Spectrum of infection and risk factors for human monkeypox, United States, 2003

Abstract

For the 2003 monkeypox virus (MPXV) outbreak in the United States, interhuman transmission was not documented and all case-patients were near or handled MPXV-infected prairie dogs. We initiated a case-control study to evaluate risk factors for animal-to-human MPXV transmission. Participants completed a questionnaire requesting exposure, clinical, and demographic information. Serum samples were obtained for analysis of immunoglobulin G (IgG) and IgM to orthopoxvirus. When data were adjusted for smallpox vaccination, case-patients were more likely than controls to have had daily exposure to a sick animal (odds ratio [OR] 4.0, 95% confidence interval [CI] 1.2-13.4), cleaned cages and bedding of a sick animal (OR 5.3, 95% CI 1.4-20.7), or touched a sick animal (OR 4.0, 95% CI 1.2-13.4). These findings demonstrate that human MPXV infection is associated with handling of MPXV-infected animals and suggest that exposure to excretions and secretions of infected animals can result in infection.

Figure 1

Age distribution of monkeypox virus–infected case-patients (A) and controls (B) and smallpox vaccination status. No study participants reported having received a smallpox vaccination within 25 years of August 2003.

Figure 2

Characteristics of exposure to infected prairie dogs of A) vaccinated and unvaccinated monkeypox case-patients and controls and B) case-patients (adults and children) and controls. *Denotes statistically significant differences in exposure between groups.