What is the risk of bacteremia in an unvaccinated (not vaccinated) child?

Risk of Bacteremia in Unvaccinated Children

Unvaccinated children have a significantly higher risk of bacteremia compared to vaccinated children, with approximately 1.5-2% of unvaccinated children developing occult bacteremia when presenting with fever without source. 1

Epidemiology and Risk

The risk of bacteremia in children has changed dramatically over the past few decades due to vaccination:

• Pre-vaccination era: Before widespread use of Haemophilus influenzae type b (Hib) vaccine and pneumococcal conjugate vaccine (PCV), bacteremia rates were 2.8-11.6% in febrile children 1

• Post-vaccination era: After introduction of these vaccines, rates decreased to 0.7-1.9% 1, 2

• Current rates in unvaccinated children: While specific data on completely unvaccinated children is limited, they remain at risk similar to pre-vaccine era levels (1.5-2%) 1

Pathogens in Unvaccinated Children

In unvaccinated children, the most common pathogens causing bacteremia are:

• Streptococcus pneumoniae: Accounts for 80-90% of occult bacteremia cases 1
• Haemophilus influenzae type b: Previously responsible for approximately 13% of occult bacteremia 1
• Other pathogens: Salmonella species, Neisseria meningitidis, Streptococcus pyogenes (Group A), and Escherichia coli 1, 2

Complications and Sequelae

The risk of developing serious complications from bacteremia is substantial:

• Overall sequelae rate: 5-20% of children with occult bacteremia will develop significant infectious sequelae 1

• Types of complications:

  • Pneumonia (most common)
  • Cellulitis
  • Osteomyelitis
  • Septic arthritis
  • Meningitis
  • Sepsis 1

• Serious complications: Approximately 1.8% of children with occult bacteremia will develop meningitis or sepsis 1

• Population risk: Among all previously healthy, well-appearing children aged 2-24 months with fever without source:

  • 0.3% will develop significant sequelae
  • 0.03% will develop sepsis or meningitis 1

Mortality Risk

The mortality risk is particularly concerning:

• Pneumococcal meningitis outcomes: Can result in:

  • Mental retardation (19%)
  • Permanent hearing loss (17%)
  • Seizure disorders (15%)
  • Paralysis (11%)
  • Death (7.7%) 1

• HIV-infected children: Have substantially higher rates of bacteremia/sepsis (0.35-0.37 per 100 child-years) compared to HIV-uninfected children (<0.01 per 100 child-years) 1

Demographic Patterns

Unvaccinated children in the US tend to have specific demographic characteristics:

• More likely to be white
• Have mothers who are married and college-educated
• Live in households with annual incomes exceeding $75,000
• Have parents who express concerns about vaccine safety
• Live in states that allow philosophical exemptions to vaccination laws 3

Clinical Implications

When evaluating febrile unvaccinated children:

• Blood culture considerations: The contamination rate (1.8-5%) now exceeds the true bacteremia rate in vaccinated populations, making interpretation challenging 2, 4

• White blood cell count: A WBC >15,000 is a poor predictor of bacteremia in vaccinated children (positive predictive value only 1.5%) 2, but may retain more value in unvaccinated children

• Geographic clustering: Unvaccinated children tend to cluster geographically, increasing community risk 3

Common Pitfalls

1. Assuming low risk: Treating unvaccinated children as if they have the same low bacteremia risk as vaccinated children

2. Over-reliance on WBC: Using white blood cell count alone to guide antibiotic decisions

3. Failing to consider vaccination status: Not asking about or documenting vaccination status when evaluating febrile children

4. Missing serious sequelae: Failing to recognize that bacteremia can lead to serious complications even in previously well-appearing children

Conclusion

Unvaccinated children represent a distinct population with significantly higher risk of bacteremia and subsequent complications compared to their vaccinated peers. Clinicians should maintain a high index of suspicion for bacteremia in febrile unvaccinated children and consider appropriate diagnostic testing and empiric antibiotic therapy.