Acute bronchitis and CAP: Basic and Updates from ATS/IDSA

Acute bronchitis

Definition: inflammation of the large airways without evidence of pneumonia

Epidemiology: approx 5% of adults develop one in a year, with high burden on the management of cough, its main symptom. Common in fall and winter.

Etiology:

• Viruses (90%): rhinovirus, coronavirus, parainfluenza. respiratory syncytial virus. HMPV, influenza. 
• Bacteria: B. pertussis, M. pneumonia, Chlamydia pneumoniae (in immunocompetent); Moraxella catarrhalis, H. influenzae, S. pneumoniae (COPD/smokers)

H&P:

• Cough, with/wo sputum, lasting 10-20 days sometimes 1 mo. Headache, rhinorrhea, systemic symptoms. Fever +/-
• Sputum purulency DOES NOT define bacterial infection or benefit from antibiotic therapy
• Must be differentiated with: pneumonia, asthma exacerbation, COPD, CHF
• In elderly, cxr and simple labs may be needed

Tx:

• Supportive; routine antitussive, steroids, and BD not recommended
• Red flags: hemoptysis, worsening dyspnea, weight loss, difficulty swallowing, persistent fever
• Antibiotics: guideline said CRP and procalcitonin should guide the decision, if needed

Pneumonia 

Definition: infection of the pulmonary parenchyma from the level of the respiratory bronchioles to alveoli.

Clinically, pneumonia can be recognized by the presence of a new lung infiltrate coupled with any of the following: 

• new or increased cough
• dyspnea
• pleuritic chest pain
• purulent sputum
• confusion
• fever
• hypoxemia
• rales 
• leukocytosis, or leukopenia

Classification

• Community acquired (CAP): in community dwelling individuals
• Hospital acquired (HAP): occuring >48H after hospitalization
• Ventilator associated (VAP): occuring >48H after intubation

Epidemiology

• 1.5 mi annual visits to ED in US, leading cause of admission
• 8th cause of death in the US, and 4th worldwide
• LRTI 2nd cause of mortality in low income countries
• 2019 US: mortality rate 10.8/100.000
• Increase mortality after hospitalization
• Higher risk in patients with CHF and COPD
• More reading: Louisville pneumonia study

Microbiology

• CDC EPIC study (2015): 62% no pathogens, 22% viral only, 11% bacterial only, 5% bacterial/viral coinfection
• In the preantibiotic era, rates of S. pneumoniae exceeded 90%. As recently as the 1990s, clinical reviews referenced S. pneumoniae as the etiology for between 20% and 75% of CAP.
• Other bacteria commonly cited as “classic” CAP pathogens include Haemophilus influenzae, Mycoplasma pneumoniae, Legionella pneumophila, Staphylococcus aureus, Moraxella catarrhalis, and Chlamydia pneumoniae.
• Virus: rhinovirus, influenza A/B, HMPV, RSV, parainfluenza, coronavirus
• Concern for antibiotic resistance: MRSA, MDR Pseudomonas. ESBL Enterobacters, ACIBA
• Traditional view: invasion of the sterile LRT by pathogen from aspiration/inhalation
• New studies suggest that it may results from dishomeostasos of lung microbiome 

Clinical evaluation

• The diagnostic hallmarks of pneumonia: CXR + clinical signs -> new infiltrate on chest imaging, clinical evidence of infection (e.g., fever or leukocytosis), and findings suggestive of respiratory tract involvement (e.g., cough, sputum production, dyspnea, or abnormalities on the pulmonary physical exam
• The presence of hemoptysis, erythematous rash, skin pustules, severe pneumonia during the summer months, and cavitary disease should raise concern for community-acquired MRSA.
• Similarly, diarrhea and hyponatremia should prompt consideration of infection with Legionella species
• Atypical features on presentation including confusion or the absence of hypoxemia
• Chest auscultation only have 0.33 sensitivity and 0.87 specificity

Imaging

• Historically, CXR is considered gold standard
• CT may have better performance and may differentiate CXR based diagnosis
• POCUS (Point of care USG)

Laboratory exams

• Only obtain blood cultures in severe CAP or if risk factors for MRSA and/or PsA are present
• Outpatient setting: recommend against any diagnostic testing (except for a chest X-ray)
• Inpatient non-severe pneumonia: recommend blood cultures and sputum gram stain/culture ONLY if risk factors for MRSA and/or PsA are present
• Inpatient severe pneumonia: recommend blood cultures, sputum gram stain/culture, Streptococcus pneumoniae urine antigen, and Legionella urine antigen and PCR/culture
• Procalcitonin should NOT be used in the diagnosis of CAP; it has roughly 65-75% sensitivity for detecting bacterial pneumonia

