Evaluation of inter-observer agreement for periportal fibrosis related to Schistosoma mansoni: A population-based study of 3302 individuals using point-of-care ultrasound images and video in the SchistoTrack cohort

Background: Schistosomiasis-related periportal fibrosis (PPF) diagnoses rely on point-of-care ultrasound imaging. Yet, the extent of agreement between sonographers, limitations of existing World Health Organization (WHO) protocols, and the applicability of ultrasound video remain poorly understood. Methods: In 2024, six sonographers performed ultrasound scans for 3302 participants aged 5–92 years within SchistoTrack, a community-based cohort in rural Uganda. We adapted and standardised the WHO Niamey protocol for the collection of curated ultrasound images of liver fibrosis patterns related to Schistosoma mansoni (ranging A–F) and liver ultrasound video sweeps. PPF was defined as patterns C–F. Images and videos were read for patterns of fibrosis by second sonographers who were blinded to field diagnoses. Second sonographers recorded their clinical confidence, the probe position and any ultrasound interference. Outcomes considered were simple agreement for individual patterns and agreement on whether any PPF pattern was present, using Cohen's κ. The influence of participant characteristics and image quality factors was evaluated against agreement outcomes. Results: Abnormal liver fibrosis patterns (B–F) were identified in 32.8% (1082/3302) of participants, and among these 2074 images were read by a second sonographer from 1040 participants. The percentage agreement was 73.0% (1515/2074) for broad pattern categories. Severe fibrosis patterns had the least agreement; E and F patterns had κ = 0.430 and 0.149, respectively. The D pattern had the most agreement (κ = 0.717). 94.0% of second sonographer readings were within one step of severity of the field diagnosis. Participant characteristics were not consistently associated with disagreement, though agreement clustered by the field sonographer. Clinical confidence, breathing/movement, fat interference and probe position were positively associated with disagreement. There was no agreement among the 1054 videos that were read by a second sonographer: κ = 0.001 for PPF agreement and ranged 0–0.062 for individual patterns. Conclusion: We have presented the largest diagnostic study of inter-sonographer agreement for schistosomal liver fibrosis patterns. Disagreement between adjacent patterns of liver fibrosis may indicate that the WHO Niamey protocol should be updated to capture a continuous progression of liver fibrosis rather than distinct patterns. The greatest disagreement was among severe patterns, which supports routine second reading to ensure life-threatening cases are prioritised and appropriately triaged.