What is the appropriate emergency department assessment and initial management for a 27‑year‑old woman with a 5‑day history of high‑grade fever, severe myalgia, headache, epigastric pain, intermittent vomiting, a non‑pruritic maculopapular petechial rash involving the lower extremities, abdomen and back, thrombocytopenia (platelet count 67 × 10⁹/L), borderline hypotension (blood pressure 100/70 mm Hg), tachycardia (heart rate 113 bpm), and recent household exposure to dengue?

Emergency Department Assessment and Initial Management

This patient requires immediate empiric doxycycline 100 mg twice daily for presumed Rocky Mountain Spotted Fever (RMSF), as the combination of fever, thrombocytopenia (platelet count 67 × 10⁹/L), maculopapular petechial rash, headache, myalgia, and household dengue exposure creates diagnostic uncertainty between dengue and life-threatening tickborne rickettsial disease—and RMSF carries a 5-10% mortality rate with 50% of deaths occurring within 9 days if treatment is delayed. 1, 2

Immediate Life-Threatening Diagnoses to Exclude

Rocky Mountain Spotted Fever (RMSF)

• The CDC mandates starting doxycycline immediately without waiting for laboratory confirmation when fever, rash, headache, and thrombocytopenia are present, as delay in treatment is the most important factor associated with death. 3, 1, 4
• This patient's presentation fits RMSF: the rash began on lower extremities and spread to abdomen and back (classic centripetal progression), appeared on day 6 of illness (typical timing), and evolved from macules to maculopapular lesions. 3, 1, 4
• Critical pitfall: Up to 40% of RMSF patients report no tick bite history, and the patient's neighborhood has "madaming lamok kasi nagllinis ng kanal" (many mosquitoes due to canal cleaning)—this environmental disruption creates tick exposure risk that patients often don't recognize. 1, 2, 4
• The absence of rash on palms and soles does NOT exclude RMSF, as less than 50% of patients have rash in the first 3 days, and palm/sole involvement indicates advanced disease. 4
• Thrombocytopenia (67 × 10⁹/L) and the severe epigastric pain (which can mimic acute abdomen in RMSF) are consistent with this diagnosis. 3, 1

Human Monocytic Ehrlichiosis (HME)

• HME presents with similar symptoms but rash occurs in only 30% of adults, appearing later (median 5 days) and rarely involving palms/soles. 1, 4
• The prominent rash in this patient makes HME less likely than RMSF, but doxycycline covers both. 1, 4

Meningococcemia

• If meningococcemia cannot be excluded based on clinical presentation (rapidly progressive petechiae, altered mental status, hypotension), add ceftriaxone 2g IV immediately. 1, 2
• This patient's stable mental status (GCS 15) and relatively slow progression over 5 days makes meningococcemia less likely, but the borderline hypotension (100/70) and tachycardia (HR 113) warrant close monitoring. 1, 2

Dengue Fever Considerations

Why Dengue Remains in the Differential

• Household exposure (child with confirmed dengue last week) and neighborhood mosquito proliferation from canal cleaning create high dengue risk. [@Patient history@]
• The temporal profile (fever day 1, thrombocytopenia by day 5, rash day 6) fits dengue's typical progression. 5, 6
• Thrombocytopenia in dengue results from both bone marrow suppression and peripheral platelet consumption/clearance. 5, 6

Critical Dengue Assessment Points

• The patient is currently in the critical phase (days 3-7 of illness) when plasma leakage and hemorrhagic complications typically occur. 5, 7
• Epigastric pain is a warning sign for severe dengue and may indicate plasma leakage or hepatic involvement. [@Patient history@]
• The dry lips and oral mucosa noted 2 hours into ER evaluation suggest evolving hemoconcentration/plasma leakage. [@Patient history@]
• Platelet counts do not correlate well with clinical bleeding in dengue—the absence of bleeding manifestations does NOT indicate safety. 7

Why Empiric Doxycycline is Still Mandatory

• Even with strong dengue exposure history, RMSF cannot be excluded without serologic testing, and waiting for results while withholding doxycycline risks preventable death. 1, 2, 4
• Doxycycline does not harm dengue patients and provides life-saving coverage for RMSF. 1, 2

Immediate Diagnostic Workup (Obtain Before Starting Antibiotics if Possible, But Do Not Delay Treatment)

