Updated Interim Case Definition for Human Monkeypox, January 2004
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The previous case definition (published July 2, 2003) has been updated as follows:
Rash (macular, papular, vesicular, or pustular; generalized or localized; discrete or confluent)
Fever (subjective or measured temperature of ≥99.3°F [≥37.4°C])
Other signs and symptoms
A case may be excluded as a suspect or probable monkeypox case if:
1 Includes living in a household, petting or handling, or visiting a pet holding facility (e.g., pet store, veterinary clinic, pet distributor)
2 Includes prairie dogs, Gambian giant rats, and rope squirrels. Exposure to other exotic or non-exotic mammalian pets will be considered on a case-by-case basis; assessment should include the likelihood of contact with a mammal with monkeypox and the compatibility of clinical illness with monkeypox
3 Includes living in a household, or originating from the same pet holding facility as another animal with monkeypox
4 Includes skin-to-skin or face-to-face contact
5 Levels of circulating IgM antibody reactive with orthopoxvirus antigen are determined by ELISA and reported as optical density (OD) values. Values greater than 3 standard deviations above the mean OD of 6 independent negative controls are considered 'elevated'. Serial specimens are not required. IgM antibody levels may be elevated in persons who have been recently (within one year) vaccinated for smallpox.
6 Factors that might be considered in assigning alternate diagnoses include the strength of the epidemiologic exposure criteria for monkeypox, the specificity of the diagnostic test, and the compatibility of the clinical presentation and course of illness for the alternative diagnosis.
7 If possible, obtain convalescent-phase serum specimen from these patients. See specimen collection guidelines (www.cdc.gov/ncidod/monkeypox/lab.htm) for details on collecting serum for convalescence evaluation.
8 The optimal timing of specimen collection for determination of IgM levels is between days 7 and 56 post-rash onset. However, elevated levels of IgM antibodies may be detectable prior to day 7, or after day 56, post rash onset, therefore a negative result during this phase should not be interpreted to indicate an absence of monkeypox infection.
Page last modified September 5, 2008