Clinical symptoms of monkeypox include fever, myalgia, lymphadenopathy and rash. Lymphadenopathy is a feature that may distinguish monkeypox from smallpox. In nearly all patients, the rash usually appears 1to 3 days after initial onset of fever and tends to be concentrated on the face and extremities, including hands and feet. In the most recent outbreak, many patients have been found to have lesions in the perineal and genital regions.
Of note, the skin eruptions are all at the same stage of development at a given time, unlike chickenpox (varicella virus), which has vesicular lesions that erupt at different stages. The monkeypox rash involves vesicles or pustules that are deep-seated, firm or hard, and well-circumscribed; the lesions may umbilicate or become confluent and progress over time to scabs.
People who have had close contact with an infected person are most at risk. Anyone can develop monkeypox. The infectious period begins when the rash and lesions are present on the body.
Case fatality for monkeypox ranges between 1% to 10%; it is higher in infections with the more virulent strain from Central Africa and lower with less virulent strains from West Africa (which are the strains identified in the current U.S. outbreak thus far).
CDC Case Definitions
Within 21 days of illness onset:
- Reports having contact with a person or people with a similar appearing rash or who received a diagnosis of confirmed or probable monkeypox OR
- Had close or intimate in-person contact with individuals in a social network experiencing monkeypox activity, this includes men who have sex with men (MSM) who meet partners through an online website, app, or social event OR
- Traveled outside the US to a country with confirmed cases of monkeypox or where monkeypox is endemic OR
- Had contact with a dead or live wild animal or exotic pet that is an African endemic species or used a product derived from such animals
An alternative diagnosis can fully explain the illness OR
An individual with symptoms consistent with monkeypox but who does not develop a rash within 5 days of illness onset OR
A case where specimens do not demonstrate the presence of orthopoxvirus or monkeypox virus or antibodies to orthopoxvirus
Possible Case: Meets one of the epidemiologic criteria AND has fever or new rash AND at least one other sign or symptom onset < 21 days after last exposure meeting epidemiologic criteria.
Probable Case: Meets one of the epidemiologic criteria AND has new rash with or without fever AND at least one other sign or symptom onset <21 days after last exposure meeting epidemiologic criteria AND demonstration of detectable levels of anti-orthopoxvirus IgM antibody during the period of 4 to 56 days after rash onset.
Person Under Investigation: Persons under investigation are individuals who are suspected of having monkeypox based on clinical presentation and/or epidemiologic links reported as suspicious but have not been tested in a Laboratory Response Network laboratory. This includes cases that health departments have been consulted on because of clinician concern.