The monkeypox case definition in the UK is broad – Authors' reply

We thank Hellen Callaby and colleagues for responding to our Correspondence.¹ We welcome the broadened case definition of possible monkeypox infection and were encouraged to hear the diversity of testing that has been done to date. The most recent version of the UK Health Security Agency's guidance, published on Aug 9, 2022, describes case definitions to inform the testing and reporting of suspected cases of monkeypox infection, with strata based on risk of monkeypox infection (possible, probable, highly probable, and confirmed). The guidance allows for the inclusion of all population groups at risk of infection, but maintains a measure of likelihood of infection.

We continue to caution against classifying individuals with a rash and who identify as gay, bisexual, or other men who have sex with men (MSM) in the same risk category (probable case) as those who have had new sexual partners in the 21 days before symptom onset, or those who have had an epidemiological link to a confirmed, probable, or highly probable case of monkeypox infection in the 21 days before symptom onset. We believe such distinctions between MSM and the general population are unnecessary, especially when subsequent recommended management of both possible and probable cases is the same (eg, take samples to test for monkeypox infection, take a relevant sexual and travel history, and, if admission to hospital is required, give access to a negative pressure isolation ward with adequate personal protective equipment). Although MSM are the majority of confirmed cases in the UK, monkeypox is not a disease that occurs only in MSM, nor are all MSM engaged in high amounts of sexual activity. Physicians and the public might make generalisations on the basis of these definitions, which could further stigmatise the MSM community, similar to previous experiences with HIV.²

We agree with Callaby and colleagues that evidence is required for monkeypox transmission beyond the MSM community; such evidence is emerging. A recent cohort study of 181 patients from Spain with PCR-confirmed human monkeypox infection found that 15 (8%) patients identified as heterosexual men or women.³ This study, together with another modelling analysis,⁴ found that the transmission of monkeypox virus is likely to have a strong behavioural component, with transmission occurring through networks where there is a high amount of both MSM and non-MSM sexual contact. Furthermore, there is now strong evidence from both the USA and the UK for fomite and potential aerosol transmission of monkeypox virus. Studies have identified culturable monkeypox virus from high-touch surfaces in the household of individuals with confirmed monkeypox infection, for at least 15 days after symptom onset.5, 6, 7 Preliminary findings from one of these studies⁷ showed that viable virus was also detected from an air sample in an infected individual's room. Together, these data suggest spillover in similar high-contact networks, such as public gyms, or in the social circles of people who engage in many close-contact (touching and non-touching) activities or are sexually very active, or both. Risk of spillover is increased in crowded households, where, as was seen in the UK and the USA during the COVID-19 pandemic, Black and Asian communities, as well as other minority ethnic groups—particularly migrant populations—are at the highest risk of acquiring infection.8, 9

We believe that greater public awareness of the transmission modes of monkeypox virus will allow clinicians and public health specialists to realise that transmission can easily occur in non-MSM communities as this outbreak evolves. This consideration is especially important because vertical transmission of monkeypox virus has been associated with adverse fetal outcomes and congenital infection.¹⁰ We also hope this debate will raise awareness of the broader case definitions of monkeypox infection in the UK so that physicians will be more likely to test individuals for suspected infection, regardless of their sexual orientation.