# Temporal and spatial distributions and clustering features of soil-transmitted helminthiases on Hainan Island: A retrospective study from 2017–2023

## TL;DR

A 7-year study tracked soil-transmitted worm infections in Hainan Island, China, finding a decline in infections but persistent hotspots and higher risks for children and older adults.

## Contribution

The study provides detailed spatial and temporal insights into soil-transmitted helminth infections in Hainan Island, identifying high-risk areas and vulnerable groups for targeted interventions.

## Key findings

- The overall STH infection rate was 5.76%, with hookworms being the most common.
- Infection rates decreased significantly over the 7-year study period.
- Hotspots were identified in central-southern mountainous areas, with high-risk groups including children and older adults.

## Abstract

To summarize the epidemiological status and transmission dynamics of soil-transmitted helminthiases (STHs) in Hainan Island from 2017 to 2023, providing an evidence-based foundation for optimizing future control strategies.

From 2017 to 2023, two mobile and one fixed surveillance sites were selected annually from 18 counties/cities in Hainan Island. Each site was divided into five geographical zones (east, west, south, north, and central), with one administrative village randomly chosen from each zone. At least 200 local residents aged ≥ 3 years were enrolled per village, totalling ≥ 1,000 participants per site. Fresh stool samples (≥ 30 g) were collected for modified Kato–Katz thick smear examination (two slides per sample) to detect hookworm, Trichuris trichiura, Ascaris lumbricoides, and Enterobius vermicularis eggs. Perianal cellophane tape swabs were used for E. vermicularis screening in children aged 3–9 years. Infection prevalence was calculated, and demographic differences were analysed by using the chi-square test. Temporal trends were assessed via Joinpoint regression analysis. ArcGIS 10.8 was used to construct a spatial database, perform kernel density estimation (KDE), and calculate global and local Moran’s I indices for spatial aggregation analysis.

A total of 29,669 individuals from 128 administrative villages across 88 townships in 18 county-level divisions were monitored. The overall STH infection rate was 5.76% (1,710/29,669), with hookworms (3.47%), A. lumbricoides (0.88%), T. trichiura (0.10%), and E. vermicularis (1.45%) as the dominant species. The infection rate showed a significant downward trend (AAPC = -18.99, P < 0.05). Regional differences were evident (χ2 = 735.316, P < 0.001), with the highest rate in Danzhou City (18.96%) and the lowest rate in Ding’an County (0.39%). Infection rates varied significantly by sex, age, ethnicity, occupation, and education level (all P < 0.001). Global spatial autocorrelation indicated clustering of T. trichiura infections (Moran’s I = 0.137, Z = 1.983, P < 0.05). Local autocorrelation identified high–high clustering in Baisha County and low–low clustering in Haikou City and adjacent areas. KDE analysis revealed core high-density zones in Wuzhishan City and neighbouring counties, with secondary hotspots in Danzhou City and the Tunchang–Qionghai–Ding’an corridor.

Although STH infection rates in Hainan Island have consistently declined, central–southern mountainous counties and vulnerable groups (e.g., children and older people) require sustained surveillance and targeted interventions to consolidate control efforts.

A consectively 7-year study (2017–2023) tracked intestinal worm infections spread through soil in Hainan Island, China. Researchers tested nearly 30,000 people across 128 villages and found an overall infection rate of 5.76%. Hookworms were the most common type (3.47%), followed by Enterobius vermicularis (1.45%), Ascaris lumbricoides (0.88%), and Trichuris trichiura (0.10%). Infection rates decreased year by year during the study period and spatial analysis revealed hotspots concentrated in central-southern mountainous areas around the Wuzhishan City. Children (aged 3–10), older adults (over 61), kindergarteners, and those with little formal education still faced higher infection risks. Females were slightly more affected than males. The study recommends that significantly more efforts will be required to achieve the goal of controlling transmission and interrupting soil-transmitted nematodiasis. Targeted interventions for high-risk groups are essential, particularly for blocking the transmission of E. vermicularis infection in children.