High Prevalence of Varicella Zoster Virus Infection among Persons with Suspect Mpox Cases during an Mpox Outbreak in Kenya, 2024.

Kenya is experiencing a clade Ib mpox outbreak, with 28 confirmed cases reported by the Ministry of Health from July to December 2024. Polymerase chain reaction testing was performed for varicella zoster virus (VZV). Testing was also part of the differential diagnosis for mpox, and a subset of cases was genetically sequenced. Of 277 specimens tested for mpox, 170 (61%) tested positive for VZV, including instances of coinfection with both viruses in four cases. Genome analysis was used to identify clade 5 human alphaherpesvirus 3 in eight of the genetically sequenced cases. Expanding laboratory capacity during this outbreak enhanced disease intelligence by confirming another etiology of rash among patients who tested negative for mpox, underscoring the need for a broad differential diagnosis when diseases present with overlapping clinical signs and symptoms.