Browse categories and answer follow-up questions to refine your symptom profile.
Approach to the Critical Patient
Immediate priorities
Recognition and isolation of threat
High pretest probability triggers
Known or suspected aerosol spore release
Suspicious mail or package handling
Cluster of severe febrile respiratory illness
Biphasic course recognition
Flu-like prodrome over hours to days
Abrupt fulminant deterioration with shock
Standard precautions adequate
Not transmitted person to person
Decontamination if visible spore exposure
Airway and breathing threats
Respiratory failure
SpO2 < 90% on room air
PaO2 < 60 mmHg
Mediastinal compression
Stridor from tracheal compression
Massive mediastinal lymphadenopathy
If airway compromise, early intubation
Anticipate difficult anatomy from edema
Rapid sequence intubation preparation
Circulation and toxemia threats
Distributive shock physiology
SBP < 90 mmHg
MAP < 65 mmHg
Toxin-mediated cardiovascular collapse
Refractory hypotension
Pericardial effusion with tamponade
If shock, aggressive crystalloid then norepinephrine
Sepsis bundle within 1 hour
Blood cultures before antibiotics when feasible
Time-critical actions
First-hour bundle
Blood cultures before antimicrobials
Sterilized after 1 to 2 doses
Alert microbiology to anthrax suspicion
Empiric combination antimicrobials
Two bactericidal agents plus protein synthesis inhibitor
CNS-penetrating regimen until meningitis excluded
Antitoxin co-administration
Obiltoxaximab or raxibacumab
Adjunct to antimicrobials for systemic disease
Source and effusion control
Drainage of pleural effusions
Survival benefit odds ratio 38.3
Bilateral chest tubes often required
Pericardiocentesis if tamponade
Echocardiographic guidance
Cardiothoracic surgery involvement
Team activation and notification
Consultation triggers
Infectious diseases mandatory
Antimicrobial and antitoxin guidance
Public health coordination
Critical care and pulmonology
Ventilator and shock management
Pleural drainage planning
Neurosurgery and neurology if meningitis
Hemorrhagic meningitis suspicion
Near-universal fatality risk
Mandatory reporting
Hospital infection control immediately
Activate bioterrorism protocol
Laboratory Response Network engagement
Public health and CDC
CDC Emergency Operations Center 770-488-7100
State and local health department
Law enforcement if bioterrorism suspected
FBI notification
Preserve specimens as evidence
History
Presentation pattern
Biphasic illness
Prodromal phase
Fever and malaise
Myalgia and fatigue
Nonproductive cough
Transient improvement
Brief apparent recovery in some patients
False reassurance pitfall
Fulminant phase
Abrupt high fever and dyspnea
Drenching diaphoresis
Shock and cyanosis
Symptom characterization
Respiratory complaints
Dyspnea
Pleuritic chest pain
Chest tightness
Systemic complaints
Drenching sweats
Headache
Nausea and vomiting
Critical negative
Rhinorrhea characteristically absent
Key distinction from influenza and URI
Exposure and timing
Incubation window
Typical onset
1 to 7 days after exposure
Median 4 days in 2001 attacks
Delayed onset
Up to 6 to 9 weeks post-exposure
Spore dormancy in lymph nodes
Exposure history
Bioterrorism context
Suspicious mail or powder
Known aerosol release event
Occupational context
Wool, hides, and animal products
Laboratory handling of B anthracis
Travel and military
Endemic regions of Central and South Asia
Sub-Saharan Africa exposure
Risk factors and collateral
Host risk factors
Comorbidities increasing severity
Diabetes
COPD
Obesity and hypertension
Vaccination status
Prior AVA vaccine in military personnel
Incomplete series
Collateral and public health
Cluster recognition
Coworkers with similar illness
Household contacts symptomatic
Shared exposure
Contacts may need postexposure prophylaxis
Notify authorities of suspected release
Physical Exam
Vitals and general
Stability snapshot
Temperature
Fever present in all 2001 cases
Hyperpyrexia in fulminant phase
Heart rate
Tachycardia in majority at presentation
Discriminating feature from ILI
Blood pressure
SBP < 90 mmHg in fulminant phase
MAP < 65 mmHg
Oxygenation
Hypoxemia in majority at presentation
Cyanosis as late marker
General appearance
Toxic and ill-appearing
Diaphoresis
Increased work of breathing
Subcutaneous edema
Chest and neck swelling in advanced disease
Reflects mediastinal involvement
Organ-system exam
Respiratory exam
Lung auscultation
Surprisingly clear early
