Mapping the global distribution of podoconiosis: Applying an evidence consensus approach

Abstract

Background

Podoconiosis is a type of elephantiasis characterised by swelling of the lower legs. It is often confused with other causes of tropical lymphedema and its global distribution is uncertain. Here we synthesise the available information on the presence of podoconiosis to produce evidence consensus maps of its global geographical distribution.

Methods and findings

We systematically searched available data on podoconiosis in SCOPUS and MEDLINE from inception, updated to 10 May, 2019, and identified observational and population-based studies reporting podoconiosis. To establish existence of podoconiosis, we used the number of cases reported in studies and prevalence data with geographical locations. We then developed an index to assess evidence quality and reliability, assigning each country an evidence consensus score. Using these summary scores, we then developed a contemporary global map of national-level podoconiosis status.

There is evidence of podoconiosis in 17 countries (12 in Africa, three in Latin America, and two in Asia) and consensus on presence in six countries (all in Africa). We have identified countries where surveillance is required to further define the presence or absence of podoconiosis. We have highlighted areas where evidence is currently insufficient or conflicting, and from which more evidence is needed.

Conclusion

The global distribution of podoconiosis is not clearly known; the disease extent and limits provided here inform the best contemporary map of the distribution of podoconiosis globally from available data. These results help identify surveillance needs, direct future mapping activities, and inform prevention plans and burden estimation of podoconiosis.

Author summary

The global distribution of podoconiosis is uncertain. With our current understanding of its distribution still incomplete, many of the countries suspected to be endemic for podoconiosis are based on expert opinion and lack published evidence of confirmed cases. In this study, we used multiple data sources and health metrics to identify countries with presence and absence of podoconiosis with appropriate uncertainties. After assembling a database of different evidence types we constructed a weighted score for each country called ‘evidence consensus scores’. We used these scores to measure the certainty of the presence and absence of podoconiosis. The maps produced help to identify evidence gaps and uncertainties in the current global distribution of podoconiosis. Countries with evidence of podoconiosis are mostly clustered in Africa, and a few in Asia and Latin America. We have also identified countries with indeterminate status on the presence and absences of podoconiosis. These countries are characterised by weak health systems and multiple co-endemic diseases causing lower leg swelling, potentially leading to misdiagnosis of podoconiosis. Given these challenges, we recommend intensified disease surveillance and active case searching be implemented in areas where evidence is lacking.