Smallpox from Other Rash Illness, Especially Varicella Chickenpox

Differentiating Smallpox from Other Rash Illness, Especially Varicella (Chickenpox) 

The discovery of even one case of smallpox in the world would be an international medical and public health emergency. Therefore, the appropriate diagnosis is essential. Physicians who have never seen smallpox might confuse smallpox with varicella 

Prodrome None or mild Severe, beginning 1-4 days before rash onset, with fever 101°F, other symptoms, including prostration, headache, backache, chills, abdominal pain, vomiting 

Distribution of lesions Centripetal, prominent on trunk, rarely on palms and soles Centrifugal, most prominent on face and extremities, palms and soles involved in almost all cases 

Development Successive crops, lesions at varying stages of development One crop, lesions at same stage of development all over the body 

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