Notes from the Field: Contact Tracing for Monkeypox virus Clade I Cases Associated with Air Travel - United States, November 2024-January 2025.

Abstract

Monkeypox is a vesicular rash illness caused by Monkeypox virus (MPXV), which can be divided into clades (e.g., clade I and II), each of which includes subclades. MPXV is usually transmitted from person to person through close, sustained physical contact. Global spread of clade II MPXV began in 2022; to date, approximately 37,500 cases have been reported in the United States (provisional data), and domestic transmission is ongoing. CDC began conducting aircraft contact investigations for clade II MPXV in 2021. In February 2023, based on data showing no evidence of in-flight transmission of clade II MPXV, CDC discontinued routine aircraft contact investigations. Although outcome data were missing for approximately one third of identified aircraft contacts, a 2024 report describing data from 2021 to 2022 on clade II MPXV transmission risk during commercial air travel found no secondary cases reported among 1,538 persons who had contact with 113 infected travelers on 221 flights (1).