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Reconciling egg- and antigen-based estimates of Schistosoma mansoni clearance and reinfection: a modelling study
Clark, Jessica Arinaitwe, Moses Nankasi, Andrina Faust, Christina L. Moses, Adriko Ajambo, Diana Besigye, Fred Atuhaire, Aaron Carruthers, Lauren V. Francoeur, Rachel
Clark, Jessica
Arinaitwe, Moses
Nankasi, Andrina
Faust, Christina L.
Moses, Adriko
Ajambo, Diana
Besigye, Fred
Atuhaire, Aaron
Carruthers, Lauren V.
Francoeur, Rachel
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Abstract
Despite decades of interventions, 240 million people have schistosomiasis. Infections cannot be directly observed, and egg-based Kato-Katz thick smears lack sensitivity, affected treatment efficacy and reinfection rate estimates. The point-of-care circulating cathodic antigen (referred to from here as POC-CCA+) test is advocated as an improvement on the Kato-Katz method, but improved estimates are limited by ambiguities in the interpretation of trace results.
Method
We collected repeated Kato-Katz egg counts from 210 school-aged children and scored POC-CCA tests according to the manufacturer’s guidelines (referred to from here as POC-CCA+) and the externally developed G score. We used hidden Markov models parameterized with Kato-Katz; Kato-Katz and POC-CCA+; and Kato-Katz and G-Scores, inferring latent clearance and reinfection probabilities at four timepoints over six-months through a more formal statistical reconciliation of these diagnostics than previously conducted. Our approach required minimal but robust assumptions regarding trace interpretations.
Results
Antigen-based models estimated higher infection prevalence across all timepoints compared with the Kato-Katz model, corresponding to lower clearance and higher reinfection estimates. Specifically, pre-treatment prevalence estimates were 85% (Kato-Katz; 95% CI: 79%–92%), 99% (POC-CCA+; 97%–100%) and 98% (G-Score; 95%–100%). Post-treatment, 93% (Kato-Katz; 88%–96%), 72% (POC-CCA+; 64%–79%) and 65% (G-Score; 57%–73%) of those infected were estimated to clear infection. Of those who cleared infection, 35% (Kato-Katz; 27%–42%), 51% (POC-CCA+; 41%–62%) and 44% (G-Score; 33%–55%) were estimated to have been reinfected by 9-weeks.
Conclusions
Treatment impact was shorter-lived than Kato-Katz–based estimates alone suggested, with lower clearance and rapid reinfection. At 3 weeks after treatment, longer-term clearance dynamics are captured. At 9 weeks after treatment, reinfection was captured, but failed clearance could not be distinguished from rapid reinfection. Therefore, frequent sampling is required to understand these important epidemiological dynamics.
Citation
Clark, J., Moses, A., Nankasi, A., Faust, C. L., Moses, A., Francoeur, R., ... & Lamberton, P. H. (2022). Reconciling egg-and antigen-based estimates of Schistosoma mansoni clearance and reinfection: a modeling study. Clinical Infectious Diseases, 74(9), 1557-1563. https://doi.org/10.1093/cid/ciab679
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Oxford University Press
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Clinical Infectious Diseases
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Description
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Clinical Infectious Diseases following peer review. The version of record Clark, J., Moses, A., Nankasi, A., Faust, C. L., Moses, A., Francoeur, R., ... & Lamberton, P. H. (2022). Reconciling egg-and antigen-based estimates of Schistosoma mansoni clearance and reinfection: a modeling study. Clinical Infectious Diseases, 74(9), 1557-1563. is available online at: https://doi.org/10.1093/cid/ciab679
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1537-6591