Decreased breath sounds with effusions
Upper airway
Stridor from mediastinal compression
No rhinorrhea
Cardiovascular exam
Shock signs
Tachycardia
Delayed capillary refill
Pericardial involvement
Muffled heart sounds
Pulsus paradoxus
Neurologic exam
Meningitis screen
Meningismus and nuchal rigidity
Altered mental status and obtundation
Hemorrhagic meningitis association
Occurs in up to 50% of cases
Near-universal fatality
Skin exam
Cyanosis in fulminant phase
Central and peripheral
Marker of respiratory failure
Concurrent cutaneous anthrax
Painless black eschar
Surrounding nonpitting edema
PITFALLS
Anchoring on influenza
Overlapping prodrome
Index of suspicion required
Absence of rhinorrhea as clue
False reassurance in transient improvement
Imminent fulminant decline
Early aggressive treatment regardless
Underestimating mediastinal disease
Clear lungs do not exclude anthrax
Pathology is mediastinitis not bronchopneumonia
Imaging of mediastinum essential
Missed early CXR findings
Subtle mediastinal widening
Repeat imaging if deterioration
Differential Diagnosis
Life threats and infectious mimics
Respiratory infections
Community-acquired pneumonia
ICD-10 J18.9 association
Distinguished by mediastinal widening and absent rhinorrhea
Influenza and ILI
Rhinorrhea and myalgias prominent
Anthrax favors tachycardia and high hematocrit
COVID-19
Overlapping constitutional symptoms
PCR differentiation
Other systemic threats
Hemorrhagic meningitis other causes
Bacterial meningitis
CSF analysis differentiation
Sepsis from other sources
ICD-10 A41.9 association
Blood culture differentiation
Widened mediastinum differentials
Vascular causes
Aortic dissection or ruptured aneurysm
No infectious prodrome
CT angiography differentiation
Superior vena cava syndrome
Malignancy-related widening
Facial and arm edema
Mediastinal infection and infiltration
Acute bacterial mediastinitis
Esophageal perforation history
Mediastinal air
Fibrous mediastinitis
Histoplasma capsulatum
Chronic rather than acute course
Anthrax-specific clue
Clinical algorithm performance
Mediastinal widening plus altered mental status plus elevated hematocrit
100% sensitive and 98.3% specific versus CAP
Laboratory Tests
Microbiologic studies
Blood cultures
Single most useful test
Obtain before antibiotics
Growth in 6 to 24 hours
Rapid sterilization
Negative after 1 to 2 antibiotic doses
Timing critical to yield
Laboratory communication
May be dismissed as B cereus contaminant
Specify anthrax suspicion to micro lab
Confirmatory testing
Peripheral blood Gram stain
Large gram-positive bacilli in massive bacteremia
Box-car morphology
PCR at reference laboratory
Definitive identification
Laboratory Response Network
Pleural fluid studies
Gram stain and culture 83% positive pre-antibiotics
Lethal factor detection by spectrometry
Hematology and chemistry
Complete blood count
Hemoconcentration
Elevated hematocrit
Discriminating feature from CAP
White cell count
Normal or mildly elevated
Not markedly leukocytic
Comprehensive metabolic panel
Hepatic markers
Elevated transaminases
Low albumin
Electrolytes
Hyponatremia
Discriminating feature in scoring tools
Coagulation studies
DIC screening
Coagulopathy in approximately 33% of inhalation cases
Prolonged PT and PTT with low fibrinogen
Trend monitoring
Serial fibrinogen
Platelet trajectory
Gas exchange and CNS sampling
Arterial or venous blood gas
Oxygenation assessment
PaO2 mmHg measurement
Hypoxemia in majority
Acid-base assessment
Lactate elevation with hypoperfusion
Metabolic acidosis in shock
Lumbar puncture
Indication
Rule out hemorrhagic meningitis
Any altered mental status
Findings
Hemorrhagic CSF
Gram-positive bacilli on stain
Diagnostic Tests
Scoring Systems
Discriminating clinical tools
Kyriacou chest radiograph algorithm
Mediastinal widening or pleural effusion plus altered mental status plus elevated hematocrit
100% sensitive and 98.3% specific versus CAP
Kuehnert ILI discrimination score
Tachycardia and high hematocrit
Low albumin and low sodium
Absence of rhinorrhea and myalgias
Score >= 4 captured all 11 anthrax cases
Excluded 96% of ILI
Severity and sepsis adjuncts
qSOFA at bedside
RR >= 22 per minute
SBP <= 100 mmHg
Altered mental status
Limitations
Not anthrax-specific
Clinical trajectory supersedes single score
ACEP Level C recommendation for adjunctive use
MRI
MRI role
Limited acute utility
Availability constraints
Unsuitable for unstable patient
Neuroimaging indications