Essential Laboratory Studies

• Complete blood count with differential: Look for leukopenia (53% of RMSF cases), thrombocytopenia severity, and hemoconcentration (hematocrit rise >20% indicates plasma leakage in dengue). 1, 4
• Comprehensive metabolic panel: Hyponatremia occurs in 94% of RMSF cases; elevated hepatic transaminases occur in 53% of RMSF and are common in dengue. 1, 4
• Peripheral blood smear: Examine for morulae (ehrlichiosis), platelet clumping, and immature platelets. 1, 4
• Immature platelet fraction (IPF): IPF% increases 3+ days before platelet recovery in dengue and can help predict severe dengue (significantly elevated on days 3-5 in severe cases). 8
• Acute serology: Send for Rickettsia rickettsii, Ehrlichia chaffeensis, and Anaplasma phagocytophilum antibodies. 1, 4
• Dengue NS1 antigen and IgM/IgG: NS1 is positive in early infection (days 1-7); IgM appears after day 5; IgG positivity with negative IgM suggests secondary dengue (higher risk for severe disease). [@Patient context@]
• Blood cultures: If sepsis is suspected, but do not delay doxycycline. 1

Critical Monitoring Parameters

• Serial hematocrit every 4-6 hours: A rise >20% from baseline indicates plasma leakage (severe dengue). [@Patient context@]
• Platelet count every 12-24 hours: Nadir typically occurs days 4-6 in dengue. 5, 6
• Vital signs every 2-4 hours: Watch for hypotension (BP <90/60), tachycardia worsening, or narrowing pulse pressure (<20 mmHg = shock). [@Patient context@]
• Strict fluid balance: Input/output monitoring to detect plasma leakage. [@Patient context@]
• Abdominal examination every 4-6 hours: Increasing epigastric tenderness, hepatomegaly, or ascites indicate severe dengue. [@Patient context@]

Immediate Management Algorithm

Step 1: Start Empiric Antibiotic Therapy (Within 1 Hour of Presentation)

• Doxycycline 100 mg PO/IV twice daily immediately. 1, 2, 4
• If meningococcemia cannot be excluded: Add ceftriaxone 2g IV once daily. 1, 2
• Expected response: Clinical improvement within 24-48 hours if RMSF/ehrlichiosis; lack of improvement suggests alternative diagnosis (likely dengue). 4

Step 2: Fluid Management (Critical for Both Dengue and RMSF)

• Start isotonic crystalloid (normal saline or lactated Ringer's) at maintenance rate initially: For 56 kg patient = approximately 80-100 mL/hour. [@Patient context@]
• If hematocrit rises >20% or signs of plasma leakage develop: Increase to 5-7 mL/kg/hour for 1-2 hours, then reassess. [@Patient context@]
• Avoid aggressive fluid resuscitation in absence of shock: Overhydration in dengue causes pulmonary edema and pleural effusions. [@Patient context@]
• The patient's current dry mucosa and borderline BP suggest she needs careful fluid repletion, but serial hematocrit will guide rate. [@Patient history@]

Step 3: Symptomatic Management

• Continue paracetamol 500-1000 mg every 6 hours for fever/pain (maximum 4g/24 hours). [@Patient history@]
• Avoid NSAIDs (patient already took Flanax): NSAIDs increase bleeding risk in both dengue and thrombocytopenia. [@Patient history@]
• Antiemetics if vomiting recurs: Ondansetron 4-8 mg IV/PO every 8 hours. [@Patient context@]
• Proton pump inhibitor for epigastric pain: Omeprazole 40 mg IV/PO once daily (the abdominal massage may have caused gastric mucosal injury). [@Patient history@]

Step 4: Transfusion Thresholds

• Platelet transfusion is NOT indicated based on platelet count alone in dengue. 7
• Transfuse platelets only if: Active bleeding (hematemesis, melena, menorrhagia, hematuria) OR platelet count <10 × 10⁹/L with high bleeding risk. 7
• This patient has no bleeding manifestations currently, so transfusion is not indicated despite platelet count of 67 × 10⁹/L. 7

Step 5: Admission Criteria and Monitoring Location

• This patient requires hospital admission due to: thrombocytopenia, warning signs (epigastric pain, vomiting), critical phase timing, and diagnostic uncertainty requiring close monitoring. 1, 2
• Admit to monitored bed (not ICU unless deterioration): She is currently stable (GCS 15, adequate BP with fluids, no active bleeding). [@Patient context@]

