Occult Bacteraemia: Children <36 months

Definition:

• Occult bacteremia¹ is the condition in which bacteremia is identified in patients without clinical evidence of sepsis (e.g., shock or purpura) or a ”toxic” ppearance, who have neither significant underlying chronic medical conditions nor clear foci of infection on examination (other than otitis media), and who are discharged to home after outpatient evaluation. These are usually in patients whom a positive result is not anticipated.

Incidence:

• ~5% of all children who present with a fever and no clear source is identified.
• Although most episodes of occult bacteremia resolve spontaneously, serious complications, such as pneumonia, septic arthritis, osteomyelitis, meningitis, sepsis, and death, may occasionally occur.

Pathogens:

• Streptococcus pneumonia is responsible for 66%-75% of all cases.
  • Peak prevalence between 6 and 24 months.
  • Association with high fever(39.4ºC or 103ºF).
  • High WBC count(>15,000).
  • Absence of evident focal soft tissue infection.
  • Whilst these incidences may have changed after introduction of the 7-valent conjuugate vaccine, there is evidence to suggest that other serotypes have simply replaced those that are now vaccinated against.
• Neisseria meningitidis
• Haemophilus influenzae type b
• Non-typhoidal salmonellae

Risks of Occult Bacteraemia:

• Low Risk:
  • Age >3 yrs
  • Temp <39.4^oC
  • WBC >5 & <15
• High Risk
  • Age <2 yrs
  • Temp >40^oC
  • WBC <5 or >15
  • Contact with H.influenzae or N. meningitidis.
• Occult bacteraemia has a low prevalence, so even though WBC is a sensitive and specific screening test, it has a low PPV. The test does not discriminate between children who have PUO who are bacteremic and those who are not.
• Therefore, blood culture is the gold standard→still has a high number of false positives, take 24-48hrs, and most cases of occult pneumococcal bacteremia clear without treatment.

Utility of Blood Cultures:

• Studies² have demonstrated that, although some patients (12%) with bacteremia return for follow-up before culture results are known because of persistent or worsening illness, most (68%) are seen for follow-up as a result of positive blood cultures. Of patients with serious complications of occult bacteremia, half returned as a direct result of notification for a positive blood culture. Since the time of these studies, improved blood culture technology has significantly reduced the time to detection of positive cultures (see earlier discussion), so the utility of obtaining blood cultures in the prevention and early treatment of patients with significant complications of occult bacteremia may be greater than that previously suggested. In addition, investigators have demonstrated that blood cultures of children infected with true pathogens become positive significantly more rapidly than do cultures growing contaminants. Scheduling 24- hour follow-up for children at risk for occult bacteremia may also be of use in the early detection of complication.

Management:³

• The benefits of laboratory screening and selective empiric antibiotic treatment of febrile children at risk for occult bacteremia have to be weighed against the costs of screening tests and blood cultures, inconvenience, temporary discomfort to patients, risks for side effects of antibiotics, and the role of antibiotics in the development of bacterial resistance⁴. Although great debate exists concerning the role of empiric antibiotics, a strategy for obtaining blood cultures and empirically administering antibiotics on the basis of an increased neutrophil count, in addition to close clinical followup, may be effective in reducing the frequency and severity of uncommon but adverse sequelae. The "highly effective" pneumococcal vaccine may have exerted a selection pressure on Str. pneumoniae - and may alter the ways that clinicians evaluate fully immunized young, febrile children.
• If empiric antibiotics are used, they should be targetted against Str. pneumoniae, N. menigitidis and H. influenzae.
• Follow up is essential.

AMH.