Risk stratification

• PSI score >> CURB-65

• Patients <50 years of age who do not have any of the above comorbid illnesses or physical examination findings are risk class I; 
• patients with a score of ≤70 are risk class II; 
• patients with a score of 71–90 are risk class III; 
• patients with a score of 91–130 are risk class IV; 
• and patients with a score of >130 are risk class V. 
• Risk classes I and II are felt appropriate for outpatient care, while risk classes IV and V should be hospitalized. Disposition for patients in risk class III should be guided by clinician judgment
• CURB-65 (confusion, blood urea nitrogen >20 mg/dL, respiratory rate ≥30 breaths per minute, systolic blood pressure <90 mm Hg or diastolic blood pressure ≤60 mm Hg, and age ≥65 years of age)
• Patients with a score of 0 to 2 are classified as low-risk and have 30-day mortality rates less than or equal to 2.1%
• Admission to ICU? 2007 IDSA-ATS major and minor criteria
• The major criteria (need for mechanical ventilation or vasopressor support) are self-evident indications for ICU admission
• A large prospective validation study of 1062 patients with CAP in the United Kingdom found the presence of greater than or equal to 3 IDSA–ATS minor criteria to be predictive of the need for mechanical ventilation or vasopressors and ICU adm

Empiric antibiotic therapy

• Macrolides are no longer recommended as first line therapy in uncomplicated outpatient CAP unless the local streptococcal resistance to azithromycin is <25% 
• Amoxicillin and doxycycline take the place of macrolides as first line treatment in uncomplicated outpatient CAP.
• Single-agent amoxicillin, while lacking activity against atypical pathogens, achieves success rates comparable to other antibiotic classes in the treatment of CAP in the outpatient setting 
• Empiric antibiotic therapy should be expanded for outpatients with comorbidities including chronic heart, lung, liver, or renal disease; patients with diabetes mellitus; alcohol use disorder; malignancy; or asplenia.
• For outpatients with comorbidities, monotherapy with a respiratory fluoroquinolone continues to receive a strong recommendation in recent guidelines
• The addition of a macrolide to β-lactam therapy may improve outcomes through several mechanisms including coverage of atypical pathogens, nonbactericidal immunomodulatory effects, and suppression of the exotoxin pneumolysin production when infection is caused by S. pneumoniae.
• Monotherapy with a respiratory fluoroquinolone for hospitalized patients with nonsevere CAP continues to receive a strong recommendation in IDSA–ATS; observational studies have reported relative reductions in mortality of 30% to 45% with the use of fluoroquinolones compared to β-lactam monotherapy for hospitalized patients with CAP
• In hospitalized patients:
• Non-severe CAP – only treat empirically for MRSA and/or PsA if the organism has been isolated from the patient’s respiratory tract in the past
• Severe CAP – treat empirically for MRSA and/or PsA if the patient has any risk factors for MRSA and/or PsA respiratory infection

• Empiric treatment of anaerobes in aspiration pneumonia remains controversial, but the new guidelines recommend only treating anaerobes if there is suspicion for or a proven lung abscess and/or empyema.
• Continue antibiotics for at least 48 hours in patients who are diagnosed with influenza pneumonia
• Duration of antibiotics is based on clinical improvement (but should be a minimum of 5 days
• If cultures are not growing MRSA and/or PsA, can stop empiric treatment for MRSA and/or PsA
• If clinically improving, stop antibiotics following 48 hours of clinical improvement after a minimum of 5 days. Clinical improvement is determined by resolution of vital sign abnormalities, ability to eat/improved appetite, and normal mentation.
• Do not use corticosteroids as adjunctive treatment and do not obtain routine follow up chest X-rays

Common presentation

Streptococcus pneumoniae

• Most common CAP cause
• Airborne droplet/contact w respiratory secretions 
• Fever, purulent rust colored sputum, pleuritic chest pain, dense consolidation on cxr
• Efusi pleura and CRP>20 - indicate bacteremia
• Gram positive lance shaped diplococci
• Recommendation: hi dose amoxicillin; ceftriaxone, respiratory floroquinolones, b-lactam macrolide combination

H. influenzae

• Small gram negative coccobacillus encapsulated/non
• High in children and elderly

Mycoplasma pneumoniae

• Smallest self replicating organism
• Obligate parasite to epithelial cells
• Most common cause of uncomplicated bronchitis and outpatient CAP
• Atypical pneumonia: subacute symptoms, less prod. cough, less sever disease and cxr features
• CT scan: bronchial thickening, ground glass opacities, centrilobular nodules
• Can cause extrapulmonary disease
• Resistant to b-lactams; use macrolide or respiratory  floroquinolones

Legionella pneumophila

• Intracellular aerobic faintly gram negative bacillus
• Inhalation from reservoir: fresh water, plumbing, soil, can also from aspiration of contaminated water
• Tx: azihtromycin 500 mg od / levofloxacin 750 mg od