Defining Persistent Hotspots: Areas That Fail to Decrease Meaningfully in Prevalence after Multiple Years of Mass Drug Administration with Praziquantel for Control of Schistosomiasis

Abstract

Abstract.Preventive chemotherapy with praziquantel for schistosomiasis morbidity control is commonly done by mass drug administration (MDA). MDA regimen is usually based on prevalence in a given area, and effectiveness is evaluated by decreases in prevalence and/or intensity of infection after several years of implementation. Multiple studies and programs now find that even within well-implemented, multiyear, annual MDA programs there often remain locations that do not decline in prevalence and/or intensity to expected levels. We term such locations “persistent hotspots.” To study and address persistent hotspots, investigators and neglected tropical disease (NTD) program managers need to define them based on changes in prevalence and/or intensity. But how should the data be analyzed to define a persistent hotspot? We have analyzed a dataset from an operational research study in western Tanzania after three annual MDAs using four different approaches to define persistent hotspots. The four approaches are 1) absolute percent change in prevalence; 2) percent change in prevalence; 3) change in World Health Organization guideline categories; 4) change (absolute or percent) in both prevalence and intensity. We compare and contrast the outcomes of these analyses. Our intent is to show how the same dataset yields different numbers of persistent hotspots depending on the approach used to define them. We suggest that investigators and NTD program managers use the approach most suited for their study or program, but whichever approach is used, it should be clearly stated so that comparisons can be made within and between studies and programs.

Improving public health control of schistosomiasis with a modified WHO strategy: a model-based comparison study

“…An emerging concern for Schistosoma transmission control is the issue of persistent hotspots-ie, villages that do not respond well to MDA in terms of reductions in prevalence and intensity of infection. 5,6 The question as to why some villages respond when others do not still needs to be explored, and strategies for early detection are urgently needed. For all of these reasons, new guidelines that consider adaptive strategies including an earlier change in strategy for updating the optimal MDA or public health strategy for schistosomiasis could yield great public health impact.…”

“…4 Many schistosomiasis control programmes have reduced local disease prevalence in affected populations with the use of targeted mass drug administration (MDA) delivered as repeated school-based or community-wide treatments. However, prevalence reduction has not been achieved in all treated communities, 5,6 and, in addition, at-risk areas often have a rebound of infection and disease prevalence after drug treatment efforts are stopped. 7,8 More effective disease control might ultimately be achieved through environmental modifications that separate humans from contaminated water sources, 9 or through snail population reductions with molluscicides, as these immediately reduce local snail populations and thus snail-to-human transmission.…”

“…However, in 2017, large-scale operational research trials identified limitations to both forms of drugtreatment-only control strategies. 5,6 The emergence of socalled persistent hot spots in the face of continued MDA implementation (as recommended) in endemic regions calls for reassessment and possible revision to global implementation guidelines. 15 Previous modelling done by the Neglected Tropical Disease Modelling Consortium 16 found that the WHO goals for morbidity control and elimination as a public health problem are likely to be attainable in lowprevalence but not moderate to high-prevalence settings using current guidelines.…”

Environmental Predictors of Schistosomiasis Persistent Hotspots following Mass Treatment with Praziquantel

“…9 Although MDA with PZQ reduces the average prevalence and intensity of Schistosoma infection, areas where the schistosomiasis burden remains high despite repeated rounds of MDA, known as "persistent hotspots" (PHSs), have been documented in multiple settings. [10][11][12][13] Possible causes of PHSs include insufficient treatment coverage, reduced rates of infection cure (or egg count reduction) among those treated, 13,14 sustained transmission within and from untreated populations, environmental conditions, and socioeconomic conditions that lead to frequent human contact with contaminated water sources. [15][16][17] A better understanding of how these and other factors shape PHS risk would enable the more efficient allocation of interventions for schistosomiasis control.…”

A search for snail-related answers to explain differences in response ofSchistosoma mansonito praziquantel treatment among responding and persistent hotspot villages along the Kenyan shore of Lake Victoria

“…Following one of the definitions of Kittur et al, six of the villages (Minya, Agok, Migiro, Miyandhe, Kanyibok, Usenge) were persistent hotspots (PHS), locations where the absolute change in S. mansoni prevalence from the beginning of the control program to the end was ≤30%. 21 By contrast, for the four remaining villages (Kotieno, Seka Dok, St. Douglas Weta, Mumbo) recorded a drop in prevalence >30% and are considered responding (RESP) villages. In each village, two shoreline habitats were identified where there was evidence of human-water contact activities, and these were established as our sampling sites.…”