What is the best treatment for a teenager with a rash, elevated WBC count, and negative tickborne illness titer?

Management of a 14-Year-Old with Rash and Elevated WBC

Immediate Treatment Recommendation

Start empiric doxycycline immediately at 2.2 mg/kg orally twice daily for a minimum of 5 days, and administer intramuscular ceftriaxone pending blood culture results, as Rocky Mountain Spotted Fever (RMSF) and meningococcemia cannot be reliably distinguished on clinical grounds alone in a patient with rash and systemic symptoms. 1

Critical Clinical Context

This presentation demands urgent action despite the negative tickborne illness titer because:

• Up to 40% of RMSF patients report no history of tick bite, and early serology is typically negative in the first week of illness 1, 2
• Mortality increases dramatically with each day of delayed treatment: 0% mortality if treated by day 5, but 33-50% mortality if treatment is delayed to days 6-9 2
• The elevated WBC count (18.3-20) with high neutrophil percentage (83.3%) and normal platelet count (412) does not exclude RMSF, as normal WBC counts are frequently observed in RMSF, and thrombocytopenia typically develops later in the disease course 1

Diagnostic Workup Required

Before initiating antibiotics, obtain:

• Blood cultures (critical for ruling out meningococcemia and other bacterial infections) 1, 3
• Comprehensive metabolic panel (to assess for hyponatremia and elevated hepatic transaminases, which are common in RMSF) 1
• Peripheral blood smear examination (to evaluate for atypical findings) 1
• Acute serum for IgG and IgM antibodies to R. rickettsii, E. chaffeensis, and A. phagocytophilum, but do not wait for results before starting treatment 1
• Rapid Streptococcus pharyngitis screen (to rule out streptococcal disease with exanthem) 1

Key Differential Diagnoses to Consider

The rash distribution (arms and legs) in this febrile patient requires consideration of:

• Rocky Mountain Spotted Fever: Rash typically begins on extremities and can progress to petechial/purpuric pattern; palm and sole involvement is pathognomonic but occurs late in only 50% of cases 1, 3, 2
• Meningococcemia: Can present with maculopapular rash progressing to petechial/purpuric pattern, but typically progresses more rapidly than RMSF 1, 2
• Enteroviral infections: Common viral cause of fever and rash, but typically self-limited 1
• Streptococcal disease with exanthem: Can cause petechial rash after pharyngitis 1

Treatment Algorithm

Empiric Dual Antibiotic Coverage

1. Doxycycline 2.2 mg/kg orally twice daily (covers RMSF, HME, HGA, and E. ewingii infection) 1, 3, 2
2. Intramuscular ceftriaxone (covers meningococcemia while awaiting blood culture results) 1, 3

Rationale for Dual Coverage

Meningococcal disease cannot be reliably distinguished from TBRD on clinical grounds alone, even with CSF analysis, as both can present with similar laboratory findings (pleocytosis, elevated protein) 1

Monitoring and Disposition

Hospitalization Criteria

Admit if any of the following are present:

• Evidence of organ dysfunction (altered mental status, respiratory distress, hypotension) 1, 2
• Severe thrombocytopenia (though not present in this case currently) 1
• Petechiae or purpura (suggesting progression to more severe disease) 2
• Progressive clinical deterioration 2

Outpatient Management Considerations

If the patient appears well and has:

• Stable vital signs
• No petechiae or purpura
• Normal mental status
• Reliable caregiver for medication compliance

Then outpatient management with close follow-up within 24 hours is acceptable, but parents must be instructed to return immediately for: 1, 3

• Breathing difficulties
• Drowsiness or difficulty rousing
• Appearance of petechiae or purpura
• Any clinical deterioration

Critical Pitfalls to Avoid

• Do not wait for serologic confirmation before starting doxycycline, as early serology is typically negative and delay in treatment significantly increases mortality 1, 2
• Do not be reassured by the absence of tick bite history, as this is reported in up to 40% of RMSF cases 1, 2
• Do not be falsely reassured by normal platelet count, as thrombocytopenia typically develops later in RMSF progression 1
• Do not withhold doxycycline based on age concerns, as the benefits far outweigh the minimal risk of dental staining in life-threatening RMSF 3, 2

Follow-Up Testing

• Convalescent-phase serology should be performed 2-4 weeks later to confirm the diagnosis 1
• Reassess clinical response to therapy within 24 hours to ensure improvement 1