Overwhelming post-splenectomy infection

OPSI may initially present with mild viral symptoms such as fever or coughing, however later in infection symptoms may include shakes, shivers, chills, diarrhea, vomiting, malaise, myalgia, headache and abdominal pain.[2][4]

The disease progresses rapidly from the above mentioned symptoms to coma to refractory septic shock and finally death in as little as 24 hours.[4]

The spleen contains many macrophages (part of the reticuloendothelial system), which are immune cells that phagocytose (eat) and destroy bacteria. In particular, these macrophages are activated when bacteria are bound by IgG antibodies (IgG1 or IgG3) or the complement component C3b. These types of antibodies and complement are immune substances called opsonizers, molecules that bind to the surface of bacteria to facilitate phagocytosis.

When the spleen is no longer present (asplenia), IgG and C3b are still bound to bacteria, but they cannot be removed from the blood circulation due to the loss of the splenic macrophages. Hence the bacteria are free to cause infection.

Patients without a spleen often need immunizations against pathogens that normally require opsonization and phagocytosis by macrophages in the spleen. These include common human pathogens with bacterial capsules (Streptococcus pneumoniae, Salmonella typhi, Neisseria meningitidis, E. coli, Hemophilus influenzae, Streptococcus agalactiae, Klebsiella pneumoniae, Pseudomonas aeruginosa). Capsules made of polysaccharides (sugars) permit bacteria to evade phagocytosis by macrophages alone, since only proteins are directly recognized by macrophages in phagocytosis. So humoral immunity in forms of IgG and complement proteins is the human immune system's response against bacterial capsules.

Measures to prevent OPSI include vaccination, prophylactic antibiotics and patient education.[8][9][10]

OPSI is almost always fatal without treatment, but modern treatment has decreased the mortality to approximately 40–70 percent.[2][3][15] Individuals with OPSI are most commonly treated with antibiotics and supportive care.[8]

The risk of OPSI is 0.23–0.42 percent per year, with a lifetime risk of 5 percent.[8] Most infections occur in the first few years following splenectomy, but the risk of OPSI is lifelong.[3][16]

The risk is greatest for children and elderly (70+ years old), but it can happen at any age. Greater risk is associated with splenectomy for hematological conditions such as sickle cell anemia, thalassemia and tumours when compared to splenectomy due to trauma.[2][4]