Browse categories and answer follow-up questions to refine your symptom profile.
Approach to the Critical Patient
Immediate priorities
Airway and mental status threats
Meningoencephalitis concern
Altered mental status
Seizures
Nuchal rigidity
If GCS < 13, immediate CT head then lumbar puncture
Neurology or critical care consult
Empiric coverage for bacterial meningitis until ruled out
Hemorrhagic manifestations
Petechiae or purpura
Active bleeding
Circulation and sepsis threats
Shock physiology uncommon but possible in severe cases
SBP < 90 mmHg
MAP < 65 mmHg
DIC concern in severe pediatric cases
Petechiae and bleeding
Thrombocytopenia on CBC
If septic shock physiology, consider bacterial co-infection or RMSF
Empiric doxycycline within 1 hour if RMSF cannot be excluded
Class I recommendation for empiric doxycycline in suspected RMSF
Cannot-miss diagnosis
Rocky Mountain spotted fever must be excluded
Same tick vector (Dermacentor andersoni)
Similar early presentation of fever, headache, myalgia
RMSF rash typically appears day 3 to 5 on wrists and ankles
Centripetal spread to trunk
Petechial progression
If RMSF cannot be excluded, start doxycycline empirically
Do not wait for confirmatory testing
Delay in treatment rapidly fatal with RMSF
Monitoring and escalation
Monitoring targets
Continuous temperature monitoring for biphasic pattern
Fever typically 39 to 40 C
Remission phase day 2 to 4 then recurrence
Neurologic status
Mental status trend
Seizure activity
Hydration status
Oral intake adequacy
Tachycardia as dehydration marker
Escalation triggers
Persistent high fever without biphasic resolution
Broadened differential
Repeat labs and cultures
Bleeding or petechiae development
DIC workup
Hematology consult
Neurologic deterioration
ICU level care
Neurology consult
History
Presentation pattern
Classic syndrome
Abrupt onset fever
Often 39 to 40 C
Chills and rigors
Severe headache
Photophobia common
Retrobulbar pain described
Myalgias
Diffuse and severe
Lower extremity predominance
Fatigue and malaise
Lethargy prominent
Weakness persisting weeks after resolution
Biphasic fever pattern
Saddleback fever in approximately 50% of patients
Initial febrile phase 2 to 4 days
Apparent remission 1 to 3 days
Second febrile phase 2 to 4 days
Prolonged convalescence
Weakness and fatigue lasting 3 or more weeks in approximately 50%
More prolonged in older adults
Tick exposure history
Tick exposure
Recent outdoor activity in endemic mountainous western US
Colorado, Utah, Montana, Wyoming, Idaho, Oregon
Elevation typically 4,000 to 10,000 feet
Activities in tick habitat
Hiking and camping
Hunting and fishing
Occupational exposure for forestry workers, ranchers, park rangers
90% report tick exposure but only approximately 52% recall a tick bite
Absence of recalled bite does not exclude CTF
Careful questioning about outdoor activities
Seasonality
98% of cases occur April through July
Peak late May to early July
Concordance with D. andersoni activity season
Associated symptoms
Gastrointestinal
Nausea
Present in approximately 20%
Vomiting
Fluid loss concern
Abdominal pain
Hepatosplenomegaly association
Ocular
Photophobia
Meningoencephalitis concern if severe
Conjunctival injection
Rare complications
Meningoencephalitis symptoms
Neck stiffness
Confusion
Seizures
Primarily in children
Orchitis
Testicular pain
Rare manifestation
Pericarditis
Chest pain
Pleuritic component
Risk factors
Demographic risk
Male sex
65% of cases
Male to female ratio approximately 2.5 to 1
Age
Median age 55 years
Highest incidence ages 51 to 70
Geographic residence or travel
Mountainous western US or southwestern Canada
Exposure risk
Infection prevalence in D. andersoni ticks ranges from 3% to 58%
Varies by geographic subregion
Higher in Colorado and surrounding states
Blood transfusion history
Rare transmission route
Virus persists in erythrocytes for weeks to months
Physical Exam
Vitals and general
Stability assessment
Temperature
Fever often greater than 39 C
Hypothermia uncommon but marker of severe illness
Heart rate
Tachycardia common with fever
Dehydration contribution
Blood pressure
Hypotension rare in uncomplicated CTF
SBP less than 90 mmHg prompts RMSF and sepsis evaluation
Oxygen saturation
Usually normal
Desaturation prompts complication evaluation
General appearance
Ill-appearing with lethargy
Degree of distress
Ability to provide history
Skin and lymph nodes
Skin examination
Full skin survey for attached ticks
Hair, axillae, groin, behind ears
