Enhanced surveillance of monkeypox in Bas-Uélé, Democratic Republic of Congo: the limitations of symptom-based case definitions

Abstract Background Following an outbreak of cases of vesicular-pustular rash with fever evocative of human monkeypox in Bas-Uélé province, Democratic Republic of Congo, surveillance was strengthened. Methods Households with at least one active generalized vesicular-pustular rash case were visited, and contact and clinical history information was collected from all household members. Whenever possible, skin lesion were screened by PCR for the monkeypox virus, followed by the varicella-zoster virus when negative for the former. Results PCR results were obtained for 77 suspect cases distributed in 138 households, of which 27.3% were positive for monkeypox, 58.4% for chickenpox, and 14.3% negative for both. Confirmed monkeypox cases presented more often with monomorphic skin lesions, on palms of hands, and on soles of feet. Integrating these three features into the case definition raised the specificity to 85%, but would miss 50% of true monkeypox cases. A predictive model fit on patient demographics and symptoms had 97% specificity and 80% sensitivity, but only 80% and 33% in predicting out-of-sample cases. Conclusion Few discriminating features were identified and the performance of clinical case definitions was suboptimal. Rapid field diagnostics are needed to optimize worldwide early detection and surveillance of monkeypox.