Suspected hemorrhagic meningoencephalitis
Brain MRI shows hemorrhage and edema
Contraindications
Hemodynamic instability
Incompatible implants
CT
CT chest indications
When CXR equivocal
High suspicion with normal radiograph
Characterize mediastinal disease
Protocol
Noncontrast detects hemorrhage
Contrast for vascular differentials when needed
Characteristic findings
Hyperdense lymphadenopathy
Hemorrhagic mediastinal nodes on unenhanced CT
Highly suggestive in context
Associated findings
Bilateral pleural effusions
Mediastinal widening and fat edema
Guidance
CT supports diagnosis when CXR nondiagnostic
ACEP Level C recommendation
Ultrasound
Thoracic ultrasound
Pleural effusion assessment
Free fluid versus loculation
Thoracentesis and drainage guidance
Effusion quantification
Bilateral effusions in 72 to 80% of cases
Operator-dependent limitation
Cardiac ultrasound
Pericardial assessment
Pericardial effusion screen
Tamponade physiology
Hemodynamic support
LV function gross estimate
Integrate with clinical exam
Disposition
Level of care selection
ICU admission
All suspected inhalation anthrax
No role for outpatient symptomatic management
Hemodynamic monitoring required
Ventilatory and shock needs
Mechanical ventilation readiness
Vasopressor support
Procedural needs
Pleural drainage
Pericardiocentesis
Specialist coordination
Infectious diseases mandatory
Antimicrobial selection
Antitoxin authorization
Critical care and surgery
Pulmonology and critical care
Cardiothoracic surgery for effusions
Exposed contacts and notification
Asymptomatic exposed individuals
Outpatient prophylaxis candidate
Close follow-up
Return precautions for any febrile illness
Prophylaxis components
60-day antimicrobial course
AVA vaccine 3-dose series
Mandatory notification
Public health reporting
State and local health department
CDC Emergency Operations Center
Law enforcement
FBI if bioterrorism suspected
Specimen preservation
Treatment
Initial stabilization
Resuscitation
Hemodynamic support
Aggressive IV crystalloid
Norepinephrine for refractory shock
Respiratory support
Oxygen titrated to SpO2 target
Lung-protective ventilation if intubated
Sepsis bundle
Blood cultures before antibiotics
Lactate-guided resuscitation
Antimicrobial therapy
Systemic anthrax with possible meningitis
Bactericidal fluoroquinolone
Ciprofloxacin 400 mg IV every 8 hours
Levofloxacin or moxifloxacin alternative
CNS-penetrating beta-lactam
Meropenem 2 g IV every 8 hours
Added until meningitis excluded
Protein synthesis inhibitor
Linezolid 600 mg IV every 12 hours
Inhibits toxin production
Systemic anthrax with meningitis excluded
Bactericidal agent
Ciprofloxacin 400 mg IV every 8 hours
Single fluoroquinolone acceptable
Protein synthesis inhibitor
Linezolid 600 mg IV every 12 hours
Clindamycin 900 mg IV every 8 hours alternative
Pharmacologic cautions
Oral monotherapy inadequate
IV combination mandatory for systemic disease
Doxycycline and minocycline favored PSIs by PK/PD
Rifampin restriction
Never used as monotherapy
Rapid resistance development
Duration
Intravenous phase
At least 2 weeks IV
Transition to oral when stable
Total course
60 days total if aerosol exposure suspected
Covers delayed spore germination
Antitoxin and adjuncts
Antitoxin therapy
Monoclonal antibodies preferred
Obiltoxaximab
Raxibacumab
Polyclonal alternative
Anthrax immune globulin AIGIV
Less preferred than monoclonals
Indication
All noncutaneous systemic anthrax
Adjunct to antimicrobials
Glucocorticoids
Anthrax meningitis
Considered per bacterial meningitis protocols
Adjunctive to antimicrobials
Mediastinal or airway edema
May reduce compressive edema
Case-by-case decision
Procedural interventions
Pleural drainage
Survival benefit
Odds ratio 38.3 for survival
Both diagnostic and therapeutic
Technique
Bilateral chest tubes often required
Repeat drainage of reaccumulation
Pericardial drainage
Pericardiocentesis if tamponade
Echocardiographic guidance
Hemodynamic monitoring
Surgical drainage
Cardiothoracic involvement
Recurrent effusion
Postexposure prophylaxis
Antimicrobial prophylaxis
First-line oral agents
Ciprofloxacin 500 mg PO twice daily
Doxycycline 100 mg PO twice daily
Duration
60 days
Extended in immunocompromised
Vaccine adjunct
AVA vaccine series
Doses at 0, 2, and 4 weeks
Adjunct to antimicrobials
Special Populations
Pregnancy
Treatment considerations
Life-threatening disease priority
Standard combination therapy not withheld
Ciprofloxacin acceptable when indicated
