What are the characteristics of misdiagnosed human mpox cases?

By Tarun Sai LomteReviewed by Aimee MolineuxDec 21 2022

In a recent study published in the International Journal of Infectious Diseases (IJID), researchers characterized overlooked cases of mpox (MPX).

Background

MPX is an emergent disease outside Africa, particularly affecting men who have sex with men (MSM). To date, more than 80,000 cases of MPX have been identified during the ongoing outbreak. MPX is mainly observed in MSM, spreading through sexual contact. Many MPX cases show genital ulcers, proctocolitis, inguinal lymphadenopathy, and fever, whereas others experience mild disease.

Around 30% of MPX cases show a concurrent sexually-transmitted infection (STI). MPX represents a new disease in regions that are not endemic and could present a spectrum of clinical features, including those similar to an STI. MPX can be easily overlooked or misdiagnosed as many physicians are unfamiliar with it, leading to delays in diagnosis, isolation, and treatment.

The study and findings

In the present study, researchers described the characteristics of MPX cases among MSM initially misdiagnosed with some other disease. Patients diagnosed with MPX between May 16 and October 6, 2022, were included. They defined misdiagnosis as not identifying MPX during the first examination but later confirming it based on a lab test.

Only patients diagnosed by a polymerase chain reaction (PCR) test were included. Overall, 26 patients were included who self-identified as MSM with a history of sexual contact. These subjects were not enquired about contact with an MPX patient during their primary examination by the physician. Five patients were positive for human immunodeficiency virus (HIV), and 17 were on HIV pre-exposure prophylaxis (PrEP).

Anogenital (46%) and skin (30.7%) lesions were common, with crusted or vesiculopustular lesions being prevalent. The number of lesions was variable across patients but was mostly less than 10 per patient. Proctitis was observed in 27% of subjects, and sore throat and fever in 23% of patients during the initial presentation. Four patients showed bacterial co-infections of gonorrhea (3 cases) and syphilis (1).

Six MPX cases were initially misdiagnosed as having bacterial tonsilitis, six as having syphilis, five as herpes, and four as proctitis. Misdiagnosing physicians included primary/emergency care physicians, dermatologists, and proctologists. Twenty-one physicians, who were emergency/primary care physicians or infectious disease specialists, correctly diagnosed MPX. The mean duration between missed and correct diagnosis was 4.4 days.

Conclusions

The researchers demonstrated that MPX might be initially easily overlooked and mistaken for other diseases, especially STIs. Given the non-classical lesion presentation around anogenital areas and the nature of transmission, MPX is confused with other STIs, including syphilis and herpes. About 23% of subjects were diagnosed with pharyngitis/tonsilitis due to oropharyngeal lesions.

In total, nine individuals showed co-infections (five had HIV, and four had bacterial STIs). Individuals with STIs or HIV have been disproportionately affected in the current MPX outbreak. Since many patients are on PrEP and likely involved in unprotected sexual intercourse, it is essential to test for STI co-infections. Continued awareness of MPX and the associated clinical symptoms and signs is necessary for prompt and correct diagnosis of MPX and curbing its transmission.