28 Apr Characterising household transmission dynamics of clade Ib mpox in Burundi: a prospective cohort study
R. Kamadjeu, F. Nsengimana, M. Nimpagaritse, E. Moturi, E. Kezakarayagwa, R. Nkiko, J. Ngendakumana, R. Nimubona, L. Nkengurutse, H. Ba, D. Nizigiyimana, P. Ngwakum, M. S Diouf, F. Bégin, J. Nyandwi, D. J Noble
Summary
Background Knowledge of intrahousehold transmission dynamics of clade Ib mpox, especially in recently epidemic
African contexts, is scarce. Our study aimed to quantify household transmission patterns of clade Ib mpox in Burundi,
with a focus on children.
Methods We conducted a prospective cohort study in two health districts, Bujumbura and Kayanza, in Burundi from
Jan 23 to March 20, 2025, enrolling 88 laboratory-confirmed primary mpox cases and 432 of their household contacts.
We estimated household secondary attack rates (SARs), serial intervals, and basic reproduction number (R₀), including
a sensitivity analysis to assess the effect of potential misclassification of mpox index cases younger than 15 years. The
primary outcome was occurrence of a secondary mpox infection within the household, defined as any laboratoryconfirmed
mpox case identified among contacts during the follow-up period.
Findings Of the 88 households, 18 (20%) experienced secondary transmission, with most primary mpox cases
generating a single secondary case. The overall SAR across all households was 6·15% (95% CI 4·02–8·95) and was
significantly higher among those younger than 15 years (8·77% [5·44 –13·22]) than among those aged 15 years or
older (2·84% [0·92–6·50]). The overall R₀ was 0·30 (95% CI 0·17–0·46), and was significantly higher for those
younger than 15 years (0·43 [0·21–0·70) than those aged 15 years or older (0·15 [0·03–0·27]). The sensitivity analysis
showed significantly higher estimates (R₀ 0·9 [0·71–1·09]; SAR 17% [13·57–21·03]).
Interpretation Intrahousehold transmission of clade 1b mpox in Burundi was limited, and unlikely to sustain a
broader community spread. The involvement of children in transmission chains within the household underscores
their vulnerability, emphasising the need for accurate household investigation, early detection, and strategies to
protect them. Our findings suggest that infection outside the household, with adults serving as a source for initial
household introductions, might be a primary driver of the outbreak. The mpox outbreak response should adopt a dual
approach combining interventions for household settings, and targeted prevention strategies for adults at risk where
community transmission is more probable.