Trends in the prevalence of microscopically-confirmed schistosomiasis in the South African public health sector, 2011-2018

Abstract

Background: Schistosomiasis, also known as bilharzia, is a chronic parasitic blood fluke infection acquired through contact with contaminated surface water. The illness may be mild or can cause significant morbidity with potentially serious complications. Children and those living in rural areas with limited access to piped water and services for healthcare are the most commonly infected. To address the prevalence of the disease in parts of South Africa (SA) effective national control measures are planned, but have not yet been implemented. This study aimed to estimate the prevalence and trends of public sector laboratory-confirmed schistosomiasis cases in SA over an eight-year (2011-2018) period, to inform future control measures.

Methodology & principal findings: This is a descriptive analysis of secondary data from the National Health Laboratory Service (NHLS). The study included all records of patients for whom microscopic examination detected Schistosoma species eggs in urine or stool specimens from January 2011 to December 2018. Crude estimates of the prevalence were calculated using national census mid-year provincial population estimates as denominators, and simple linear regression was used to analyse prevalence trends. A test rate ratio was developed to describe variations in testing volumes among different groups and to adjust prevalence estimates for testing variations. A total number of 135 627 schistosomiasis cases was analysed with the highest prevalence observed among males and individuals aged 5-19 years. We describe ongoing endemicity in the Eastern Cape Province, and indicate important differences in the testing between population groups.

Conclusion: While there was no overall change in the prevalence of schistosomiasis during the analysis period, an average of 36 people per 100 000 was infected annually. As such, this represents an opportunity to control the disease and improve quality of life of affected people. Laboratory-based surveillance is a useful method for reporting occurrence and evaluating future intervention programs where resources to implement active surveillance are limited.

Fig 1. Trends in national annual prevalence estimates and testing for microscopically-confirmed S. haematobium in the public sector, South Africa, 2011–2018.

The national prevalence estimate (solid black line) did not change substantially, while the national test estimate (grey dashed line) steadily increased each year. The mean, slope and statistical significance (p-value) of the linear trends are provided in the text box.

Fig 2. Province-specific period prevalence estimates of microscopically-confirmed S. haematobium in the public sector, South Africa, 2011–2018.

Prevalence estimates are given per 100 000 persons and the intervals were selected using the Jenks natural breaks method. The map was made for this paper using Esri ArcGIS 10.2, with the 2016 provincial boundary shapefile from OCHA ROSEA under a Creative Commons Attribution for Intergovernmental Organisations (CC BY-IGO) license (https://data.humdata.org/dataset/south-africa-admin-level-1-boundaries).