We conducted a retrospective descriptive study. By using results from all specimens collected from patients with suspected mpox under the national mpox surveillance program during 2016–2022, we aimed to describe the mpox landscape in CAR and evaluate the agreement of mpox test results (including cycle threshold [Ct] values) generated using the G2RG and C3L primers and different specimen types (blood, active lesion, or scab).

Figure 1

Figure 1. Laboratory test results for persons with suspected mpox cases, by year, Central African Republic, 2016–2022. Of 302 suspected cases during the study period, 105 (35%) had positive results for monkeypox...

During 2016–2022, a total of 494 specimens (278 blood, 99 active lesion, 95 scab, and 22 oropharyngeal) from 302 patients were received and tested for suspected mpox at IPB. Of the total 302 suspected case-patients, 105 (35%) were positive for MPXV on >1 specimen (varying 19%–64% annually) (Figure 1). Of the 105 MPXV-positive patients, 3 (3%) were also positive for VZV. Of the 197 MPVX-negative patients, 82 (42%) were positive for VZV and 108 (55%) were negative for both MPXV and VZV. The remaining 7 patients were not tested for VZV.

The highest percentage of MPXV-positive specimens derived from the Lobaye and Mbomou prefectures, which together contributed 58% of mpox cases overall. MPXV detection rates varied by prefecture: Sangha Mbaere, 24/40 specimens (60%); Lobaye, 35/106 specimens (33%); Mbomou, 25/74 specimens (34%); and Bangui 2/41 specimens (5%) (Appendix Table 1).

Significantly more female patients were among MPXV-positive than VZV-positive case-patients (p = 0.03) but not among case-patients who were negative for both viruses. The median age across all suspected case-patients was 14 years; we observed no statistically significant difference between the median ages of confirmed case-patients with mpox (17 years) and VZV (20 years) infections. The median age of case-patients who tested negative on both tests was significantly lower (9 years) (Appendix Table 1).

Blood specimens were positive for MPXV on G2RG in 77/278 (28%) of cases, active lesions in 45/102 (44%), scabs in 36/98 (37%), and oropharyngeal specimens in 3/22 (14%) (Table 1). Of specimens returning a positive result on G2RG, the median Ct was 32.11 (interquartile range [IQR] 29.12–35.45) for blood specimens, 18.92 (IQR 17.42–23.43) for active lesions, 18.07 (16.19–19.82) for scabs, and 30.15 (28.04–32.56) for oropharyngeal specimens (Table 2). Similar values were returned by C3L. For paired specimens (Appendix Table 2), we observed either substantial (κ 0.61–0.80) or almost perfect (κ 0.81–1.00) agreement of a positive or negative result on pairwise comparisons of tests conducted on different specimens types on either G2RG or C3L.

Figure 2

Figure 2. Distribution of Ct values obtained using G2RG and C3L primers of monkeypox virus–positive active lesion, blood, and scab specimens in study assessing laboratory diagnosis of mpox, Central African Republic, 2016–2022....

The Ct values of G2RG and C3L on blood were significantly higher than in active lesion and scabs, whereas we observed no difference between active lesion and scab specimens. We observed no statistically significant difference between the Ct values generated on G2RG and C3L on the same specimens. (Figure 2)

Approximately one third of suspected mpox cases in CAR are confirmed MPXV infections; an additional 2/5 are VZV infections, leaving ≈3/5 cases of papulovesicular cutaneous eruptions undiagnosed. Most mpox and VZV infections were diagnosed in teenagers and young adults, with an even younger population remaining undiagnosed.

Although cases of mpox are generally detected across the heavily forested, southern parts of CAR, mpox detection rates vary across prefectures. Some prefectures, such as Sangha Mbaere, have a high detection rate of MPXV (60%) over VZV (5%), whereas in others, such as Bangui, detection is much lower (MPXV 5%, VZV 46%). The varying detection rates between prefectures could be linked to local lifestyles and practices, as well as social instability. In the southwest region, local communities primarily subsist through hunting and gathering, spending long periods in mpox-endemic forest, which may increase the risk for exposure to the virus; however, in the southeast, mpox-endemic bushlands are used for farming and as a place of passage or temporary habitation for communities that have been displaced by social instability.

Our study also detected significantly more female patients among mpox-positive than VZV-positive cases, which may be explained by increased risk for infection through multiple routes of exposure to potentially infected sources. For example, women are primarily responsible for skinning and cooking wild game hunted in the forest and are the primary caretakers for family members who fall ill.

Our results demonstrate very high agreement in PCR results between primers. The results also highlight the need to prioritize active lesion and scab specimens over blood specimens, given that their relatively higher viral loads for MPXV and VZV enable better detection.

CAR faces special geographic, social, and healthcare challenges, leading to substantial delays between symptoms onset, diagnosis, and care. The reported case-fatality ratio for clade I mpox cases varies widely and is often cited as 11% (8) but has also been as low as 1.4% in Democratic Republic of Congo (P.R. Pittman et al., unpub. data, https://doi.org/10.1101/2022.05.26.22273379) and 6.7% in CAR (9). To improve patient outcomes in CAR, diagnostic capacity needs to be strengthened through greater availability of point-of-care testing and through support by more active epidemiologic and genomic surveillance that can be implemented with a wider range of partners.