Agent caution
Doxycycline weighed against fetal risk
Use when benefit outweighs risk in severe disease
Supportive measures
Maternal SpO2 >= 95% when feasible
Fetal monitoring at viable gestation
Prophylaxis approach
Ciprofloxacin preferred for PEP
60-day course
Doxycycline alternative with counseling
Vaccine consideration
AVA per public health guidance
Risk-benefit individualized
Geriatric
Severity and presentation
Higher complication risk
Comorbid COPD and diabetes
Reduced physiologic reserve
Atypical features
Delirium as early sign
Blunted febrile response possible
Medication adjustment
Renal dosing
Fluoroquinolone adjustment for clearance
Meropenem renal dosing
Adverse effect monitoring
QT prolongation with fluoroquinolones
Linezolid thrombocytopenia
Pediatrics
Weight-based antimicrobials
Fluoroquinolone
Ciprofloxacin 30 mg/kg/day IV divided every 8 hours
Maximum 400 mg per dose
Carbapenem
Meropenem 120 mg/kg/day IV divided every 8 hours
Maximum 2 g per dose
Protein synthesis inhibitor
Linezolid 30 mg/kg/day IV divided every 8 hours
Maximum 600 mg per dose
Prophylaxis and supportive care
Oral PEP
Ciprofloxacin 30 mg/kg/day PO divided every 12 hours
Doxycycline weight-based alternative
Resuscitation
Weight-based fluid boluses
Age-appropriate vital sign targets
Background
Epidemiology
Burden and lethality
Category A bioterrorism agent
Most lethal form of anthrax
Aerosol weaponization concern
Case fatality
Historically 89 to 90%
Reduced to approximately 45% in 2001 attacks
Rapidity of death
Fatal cases had median hospital stay of 1 day
All untreated fulminant 2001 cases died
Complication frequency
Major complications
Sepsis in approximately 70%
Secondary meningitis in approximately 33%
Additional complications
Coagulopathy in approximately 33%
Respiratory failure requiring ventilation in approximately 23%
Pathophysiology
Organism and entry
Bacillus anthracis spores
Inhaled into alveoli
Engulfed by alveolar macrophages
Lymphatic transport
Germination in mediastinal lymph nodes
Hemorrhagic mediastinitis
Toxin-mediated injury
Tripartite toxin
Protective antigen mediates cell entry
Lethal factor and edema factor cause injury
Systemic effects
Capillary leak and edema
Toxin-mediated cardiovascular collapse
Not a true pneumonia
Pathology is mediastinitis and toxic effusions
Infiltrates represent atelectasis and ARDS
Therapeutic Considerations
Antimicrobial strategy principles
Combination rationale
Bactericidal kill plus toxin suppression
CNS coverage until meningitis excluded
Resistance avoidance
No rifampin monotherapy
Avoid penicillin alone given inducible beta-lactamase
Adjunctive importance
Antitoxin and source control
Antitoxin neutralizes circulating toxin
Pleural drainage improves survival
Meningitis prognosis
Near-100% mortality with meningitis
All 2001 meningitis patients died
Prophylaxis principles
Prolonged course rationale
Spores germinate over weeks
60-day antimicrobial course required
Adherence challenge
Compliance under 50% in 2001 attacks
Counseling and follow-up essential
Patient Discharge Instructions
copy discharge instructions
Postexposure prophylaxis home care
Take antibiotics every day for the full 60 days
Do not stop early even if you feel well
Complete all 3 vaccine doses if offered
Keep all follow-up appointments
Warning signs to return to ER immediately
Fever or chills
New cough or trouble breathing
Drenching sweats
Chest pain
Severe headache or neck stiffness
Confusion or severe drowsiness
Fainting or feeling like you may pass out
Medication safety
Report rash, swelling, or trouble breathing as possible allergy
Report severe diarrhea
Avoid stopping the antibiotic without medical advice
Follow up
Clinician follow up as scheduled during prophylaxis
Public health may contact you about exposure
Report any new illness in household contacts
References
Guidelines and key sources
Guideline sources
CDC Guidelines for Prevention and Treatment of Anthrax 2023
Anthrax as a Biological Weapon Updated Recommendations JAMA 2002
Clinical Management of Potential Bioterrorism-Related Conditions NEJM 2015
Landmark studies and reviews
Hendricks systematic review of hospitalized anthrax 1880 to 2018
Kyriacou clinical algorithm distinguishing anthrax from CAP
Kuehnert clinical features discriminating inhalational anthrax
Coding standards
ICD-10 A22.1 pulmonary anthrax
SNOMED CT inhalation anthrax disorder concept
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.