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Occult bacteremia is the presence of bacteria in the bloodstream of febrile young children who have no apparent foci of infection and look well. Diagnosis is by blood culture and exclusion of focal infection. Treatment is with antibiotics, either in the hospital or as outpatients; select children are treated pending blood culture results.

About 3% (range 2 to 10%) of children aged 1 to 36 mo with a febrile illness (temperature ≥ 39° C) and no localizing abnormalities have bacteremia, which is hence considered occult. Of these, about 5 to 10% develop focal bacterial infections (eg, septic arthritis, osteomyelitis, meningitis) or sepsis (see Sepsis and Septic Shock; see Infections in Neonates: Neonatal Sepsis), which could be minimized by early identification and treatment of the bacteremia. The likelihood of progression to serious focal illness depends on the cause: 7 to 25% for Haemophilus influenzae type b (Hib) bacteremia but 4 to 6% for Streptococcus pneumoniae bacteremia.

Organisms: In the 1980s, 80% of occult bacteremia cases were caused by Streptococcus pneumoniae. The remainder was caused by Hib (10%), Neisseria meningitidis (5%), and others (predominantly Staphylococcus aureus and Salmonella sp). In the US, since the 1990s, routine Hib conjugate vaccination in infancy essentially eliminated Hib bacteremia. More recent routine use of the S. pneumoniae conjugate vaccine in infancy has reduced invasive pneumococcal disease in young children by > 66%, and increased use is expected to essentially eliminate the problem. When meningococcal conjugate vaccines are proven effective in this age group and licensed, the vast majority of occult bacteremia will be prevented.

Symptoms, Signs, and Diagnosis

The major symptom is fever; by definition, children with apparent focal disease (eg, cough, dyspnea, and pulmonary crackles suggesting pneumonia; skin erythema suggesting cellulitis or septic arthritis) are excluded. A toxic appearance (eg, limp and listless, lethargy, signs of poor perfusion, cyanosis, marked hypoventilation or hyperventilation) suggests sepsis or septic shock; bacteremia in such children is not classified as occult. However, early sepsis can be difficult to distinguish from occult bacteremia.

Diagnosis requires blood culture; typically one sample is obtained, and results are available within 24 h. Urinalysis and examination of the stool for leukocytes (if diarrhea is present) will help to identify specific infections and stratify risk. Recommendations regarding selection of children for testing and choice of tests vary with age, temperature, and clinical appearance (see Fig. 1: Infections in Infants and Children: Evaluation and management of the febrile infant aged < 3 mo. and Fig. 2: Infections in Infants and Children: Evaluation and management of the febrile child aged 3 to 36 mo.); the goal is to minimize testing without missing bacteremia. These recommendations are sensitive but relatively nonspecific, making them much more effective in identifying children at low risk of infection who can be treated expectantly rather than in identifying children with true bacteremia.

CBC usually shows an elevated WBC count; however, only about 10% of children with WBC counts of > 15,000/μL are bacteremic, so specificity is low. Acute-phase reactants (eg, ESR, C-reactive protein) are used by some clinicians but add little information; however, in combination with elevated procalcitonin levels, acute-phase reactants may be more specific for serious illness. In children < 3 mo, band counts > 1,500/μL and either low (< 5,000) or high (>15,000) WBC counts may indicate bacteremia.

Prognosis and Treatment

Children who receive antibiotics before bacteremia is confirmed by blood culture appear less likely to develop focal infections, although data are inconsistent. However, because of the low overall incidence of bacteremia, many children would receive unnecessary treatment if all who were tested were empirically treated. One common system for management before culture results (see Fig. 1: Infections in Infants and Children: Evaluation and management of the febrile infant aged < 3 mo. and Fig. 2: Infections in Infants and Children: Evaluation and management of the febrile child aged 3 to 36 mo.) minimizes antibiotic use in most febrile infants and children who do not have serious bacterial infection and provides antibiotics promptly to the few who need them. Nevertheless, some authorities prefer to hospitalize all febrile infants < 1 to 2 mo of age and administer parenteral antibiotics (eg, ceftriaxone Some Trade Names
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) pending results of blood, urine, and CSF cultures.

Fig. 1
Evaluation and management of the febrile infant aged < 3 mo. hpf = high-power field. (See also Infections in Neonates.)

Fig. 2
Evaluation and management of the febrile child aged 3 to 36 mo. hpf = high-power field.

All children are reexamined in 24 to 48 h. Those with persistent fever or positive blood or urine cultures have further cultures obtained and are admitted for evaluation of possible sepsis and administration of parenteral antibiotics. Those who are afebrile and well but had S. pneumoniae in the initial blood culture or an initial positive urine culture receive appropriate oral antibiotics (see elsewhere in The Manual).

Last full review/revision November 2005

Content last modified November 2005