Tick removal if found
Rash
Maculopapular or petechial rash in fewer than 20%
Petechial rash raises concern for RMSF or meningococcemia
Eschar
Absence helps distinguish from some other tick-borne illnesses
Lymphadenopathy
Cervical and axillary nodes
Soft and tender typical
Hard or fixed nodes suggest alternative diagnosis
Neurologic exam
Mental status
Level of alertness and orientation
Confusion or agitation as meningoencephalitis marker
GCS assessment
Meningeal signs
Kernig sign
Brudzinski sign
If positive meningeal signs, immediate CT head then LP
Meningoencephalitis rare but life-threatening
Primarily affects children
Systemic exam
Eyes
Conjunctival injection
Common finding in CTF
Photophobia assessment
Oropharynx
Pharyngeal erythema
Nonspecific finding
Abdomen
Hepatosplenomegaly
Uncommon
Liver and spleen palpation
Cardiac
Pericardial friction rub
Rare pericarditis complication
ECG if suspected
Genitourinary
Testicular tenderness
Rare orchitis
Scrotal exam in male patients with GU complaints
Differential Diagnosis
Life threats
Rocky Mountain spotted fever
ICD-10 A77.0
Same tick vector and geography
Early presentation identical to CTF
Characteristic rash wrists and ankles spreading centripetally day 3 to 5
Rapidly fatal without doxycycline treatment
Cannot be excluded clinically early — empiric doxycycline required if suspected
Meningococcemia
ICD-10 A39.4
Petechial or purpuric rash
Meningeal signs
Rapid deterioration
Tick-borne co-infections and mimics
Ehrlichiosis and anaplasmosis
ICD-10 A77.4 and A79.82
Fever, headache, myalgias
Leukopenia and thrombocytopenia overlap with CTF
Morulae on peripheral smear distinguishes
Tick-borne relapsing fever
Biphasic or relapsing fever pattern similar to CTF
Spirochetes visible on peripheral blood smear
Borrelia species
Lyme disease
ICD-10 A69.2
Erythema migrans rash in 70 to 80%
Different tick vector Ixodes species
Different geographic distribution eastern and upper midwest US
Tularemia
ICD-10 A21
Also transmitted by Dermacentor ticks
Fever and lymphadenopathy
Ulceroglandular form with skin ulcer
Powassan virus
Northeastern US and Great Lakes region
Progresses to meningoencephalitis
Different geographic distribution
Non tick-borne mimics
Influenza
ICD-10 J09 to J11
Fever, myalgia, headache overlap
No tick exposure history
Respiratory symptoms more prominent
Enteroviral illness
Summer and fall seasonal overlap
GI symptoms prominent
No tick exposure
EBV or CMV mononucleosis
Lymphadenopathy and splenomegaly
Pharyngitis prominent
Heterophile antibody testing
Dengue fever
ICD-10 A90
Travel to endemic tropical regions
Saddle-back fever pattern similar
Retro-orbital pain prominent
Laboratory Tests
Core labs
Complete blood count
Leukopenia characteristic of CTF
White cell count typically 2.0 to 4.0 x10^9/L
Lymphopenia common
Thrombocytopenia
Moderate reduction typical
Platelet count below 150 x10^9/L common
Anemia uncommon unless prolonged illness
Comprehensive metabolic panel
Generally unremarkable in uncomplicated CTF
Mild transaminase elevation possible
ALT and AST
Not usually severe
Electrolytes for dehydration assessment
Sodium trend
Renal function baseline
Confirmatory and specialized testing
RT-PCR for CTF virus RNA
Preferred acute diagnostic test
Detects viral RNA from day 1 of symptoms through first 2 weeks
High sensitivity in early illness phase
Sample type
Whole blood preferred
Available at some commercial labs, state health departments, and CDC
Sensitivity highest in first week of illness
Serology
Antibody production delayed 14 to 21 days after symptom onset
Acute serology often negative and not useful early
Convalescent serology required for retrospective confirmation
Paired sera collection
IgM-capture EIA or indirect fluorescent antibody (IFA)
Plaque-reduction neutralization test (PRNT) as reference standard
Samples collected at least 2 weeks apart
Additional studies for complications and co-infections
Peripheral blood smear
Evaluate for babesiosis if co-infection suspected
Ring-form intraerythrocytic parasites
Morulae in white cells suggests ehrlichiosis or anaplasmosis
Blood cultures
Rule out bacterial etiologies
Particularly if clinical deterioration
Prior to empiric antibiotics when feasible
Lumbar puncture
Indicated when meningeal signs present
Expect lymphocytic pleocytosis in CTF meningoencephalitis
Mildly elevated protein
Normal glucose
CSF viral PCR for CTF virus if available
Coagulation studies
PT, PTT, fibrinogen, D-dimer
