7.2 Bacterial & Spirochetal Infections (Sepsis, Meningitis)

7.2 Bacterial & Spirochetal Infections (Sepsis, Meningitis)

Why This Matters for the PANCE

Bacterial emergencies require rapid clinical recognition and immediate treatment. The PANCE tests the ability to distinguish SIRS from sepsis, initiate the 1-hour resuscitation bundle, differentiate etiologies of bacterial meningitis via lumbar puncture CSF findings, and select age-specific empiric antibiotic regimens. Missing these clinical indicators leads to catastrophic patient outcomes, which is why these protocols are heavily represented on the exam. Detailed understanding of diagnostic nuances and treatment rationales will separate well-prepared candidates.

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Sepsis & Septic Shock

Pathophysiology & Diagnosis

Sepsis is a dysregulated host systemic response to infection, causing life-threatening organ dysfunction. Pathogen components trigger pro-inflammatory cytokines (TNF-alpha, IL-1), leading to endothelial injury, vasodilation, capillary leak, microvascular thrombosis, and tissue hypoperfusion. Distinguishing between the various scoring systems is a highly tested concept:

• SIRS Criteria: Systemic Inflammatory Response Syndrome is a sensitive but non-specific indicator of inflammation. It requires $\ge$ 2 of the following: Temperature > 38°C (100.4°F) or < 36°C (96.8°F); Heart Rate > 90 bpm; Respiratory Rate > 20 bpm (or $PaCO_2$ < 32 mmHg); WBC > 12,000/uL, < 4,000/uL, or > 10% band forms. While SIRS criteria are no longer used to strictly define sepsis, they are still clinically useful for early identification of potentially infected patients.
• qSOFA Score: The quick SOFA score is a rapid bedside tool to identify patients with suspected infection who are at high risk for poor outcomes outside the ICU. Assign 1 point for each of: Respiratory Rate $\ge$ 22 bpm, Altered mental status (Glasgow Coma Scale < 15), and Systolic Blood Pressure $\le$ 100 mmHg. A score $\ge$ 2 indicates high mortality risk and should prompt further evaluation for organ dysfunction.
• SOFA Score: The Sequential Organ Failure Assessment (SOFA) score evaluates respiratory, cardiovascular, hepatic, coagulation, renal, and neurological systems. Sepsis-3 definitions state that sepsis is diagnosed when there is a suspected or confirmed infection PLUS an acute increase in the SOFA score $\ge$ 2 points.
• Septic Shock: The most severe manifestation of sepsis. It is defined as sepsis with persistent hypotension requiring vasopressors to maintain a Mean Arterial Pressure (MAP) $\ge$ 65 mmHg AND a serum lactate level > 2 mmol/L despite adequate and appropriate volume resuscitation.

Resuscitation (1-Hour Bundle)

Aggressive initial management is paramount to survival.

• Lactate: Measure immediately to assess tissue hypoperfusion; re-measure within 2-4 hours if initial lactate is > 2 mmol/L to ensure clearance.
• Blood Cultures: Obtain at least two sets (aerobic and anaerobic) from different sites prior to administering antibiotics. PANCE Trap: Do not delay antibiotic administration by more than 45 minutes to obtain cultures. If cultures cannot be obtained rapidly, give the antibiotics anyway.
• Broad-Spectrum Antibiotics: Administer empiric IV antibiotics within 1 hour. Typical regimens include Piperacillin-tazobactam or Cefepime, plus Vancomycin for suspected MRSA.
• Fluid Resuscitation: Infuse 30 mL/kg of IV crystalloids (e.g., Lactated Ringer's or normal saline) within the first 3 hours for patients with hypotension or a lactate $\ge$ 4 mmol/L. Careful monitoring is needed to prevent fluid overload, especially in patients with heart failure or renal disease.
• Vasopressor: If the patient remains hypotensive during or after the fluid challenge, initiate Norepinephrine (Levophed). It is the first-line agent because it is a potent alpha-1 agonist causing significant vasoconstriction with minimal beta-1 induced tachycardia compared to dopamine. Add Vasopressin if a second agent is needed.

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Bacterial Meningitis

Clinical Presentation

Bacterial invasion of the subarachnoid space leads to severe meningeal inflammation and increased intracranial pressure (ICP). The classic clinical triad is fever, altered mental status, and nuchal rigidity (neck stiffness). However, the full triad is present in fewer than 50% of adults. Neisseria meningitidis is notably associated with a rapidly progressive petechial or purpuric rash and can progress to Waterhouse-Friderichsen syndrome (adrenal hemorrhage).

• Kernig's Sign: Passive flexion of the hip and knee to 90 degrees, followed by knee extension, causes pain and hamstring resistance.
• Brudzinski's Sign: Passive neck flexion causes involuntary flexion of the hips and knees.

Diagnostics & CSF Findings

• Lumbar Puncture (LP): The absolute gold standard for diagnosis. Fluid must be sent for cell count with differential, protein, glucose, Gram stain, and culture.
• CT Head Before LP Rule: A non-contrast head CT must be performed before the LP if any of the following are present to prevent catastrophic brain herniation:
  • Papilledema, focal neurologic deficits, new-onset seizures, immunocompromised state, history of CNS disease, or moderate-to-severe altered consciousness.
  • Resuscitation Pearl: If a CT is indicated, obtain blood cultures and administer empiric antibiotics and dexamethasone FIRST to avoid delaying life-saving therapy while waiting for imaging.

Empiric Antibiotic Management & Prophylaxis

Prompt administration of bactericidal antibiotics that cross the blood-brain barrier is essential. Dosages are typically maximal to achieve adequate CSF penetration.

• Neonates (< 1 month): Pathogens: Group B Streptococcus, E. coli, Listeria monocytogenes. Treatment: Ampicillin (for Listeria) PLUS Cefotaxime or Gentamicin. PANCE Trap: Avoid Ceftriaxone in neonates because it displaces bilirubin from albumin (increasing the risk of kernicterus) and can precipitate with calcium in IV fluids causing fatal deposits in the lungs and kidneys.
• Infants, Children, and Adults (1 month to 50 years): Pathogens: Streptococcus pneumoniae, Neisseria meningitidis. Treatment: Ceftriaxone (2g IV q12h) PLUS Vancomycin. The vancomycin is necessary to cover highly penicillin-resistant pneumococci.
• Older Adults (> 50 years) or Immunocompromised: Pathogens: S. pneumoniae, N. meningitidis, Listeria. Treatment: Ceftriaxone PLUS Vancomycin PLUS Ampicillin (added specifically to cover Listeria).
• Adjunctive Dexamethasone: Give prior to or with the first antibiotic dose in adults with suspected Streptococcus pneumoniae meningitis. It blunts the subarachnoid inflammatory response to bacterial lysis, significantly reducing neurologic complications like sensorineural hearing loss.
• Post-Exposure Prophylaxis: Close contacts of patients with Neisseria meningitidis (e.g., household members, those sharing saliva, healthcare workers who intubated without a mask) require chemoprophylaxis. The regimens of choice are Rifampin (600 mg PO twice daily for 2 days), Ciprofloxacin (500 mg PO single dose), or Ceftriaxone (250 mg IM single dose).