bacteria.

Epidemiology:

• Leading cause of death among infectious diseases.

• Lower respiratory infections: 3rd leading cause of death in 2000, 4th in 2016.

• COVID-19: 10th leading cause of death globally, 3rd in the United States.

Diagnosis:

• Diagnostic components: Identification, differentiation, pathogen, severity.

• Role of X-ray:

• Essential in diagnosing pneumonia, helping to identify the progression of lung tissue damage.

• Helps identify underlying pathologies, causes of pneumonia.

• Assesses severity, prognosis.

• Monitors treatment and detects complications.

• X-ray findings:

• Description: Consolidation, alveolar damage, opacities, parenchymal opacity, increased density.

• Poor specificity: Requires clinical correlation to rule out other conditions.

• Poor sensitivity: Pneumonia may still have normal X-ray results.

• X-ray does not help identify the pathogen: It helps group causes.

• Damage by type:

• Lobe: *S. pneumoniae, Klebsiella, H. influenza, gram-negative bacteria.*

• Patchy: Atypical bacteria, viruses, *Legionella*.

• Interstitial: Viruses, *Pneumocystis, Legionella*.

• Cavity: Anaerobic bacteria, *Klebsiella, tuberculosis, Staphylococcus, fungi.*

• Significant effusion: *Staphylococcus, anaerobic bacteria, Klebsiella.*

• Microbiological testing:

• Non-invasive: Sputum, sputum with nebulization.

• Invasive: Endotracheal aspiration, transthoracic biopsy, blind bronchoalveolar lavage or bronchoscopy, protected blind brushing or bronchoscopy.

• Indications for microbiological testing:

• Low risk: Not mandatory.

• Moderate (hospitalization) or high (ICU): 2 blood cultures, Gram stain/sputum culture, *Legionella* testing in urine.

• Culture time: No more than 48 hours.

• Positive blood culture: Does not equate to 100% pneumonia.

• *Staphylococcus coagulase negative*: Not a cause of pneumonia in immunocompetent individuals.

• Viral pneumonia: Epidemiological factors are key to diagnosis.

• Thin, watery sputum: Often seen with viruses and *Mycoplasma*.

• Few bacteria on sputum stain: May indicate *Legionella, Mycoplasma, viruses*.

Clinical:

• Acute cough with dyspnea, tachypnea, fever, crackles: New or progressive X-ray findings.

• Differential diagnoses: Bronchitis, heart failure, pulmonary embolism, pulmonary infarction, tuberculosis, lung cancer.

• Gold standard for diagnosis: No gold standard.

• Clinical findings aid in accurate diagnosis 70% of the time.

• Imaging, blood cultures, CRP increase accuracy.

Differentiating between community-acquired and hospital-acquired pneumonia:

• Time of onset: Within 1 day or consecutively, not exceeding 1 day, from the last symptom.

• Location of onset: Less than 2 days from the point of transfer, more than 2 days from the point of admission (within 48 hours after discharge is hospital-acquired pneumonia).

Treatment:

• Not targeted in treatment: Clinical findings do not help guide the cause, testing is insufficient.

• Common bacteria in the community: *S. pneumoniae, Haemophilus influenza, atypical bacteria, gram-negative bacteria, Staphylococcus*.

• Pneumonia pathogens in Vietnam: *S. pneumoniae (39%), atypical bacteria (38%), Haemophilus influenza (14%)*.

• *S. pneumoniae* with oral penicillin:

• MIC > 2: Resistant.

• MIC < 0.06: Sensitive.

• *S. pneumoniae* with penicillin injection 12 million units/day:

• MIC > 8: Resistant.

• MIC < 2: Sensitive.

• *S. pneumoniae* with penicillin > 18 million units/day:

• MIC > 12: Resistant.

• MIC < 6: Sensitive.

PSI Score:

• Groups I, II: Outpatient.

• Group III: Outpatient/Inpatient.

• Groups IV, V: Inpatient.

Pathogen by severity:

• Outpatient, no risk factors: *Streptococcus, Mycoplasma, Chlamydia, Haemophilus influenza* (5% mortality).

• Outpatient, risk factors: *Streptococcus, Mycoplasma, Chlamydia, Haemophilus influenza, gram-negative bacteria* (mortality < 5%, hospitalization < 20%).

• Inpatient, non-ICU: *Streptococcus, Mycoplasma, Chlamydia, Haemophilus influenza, gram-negative bacteria, Legionella* (5-25% mortality).

• ICU: *Streptococcus, Mycoplasma, Haemophilus influenza, gram-negative bacteria, Legionella, Pseudomonas, Staphylococcus* (mortality < 50%).

Pathogen by pre-existing conditions:

• Alcoholism: *Streptococcus, Klebsiella, Acinetobacter, oral anaerobic bacteria.*

• COPD and smoking: *Streptococcus, Haemophilus influenza, Mycoplasma, Chlamydia, Legionella, Pseudomonas.*

• Rare pneumonia: Gram-negative gut bacteria, oral anaerobic bacteria.