Indicated when DIC concern in severe or pediatric cases
Thrombocytopenia with petechiae triggers workup
Diagnostic Tests
Scoring Systems
No validated clinical scoring systems specific to CTF
Clinical diagnosis relies on epidemiologic and clinical criteria
Tick exposure in endemic western US mountainous region
Appropriate season April through July
Classic biphasic fever with leukopenia and thrombocytopenia
Clinical probability framework
Definite CTF: laboratory confirmed by RT-PCR or serology
Probable CTF: clinical syndrome with epidemiologic link without confirmatory testing
Risk stratification approach
Severity markers warranting admission
Neurologic involvement
Hemorrhagic manifestations
DIC
Severe dehydration
Features favoring safe discharge
Alert and oriented
Tolerating oral fluids
Reliable follow-up available
Fever without complications
MRI
MRI brain indications in CTF
Meningoencephalitis evaluation
Altered mental status not explained by fever alone
Focal neurologic deficits
Seizures with neurologic concern
MRI findings in CTF meningoencephalitis
May show T2 signal abnormalities in white matter
Leptomeningeal enhancement with gadolinium
Limitations
MRI not required in typical uncomplicated CTF
Availability constraints in acute setting
CT head may be obtained first for rapid evaluation
CT
CT head indications
Neurologic complications
Before lumbar puncture when meningeal signs present
Altered mental status or seizures
Focal neurologic deficits
CT findings
Usually normal in CTF
Cerebral edema in severe encephalitis
Mass effect evaluation before LP
Chest CT
Atypical pneumonitis as rare complication
Respiratory symptoms not explained by other etiology
Evidence level
CT head before LP for altered mental status
Standard emergency medicine practice
Herniation risk assessment
Ultrasound
Point-of-care ultrasound applications
Cardiac POCUS when pericarditis suspected
Pericardial effusion detection
Regional wall motion assessment
ECG changes with chest pain and friction rub
Scrotal ultrasound
Testicular torsion exclusion when orchitis suspected
Epididymo-orchitis blood flow assessment
Abdominal POCUS
Splenomegaly assessment
Hepatomegaly assessment
Disposition
Admission indications
Hospital admission criteria
Neurologic involvement
Altered mental status
Seizures
Meningeal signs
Hemorrhagic manifestations
Petechiae
Active bleeding
DIC concern
Severe dehydration
Inability to tolerate oral fluids
Persistent vomiting
Cannot exclude RMSF or other serious tick-borne illness
Empiric doxycycline required while awaiting testing
Significant comorbidities
Immunocompromised state
High risk for complications
ICU indications
Critical illness triggers
Meningoencephalitis with GCS less than 13
Intracranial pressure monitoring consideration
Neurology and critical care consult
DIC with active bleeding
Blood product replacement
Hematology consult
Septic shock physiology
Vasopressor requirement
Broad differential including RMSF and bacterial sepsis
Discharge criteria
Safe discharge criteria
Confirmed or probable CTF without complications
Alert and oriented with stable mental status
Tolerating oral fluids and medications
Vital signs acceptable
Afebrile or low-grade fever with typical biphasic pattern
Heart rate and blood pressure within normal limits
RMSF and other serious diagnoses excluded or deemed low probability
Reliable follow-up available within 24 to 48 hours
Blood donation restriction
CTF virus persists in erythrocytes for weeks to months
No blood donation for at least 6 months after illness
Patient education required at discharge
Treatment
Supportive care
Symptomatic management
Antipyretics and analgesics
Acetaminophen 650 to 1000 mg PO every 6 to 8 hours in adults
Maximum 4 g per day in adults without liver disease
Preferred agent for fever and myalgia
Ibuprofen 400 to 600 mg PO every 6 to 8 hours in adults
Avoid in dehydration or renal compromise
Avoid in children with viral illness if salicylate use is also a risk
Avoid aspirin in children
Risk of Reye syndrome with viral illness
Acetaminophen preferred in pediatric patients
Hydration
Oral rehydration encouraged
Small frequent sips if nausea present
Target urine output greater than 0.5 mL/kg/hour
IV hydration when oral intake insufficient
Normal saline 500 mL to 1 L IV bolus for moderate dehydration
Reassess volume status after each bolus
Empiric antibiotic therapy
Doxycycline when RMSF cannot be excluded
Adult dosing
Doxycycline 100 mg PO or IV every 12 hours
