An Investigation of the First Non-sexual Household-transmitted Mpox Cluster with Rapid Situation Analysis of Mpox Epidemic in Thailand

On 22 May 2023, the mpox cluster was reported in a household in Nonthaburi Province, Thailand. We investigated to confirm the outbreak and diagnoses, describe its possible linkage and source, and identify potential fomite transmission. We interviewed all cases, traced their contacts, and swabbed household surfaces for mpox. We conducted a rapid situation analysis of mpox cases in Thailand until July 2023. Three cases were confirmed within the same household involving five individuals. The first case was a sexually active male and the second case was his intimate partner. The third case was the mother of the second case. The first two cases reported no sexual activity after symptoms appeared. They both attended a shaving ceremony and engaged in activities without wearing face masks. The third case had direct contact with her son's droplets and rash and then developed symptoms, without rash and fever. No additional case was detected among participants of the ceremony. One of two other household members tested negative after developing symptom while the other was asymptomatic. Despite house cleaning with 70%-ethanol, before investigation, 18 of 27 environmental swabs tested positive, with cycle threshold values ≥30. Since situation analysis revealed no previously reported non-sexual household mpox transmission, this investigation confirmed its existence. Risk communication should address the plausibility of non-sexual transmission. Mpox symptom may occur without rash and fever, emphasizing the importance of testing suspected individuals and revising mpox investigation guidelines accordingly. Surface cleaning with 70%-ethanol may reduce fomite transmissibility.