Specific Clinical Pitfalls to Avoid

Pitfall 1: Excluding RMSF Based on Dengue Exposure

• The household dengue case creates anchoring bias—clinicians may assume dengue and withhold doxycycline. [@Patient context@]
• Both diseases can coexist in the same geographic area, and RMSF mortality is preventable with early treatment. 1, 2, 4

Pitfall 2: Waiting for the "Classic Triad" of RMSF

• Fever + rash + tick bite history occurs in only a minority of patients at initial presentation. 2, 4
• This patient has fever + rash + headache + thrombocytopenia, which is sufficient to mandate empiric doxycycline. 1, 2, 4

Pitfall 3: Aggressive Fluid Resuscitation Without Hemoconcentration

• The patient's dry mucosa may prompt overzealous IV fluids, but without documented hematocrit rise, aggressive fluids risk pulmonary edema in dengue. [@Patient context@]
• Start conservative, monitor hematocrit every 4-6 hours, and escalate fluids only if hemoconcentration develops. [@Patient context@]

Pitfall 4: Prophylactic Platelet Transfusion

• Transfusing platelets "to prevent bleeding" in dengue is not evidence-based and wastes blood products. 7
• Platelet counts do not correlate with bleeding risk in dengue; transfuse only for active hemorrhage. 7

Pitfall 5: Attributing Epigastric Pain to the "Manghihilot" Massage

• While the massage may have caused trauma, epigastric pain is a warning sign for severe dengue (hepatic involvement, plasma leakage). [@Patient history@]
• Do not dismiss this symptom—it requires serial abdominal exams and liver function monitoring. [@Patient history@]

Additional Diagnostic Considerations (Lower Priority)

Secondary Syphilis

• Can cause maculopapular rash involving palms/soles, but this patient lacks palm/sole involvement and has no genital lesions or lymphadenopathy. 1, 4
• RPR/VDRL can be sent if RMSF/dengue are excluded, but not urgent. 1

Drug Hypersensitivity (DRESS Syndrome)

• The patient took Flanax (NSAID) and paracetamol, but DRESS typically occurs 2-8 weeks after drug initiation and presents with eosinophilia and hepatitis. 4
• The acute onset (5 days) and lack of eosinophilia make this unlikely. 4

Viral Exanthems (Enterovirus, EBV, Parvovirus B19)

• Enteroviral rashes typically spare palms, soles, face, and scalp—this patient's rash distribution doesn't fit. 1, 4
• EBV causes rash especially after ampicillin/amoxicillin exposure, which this patient lacks. 4
• These are diagnoses of exclusion after ruling out life-threatening causes. 1, 4

Disposition and Follow-Up

Admission Orders

• Doxycycline 100 mg PO/IV twice daily. 1, 2, 4
• Isotonic crystalloid at 80-100 mL/hour, adjust based on hematocrit. [@Patient context@]
• Paracetamol 500-1000 mg PO/IV every 6 hours PRN fever/pain. [@Patient context@]
• Omeprazole 40 mg PO/IV once daily. [@Patient context@]
• NPO until vomiting resolves, then advance diet as tolerated. [@Patient context@]
• Strict input/output monitoring. [@Patient context@]
• Vital signs every 2-4 hours. [@Patient context@]
• CBC with differential and hematocrit every 4-6 hours initially, then every 12 hours once stable. [@Patient context@]
• Comprehensive metabolic panel daily. [@Patient context@]
• Abdominal examination every 4-6 hours. [@Patient context@]

Reassessment Timeline

• 24 hours: If clinical improvement (defervescence, improved energy, stable hematocrit), RMSF/ehrlichiosis is likely and continue doxycycline for 7-10 days total. 4
• 24-48 hours: If no improvement and dengue serology positive, dengue is confirmed—continue supportive care and complete doxycycline course (no harm in dengue). [@Patient context@]
• 48-72 hours: Platelet nadir expected in dengue; if platelets stabilize/rise and hematocrit normalizes without plasma leakage, patient can be discharged with close outpatient follow-up. 5, 8, 6

Discharge Criteria (Once Met)

• Afebrile for 24 hours without antipyretics. [@Patient context@]
• Platelet count rising (IPF% increase precedes platelet recovery by 3+ days). 8
• Hematocrit stable without IV fluids. [@Patient context@]
• Tolerating oral intake. [@Patient context@]
• No warning signs (abdominal pain resolved, no bleeding, no lethargy). [@Patient context@]
• Reliable follow-up arranged within 24-48 hours. [@Patient context@]