• Lung abscess: *CA-MRSA, anaerobic bacteria, fungi, atypical Mycobacteria*.

• Exposure to bat or bird guano: *Histoplasma capsulatum*.

• Endobronchial obstruction: Anaerobic bacteria, *Streptococcus, Haemophilus influenza, Staphylococcus*.

• Structural lung disease: *Pseudomonas, Staphylococcus, Burkholderia*.

Factors increasing antibiotic resistance:

• Age > 65.

• Beta-lactam use in the past 3 months.

• Alcoholism.

• Corticosteroid use.

• Multiple comorbidities.

• Exposure to children in day care centers.

• History of *Staphylococcus* isolation in the past.

• *Staphylococcus* colonization.

• Recent antibiotic therapy.

Factors increasing Pseudomonas resistance:

• Recent *Pseudomonas* isolation.

• Structural lung disease (bronchiectasis).

• Corticosteroid use at 10mg daily.

• Broad-spectrum antibiotic therapy > 7 days in the past month.

• Malnutrition.

Principles of antibiotic therapy development:

• Severity.

• Antibiotic resistance in bacteria.

• Mortality rate.

• Antibiotic spectrum.

• Number of antibiotics.

• Risk of increased resistance.

• Risk of missing a pathogen.

Treatment choices based on experience:

• Mild community-acquired pneumonia with atypical bacterial pathogens accounts for 20-40%.

• IDSA, ATS: Macrolide (covers *Pneumocystis, atypical bacteria*, reduces severity, improves mortality in hospitalized patients).

• Europe: Beta-lactam (covers *S. pneumoniae*, atypical bacteria self-resolve, *Legionella* rare, avoids overuse of antibiotics).

Treatment choices based on CURB:

• CURB 0-1: Amoxicillin 500-1g x 3/day, Clarithromycin 500mg x 2/day, or amoxicillin + clarithromycin when atypical bacteria are suspected, amoxicillin/clavulanate + macrolide, 2nd generation cephalosporin: ceftriaxone 0.5g x 3.

• CURB 2: Amoxicillin/clavulanate 1g x 3 in combination with a macrolide. If oral administration is not possible, switch to intravenous, or levofloxacin 750mg, or moxifloxacin 400mg/day. Maintain fluid and electrolyte balance, fever > 38.5 degrees Celsius should be reduced with medication.

• CURB 3-5: Amoxicillin/clavulanate 1-2g x 3, clarithromycin 500mg x 2/intravenous, penicillin G 1-2 x 4/time + levofloxacin 500 x 2/Ciprofloxacin 400 x 2, cefuroxime 1.5g x 3/day or ceftriaxone 2g/day + clarithromycin 500mg x 2/day intravenous. If *Legionella* is suspected, use levofloxacin 750. If *Staphylococcus aureus* is suspected, use vancomycin 1g x 2/linezolide 600mg x 2.

Factors suggesting *Pseudomonas*:

• Corticosteroid use.

• Broad-spectrum antibiotic use for more than 1 week in the past month.

• Malnutrition.

• Structural lung disease like bronchiectasis.

Antibiotic therapy for *MRSA*:

• Vancomycin 15mg/kg/12h, adjust dose based on renal function.

• Linezolide 600mg/12h.

Antibiotic therapy for *Pseudomonas*:

• Piperacillin-tazobactam: 4.5g/6h.

• Cefepime 2g/8h.

• Ceftazidime 2g/8h.

• Aztreonam 2g/8h.

• Meropenem 1g/8h.

• Imipenem 500mg/6h.

Indications for antibiotics against *MRSA* or *Pseudomonas*:

• Based on risk factors for infection according to local epidemiology.

• Should have relevant factors like pre-existing conditions, intravenous antibiotic indications.

• If currently on antibiotics and culture results do not suggest a pathogen + clinical stability -> downgrade standard treatment.

Aspiration pneumonia:

• Antibiotics covering anaerobic bacteria are not routinely indicated.

• Except in cases of lung abscess, or empyema.

Corticosteroid use:

• Routine corticosteroid use is not recommended in patients with non-severe pneumonia.

• Avoid in severe patients with HIV infection.

• May be used in patients with community-acquired pneumonia with resistant sepsis.

Positive influenza test:

• Antiviral therapy is recommended, with inpatient (strong recommendation) and outpatient (weak recommendation) treatment.

• Antibiotics: Standard antibiotic use is recommended.

• Antibiotic use is recommended in patients with community-acquired pneumonia with positive influenza because a positive influenza test may indicate co-infection with bacteria, most commonly *Staphylococcus, Streptococcus, Haemophilus influenza*. Mortality rate of 10%.

• Procalcitonin and other biomarkers do not help rule out the diagnosis of bacterial pneumonia.

