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Answer
Answer: A - Middle East Respiratory Syndrome Coronavirus (MERS-CoV)
Key clues in this question:
- Arabian Peninsula travel - MERS-CoV is endemic to the Arabian Peninsula
- Close contact with dromedary camels - Dromedary camels are the primary zoonotic reservoir for MERS-CoV
- Bilateral pneumonia + respiratory isolation - MERS presents as severe respiratory illness requiring airborne/droplet precautions
- Fever, dry cough, worsening dyspnea - Classic MERS presentation
Why the other options are wrong:
| Option | Why Incorrect |
|---|---|
| Influenza A | No specific camel/Arabian Peninsula exposure link; common community-acquired illness |
| Mycobacterium tuberculosis | Chronic, subacute course (weeks-months); not linked to camel contact |
| Legionella pneumophila | Associated with contaminated water/air conditioning systems, not animal contact |
| Streptococcus pneumoniae | Most common bacterial CAP, but no zoonotic exposure link |
High-yield MERS-CoV facts for USMLE Step 2 CK:
- Caused by a betacoronavirus (same genus as SARS-CoV-2)
- Dromedary camels are the confirmed animal reservoir
- Incubation: 2-14 days
- Mortality rate: ~35% (much higher than COVID-19)
- Diagnosis: RT-PCR of lower respiratory tract specimens
- No approved vaccine or specific antiviral; supportive care
- Requires contact + droplet precautions (airborne for aerosol-generating procedures)
The answer is A.
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