Adenovirus is one of those “classic Step viruses” that shows up everywhere: pediatric respiratory infections, outbreaks in close quarters, hemorrhagic cystitis, and even conjunctivitis you can practically diagnose from the vignette alone. If you can connect structure (nonenveloped dsDNA) to transmission (hardy in the environment) to clinical syndromes (pharyngoconjunctival fever, pneumonia, hemorrhagic cystitis), you’ll reliably pick up points on both Step 1 and Step 2.
Big Picture: What Is Adenovirus?
Adenoviruses are nonenveloped, icosahedral, linear double-stranded DNA (dsDNA) viruses.
Why Step Cares (One-Liner)
Because adenovirus is environmentally stable (nonenveloped) and causes respiratory disease + conjunctivitis + hemorrhagic cystitis, often in kids, military recruits, and immunocompromised patients.
High-Yield Micro ID Card
| Feature | Adenovirus (HY) |
|---|---|
| Genome | Linear dsDNA |
| Envelope | No envelope (resists drying, detergents → survives on surfaces) |
| Capsid | Icosahedral |
| Replication site | Nucleus (DNA virus rule; exceptions are pox) |
| Transmission | Respiratory droplets, fecal–oral, fomites, contaminated pools |
| Key settings | Daycare, military barracks, transplant patients |
| Classic syndromes | Pharyngitis, pneumonia, pharyngoconjunctival fever, epidemic keratoconjunctivitis, hemorrhagic cystitis |
| Notable complication | Severe disease in immunocompromised (esp. transplant) |
Structure & Pathophysiology (Step 1-Friendly)
1) Nonenveloped = tough virus
Adenovirus lacks a lipid envelope, so it doesn’t rely on fragile envelope proteins and is:
- Hardy on surfaces
- More resistant to detergents/disinfectants than enveloped viruses
This is why adenovirus is notorious for outbreaks in: - Dorms/barracks
- Daycares
- Swimming pools (chlorination issues / crowded exposure)
2) DNA virus → nucleus replication
As a dsDNA virus, adenovirus replicates in the nucleus using host machinery (general DNA virus pattern). Step-style tie-in:
- Nuclear replication → think intranuclear inclusion bodies as a general DNA virus concept (not always tested as a must-know for adenovirus, but the “DNA viruses go to the nucleus” rule is).
3) Tissue tropism → explains the syndromes
Adenovirus tends to infect:
- Respiratory epithelium → pharyngitis, pneumonia
- Conjunctiva/cornea → conjunctivitis/keratoconjunctivitis
- Urothelium → hemorrhagic cystitis
And in immunocompromised hosts: - Dissemination → severe pneumonia, hepatitis, colitis (organ-specific manifestations vary)
Clinical Syndromes You Must Know
1) Pharyngitis (often kids)
Typical presentation:
- Sore throat, fever
- Cervical lymphadenopathy may be present
- Can mimic strep throat clinically (Step 2 trick: viral clues—cough, conjunctivitis, rhinorrhea—push away from GAS)
2) Adenoviral Pneumonia (especially outbreaks)
Common vignette: febrile respiratory illness spreading through a military training camp.
- Can cause atypical pneumonia-like presentation
- More severe in:
- Infants
- Elderly
- Immunocompromised (e.g., post-transplant)
3) Pharyngoconjunctival Fever (PCF)
This one is very Step-friendly.
- Fever + pharyngitis + conjunctivitis
- Classically associated with:
- Swimming pools (“pool conjunctivitis”)
- Summer camps / daycare outbreaks
4) Epidemic Keratoconjunctivitis (EKC)
More severe ocular involvement than simple conjunctivitis.
- Painful red eye, foreign body sensation
- Photophobia
- Tearing
- Often highly contagious (fomites, hand-to-eye transmission)
- Can be associated with outbreaks in clinics/close-contact settings
Step 2 red-eye triage tie-in: adenoviral conjunctivitis is common, but pain + photophobia should make you consider corneal involvement and broaden the differential. EKC can cause significant discomfort and decreased vision due to keratitis.
5) Hemorrhagic Cystitis (classic!)
Hematuria + dysuria in a child with recent viral symptoms.
- Typically self-limited
- Especially high-yield in:
- Children
- Immunocompromised (can be more severe/prolonged)
Vignette clue: “A child has painful urination and gross hematuria; urine culture is negative.” → think adenovirus.
