Community-Acquired Pneumonia (CAP)

A 68-year-old man with a history of diabetes mellitus, COPD, and chronic smoking presents with 4 days of fever, productive cough, pleuritic chest pain, and progressive shortness of breath. His family reports new-onset confusion since this morning. He has had no recent hospitalizations or antibiotic use. On examination, his temperature is 38.8°C, heart rate 112/min, respiratory rate 32/min, blood pressure 92/58 mm Hg, and oxygen saturation 88% on room air. Chest examination reveals dullness to percussion, bronchial breath sounds, and crackles over the right lower lung field. Laboratory studies show leukocytosis, elevated CRP, mild hyponatremia, and elevated blood urea nitrogen. A chest X-ray demonstrates right lower lobe consolidation. Diagnosis?

Diagnosis is community-acquired pneumonia (CAP).

1. Definition

Community-acquired pneumonia is an acute infection of the lung parenchyma acquired outside hospital settings, characterized by:

1.1 Diagnostic Criteria

1. Symptoms and/or signs of lower respiratory tract infection
2. New pulmonary infiltrate on imaging
3. Supportive systemic or laboratory features of inflammation

There is no single gold-standard diagnostic test, and clinical examination alone cannot confirm the diagnosis. Imaging is a key step in securing it.

2. Etiology

2.1 Common Bacterial Causes

1. Streptococcus pneumoniae most frequently detected bacterial cause worldwide
2. Haemophilus influenzae
3. Staphylococcus aureus
4. Enterobacteriaceae spp.

2.2 Atypical Pathogens

1. Mycoplasma pneumoniae
2. Chlamydophila pneumoniae
3. Legionella pneumophila

2.3 Viral Causes

1. Influenza A and B
2. Rhinovirus
3. RSV
4. Human metapneumovirus
5. Parainfluenza viruses
6. Coronaviruses, including SARS-CoV-2 in the right context

Respiratory viruses are detectable in about one-third of adults with CAP, and viral–bacterial co-infection is important clinically.

2.4 Special Clinical Settings

1. Alcohol misuse, aspiration risk, or neurologic depressants increase susceptibility
2. Profound immunocompromise raises concern for opportunistic pathogens
3. Risk factors for MRSA or Pseudomonas aeruginosa should guide broader empiric therapy rather than severity alone

3. Pathophysiology

3.1 Route of Infection

1. Most bacterial CAP arises via microaspiration of pharyngeal secretions
2. Inhalation of infectious particles also contributes, especially in viral CAP

3.2 Core Process

1. Pathogens proliferate in the lower respiratory tract
2. Macrophages initiate cytokine and chemokine release
3. Neutrophils and inflammatory monocytes are recruited
4. Alveolar epithelial injury leads to edema, exudate, and impaired gas exchange

3.3 Consequences

1. Breathlessness, fever, hypoxia, and sometimes hypercarbia
2. Severe disease may progress to sepsis, shock, and extrapulmonary organ failure

4. Physiological Consequences

1. Ventilation–perfusion mismatch
2. Hypoxemia
3. Increased work of breathing
4. In severe disease: acute respiratory failure, septic shock, and multiorgan dysfunction

5. Classification and Severity

5.1 By Setting

1. Community-acquired pneumonia
2. Hospital-acquired pneumonia
3. Ventilator-associated pneumonia

5.2 CURB-65

1. Confusion
2. Urea >7 mmol/L or BUN >19 mg/dL
3. Respiratory rate ≥30/min
4. Blood pressure <90 systolic or ≤60 diastolic
5. Age ≥65 years

5.2.1 Interpretation

1. 0–1 low risk, outpatient usually appropriate
2. 2 consider admission
3. ≥3 severe CAP, consider ICU

5.3 IDSA/ATS Severe CAP Criteria

5.3.1 Major criteria

1. Need for invasive mechanical ventilation
2. Septic shock requiring vasopressors

5.3.2 Minor criteria

1. Respiratory rate >30/min
2. PaO₂/FiO₂ <250
3. Multilobar infiltrates
4. Confusion or disorientation
5. BUN ≥20 mg/dL
6. Leukocyte count <4000/μL
7. Platelets <100000/μL
8. Core temperature <36°C
9. Hypotension requiring aggressive fluid resuscitation

Severe CAP is diagnosed by 1 major or 3 or more minor criteria.

