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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
Key points
- Suspected bioterrorism or high-consequence pathogen requires immediate public health notification and infection-control escalation
- Anthrax: painless black eschar for cutaneous disease; inhalational disease has widened mediastinum and severe sepsis after prodrome
- Smallpox: febrile prodrome then deep firm synchronous vesiculopustular rash involving face/extremities including palms/soles; airborne/contact isolation
- Plague: bubonic painful lymphadenitis, septicemic shock, or pneumonic plague with hemoptysis; pneumonic plague needs droplet precautions and prophylaxis for contacts
- Botulism: descending symmetric flaccid paralysis with cranial nerve palsies and normal sensation/mental status; give antitoxin and ventilatory support
- Tularemia: ulceroglandular disease after rabbits/ticks/deer flies; treat severe disease with gentamicin or streptomycin
Overview
Bioterrorism agents are uncommon but high-impact infectious threats because delayed recognition can lead to death, healthcare exposure, public panic, and secondary transmission. Step 2 CK focuses on pattern recognition: anthrax eschar or widened mediastinum, smallpox synchronous rash with prodrome, pneumonic plague, botulism descending paralysis, and tularemia after rabbit/tick exposure. Management includes stabilization, empiric treatment, isolation, prophylaxis of contacts when indicated, and immediate public health coordination.
Epidemiology
CDC Category A agents include anthrax, botulism, plague, smallpox, tularemia, and viral hemorrhagic fevers because they can be easily disseminated or transmitted, cause high mortality, create public health impact, and require preparedness. Natural sporadic cases still occur for anthrax, plague, botulism, and tularemia in the United States. Smallpox has been eradicated globally, so any suspected case is an international public health emergency.
Clinical Features
Symptoms
Anthrax cutaneous: painless pruritic papule progressing to vesicle and black eschar with marked edema
Inhalational anthrax: flu-like prodrome followed by dyspnea, chest pain, shock, widened mediastinum
Smallpox: high fever and severe prodrome before rash; lesions deep, firm, same stage, face/extremities, palms/soles
Plague: fever with painful bubo; pneumonic plague causes cough, dyspnea, hemoptysis, rapidly fatal pneumonia
Botulism: diplopia, ptosis, dysarthria, dysphagia, dry mouth, descending weakness, respiratory failure
Tularemia: fever plus ulcer at inoculation site and tender lymphadenopathy after rabbit/tick/deer fly exposure
Signs
Black eschar with surrounding nonpitting edema in cutaneous anthrax
Toxic appearance with mediastinal widening or pleural effusions in inhalational anthrax
Smallpox lesions are synchronous and centrifugal; varicella lesions are different stages and trunk-predominant
Tender regional lymphadenopathy/buboes in plague or tularemia
Botulism has cranial nerve palsies, descending paralysis, normal sensation, and usually no fever
Investigations
First-line
Immediate public health and laboratory coordinationNotify local/state health department and CDC pathways before sending high-risk specimens when suspected
Syndrome-directed cultures/PCRBlood, lesion, sputum, lymph node aspirate, stool/serum toxin testing depending agent
Chest imagingWidened mediastinum/pleural effusion in inhalational anthrax; severe pneumonia in pneumonic plague
Second-line
Gram stain/culturePlague may show bipolar "safety pin" gram-negative coccobacilli; anthrax shows large gram-positive rods
Botulinum toxin testingSerum, stool, gastric contents, or food testing; treatment should not wait for confirmation
Smallpox testingOnly through public health-approved specialized laboratory pathways; avoid routine lab processing without notification
Specialist
ICU monitoringRespiratory failure risk in botulism, inhalational anthrax, plague, severe tularemia, or shock
Exposure investigationIdentify contacts needing prophylaxis, vaccination, quarantine, or symptom monitoring
1
Immediate response
- Stabilize airway, breathing, circulation; use appropriate PPE and isolation
- Notify infection prevention, hospital leadership, local/state public health, and law enforcement/public health channels as appropriate
- Collect diagnostic specimens safely before antibiotics if feasible, but do not delay life-saving therapy
- Protect healthcare workers and identify exposed contacts
2
Agent-specific treatment
- Anthrax systemic/inhalational: combination IV antibiotics including a fluoroquinolone plus additional agents and antitoxin when indicated
- Cutaneous anthrax without systemic disease: oral ciprofloxacin or doxycycline; duration depends on exposure context
- Plague: gentamicin or fluoroquinolone/doxycycline depending severity; pneumonic plague requires droplet precautions and contact prophylaxis
- Botulism: heptavalent botulinum antitoxin urgently plus ventilatory support; infant botulism uses human botulism immune globulin
- Tularemia severe disease: gentamicin or streptomycin; doxycycline or ciprofloxacin may be used for mild disease or prophylaxis scenarios
3
Smallpox
- Airborne plus contact precautions in negative-pressure room; vaccinate contacts when directed by public health
- Tecovirimat may be used under public health/emergency protocols
- Do not confuse with varicella: smallpox lesions are deeper, same developmental stage, and centrifugal with prodrome
4
Post-exposure prophylaxis
- Anthrax inhalational exposure: prolonged antibiotics plus anthrax vaccine when recommended
- Pneumonic plague contacts: doxycycline or ciprofloxacin prophylaxis per public health guidance
- Smallpox contacts: vaccination as soon as possible after exposure under public health direction
Complications
- Mass casualty impact: Delayed recognition can expose healthcare workers and the public
- Respiratory failure: Botulism, pneumonic plague, inhalational anthrax
- Septic shock: Anthrax, plague, tularemia can progress rapidly
- Secondary transmission: Pneumonic plague and smallpox are major infection-control concerns
- Neurologic injury: Botulism recovery may require prolonged ventilation and rehabilitation
USMLE Step 2 CK Exam Tips
- 1Painless black eschar with massive edema = cutaneous anthrax
- 2Flu-like illness then abrupt respiratory failure + widened mediastinum = inhalational anthrax
- 3Smallpox rash is synchronous and centrifugal with palms/soles; varicella is crops in different stages, trunk-predominant
- 4Painful bubo + fever = plague; pneumonia with hemoptysis after exposure = pneumonic plague and droplet isolation
- 5Descending paralysis with normal sensation and no fever = botulism; give antitoxin before confirmation
- 6Rabbit exposure + ulceroglandular disease = tularemia
- 7Any suspected smallpox or bioterrorism event = immediate public health notification
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