Why does splenectomy (removal of the spleen) increase the risk of infections from encapsulated organisms?

Why Splenectomy Increases Risk of Encapsulated Organism Infections

Splenectomy significantly increases the risk of infections from encapsulated bacteria because the spleen plays a crucial role in filtering and mounting immune responses against these pathogens, with asplenic patients having a 10-50 fold higher risk of developing overwhelming post-splenectomy infection (OPSI) compared to the general population. 1

Mechanisms of Increased Infection Risk

Immunological Functions Lost After Splenectomy

• Filtration function: The spleen normally filters blood and removes encapsulated bacteria
• Antibody production: The spleen contains specialized B-cells that produce antibodies against polysaccharide capsules
• Opsonization: Splenic macrophages facilitate opsonization of encapsulated bacteria
• IgM production: The spleen is a major site for IgM production, which is critical for early response to encapsulated organisms

Primary Encapsulated Organisms of Concern

1. Streptococcus pneumoniae - responsible for over 50% of OPSI cases 2
2. Haemophilus influenzae - particularly type b (Hib)
3. Neisseria meningitidis - all serogroups

Clinical Significance of OPSI

• Mortality rate: Up to 50% within 48 hours if untreated 1
• Lifelong risk: Cases have been reported more than 20 years after splenectomy 3
• Age impact: Children under 5 years have infection rates >10% compared to <1% in adults 3
• Rapid progression: OPSI can progress from mild symptoms to fulminant sepsis within hours

Why Encapsulated Bacteria Are Particularly Problematic

Encapsulated bacteria have polysaccharide capsules that:

• Resist phagocytosis without opsonization
• Require specific antibody responses for clearance
• Evade complement-mediated killing without antibody assistance

Without the spleen:

• There is reduced filtering of these bacteria from the bloodstream
• Decreased production of specific antibodies against capsular polysaccharides
• Impaired opsonization leading to delayed bacterial clearance

Prevention Strategies

Vaccination

• Pneumococcal: PCV13 followed by PPSV23 with at least 8 weeks interval 4
• Haemophilus influenzae type b: Single dose for adults 3
• Meningococcal: Tetravalent conjugated vaccine (MenACWY) with revaccination every 5 years 3
• Timing: At least 2 weeks before elective splenectomy or 14 days after emergency splenectomy 4

Antibiotic Prophylaxis

• Duration: At least 2 years post-splenectomy, with lifelong prophylaxis for high-risk patients 3, 4
• Regimen: Phenoxymethylpenicillin 250-500 mg twice daily or erythromycin 500 mg twice daily for penicillin-allergic patients 3
• Emergency antibiotics: Patients should keep a supply of antibiotics at home for immediate use if fever develops 3

Special Considerations

• Functional hyposplenism: Patients with sickle cell anemia, thalassemia major, and certain other conditions have similar risks due to splenic dysfunction 3
• Patient education: Critical to inform patients about lifelong infection risk and need for immediate medical attention if fever >38°C (101°F) occurs 3
• Medical alert: Patients should carry identification indicating their asplenic status 3

Common Pitfalls in Management

• Underestimating lifelong risk: The risk of OPSI remains elevated throughout life, not just in the immediate post-operative period
• Inadequate vaccination: Studies show poor vaccination coverage among splenectomized patients (only 27-31% fully vaccinated) 5, 6
• Discontinuing prophylaxis too early: Antibiotic prophylaxis should continue for at least 2 years, and potentially lifelong in high-risk patients
• Delayed treatment of fever: Any fever in an asplenic patient should be treated as a medical emergency

Proper education, vaccination, and antibiotic prophylaxis are essential to reduce the significant morbidity and mortality associated with post-splenectomy infections from encapsulated organisms.