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Occult Bacteremia

by Geoffrey A. Weinberg, MD

Occult (hidden) bacteremia is the presence of bacteria in the bloodstream of a child who has a fever but who may not appear particularly sick and who has no apparent other source of infection.

  • Most commonly, occult bacteremia is caused by the bacteria Streptococcus pneumoniae .

  • Typically, children have no symptoms other than fever.

  • The diagnosis is based on blood tests.

  • Antibiotics can eliminate the infection.

Children younger than 3 years commonly develop fevers. Most of the time, they have other symptoms, such as a cough and runny nose, which allow doctors to diagnose the cause. About one third of the time, children have no symptoms besides fever. Most of these children have viral infections that go away without treatment. However, about 3% of such children have bacteria circulating in the bloodstream (bacteremia). Streptococcus pneumoniae is the most common type of bacteria causing occult bacteremia. Circulating bacteria are almost never present in older children or adults with fever and no other symptoms. These circulating bacteria may attack various organs and result in serious illnesses, such as pneumonia or meningitis. Although only about 5 to 10% of children with occult bacteremia develop these serious problems, doctors perform blood cultures to identify the bacteria before such problems develop. An elevated white blood cell count indicates a higher risk of bacterial infection. In this case, a doctor may choose to start antibiotics before blood culture results are available.

Because doctors cannot tell with certainty which children who have a fever have bacteremia, doctors may perform a complete blood cell count and blood cultures if children are younger than 3 years, have a temperature higher than 102° F (38.9° C), and do not have an apparent reason for their fever. Because occult bacteremia is much less common among children older than 3 years, these children do not usually require blood cultures.

If children may have occult bacteremia, doctors reevaluate them in 24 to 48 hours, when culture results are available. Children with positive culture results are given oral antibiotics at home if they do not appear very ill. Children who show signs of serious illness are typically given intravenous antibiotics in the hospital. Sometimes before obtaining culture results, doctors treat children who have a fever and who appear seriously ill or have risk factors for bacteremia (such as an elevated white blood cell count) with a single injection of an antibiotic, such as ceftriaxone.

The Haemophilus influenzae type b conjugate vaccine, now given to nearly all children in the United States, has nearly eliminated occult bacteremia due to Haemophilus influenzae type b. The relatively new conjugate vaccine against Streptococcus pneumoniae, given to infants, has greatly reduced the incidence of occult pneumococcal bacteremia. Newer conjugate vaccines against Neisseria meningitidis are being tested for use in young children. The use of these vaccines is expected to essentially eliminate occult bacteremia in children.

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