Splenic function is lost when the spleen has been surgically removed, is congenitally absent, has atrophied following repeated infarction (eg, sickle cell disease), or following splenic artery thrombosis . In addition, splenic function is reduced in the neonate and may be abnormally reduced (ie, hyposplenism or functional asplenia) when the spleen is engorged with blood (eg, splenic sequestration crisis associated with sickle cell disease, malaria, splenic vein thrombosis), or infiltrated (eg, sarcoidosis, amyloidosis, tumors, or cysts). (See "Approach to the adult patient with splenomegaly and other splenic disorders".)
Asplenic patients and those with impaired splenic function are at risk for a fulminant sepsis syndrome usually due to Streptococcus pneumoniae. The terms "postsplenectomy sepsis" and "asplenic sepsis" are largely interchangeable since the functional defects are the same regardless of whether the causative process is congenital or acquired. In this topic review, we will use the term "asplenic sepsis" to include all asplenic patients.
The prevention of sepsis will be reviewed here. The importance of the spleen for clearance of bacteria and humoral immune response, conditions leading to asplenia, clinical manifestations of infection in the asplenic patient, and management of sepsis in the asplenic patient are discussed separately. (See "Clinical features and management of sepsis in the asplenic patient".)
Patients must be instructed that the asplenic state carries a small risk of overwhelming and life-threatening infection. Fulminant sepsis in asplenic patients is classically caused by encapsulated organisms, particularly Streptococcus pneumoniae but also Haemophilus influenzae and Neisseria meningitidis. Fulminant sepsis in asplenic patients has also been caused by Capnocytophaga canimorsus, which is almost exclusively observed after close contact with dogs (bites, scratches, or even saliva exposure). Asplenic individuals are also at risk for severe babesiosis, a tick-borne illness that is endemic in parts of the United States Northeast. These and other infections in asplenic patients are discussed in detail separately. (See "Clinical features and management of sepsis in the asplenic patient".)
It is crucial that asplenic individuals adhere to the preventive measures outlined below and that they inform all caregivers of their asplenic state. The combined use of pneumococcal immunization and early administration of oral empiric antibiotic therapy for fever offers a high level of protection against sepsis in asplenic patients . Asplenic individuals should also be counseled about avoiding dog bites, scratches, and contact with dog saliva to prevent C. canimorsus infection as well as avoiding tick bites in Babesia-endemic regions.