• However, if there is no evidence of bacterial infection, and clinical improvement occurs early, consider discontinuing antibiotics after 48-72 hours.

Duration of antibiotic use:

• Antibiotics are recommended based on clinical improvement after 48-72 hours.

• Should continue until the patient is stable, and the minimum duration is 5 days.

• If pneumonia is suspected of being *MRSA* or *Pseudomonas*, the minimum duration of antibiotic use is 7 days.

• Longer antibiotic regimens are recommended for pneumonia with meningitis, endocarditis, other deep infections, infection with agents like *Burkholderia, tuberculosis, fungi*.

Procalcitonin use:

• Should only be used to guide antibiotic duration when the patient’s hospital stay exceeds the average length of stay (5-7 days).

Patients who do not achieve stability after 5 days of treatment:

• Increased risk of mortality and adverse outcomes.

• Thoroughly assess bacterial resistance to current treatment or complications of pneumonia (abscess, empyema), or infection vulnerabilities, or other causes of inflammatory response.

Principles of antibiotic use:

• Use adequate doses.

• Use bactericidal antibiotics.

• Use pharmacokinetic/pharmacodynamic (PK/PD) principles.

• Do not change antibiotics in the first 72 hours unless clinical deterioration occurs or there is microbiological evidence for a change.

Switching to oral administration:

• Reduced cough, reduced dyspnea.

• Fever resolution twice, 8 hours apart, and the patient can swallow.

Discharge:

• Clinical stability and antibiotics switched to oral administration.

Treatment goals:

• Eliminate bacteria or minimize bacteria at the infection site.

• Reduce the carriage of antibiotic-resistant bacteria.

• Minimize impact on normal bacteria.

Effectiveness of eliminating bacteria:

• Maximize clinical effectiveness.

• Cost-effective.

• Minimize the selection of drug resistance.

Reduce the carriage of antibiotic-resistant bacteria:

• Minimize the spread of antibiotic-resistant bacteria.

Minimize impact on normal bacteria:

• Minimize the selection of drug-resistant bacterial strains.

Start antibiotic therapy as early as possible:

• Mortality rate increases with each hour of delay.

• Mortality rate significantly reduces if antibiotics are administered within the first 8 hours.

Treatment duration:

• Outpatient: 5-7 days.

• Inpatient: 7-10 days (more common with *Pseudomonas*).

• Atypical bacteria: 10-14 days.

• Chronic corticosteroid use: > 14 days.

Key to infection control:

• Optimizing antibiotic activity.

T>MIC:

• Penicillin, cephalosporins, carbapenem, monobactam, aztreonam, clindamycin, macrolide.

Peak/MIC:

• Aminoglycoside, respiratory quinolone, linezolide, daptomycin.

AUC/MIC:

• Fluoroquinolone, azithromycin, vancomycin, tetracycline.

AUC/MIC helps:

• Predict 90% of clinically successful treatment cases.

AUC/MIC index in gram-negative bacteria:

• > 100-125: Predicts 90% of treatment success cases.

AUC/MIC index in gram-positive cocci:

• > 25-30: Predicts 90% of treatment success cases.

Treatment of atypical bacteria:

• Reduces mortality rate when treating this group.

Benefits of antibiotic combination therapy:

• Wider antibacterial spectrum (increased effectiveness).

• Early and effective treatment (avoiding delayed combination).

• Reduced risk of resistance development.

• Synergistic effects.

• Anti-inflammatory, reduced endotoxin levels.

Disadvantages of antibiotic combination therapy:

• Broad antibiotic spectrum may promote the development of antibiotic resistance.

• Increased risk of superinfection.

• Increased interactions and toxicity.

• Increased treatment costs.

Drug dosage:

• Intravenous: Amoxicillin/clavulanate 1g x 3, ceftazidime 1g x 3-4/day, 2g x 2/day, ceftriaxone 1-2g/day, cefotaxime 1g x 3-4/day, cefoperazone/sulbactam 1-4g x 2, cefepime 1g x 2-3/day.

• TTM: Ertapenem 1g x 1/day, ticarcillin/clavulanate 3.2g x 3/day, piperacillin/tazobactam 4.5g x 4/day, imipenem 0.5g x 4/day, meropenem 1g x 3/day.

• Quinolone: Ciprofloxacin 0.2g x 3/day, levofloxacin 750mg x 1 or 0.5g x 2/day, moxifloxacin 400mg x 1/day, azithromycin 0.5g x 1-2/day.

Methicillin-resistant Staphylococcus:

• Vancomycin 1g x 2/day.

• Linezolide 600mg x 2/day.

• Teicoplanin 800mg/day x 2-3 days -> 400mg/day.

Methicillin-sensitive Staphylococcus:

• Clindamycin 600mg x 4/day.

• Oxacillin 0.5g x 4/day.

Note: This article is for reference purposes only and does not replace the advice of a healthcare professional. Patients should be examined and treated by a specialist.