6. Clinical Features

6.1 Symptoms

1. Cough, often productive
2. Dyspnea
3. Pleuritic chest pain
4. Fever

6.2 Signs

1. Tachypnea
2. Rales or rhonchi
3. Dullness to percussion
4. Egophony
5. Bronchial breathing may indicate consolidation

6.3 Atypical Presentation

1. Older adults may have confusion or functional decline rather than classic symptoms
2. Immunocompromised patients may have mild respiratory symptoms despite significant disease

7. Diagnosis

7.1 Laboratory Features

1. Leukocyte count <4000/μL or >10000/μL can support the diagnosis
2. Neutrophilia or bandemia may be present
3. CRP and procalcitonin may be elevated

Important correction: CRP and procalcitonin have only modest diagnostic performance and should not be used to decide whether to start antibiotics. Procalcitonin may assist antibiotic discontinuation in selected patients.

7.2 Imaging

1. Chest radiography is standard first-line imaging
2. CT is more sensitive and is advised for uncertain or inconclusive cases
3. Lung ultrasound can be a valid alternative where expertise is available
4. Dynamic air bronchograms are a highly specific sonographic sign
5. Lung ultrasound is helpful but does not have enough sensitivity to rule out pneumonia

7.3 Microbiology

1. Low-severity community-managed CAP usually does not require routine microbiological sampling
2. Hospitalized patients often have sputum and blood cultures, though yield is low
3. Urinary antigen tests are available for S pneumoniae and L pneumophila
4. Antigen tests have good positive predictive value, but false negatives are common and they do not exclude co-infection

7.4 Molecular Testing

1. NAATs improve pathogen detection, especially for viruses and atypicals
2. Influenza and SARS-CoV-2 testing is recommended when exposure is suspected or circulating
3. Expanded viral testing may be useful in severe CAP
4. Evidence that syndromic NAATs reliably change antibiotic prescribing remains uncertain

8. Management

8.1 Empirical Antimicrobial Therapy

8.1.1 Outpatient

1. Amoxicillin or doxycycline
2. If chronic lung disease or asplenia: amoxicillin-clavulanate or oral cephalosporin plus macrolide or doxycycline
3. If allergic: respiratory fluoroquinolone
4. If respiratory viral PCR positive and no comorbidity and no suspicion of bacterial co-infection, empiric antibacterials may be avoided; with comorbidity, consider empiric antibacterials

8.1.2 Hospital ward

1. Beta-lactam plus macrolide is standard
2. Respiratory fluoroquinolone is an alternative in selected cases

8.1.3 ICU / severe CAP

1. Broad treatment is guided by risk factors and likely pathogens
2. If prior MRSA or Pseudomonas infection or recent hospitalization with IV antibiotics, use MRSA plus antipseudomonal coverage
3. In severe influenza, oseltamivir is recommended

8.2 Key Stewardship Principles

1. Severity alone is not a reason to add antipseudomonal or anti-MRSA agents
2. Known carriage, prior colonization, or recent IV antibiotics are important risk factors
3. If empiric MDR coverage is started, de-escalate rapidly when screening is negative

8.3 Anaerobic Coverage

Routine anaerobic coverage is not recommended, even when aspiration is present, unless there is a specific complication such as abscess or another clear indication.

8.4 Adjunctive Therapy

1. Corticosteroids are not recommended for non-severe CAP
2. For severe CAP, corticosteroids are suggested, except in influenza pneumonia
3. Guidelines are more supportive when septic shock coexists

8.5 Duration of Therapy

1. Minimum 5 days AND until clinical stability is achieved
2. Outpatient: 3–5 days
3. Inpatient without ICU: 5–7 days
4. ICU: 7–10 days, tailored to response and microbiology
5. Prolonged courses should be avoided unless specific indications (necrotizing pneumonia, empyema, bacteremia, S aureus, Pseudomonas, Legionella, or slow response)

9. Acute Severe CAP

1. Early antibiotics should not be delayed by testing
2. Oxygen and ventilatory support as needed
3. Vasopressors for septic shock
4. ICU admission based on severity criteria and organ support needs

10. Prognosis and Monitoring

1. Hospitalized CAP 30-day mortality: 4.1% to 9.6%
2. ICU CAP 30-day mortality up to 49.4%
3. Clinical stability guides transition to oral therapy and discharge
4. Stability criteria include afebrile, HR <100, RR <24, adequate oxygenation, and SBP >90 mm Hg

11. Long-Term Follow-Up

1. CAP has important post-acute sequelae
2. Persistent respiratory dysfunction, bronchiectasis risk, and COPD exacerbations can occur
3. Follow-up imaging not required if symptoms resolve
4. Imaging at 4–6 weeks if persistent symptoms or lung cancer risk factors
5. Cardiovascular complications: MI, arrhythmias, heart failure, stroke
6. Rehabilitation, vaccination, smoking cessation, cardiovascular risk management

12. Key Clinical Insight

Fever + cough + dyspnea + new infiltrate on imaging strongly indicates CAP. Early severity assessment (CURB-65) determines the site of care and guides initial management.

