Diagnosis
of Smallpox
CDC
Smallpox Diagnostic Algorithm (22:V4:3)
The Algorithm
was created so that clinicians would have a tool with a high specificity
and a minimum of false positives in order to determine variola
from other rash illnesses. It is estimated that there will be approximately
1 million cases of varicella (or chickenpox) in the US in 2003
and many more millions of cases of other rash illnesses. With this
number of cases, if 1 out of every 1000 varicella cases were suspected
to be smallpox, there would be 1000 false alarms per year. Most
public health systems cannot easily deal with thousands of false
alarms.
The algorithm
strategy needed was one that has high specificity to accurately
detect the first case of smallpox (should there ever be one). High
specificity strategy will serve to minimize unnecessary laboratory
testing for smallpox, that would have the potential risk of producing
a false positive lab test. The algorithm provides a method to focus
resources on the most suspicious cases.
There are two
primary goals of the Rash Illness Algorithm. (22:V4:39) The
first goal is that the rash illness algorithm is to provide a systemic
approach to evaluation of cases of febrile vesicular or pustular
rash illness. The second goal is that the algorithm uses the main
clinical features of smallpox to establish major and minor criteria
and uses these criteria to classify cases of vesicular/pustular
rash illness into risk categories (likelihood of being smallpox).
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