Bacterial infection poses a serious threat to the child with sickle cell anemia. In the first 10 years of life the most common infections are bacteremia, pneumonia, osteomyelitis, meningitis, and urinary tract infections. In the group under 5 years of age, it is often fatal; it occurs rapidly and can be overwhelming. The primary pathogens are usually encapsulated organisms: Streptococcus pneumoniae, Haemophilus influenzae, Escherichia coli, and Staphylococcus aureus. Other common infections include pneumonia caused by Mycoplasma pneumoniae, and osteomyelitis due to Salmonella typhimurium, Staph. aureus, and E. coli.
Repeated splenic infarction resulting in functional asplenia is felt to be the most likely reason for the increased risk of infection. Splenic infarction can occur as early as 5 months and is routine by 5 years of age. The susceptibility to bacterial infections results from deficient antibody formation and impaired phagocytosis. The complement activation system is impaired as well. Serum levels of IgM are also decreased.
During the first 5 years of life, the most common bacterial pathogen appears to be Strep. pneumoniae, and sepsis from this organism is the most common cause of death in this age group. The middle ear and the lungs tend to be the typical foci. Beyond 5 years, there tends be an increased frequency of gram-negative infections.
Children with SCD tend to become infected with H. influenzae at higher rates than other children. The course of these infections tends to be more insidious than that of those with Strep. pneumoniae.
Pneumonia of bacterial etiology is approximately 100 times more common in SCD patients than in the general population. Pneumonia generally causes hypoxia that further exacerbates the sickling. Strep. pneumoniae and H. influenzae are the two most common etiologic agents, but mycoplasmal infections are also common and should be considered when patients fail empiric (i.e., "nonmacrolide") antibiotic therapy. Viral pneumonia is also common, especially under the age of 2.
SCD patients also have an increased incidence of osteomyelitis. Often the etiologic agent is S. typhirium (about 50 percent). It can also be caused by Staph. aureus and E. coli. Also seen in increased frequency from the general population are meningitis and urinary tract infections. Bacterial meningitis and septicemia are approximately 600 times more common in SCD patients than in other children.
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