Case Definitions† for Use in the 2022 Mpox Response

Suspect Case

• New characteristic rash* OR
• Meets one of the epidemiologic criteria and has a high clinical suspicion^† for mpox

Probable Case

• No suspicion of other recent Orthopoxvirus exposure (e.g., Vaccinia virus in ACAM2000 vaccination) AND demonstration of the presence of
  • Orthopoxvirus DNA by polymerase chain reaction of a clinical specimen OR
  • Orthopoxvirus using immunohistochemical or electron microscopy testing methods OR
  • Demonstration of detectable levels of anti-orthopoxvirus IgM antibody during the period of 4 to 56 days after rash onset

Confirmed Case

• Demonstration of the presence of mpox virus DNA by polymerase chain reaction testing or Next-Generation sequencing of a clinical specimen OR isolation of mpox virus in culture from a clinical specimen

Epidemiologic Criteria

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 mpox OR
• Had close or intimate in-person contact with individuals in a social network experiencing mpox activity, this includes men who have sex with men (MSM) who meet partners through an online website, digital application (“app”), or social event (e.g., a bar or party) OR
• Traveled outside the US to a country with confirmed cases of mpox or where mpox virus 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 (e.g., game meat, creams, lotions, powders, etc.)

Exclusion Criteria

A case may be excluded as a suspect, probable, or confirmed case if:

• An alternative diagnosis* can fully explain the illness OR
• An individual with symptoms consistent with mpox does not develop a rash within 5 days of illness onset OR
• A case where high-quality specimens do not demonstrate the presence of Orthopoxvirus or mpox virus or antibodies to orthopoxvirus

†Clinical suspicion may exist if presentation is consistent with illnesses confused with mpox (e.g., secondary syphilis, herpes, and varicella zoster).

*The characteristic rash associated with mpox lesions involve the following: deep-seated and well-circumscribed lesions, often with central umbilication; and lesion progression through specific sequential stages—macules, papules, vesicles, pustules, and scabs.; this can sometimes be confused with other diseases that are more commonly encountered in clinical practice (e.g., secondary syphilis, herpes, and varicella zoster). Historically, sporadic accounts of patients co-infected with mpox virus and other infectious agents (e.g., varicella zoster, syphilis) have been reported, so patients with a characteristic rash should be considered for testing, even if other tests are positive.

Categorization may change as the investigation continues (e.g., a patient may go from suspect to probable).