CDC AND STATE and local health departments continue to investigate cases of monkeypox among persons in the United States who had contact with wild or exotic mammalian pets or with persons with monkeypox.^1-4 This report updates results of the epidemiologic investigation, provides information on the use of smallpox vaccine during the outbreak, and summarizes the animal tracing activities to identify the origin and subsequent distribution of infected animals.

As of July 8, 2003, a total of 71 cases of monkeypox 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.¹ 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;^1-4 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 monkeypox. No patients have been confirmed to have had exposure to persons with monkeypox as their only possible exposure.