What is the recommended treatment for a 6-year-old immunocompromised patient with a history of scarlet fever, presenting with a rash on the tongue and lower back?

Urgent Evaluation and Treatment for Suspected Tickborne Rickettsial Disease

This immunocompromised 6-year-old with a rash on the tongue and lower back/buttock area requires immediate empiric treatment with doxycycline for presumed Rocky Mountain Spotted Fever (RMSF) or other tickborne rickettsial disease, regardless of whether a tick bite is recalled.

Immediate Diagnostic Considerations

The combination of rash distribution (tongue and lower back/buttock region) in an immunocompromised child with a history of scarlet fever requires urgent evaluation for several life-threatening conditions 1:

• Rocky Mountain Spotted Fever (RMSF) is the primary concern, as rash typically begins on extremities and can involve unusual locations, with up to 40% of patients reporting no history of tick bite 2
• Meningococcemia must be ruled out urgently if the rash becomes petechial or purpuric 1
• Recurrent Group A Streptococcal infection given the scarlet fever history, though the rash distribution is atypical 3, 4
• Herpes zoster (shingles) should be considered in immunocompromised patients, particularly with lower back/buttock distribution 2

Critical Clinical Assessment

Key Historical Features to Obtain Immediately:

• Duration of fever and when rash appeared relative to fever onset 1
• Recent outdoor activities in grassy or wooded areas, even without recalled tick exposure 2
• Characteristics of the rash: maculopapular versus petechial, presence on palms/soles 2, 1
• Tongue appearance: "strawberry tongue" suggests streptococcal infection 3
• Presence of headache, myalgias, nausea, vomiting, or altered mental status 2

Essential Physical Examination:

• Careful inspection of scalp, axillae, and inguinal regions for attached ticks 2
• Assessment for petechiae or purpura development 1
• Evaluation for tender lymphadenopathy 1
• Documentation of vital signs including orthostatic changes 2

Immediate Laboratory Evaluation

Obtain the following tests urgently 2, 1:

• Complete blood count with differential (looking for thrombocytopenia, leukopenia, bandemia) 2
• Comprehensive metabolic panel (AST/ALT elevation common in RMSF) 2
• Blood culture 2
• Acute serology for R. rickettsii, E. chaffeensis, and A. phagocytophilum (though results will not be available for days) 2

Critical caveat: Serologic testing for rickettsial diseases is typically negative in the first week of illness and should NOT delay treatment 2

Empiric Treatment Protocol

For Suspected Tickborne Rickettsial Disease:

Doxycycline is the drug of choice regardless of age, including children under 8 years old 2:

• Dosing: 2.2 mg/kg orally or IV twice daily (maximum 100 mg per dose) 2
• Duration: Minimum 5-7 days, continuing at least 3 days after fever subsides 2
• Route: IV therapy indicated if hospitalized or unable to take oral medications 2

The American Academy of Pediatrics identifies doxycycline as the drug of choice for treating presumed or confirmed RMSF and ehrlichial infections in children of any age, as limited courses do not pose substantial risk for tooth staining 2

If Streptococcal Infection Cannot Be Excluded:

Given the history of scarlet fever and tongue involvement, consider adding coverage for Group A Streptococcus 3, 4:

• Penicillin V: 250 mg orally 3-4 times daily for 10 days (or 500 mg twice daily) 5, 6
• Alternative if penicillin allergic: Azithromycin 12 mg/kg once daily for 5 days (maximum 500 mg) 7

However, if RMSF is strongly suspected, doxycycline must be started immediately as it provides no coverage for streptococcal infections but is life-saving for rickettsial disease 2

Hospitalization Criteria

Admit this immunocompromised child if any of the following are present 1:

• Evidence of organ dysfunction or severe thrombocytopenia 1
• Mental status changes or severe headache 1
• Petechial or purpuric rash 1
• Signs of sepsis or hemodynamic instability 1
• Inability to tolerate oral medications 2

Immunocompromised patients warrant a lower threshold for hospitalization and empiric antimicrobial therapy 1

Special Considerations for Immunocompromised Status

This child's immunocompromised state significantly increases risk 2:

• Higher risk for severe disease from both rickettsial infections and streptococcal infections 2
• May present with atypical manifestations 1
• Consider varicella-zoster virus if vesicular lesions develop in dermatomal distribution on lower back/buttock 2
• Prophylaxis considerations per HIV guidelines if applicable (though specific immune deficiency not stated) 2

Critical Pitfall to Avoid

The most dangerous error is delaying doxycycline treatment while awaiting laboratory confirmation for suspected RMSF 2. RMSF can have a rapid fatal course, with 50% of deaths occurring within 9 days of illness onset 2. Broad-spectrum antimicrobials including penicillins, cephalosporins, and aminoglycosides are NOT effective against rickettsiae 2.

Follow-Up Requirements

• Daily reassessment until clinical improvement documented 2
• If discharged, clear return precautions for worsening symptoms, development of petechiae, or altered mental status 8
• Convalescent serology at 2-4 weeks if rickettsial disease suspected 2