What is the cause and treatment of a petechial rash, fever, and vomiting?

Petechial Rash with Fever and Vomiting: Immediate Life-Threatening Diagnosis

This presentation demands immediate empiric doxycycline therapy for presumed Rocky Mountain Spotted Fever (RMSF) or meningococcemia—do not wait for confirmatory testing, as 50% of RMSF deaths occur within 9 days and delay significantly increases mortality. 1

Critical Differential Diagnosis

The combination of petechial rash, fever, and vomiting represents a medical emergency with two primary life-threatening causes:

Rocky Mountain Spotted Fever (RMSF)

• Classic presentation: Fever, headache, and rash appearing 2-4 days after fever onset, beginning as small blanching pink macules on ankles, wrists, or forearms that evolve to maculopapular lesions with central petechiae by day 5-6 2
• Critical pitfall: Up to 20% of RMSF cases never develop a rash, and absence of rash is associated with increased mortality 2, 3
• Facial involvement: The rash typically spares the face in RMSF, making facial petechiae less consistent with this diagnosis 2
• Tick exposure: Only 60% of patients recall tick exposure, so absence does not exclude diagnosis 1
• Associated symptoms: Nausea, vomiting, and anorexia occur early in the course, especially in children 2
• Mortality: 5-10% case-fatality rate if untreated 2

Meningococcemia (Neisseria meningitidis)

• Rapid progression: Petechial or purpuric rash that can rapidly progress to purpura fulminans alongside high fever, severe headache, and altered mental status 1, 3
• Facial involvement: Petechiae on the face are more consistent with meningococcemia than RMSF 2
• Clinical features: Fever, lethargy, vomiting, and petechiae or purpura with shock in 20% of cases 1
• Rash characteristics: When a rash was present in the context of meningitis, the causative organism was N. meningitidis in 92% of cases (petechial in 89%) 2
• Important caveat: 37% of meningococcal meningitis patients did not have a rash 2

Immediate Diagnostic Approach

History Elements to Obtain Immediately

• Tick exposure: Recent outdoor activities, travel to endemic areas, or contact with dogs 2
• Timing: Duration of fever before rash appearance (RMSF typically 2-4 days, meningococcemia more rapid) 2, 1
• Neurologic symptoms: Headache severity, altered mental status, photophobia 2
• Systemic toxicity: Confusion, hypotension, tachycardia 1
• Clustering: Similar illness in family members or close contacts 2

Physical Examination Priorities

• Rash distribution: Facial petechiae suggest meningococcemia; ankle/wrist distribution suggests RMSF 2, 3
• Rash characteristics: Blanching vs. non-blanching; petechial vs. purpuric 2, 1
• Palms and soles: Involvement indicates advanced RMSF and severe illness 3
• Mental status: Glasgow Coma Scale assessment 2
• Meningeal signs: Neck stiffness (present in only 83% of bacterial meningitis cases) 2
• Capillary refill time: Prolonged refill suggests shock 2

Essential Laboratory Studies

• Complete blood count with differential: Look for thrombocytopenia, leukopenia, or bandemia 1, 4
• Comprehensive metabolic panel: Hyponatremia and elevated hepatic transaminases suggest rickettsial disease 2, 4
• Blood cultures: Obtain before antibiotics if possible, but do not delay treatment 1
• C-reactive protein: Values >6 mg/L warrant admission 5

Treatment Algorithm

Immediate Empiric Therapy (Within 1 Hour)

Start doxycycline 100 mg twice daily immediately if ANY suspicion for RMSF or ehrlichiosis exists—clinical improvement expected within 24-48 hours. 1, 4

Add ceftriaxone 2g IV if meningococcemia cannot be excluded based on clinical presentation (facial petechiae, rapid progression, altered mental status, shock). 1

Hospitalization Criteria

• Systemic toxicity (altered mental status, hypotension, tachycardia) 1
• Rapidly progressive rash 1
• Diagnostic uncertainty between serious causes 1
• Petechiae extending beyond superior vena cava distribution 5

Outpatient Management (Only if ALL criteria met)

• Petechiae confined to superior vena cava distribution (face, neck, upper chest) 5
• Well-appearing child 5
• Normal capillary refill time 5
• Normal C-reactive protein 5
• Reliable follow-up in 24 hours 5

Critical Pitfalls to Avoid

Do not wait for the classic triad of fever, rash, and tick bite—it is present in only a minority of RMSF patients at initial presentation. 1, 3

Do not exclude serious disease based on absence of rash—up to 20% of RMSF cases and 50% of early meningococcal cases lack rash. 1, 3

Do not rely on Kernig's or Brudzinski's signs—sensitivity as low as 5% for bacterial meningitis. 2

In darker-skinned patients, petechial rashes may be difficult to recognize, increasing risk of delayed diagnosis. 2, 3

Do not delay antibiotics for lumbar puncture or imaging—treatment must begin immediately. 1

Alternative Diagnoses (Lower Priority)

Viral Causes

• Enteroviruses, human herpesvirus 6, parvovirus B19, Epstein-Barr virus can cause petechial rash but typically progress more slowly than bacterial infections 1, 3

Ehrlichiosis

• Rash occurs in only 30% of adults with Human Monocytic Ehrlichiosis, appearing later in disease course 4
• Also treated with doxycycline 4

Mechanical Petechiae

• Petechiae confined to face/neck/upper chest following vomiting, coughing, or seizure activity 6, 5
• Patient appears well otherwise 5