On Jul. 8, 2003, the U.S. Centers for Disease Control and Prevention (CDC) announced a total of 71 cases of mpox have been reported to CDC from Wisconsin (39), Indiana (16), Illinois (12), Missouri (two), Kansas (one), and Ohio (one); these include 35 (49%) cases laboratory-confirmed at CDC and 36 (51%) suspect and probable cases under investigation by state and local health departments. Eleven cases were excluded from those reported previously because they met the exclusion criteria outlined in the updated national case definition, and one new case was added. The number of cases increased from May 15 through the week ending June 8 and declined subsequently; the date of onset for the last case was June 20. Of the 71 cases, 39 (55%) occurred among females; the median age was 28 years (range: 1–51 years). Age data were unavailable for one patient. Among 69 patients for whom data were available, 18 (26%) were hospitalized; some patients were hospitalized for isolation precautions only. Two patients, both children, had serious clinical illness; both of these patients have recovered. The majority of patients were exposed to prairie dogs. Some patients were exposed in premises where prairie dogs were kept, and others were exposed to persons with mpox. No patients have been confirmed to have had exposure to persons with mpox as their only possible exposure.

Of the 35 laboratory-confirmed cases, 32 (91%) tested positive for mpox by polymerase chain reaction (PCR), culture, immunohistochemical testing (IHC), and/or electron microscopy in skin rash lesions; two tested positive by PCR and/or culture of an oropharyngeal or nasopharyngeal swab; and one tested positive by PCR and culture of a lymph node aspirate. For laboratory-confirmed cases, onset of illness ranged from May 16 to June 20. The majority of patients reported a clinical illness that included rash (one patient had a single, atypical plaque-like skin lesion) and fever. The median incubation period was 12 days (range: 1–31 days).

To prevent transmission of mpox, 30 persons (28 adults and two children) in six states have received smallpox vaccine since June 13. Vaccine was administered pre-exposure to seven persons (three veterinarians, two laboratory workers, and two health-care workers) and post-exposure to 23 persons (10 health-care workers, seven household contacts, three laboratory workers, one public health veterinarian, one public health epidemiologist, and one work contact). No serious adverse events were reported following smallpox vaccination, and no requests for vaccinia immune globulin have been received. Among the 30 persons who received smallpox vaccine, three (10%) reported rash within 2 weeks of vaccination. One of the three was confirmed as having monkeypox; another person had two skin lesion specimens that tested negative for orthopoxvirus and varicella zoster virus at the state health laboratory; no specimens were obtained for the third person who reported a single, dime-sized, pruritic and erythematous skin lesion (not pustular) remote from the vaccination site that appeared 4 days after vaccination and faded within a week.