Infections

Early loss of splenic function from recurrent vaso-occlusion and the inability to make specific immunoglobulin G (IgG) antibodies to polysaccharide antigens increases the risk of fulminant sepsis. Pneumococcal infection is a serious problem in SCD, particularly in children under 3 years (Figure 7.3a-c). Meningitis can accompany pneumococcal sepsis, and the overall mortality rate is 20-50%. Patients who have had previous pneumococcal sepsis are at increased risk for recurrent episodes and must remain on lifelong penicillin prophylaxis. Haemophilus influenzae type B is the next most common organism and affects older children. There is considerable variation in the relative incidence of bacterial organisms causing sepsis in young children with SCD in various regions of the world. In Africa, Salmonella spp., Klebsiella spp., Escherichia coli and Staphylococcus spp. are more commonly isolated from the blood of febrile children than Streptococcus pneumoniae. Pneumococcal infections are particularly infrequent in the eastern province of Saudi Arabia and Nigeria. Furthermore, the incidence of pneumococcal and H. influenzae sepsis has declined owing to penicillin prophylaxis and vaccination of infants. The risk of death during septic episodes has decreased considerably owing to empirical use of antibiotics to treat fever in SCD.

Of the other infections, pneumonia is particularly common in SCD and can be difficult to differentiate from non-infective causes of acute chest syndrome. The most frequent organisms responsible for pneumonia are Mycoplasma pneumoniae, Chlamydia pneumoniae, S. pneumoniae and H. influenzae. Lung infections can also arise due to respiratory viruses. In adults, bacteraemia and urinary tract infections due to E. coli and other Gram-negative organisms are more frequent. Patients with SCD are susceptible to osteomyelitis owing to bone infarction resulting from vaso-occlusion. The infection is typically due to Salmonella spp. or Staphylococcus aureus.

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Figure 7.3 Overwhelming pneumococcal sepsis in 7-year-old child. (a) Numerous bacteria in the blood adjacent to the right ventricular wall. Massive sequestration of the spleen (b) and the liver (c).
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