13. Exam Level Pearls

1. Streptococcus pneumoniae is the most common cause
2. Viral CAP common (~30%)
3. Imaging required for diagnosis
4. Procalcitonin → de-escalation, not initiation
5. Dynamic air bronchograms support diagnosis
6. Do not add MRSA/Pseudomonas coverage without risk factors
7. Do not routinely add anaerobic coverage
8. Steroids: no in non-severe, yes in severe non-influenza CAP

Aortic Dissection

A 60-year-old man with a history of long-standing hypertension presents with sudden onset severe chest pain described as tearing and ripping, radiating to the back between the scapulae. The pain reached maximum intensity at onset. He appears diaphoretic and anxious. Blood pressure is 180/100 mmHg in the right arm and 150/90 mmHg in the left arm. On examination, there is pulse asymmetry between the upper limbs. A chest X-ray shows widened mediastinum. Diagnosis?

Diagnosis is Aortic dissection.

1. Definition

Aortic dissection is a life-threatening condition characterized by a tear in the intimal layer of the aorta, allowing blood to enter between the intima and media, forming a false lumen that propagates proximally or distally, leading to compromised blood flow to vital organs.

2. Classification

2.1 Stanford Classification

1. Type A – involves ascending aorta (proximal)
2. Type B – involves descending aorta distal to left subclavian artery

2.2 DeBakey Classification

1. Type I – ascending + arch + descending aorta
2. Type II – ascending aorta only
3. Type III – descending aorta only
• IIIa – above diaphragm
• IIIb – below diaphragm

3. Etiology / Risk Factors

1. Hypertension (most common, ~70–75%)
2. Sudden increase in blood pressure (e.g. cocaine, heavy lifting, stimulants)
3. Connective tissue disorders
• Marfan syndrome
• Ehlers–Danlos syndrome
4. Congenital conditions
• Bicuspid aortic valve
• Coarctation of aorta
5. Preexisting aortic aneurysm
6. Atherosclerosis
7. Pregnancy (especially third trimester)
8. Iatrogenic (cardiac surgery, catheterization)
9. Family history

4. Pathophysiology

1. Intimal tear → blood enters media → false lumen formation
2. Dissection propagates anterograde (distal) or retrograde (proximal)
3. Proximal (Type A) leads to:
• Acute aortic regurgitation
• Cardiac tamponade
• Aortic rupture
4. Distal (Type B) leads to:
• Branch vessel occlusion → organ ischemia
5. False lumen expansion compresses true lumen → malperfusion

5. Clinical Features

5.1 Core Features

1. Chest pain – sudden onset, severe, tearing / ripping
2. Pain reaches maximum intensity immediately
3. Pain location:
• Anterior chest → Type A
• Back / interscapular → Type B
4. Pain may migrate with progression

5.2 Associated Features

1. Diaphoresis, nausea, vomiting
2. Hypertension (common)
3. Hypotension → suggests rupture or tamponade (poor prognosis)
4. Pulse deficit / BP difference >20 mmHg between arms
5. Neurological deficits (~20%)
6. Syncope
7. New early diastolic murmur → acute aortic regurgitation
8. Dyspnea or hemoptysis (rupture)

6. Complications

1. Aortic rupture (most fatal)
2. Cardiac tamponade
3. Acute aortic regurgitation
4. Myocardial infarction (coronary involvement)
5. Stroke (carotid involvement)
6. Renal failure (renal artery involvement)
7. Mesenteric ischemia
8. Limb ischemia
9. Multiorgan failure and death

7. Diagnosis

7.1 Initial Evaluation

1. ECG – may show ischemia; can be normal
2. Chest X-ray – widened mediastinum, pleural effusion
• May be normal in up to 20%

7.2 Laboratory

1. D-dimer elevated (sensitive, not specific)
2. Troponin elevated if coronary involvement
3. CBC → leukocytosis or anemia
4. Renal function tests → renal ischemia
5. Lactate elevated → tissue hypoperfusion

