How to distinguish mpox from its mimickers: An observational retrospective cohort study

During the current global outbreak of mpox (formerly monkeypox), atypical features were frequently described outside endemic areas, raising concerns around differential diagnosis. In this study, we included 372 adult patients who had clinical signs consistent with mpox and who were screened using non-variola orthopoxvirus specific quantitative polymerase chain reaction (PCR) between 15 May and 15 November 2022 at the University Hospital Institute Méditerranée Infection, Marseille, France. At least one clinical sample was positive for 143 (38.4%) of these patients and 229 (61.6%) were negative. Clinically, patients who had mpox presented more frequently with systemic signs (69.9% vs. 31.0%, p < 10-6 ) including fever (51.0% vs. 30.1%, p < 10-3 ), myalgia (33.5% vs. 17.9%, p = 0.002), and lymphadenopathy (38.5% vs. 13.1%, p < 10-6 ). Among the patients who were negative for the non-variola orthopoxvirus, an alternative diagnosis was identified in 58 of them (25.3%), including chickenpox (n = 30, 13.1%), syphilis (n = 9, 4%), bacterial skin infection (n = 8, 3.5%), gonococcus (n = 5, 2.2%), HSV infection (n = 5, 2.2%), and histoplasmosis (n = 1, 0.4%). Overall, in the current outbreak, we show that mpox has a poorly specific clinical presentation. This reinforces the importance of microbiological confirmation. In symptomatic patients who are negative for the monkeypox virus by PCR, a broad differential diagnosis should be maintained.

Observational Cohort Study of Evolving Epidemiologic, Clinical, and Virologic Features of Monkeypox in Southern France

We enrolled 136 patients with laboratory-confirmed monkeypox during June 4-August 31, 2022, at the University Hospital Institute Méditerranée Infection in Marseille, France. The median patient age was 36 years (interquartile range 31-42 years). Of 136 patients, 125 (92%) were men who have sex with men, 15 (11%) reported previous smallpox vaccinations, and 21 (15.5%) were HIV-positive. The most frequent lesion locations were the genitals (68 patients, 53%), perianal region (65 patients, 49%), and oral/perioral area (22 patients, 17%). Lesion locations largely corresponded with the route of contamination. Most (68%) patients had isolated anal, genital, or oral lesions when they were first seen, including 56 (61%) who had >1 positive site without a visible lesion. Concurrent sexually transmitted infections were diagnosed in 19 (15%) patients, and 7 patients (5%) were asymptomatic. We recommend vaccination campaigns, intensified testing for sexually transmitted infections, and increased contact tracing to control the ongoing monkeypox outbreak.