Continue until RMSF excluded or minimum 3 days afebrile
Pediatric dosing
Doxycycline 2.2 mg/kg PO or IV every 12 hours for children under 45 kg
Maximum 100 mg per dose
Safe in children for short courses despite age below 8 years per CDC guidance
Do not delay doxycycline awaiting rash development
RMSF can be fatal without treatment within 5 to 8 days of symptom onset
Clinical suspicion alone warrants empiric therapy
No specific antiviral for CTF
Ribavirin has been considered in severe cases
Evidence limited to in vitro and animal models
Not standard of care
Infectious disease consult for severe or unusual cases
Complication management
Meningoencephalitis
Supportive care in ICU
Seizure precautions
Airway protection readiness
Antiseizure therapy if seizures occur
Lorazepam 0.1 mg/kg IV for acute seizure up to 4 mg per dose
Levetiracetam 20 to 60 mg/kg IV load for status epilepticus
Neurology consult for ongoing management
DIC management
Treat underlying viral illness supportively
No specific antiviral available
Blood product replacement
Fresh frozen plasma for coagulopathy with bleeding
Platelet transfusion for counts below 10 x10^9/L or bleeding
Cryoprecipitate for fibrinogen less than 1.0 g/L
Hematology consult for severe DIC
Pericarditis
NSAIDs as first-line for pericardial inflammation
Ibuprofen 600 mg PO every 8 hours for 1 to 2 weeks
Colchicine 0.5 mg PO twice daily as adjunct
Cardiology consult for large effusion or hemodynamic compromise
Special Populations
Pregnancy
Pregnancy considerations
CTF in pregnancy risk profile
Rare documented cases
Potential for fetal infection via transplacental transmission
Spontaneous abortion and intrauterine fetal demise reported
Fever management in pregnancy
Acetaminophen preferred for antipyresis
650 to 1000 mg PO every 6 to 8 hours
Avoid NSAIDs especially in third trimester
Aggressive fever control to reduce teratogenic risk
Diagnostic considerations
RT-PCR preferred for diagnosis
Fetal monitoring when fever present
Obstetrics consult for pregnant patients
Antibiotic considerations if RMSF cannot be excluded
Doxycycline risk-benefit discussion
RMSF is rapidly fatal and outweighs doxycycline risks
Discuss with obstetrics and infectious disease
Geriatric
Older adult features
More severe and prolonged illness
Prolonged convalescence greater than 3 weeks common
Weakness and fatigue prominent
Atypical presentation risk
Delirium as primary presentation
Afebrile infection possible despite serious illness
Baseline cognitive status clarification important
Comorbidity considerations
Medication interactions with doxycycline
Antacids reduce doxycycline absorption
Renal and hepatic dosing adjustments
Dehydration risk higher
Lower physiologic reserve
Early IV hydration threshold lower
Disposition bias toward admission
Frailty and limited home supports
Higher complication risk
Pediatrics
Pediatric-specific features
Meningoencephalitis more common in children than adults
Altered mental status and seizures require urgent evaluation
LP if meningeal signs present after CT head
DIC risk higher in pediatric CTF
Rare but can be fatal
Petechiae or bleeding in child with CTF is emergency
Fever management in children
Acetaminophen 15 mg/kg PO or PR every 4 to 6 hours
Maximum 75 mg/kg/day up to 4 g/day
Ibuprofen 10 mg/kg PO every 6 to 8 hours
Maximum 40 mg/kg/day
Aspirin contraindicated
Risk of Reye syndrome
Doxycycline in children
2.2 mg/kg IV or PO every 12 hours for children under 45 kg
Maximum 100 mg per dose
CDC recommends doxycycline for suspected RMSF regardless of age
Background
Epidemiology
Incidence and distribution
Reported cases typically 200 to 400 per year in US
Likely underreported due to mild illness and limited testing
Reportable disease in most endemic states
Geographic distribution
Rocky Mountain region and western US
Colorado, Utah, Montana, Wyoming, Idaho, Oregon
Southwestern Canada at lower frequency
Seasonal distribution
98% of cases April through July
Peak late May to early July
Concordance with D. andersoni adult activity
Demographics
Male sex predominance
65% of cases
2.5 to 1 male to female ratio
Median age 55 years
Highest incidence ages 51 to 70
Children account for minority but have highest complication risk
Tick infection prevalence
D. andersoni tick infection rate ranges from 3% to 58%
Geographic variation within endemic range
Pathophysiology
Viral biology
CTF virus (Coltivirus genus, Reoviridae family)
Double-stranded RNA virus
12-segmented genome
