Diagnosis of Smallpox

Diagnosis (19:10)

Three major criteria and five minor criteria have been developed to assist clinicians in determining whether or not a disease is smallpox. Based on the major and minor criteria that describes the patients symptoms, or a combination thereof, the likelihood of the patients illness being smallpox can be evaluated.

There are three major smallpox criteria. The first criterion is that the person had a significant febrile prodrome 1 to 4 days before rash onset. A significant febrile prodrome is described as having a fever that must be greater than or equal to 101° Fahrenheit, and at least one of the following systemic complaints: prostration, headache, backache, chills, vomiting or abdominal pain. The second criterion is that the rash lesions are deep in the skin, firm, or hard to the touch and well circumscribed. They have a “shotty” feel, like rolling a pea around under the skin. (22:V4:9) The third criterion is that on any one part of the body, all the lesions are in the same stage of development. This means that all lesions on the arm or all lesions on the trunk would be all vesicles, all pustular, or all crusting – not a mixture of different skin lesions. (22:V4:9)

There are five minor smallpox criteria. The first criteria is that the distribution of the rash is centrifugal. The second criteria is that first lesions of the rash appeared on the oral mucosa or palate, or on the face or forearms. The third is that the patient appears toxic or moribund (typically a patient is so sick that they are bed ridden). The fourth is that lesions progressed slowly, in other words they evolved from macules to papules to pustules over several days. The final minor criteria is that there are lesions on the palms or soles.

Evaluation based on Major and Minor Criteria will determine whether the patient is considered high, moderate or low risk for smallpox.

A person is considered at high risk for smallpox if he or she meets all three major criteria. Immediate action should be taken to make sure that contact precautions and respiratory isolation are in place. These patients should be reported to local health authorities immediately. High Risk Response.

A person is considered at moderate risk of smallpox must have had a febrile prodrome and either one other major criterion or at least 4 minor. Patients should be isolated and be evaluated urgently to determine the cause of illness. Persons classified as high or moderate risk be seen in consultation with a specialist in infectious diseases and/or dermatology whenever possible. Moderate Risk Response.

Any person who did not have a febrile prodrome is considered low risk, as are persons who had a febrile prodrome and less than 4 minor criteria. These patients should be managed as clinically indicated. Low Risk Response.

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