Immunocompromised Patients: Where Adenovirus Gets Serious
In transplant recipients (bone marrow/solid organ) and other immunosuppressed states, adenovirus can cause:
- Severe pneumonitis
- Hemorrhagic cystitis (can be significant)
- Colitis
- Hepatitis
- Disseminated disease
Board-style point: A virus that is “usually self-limited” in healthy kids can become life-threatening after transplant.
Diagnosis (What Boards Expect)
Most cases are clinical
For uncomplicated conjunctivitis or URI, you often don’t need testing clinically.
When testing matters (severe disease, outbreaks, immunocompromised)
- PCR (respiratory sample, blood, stool, urine depending on syndrome)
- Fast, sensitive, common board answer for modern viral diagnosis
- Viral culture exists but is slower and less emphasized for Step questions
- Urinalysis in hemorrhagic cystitis:
- Hematuria
- Often negative bacterial culture (helps differentiate from bacterial UTI)
Pitfall: Don’t confuse adenovirus hemorrhagic cystitis with UTI—Step vignettes often emphasize negative nitrites/culture or recent viral illness.
Treatment (Step 1 vs Step 2 Practical)
Uncomplicated infections: supportive care
- Hydration, antipyretics/analgesics
- Lubricating eye drops, cold compresses for conjunctivitis
- Counsel on hand hygiene and avoiding close contact—very contagious
Severe/disseminated disease (usually immunocompromised)
- Reduce immunosuppression when feasible (core principle)
- Antivirals may be used in select severe cases (specialist territory):
- Cidofovir has been used for severe adenovirus, especially in transplant patients (nephrotoxicity is a major limitation)
- Brincidofovir (lipid conjugate) may be used in certain settings; less commonly tested
For USMLE purposes, the key is:
- Most adenovirus infections: supportive
- Severe immunocompromised disease: consider antivirals + adjust immunosuppression
Prevention & Infection Control (Outbreak Logic)
Because adenovirus is nonenveloped, it survives well in the environment:
- Strong emphasis on hand hygiene
- Disinfection of surfaces and shared equipment
- Avoid sharing towels, eye makeup, etc.
- Outbreak settings (barracks/daycare/pools) are classic question stems
Differentials You Should Be Able to Separate Quickly
Adenovirus vs Rhinovirus
- Rhinovirus: common cold; more “mild URI,” less classic for hemorrhagic cystitis
- Adenovirus: conjunctivitis, outbreaks, can do pneumonia and hemorrhagic cystitis
Adenovirus conjunctivitis vs HSV keratitis
- HSV keratitis: classically dendritic lesions on fluorescein, often recurrent; can be unilateral; treat with antivirals
- Adenovirus: very contagious conjunctivitis ± keratitis; supportive unless severe/special cases
Hemorrhagic cystitis: Adenovirus vs Cyclophosphamide
- Adenovirus: infectious prodrome, child, culture negative
- Cyclophosphamide/ifosfamide: chemo history; prevent with MESNA (classic pharm integration)
High-Yield Associations (What to Memorize)
Vignette triggers
- Military recruit outbreak → adenovirus respiratory disease/pneumonia
- Daycare + conjunctivitis → adenovirus
- Swimming pool + fever/pharyngitis + conjunctivitis → pharyngoconjunctival fever
- Child + dysuria + gross hematuria + negative culture → adenovirus hemorrhagic cystitis
- Transplant patient + severe pneumonia/hemorrhagic cystitis → adenovirus can disseminate
Core fact cluster
- Nonenveloped, linear dsDNA, icosahedral
- Respiratory + conjunctiva + bladder
- Outbreaks in close quarters
- Supportive care unless severe/immunocompromised
First Aid Cross-References (Where This Lives)
In First Aid for the USMLE Step 1, adenovirus is typically covered under:
- Microbiology → Viruses → DNA viruses
Key First Aid-style bullets you should see mirrored: - “Adenovirus: pharyngitis, pneumonia, conjunctivitis, hemorrhagic cystitis”
- Classification among dsDNA viruses (nonenveloped)
(Edition layouts vary, so use your book’s index for “Adenovirus” and cross-check the DNA virus table.)
Rapid Review (Exam-Day Checklist)
- Nonenveloped dsDNA → survives on surfaces → outbreaks
- Causes:
- Pharyngitis
- Pneumonia (military recruits)
- Conjunctivitis/keratoconjunctivitis
- Hemorrhagic cystitis (child, culture negative)
- Diagnosis: usually clinical; PCR when severe/outbreak/immunocompromised
- Treatment: supportive; severe in immunocompromised may require cidofovir + immunosuppression adjustment