Transmission
Bite of infected Dermacentor andersoni (Rocky Mountain wood tick)
Incubation period 1 to 14 days, typically 3 to 6 days
Rare person-to-person via blood transfusion
Viral persistence and immune response
Virus infects erythrocyte precursors in bone marrow
Persists within mature red blood cells protected from immune clearance
Persistence for weeks to months in circulating erythrocytes
Leukopenia and thrombocytopenia mechanism
Bone marrow suppression
Peripheral destruction
Biphasic fever pathophysiology
Initial viremic phase
Transient immune control then secondary viremia
Occurs in approximately 50% of patients
Complication mechanisms
Meningoencephalitis
CNS invasion via viremia
Direct viral neuronal injury
DIC
Endothelial injury and coagulation cascade activation
More severe in children with immature immune response
Therapeutic Considerations
Antiviral strategy
No proven specific antiviral therapy for CTF
Management entirely supportive
Ribavirin in vitro activity not confirmed in clinical trials
Empiric doxycycline for RMSF exclusion
Critical decision point in all tick-fever presentations in endemic area
Safety profile well-established including in children and with brief pregnancy exposure
Blood product considerations
CTF virus persistence in erythrocytes is clinically important
Patients must not donate blood for 6 months after illness
Transfusion-transmitted CTF has been documented
Routine blood screening does not include CTF testing
Supportive care evidence
Hydration and antipyretics are mainstay of treatment
No clinical trials for specific interventions in CTF
Management extrapolated from general viral illness principles
Isolation not required
No person-to-person transmission by respiratory or contact routes
Standard precautions appropriate
Patient Discharge Instructions
copy discharge instructions
Colorado Tick Fever home care
Rest and increase fluid intake
Water, electrolyte drinks, broth
Aim for clear to pale yellow urine
Fever and pain management
Acetaminophen as directed for fever and muscle aches
Do not give aspirin to children
Return if fever not improving after several days
Expect a second wave of symptoms
Fever may go away for 1 to 3 days then return
This saddleback pattern is typical of Colorado Tick Fever
Persistent worsening or new severe symptoms require re-evaluation
Activity
Rest during febrile phase
Gradual return to activity as tolerated
Prolonged fatigue and weakness may last several weeks
Blood donation restriction
No blood donation for at least 6 months after illness
Virus can persist in red blood cells
Inform any future blood donation center of recent CTF
Tick prevention
Use insect repellent with DEET or picaridin in endemic areas
Wear long sleeves and tuck pants into socks in tick habitat
Perform tick checks after outdoor activities
Remove attached ticks promptly with fine-tipped tweezers
Return to ER immediately for
Confusion or difficulty waking up
Stiff neck
Seizures
Rash developing especially on wrists, ankles, or spreading rash
Bleeding or bruising not explained by injury
Persistent vomiting unable to keep fluids down
Severe worsening headache
High fever not controlled with acetaminophen
Follow-up
Primary care within 48 to 72 hours
Repeat CBC recommended to confirm resolution of leukopenia and thrombocytopenia
Notify provider if symptoms persist beyond 3 weeks
References
Guidelines and key sources
Guideline and authoritative sources
CDC Division of Vector-Borne Diseases: Colorado Tick Fever guidance
Diagnostic testing algorithms and RT-PCR protocols
Epidemiologic case definitions
ACEP Clinical Policy on evaluation and management of tick-borne illness
Infectious Diseases Society of America (IDSA) tick-borne illness guidance
Key evidence sources
Epidemiologic studies
Male predominance 65% and median age 55 years data
Seasonal distribution 98% of cases April through July
Male to female ratio 2.5 to 1
Clinical natural history data
Biphasic fever pattern in approximately 50%
Prolonged convalescence greater than 3 weeks in approximately 50%
Only 52% of patients recall tick bite despite 90% reporting tick exposure
Diagnostic test performance
RT-PCR sensitivity highest in first 2 weeks of illness
Serology delayed 14 to 21 days requiring convalescent specimens
Coding standards
ICD-10 A93.2 Colorado tick fever
SNOMED CT Colorado tick fever disorder
Rocky Mountain spotted fever ICD-10 A77.0 for differential coding
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.