7.3 Definitive Imaging

1. CT angiography (CTA) – first-line in stable patients
2. Transesophageal echocardiography (TEE) – unstable patients
3. MRI – highly accurate (used in stable or follow-up cases)
4. Transthoracic echocardiography (TTE) – limited but useful for complications
5. Aortography – rarely used now

8. Treatment

8.1 Initial Stabilization

1. ICU monitoring (arterial line, IV access)
2. Pain control → IV morphine
3. Heart rate control → IV β-blockers (first-line)
• Esmolol, labetalol
• Target HR ≈ 60 bpm
4. Blood pressure target: 100–120 mmHg systolic (maintain end-organ perfusion)
5. Add vasodilator (nitroprusside or nicardipine) only after β-blocker

8.2 Type A Dissection

1. Surgical emergency
2. Requires urgent surgical repair
3. Includes:
• Excision of intimal tear
• Aortic graft replacement
• ± Aortic valve repair/replacement
4. Untreated mortality ~50% within 48 hours

8.3 Type B Dissection

1. Medical management (uncomplicated)
2. Indications for intervention:
• Malperfusion syndromes
• Aortic rupture / impending rupture
• Persistent pain or expansion
3. Endovascular repair (TEVAR) preferred in complicated cases

9. Key Clinical Insight

Sudden severe “tearing” chest pain + radiation to back + pulse/BP asymmetry + widened mediastinum = aortic dissection → initiate emergent imaging (CTA) and immediate BP/HR control (IV β-blocker) → urgent surgical management for type A (ascending) dissections

10. Exam Level Pearls

1. Tearing chest pain radiating to back = classic
2. Pain maximal at onset
3. Type A = surgery, Type B = medical management
4. β-blocker FIRST, then vasodilator
5. BP difference >20 mmHg = key diagnostic clue
6. CTA = first-line imaging; TEE = unstable patients
7. Hypotension = rupture/tamponade (poor prognosis)
8. Most common risk factor is hypertension
9. Always exclude before thrombolysis for MI

Helicobacter Pylori Infection

A 45-year-old man presents with chronic epigastric pain for the past 3 months. The pain is burning in nature, occurs 2–3 hours after meals, and often awakens him at night. He reports that the pain is relieved by eating and antacids. He also complains of bloating and intermittent nausea. He has been taking NSAIDs intermittently for joint pain. There is no history of weight loss, dysphagia, vomiting, or gastrointestinal bleeding. On examination, he has mild epigastric tenderness without guarding or rigidity. Laboratory studies show mild microcytic anemia. A urea breath test is positive. Diagnosis?

Diagnosis is Helicobacter pylori–associated duodenal ulcer disease.

1. Definition

Helicobacter pylori is a spiral-shaped, Gram-negative, urease-producing bacterium that colonizes the gastric mucosa and causes chronic gastritis, peptic ulcer disease, and increases the risk of gastric adenocarcinoma and MALT lymphoma.

2. Epidemiology

1. Very common worldwide infection
2. Approximately 50 percent of the global population is infected
3. Prevalence in North America is about 30 to 40 percent
4. Typically acquired in childhood
5. Infection persists lifelong unless treated
6. Higher prevalence with overcrowding, poor sanitation, low socioeconomic status, and endemic regions

3. Etiology and Transmission

1. Humans are the primary reservoir
2. Transmission via oral-oral or fecal-oral routes
3. Infection usually acquired early in life
4. Risk increases with poor hygiene and crowded living conditions

4. Pathophysiology

1. Produces urease → ammonia → neutralizes gastric acid locally
2. Causes chronic gastric mucosal inflammation
3. Antral-predominant gastritis → increased acid → duodenal ulcer
4. Corpus-predominant gastritis → reduced acid → gastric ulcer and cancer risk
5. Chronic inflammation → atrophic gastritis → intestinal metaplasia → dysplasia → gastric adenocarcinoma
6. Associated with MALT lymphoma (may regress after eradication)
7. Virulence factors:
   o CagA → increased inflammation and cancer risk
   o VacA → mucosal injury

5. Clinical Features

5.1 Common Presentation

1. Often asymptomatic
2. Dyspepsia
3. Epigastric pain or burning
4. Bloating
5. Nausea
6. Early satiety
7. Belching

5.2 Ulcer-Type Symptoms

1. Duodenal ulcer pain relieved by food or antacids
2. Gastric ulcer pain worsened by food
3. Nocturnal pain

5.3 Alarm Features

1. GI bleeding (hematemesis, melena, hematochezia)
2. Unintentional weight loss
3. Iron deficiency anemia
4. Dysphagia or odynophagia
5. Persistent vomiting
6. Palpable abdominal mass or lymphadenopathy
7. Jaundice

