The clinical definition of smallpox is an illness with acute onset of fever greater than 101°F (38.3°C) followed by a rash characterized by firm, deep seated vesicles or pustules in the same stage of development without other apparent cause. If a clinical case is observed, smallpox is confirmed using laboratory tests.
Chickenpox was commonly confused with smallpox in the immediate post-eradication era. Chickenpox and smallpox can be distinguished by several methods. Unlike smallpox, chickenpox does not usually affect the palms and soles. Additionally, chickenpox pustules are of varying size due to variations in the timing of pustule eruption: smallpox pustules are all very nearly the same size since the viral effect progresses more uniformly. A variety of laboratory methods are available for detecting chickenpox in evaluation of suspected smallpox cases. 1
1.”Smallpox Disease and Its Clinical Management” (pdf). Training course titled “Smallpox: Disease, Prevention, and Intervention” http://www.bt.cdc.gov/agent/smallpox/training/overview). http://emergency.cdc.gov/agent/smallpox/training/overview/pdf/diseasemgmt.pdf. Retrieved 2009-10-26.
Overall the case-fatality rate for ordinary-type smallpox is 30%, but varies by pock distribution. Ordinary type-confluent is fatal 50–75% of the time, ordinary-type semi-confluent 25–50% and in cases where rash is discrete the fatality rate is less than 10%. The overall fatality rate for children younger than 1 year of age is 40%–50%. Hemorrhagic and flat types have the highest fatality rates. The fatality rate for flat-type is 90% or greater and nearly 100% is observed in cases of hemorrhagic smallpox. The case-fatality rate for variola minor is 1% or less.1
1.”Smallpox Disease and Its Clinical Management” (pdf). Training course titled “Smallpox: Disease, Prevention, and Intervention” (www.bt.cdc.gov/agent/smallpox/training/overview). http://emergency.cdc.gov/agent/smallpox/training/overview/pdf/diseasemgmt.pdf. Retrieved 2009-10-26.
Complications of smallpox most commonly occur in the respiratory system and range from simple bronchitis to fatal pneumonia. Respiratory complications can be either viral or bacterial in origin and usually develop around the eighth day of the illness. A relatively uncommon complication of smallpox is secondary bacterial infection of the skin. When this occurs, the fever usually remains elevated.1
1.Atkinson W, Hamborsky J, McIntyre L, Wolfe S (eds.) (2005). “Smallpox” (PDF). Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) (9th ed.). Washington DC: Public Health Foundation. pp. 281–306. http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/smallpox.pdf.
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