CD40LG and infection: Possible undetected mpox infection was defined as 1) detectable antiorthopoxvirus IgG (optical density minus cutoff value [OD-COV] ≥0.1) in a participant aged <50 years without reported smallpox or mpox vaccination or 2) detectable antiorthopoxvirus IgM (OD-COV ≥0.1) in a participant without reported mpox vaccination.