6. Complications

1. Peptic ulcer disease (duodenal > gastric)
2. Upper GI bleeding (most common complication)
3. Perforation
4. Gastric outlet obstruction
5. Gastric adenocarcinoma
6. MALT lymphoma
7. Iron deficiency anemia
8. Immune thrombocytopenic purpura

7. When to Test for H. pylori

1. Dyspepsia <60 years without alarm features (test-and-treat)
2. Dyspepsia with alarm features → endoscopy with biopsy
3. Current or prior peptic ulcer disease
4. Unexplained iron deficiency anemia
5. Immune thrombocytopenic purpura
6. Adult household contacts of infected individuals
7. High-risk gastric conditions (atrophy, intestinal metaplasia, dysplasia, autoimmune gastritis)
8. Family history of gastric cancer
9. High-prevalence regions or high-risk populations
10. MALT lymphoma
11. Chronic NSAID use or before long-term aspirin therapy

8. Diagnosis

8.1 Noninvasive Tests

1. Urea breath test (preferred for active infection)
2. Stool antigen test (diagnosis and test-of-cure)
3. Serology (IgG)
   o Cannot distinguish active vs past infection

8.2 Invasive Tests (Endoscopy with Biopsy)

1. Rapid urease test
2. Histology
3. Culture (antibiotic susceptibility)
4. PCR (specialized use)

8.3 Medication Hold Before Testing

1. Stop PPIs or PCABs ≥2 weeks before testing
2. Stop antibiotics and bismuth ≥4 weeks before testing
3. Prevents false-negative results

9. Treatment

9.1 Principle

1. All patients with confirmed H. pylori infection should be treated

9.2 First-Line Therapy (Preferred)

Optimized Bismuth Quadruple Therapy (14 days)

1. PPI twice daily
2. Bismuth four times daily
3. Tetracycline 500 mg four times daily
4. Metronidazole 500 mg three or four times daily

9.3 Alternative Regimens

1. Rifabutin-based triple therapy
2. Vonoprazan + amoxicillin dual therapy (PCAB-based)
3. Vonoprazan + amoxicillin + clarithromycin
   o Only if clarithromycin susceptibility confirmed

9.4 Important Treatment Considerations

1. Avoid empiric clarithromycin-based triple therapy
2. Clarithromycin and levofloxacin resistance ↑ → reduced efficacy
3. Eradication rates drop markedly in resistant strains
4. Doxycycline is NOT a substitute for tetracycline in BQT

10. Test of Cure

1. Required in all patients
2. Perform ≥4 weeks after antibiotics
3. Stop PPIs/PCABs ≥2 weeks before testing
4. Use:
   o Urea breath test
   o Stool antigen test
   o Biopsy-based testing

11. Resistance Considerations

1. Clarithromycin resistance increasing globally
2. Levofloxacin resistance increasing
3. Amoxicillin resistance rare
4. Susceptibility-guided therapy preferred

12. Endoscopy Indications

1. Dyspepsia with alarm features
2. Persistent dyspepsia in older or high-risk patients
3. Failed empiric therapy
4. Suspected complications (bleeding, obstruction, malignancy)

13. Adjunct Measures

1. Discontinue NSAIDs when possible
2. Avoid smoking
3. Limit alcohol if symptomatic
4. No specific dietary restriction required
5. Evaluate penicillin allergy if limiting therapy

14. Key Clinical Insight

Dyspepsia/PUD/IDA/ITP or gastric cancer risk + positive H. pylori testing = H. pylori infection → treat with 14-day bismuth quadruple therapy → confirm eradication (urea breath test or stool antigen ≥4 weeks post-treatment, off PPI ≥2 weeks)

15. Exam Level Pearls

1. Helicobacter pylori is a major cause of peptic ulcer disease, especially duodenal ulcers
2. It is a World Health Organization class I carcinogen
3. Urea breath test and stool antigen test detect active infection
4. Serology cannot distinguish active from prior infection
5. Stop proton pump inhibitors for 2 weeks and antibiotics or bismuth for 4 weeks before testing
6. Bismuth quadruple therapy is the preferred first-line treatment
7. Avoid empiric clarithromycin triple therapy
8. Always confirm eradication after treatment
9. NSAID use plus Helicobacter pylori increases ulcer risk