Diagnostic approach to monkeypox outbreak, a case-control study.

Background: An international outbreak of the monkeypox (MPX) virus is ongoing with a different clinical presentation than previously reported.

Objective: A monocentric retrospective study was designed to investigate clinical predictors of confirmed MPX cases among a group of patients referred for MPX screening. Furthermore, the additional value of performing a real-time polymerase chain reaction (RT-PCR) on multiple anatomical sites was analyzed.

Methods: Between 28/05/2022 and 22/07/2022, the medical records of patients referred for MPX screening were investigated. Patients with positive RT-PCR were defined as cases, while the ones with negative RT-PCR as controls. Multivariable regression analysis was performed to estimate predictors of MPX diagnosis.

Results: Among the 141 included patients, 85 (60%) had at least one positive RT-PCR for MPX. Carrying out RT-PCR only on the swab obtained by skin lesion sampling, 7 patients (7/85: 8%) would have been misdiagnosed. Multivariable regression analysis showed significant differences in the independent variables: "being men who have sex with men (MSM)", "living with HIV", "having multiple sexual partners in the last 3 weeks", and "having skin lesions in the anogenital area" for prediction of MPX diagnosis. These four discriminants were used to create a score to improve diagnosis in patients screened for MPX.

Conclusion: MPX diagnosis was associated with being MSM, living with HIV, having multiple sexual partners, and presenting with anogenital skin lesions. In this study, the derived score had good sensitivity and specificity to predict MPX diagnosis. Finally, performing multi-site swabs for MPX RT-PCR might lower false negative rates.