Suspected and confirmed mpox cases in DR Congo: a retrospective analysis of national epidemiological and laboratory surveillance data, 2010-23

Abstract

Background: DR Congo has the highest global burden of mpox, a disease caused by infection with the monkeypox virus. The incidence has risen since 1980, but recent analyses of epidemiological trends are lacking. We aimed to describe trends in suspected and confirmed mpox cases in DR Congo using epidemiological and laboratory mpox surveillance data collected from 2010 to 2023, and provide insights that can better inform the targeting and monitoring of control strategies.

Methods: We analysed aggregated national epidemiological surveillance data and individual-level laboratory data from 2010 to 2023. We calculated incidence based on suspected cases, case-fatality ratios, and percentage of laboratory-confirmed cases and assessed geospatial trends. Demographic and seasonal trends were investigated using generalised additive mixed models.

Findings: Between Jan 1, 2010, and Dec 31, 2023, a total of 60 967 suspected cases and 1798 suspected deaths from mpox were reported in DR Congo (case-fatality ratio 2·9%). The number of reporting provinces increased from 18 of 26 provinces in 2010 to 24 of 26 provinces in 2023. The annual incidence increased from 2·97 per 100 000 in 2010 to 11·46 per 100 000 in 2023. The highest incidence (46·38 per 100 000) and case-fatality ratio (6·0%) were observed in children younger than 5 years. Incidence was higher in rural compared with urban areas. PCR testing was performed for 7438 suspected cases (12·2%), with 4248 (57·1%) of 7438 samples testing positive. Median age of confirmed cases (13·0 years [IQR 6·0-25·0]) remained stable, although the 95th percentile of age increased over time.

Interpretation: The incidence and geographical distribution of suspected mpox cases have increased substantially since 2010. Improvements in surveillance and decentralised testing are essential to monitor mpox trends and direct interventions effectively, to address the public health emergency declarations issued in August, 2024.

Funding: Belgian Directorate-General Development Cooperation and Humanitarian Aid; European and Developing Countries Clinical Trials Partnership; Research Foundation-Flanders; European Civil Protection and Humanitarian Aid Operations; Department of Economy, Science, and Innovation of the Flemish Government; Canadian Institutes of Health Research; and the International Development Research Centre.

Figure 1. Evolutions in case notifications and deaths of mpox suspected cases in DR Congo, 2010–23

(A) Suspected case notifications by year. (B) Suspected cases per 100 000 population by year. (C) Weekly observed incidence per 100 000 population of mpox suspected cases (red line) and moving average of the weekly incidence (grey line). (D) Suspected yearly incidence of mpox cases stratified by age categories, in 2023†. (E) Weekly observed case-fatality ratio (red line) with moving average over time (grey line); incidence estimates are shown above the bars. (F) Case-fatality of suspected mpox cases stratified by age group in 2023. *Case-fatality percentages are shown above each bar. †Years for which age distribution was available in cases and death notifications data.

Figure 2. Spatial distribution of mpox suspected case notifications and incidence by province in DR Congo, 2010–23

Cumulative number of mpox suspected case notifications per province (A). Mean yearly incidence per province (B).

Figure 3. Spatial evolution in incidence of mpox suspect cases

Yearly incidence of suspected mpox cases per province (A) and per health zone (B), from 2010 to 2023

Figure 4. Observed and smoothed yearly incidence of mpox suspected cases in provinces with an incidence of one or more per 100 000 population

*Smoothed using a generalised additive model per province.

Figure 5. Seasonal and ecological trends in weekly incidence of mpox suspected case notifications per 100 000 population over time

(A) Predicted weekly incidence per 100 000 population of suspected mpox cases for rural and urban areas from 2010 to 2023 based on the GAMM. (B) Predicted long-term trend (2010–23) in weekly incidence of mpox suspected cases based on the GAMM. Provinces were classified into three major Köppen–Geiger climate zones: tropical rainforest, tropical monsoon, and tropical savanna. (C) Weekly mpox suspected case incidence (per 100 000 population) based on the observed data (grey), and model predictions based on the GAMM (red); by Köppen–Geiger climate zones*. (D) Predicted long-term trend (from 2010 to 2023) in weekly incidence (per 100 000 population) of mpox suspected cases (top) and predicted yearly recurring seasonal effect (from 2010 to 2023) in weekly incidence (per 100 000 population) of mpox suspected cases (bottom), stratified by Köppen–Geiger climate zones*; based on the GAMM model. GAMM = generalised additive mixed model. (s)time = smooth term for long-term non-linear trend in incidence expressed in weeks. s(week) = yearly recurring smoothed non-linear trend incidence expressed in weeks. *As the province of Haut-Katanga is the only province in the subtropical climate zone and has mean annual incidence over all years of zero, it was further excluded from all seasonality analyses.

Figure 6. Trends in laboratory sample referral, laboratory testing, case confirmation, and age distribution of confirmed cases

(A) Attrition plot with total number of mpox suspected cases 2010–23, number of cases with samples received at the central laboratory, number of suspected cases with samples received at the central laboratory, number of suspected cases with successfully performed laboratory analyses of samples, and number of suspected cases testing positive for OPXV on PCR. (B) Yearly sampling ratio (proportion of mpox suspected cases for whom samples were received at the central laboratory) and yearly test positivity ratio (proportion of analysed samples that were positive on OPXV PCR) from 2010 to 2023. (C) Yearly number of confirmed cases, from 2010 to 2023. (D) Yearly incidence per 100 000 population of confirmed cases over time. (E) Map of the cumulative number of cases for which mpox tests were requested at the central laboratory by province, from 2010 to 2023. (F) Map of the overall test positivity ratio in percentages per province, from 2010 to 2023. (G) Age distribution of confirmed mpox cases; 2010 to 2023. (H) Quantile regression of age of confirmed mpox cases at 5th, 50th, and 95th percentile from 2004 to 2023*. OPXV = orthopoxvirus. *For this analysis laboratory data were available from 2004 onwards. To use all available data and show long-term trends, all data were included.