Vital Surveillances: Epidemic Status of Soil-Transmitted Helminthiasis — China, 2023–2024

Introduction: This study reports on 2023–2024 national surveillance data from China's soil-transmitted helminthiasis surveillance network, which covers over 400 counties across 31 provincial-level divisions (PLADs) and the Xinjiang Production and Construction Corps (XPCC). These findings aim to guide future control strategies.

Methods: In 2023 and 2024, each PLAD will select 10%–15% of its jurisdictions as annual surveillance counties, resulting in 437 and 459 counties being chosen, respectively. Using geographically stratified cluster random sampling, 1,000 participants were enrolled in each county. Stool samples from all participants and soil samples from five households in each village were collected and examined. Infection rates and intensities were calculated and compared using the Chi-square test.

Results: In 2023 and 2024, the infection rates of soil-transmitted helminth (STH) were 0.53% (2,381/449,220) and 0.47% (2,233/476,756) , respectively, with significant differences. High STH prevalence was concentrated in Sichuan, Yunnan, and Chongqing in both years, with obvious infection heterogeneity according to sex and age. Hookworm infection was the dominant type, followed by Ascaris lumbricoides and Trichuris trichiura. Environmental soil monitoring confirmed the presence of Ascaris eggs and hookworm larvae.

Conclusion: Despite the low overall prevalence, soil-transmitted helminthiasis in China remains geographically and demographically heterogeneous. Targeted strategies are required to strengthen control measures and work toward control and eventual interruptions.

Soil-transmitted helminths (STH), primarily hookworms, Ascaris lumbricoides and Trichuris trichiura (1), pose a major health threat in China. Heavy infections cause intestinal damage, leading to malnutrition, stunting, anemia, impaired immune function in children, and adverse pregnancy outcomes (2–3). Despite historical declines in prevalence due to control programs and improved living standards, STHs remain widely distributed (4–6). A 2015 national survey on key parasitic diseases reported an overall STH infection rate of 4.49% in China, corresponding to an estimated 29.12 million infected individuals (6).

In 2016, China integrated STH surveillance into a Central Government-funded Project for the Control of Malaria and Other Key Parasitic Diseases, establishing a nationwide surveillance system (7). From 2016 to 2022, the national STH surveillance program gradually expanded to over 400 monitoring counties across all 31 provincial-level divisions (PLADs) and the Xinjiang Production and Construction Corps (XPCC). Epidemiological patterns of STH infections have evolved (7–13). Using 2023–2024 national STH surveillance data, this study analyzed infection status in China to provide evidence for future control strategies.

National surveillance across all 31 PLADs and the XPCC in 2023–2024 will employ a stratified cluster random sampling design. Annually, each PLAD selects 10%–15% of its counties (totaling 437 and 459 counties, respectively). Each county was stratified into five geographical sectors (east, west, south, north, and central) with one administrative village randomly selected per sector. From each village, 200 permanent residents were enrolled by cluster sampling, with 1,000 participants per county (7–13) representing all age groups. Each participant provided a fresh stool specimen (30 g).

Five households per village were randomly chosen for environmental sampling. One composite soil sample (≥400 g) was collected from each household's farmland or garden, subdivided for pathogen-specific analysis: 350 g for hookworm larval detection and 50 g for Ascaris lumbricoides egg identification.

Fecal samples were analyzed for soil-transmitted helminth eggs using the modified Kato-Katz thick smear method, with duplicate slides per sample. Soil samples were processed for hookworm larvae via warm saline (5% NaCl, 45 °C) sedimentation and for Ascaris lumbricoides eggs via saturated sodium nitrate flotation.

The National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention (National Center for Tropical Diseases Research), hereafter referred to as the National Institute of Parasitic Diseases (NIPD), delivers standardized training and on-site supervision. Provincial and municipal CDCs provided technical training and validated the results by reexamining 10% of positive and 5% of negative slides from each site. The NIPD also performed random slide rechecks.

All data were entered into the national Parasitic Disease Control Information Management System at the county level and subjected to multi-tier verification (municipal, provincial, and national). At each stage, discrepancies triggered the return and correction of data. The national authorities conducted a final review to obtain a definitive dataset.

Data were analyzed using SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Overall and species-specific (hookworm, Ascaris lumbricoides, Trichuris trichiura) infection rates and intensities were calculated, stratified by PLAD, sex, and age group, with between-group comparisons made by chi-square test (α=0.05). Soil detection rates for hookworm larvae and Ascaris eggs were also determined using the following formula:

The STH infection rates in 2023 and 2024 were 0.53% (2,381/449,220) and 0.47% (2,233/476,756) respectively (Table 1). The infection rate is significantly lower in 2024 than in 2023 (χ²=7.56; P<0.05).

The STH infection rates in PLADs and XPCC demonstrated marked geographical heterogeneity, and the highest PLAD prevalence was recorded in Sichuan, Yunnan, and Chongqing in both years. No infections were detected in the four PLADs in 2023 or in eight PLADs in 2024 (Table 1).

Sex heterogeneity was observed in both years. The infection rate was significantly higher in women compared to men both in 2023 (χ²=23.15, P<0.0001) and in 2024 (χ²=6.87, P<0.01).

Age group heterogeneity was found, with the highest infection rate observed in individuals aged 60 years and above, and the lowest in individuals aged 0–6 years in both years. Statistically significant differences in infection rates were identified among all age groups in 2023 (χ²=350.72, P<0.0001) and 2024 (χ²=364.77, P<0.0001) (Table 2).

The overall hookworm infection rate was 0.31% (1,413/449,220) and 0.31% (1,456/476,756) in 2023 and 2024 respectively, and no significant difference was found (χ²=0.63, P>0.05) between them. The infection rates exceeded 1.00% in three PLADs – Chongqing, Yunnan, and Sichuan – in both years. No infections were detected in 16 PLADs in 2023 or 17 PLADs in 2024 (Table 1). Moreover, sex and age differences were statistically significant in both years (P<0.001) (Table 2).

The overall infection rate of Ascaris lumbricoides was 0.13% (603/449,220) in 2023 and 0.08% (383/476,756) in 2024, the infection rate was higher in 2023 than in 2024 (χ²=63.17, P<0.001). Rates were above 1.00% in two PLADs by 2023 and in no PLADs by 2024. No infections were detected in 9 PLADs in 2023 and in 14 PLADs in 2024 (Table 1). Moreover, sex and age differences were statistically significant in both years (P<0.001), except for sex, which showed no statistical significance in 2023 (P>0.05) (Table 2).

The overall Trichuris trichiura infection rate was 0.10% (459/449,220) in 2023 and 0.10% (459/476,756) in 2024 respectively, and no significant difference was found (χ²=0.81, P>0.05) between them. The prevalence was <1.00% in all PLADs in both years, except Sichuan in 2023. No infections were detected in 14 PLADs in 2023 or in 17 PLADs in 2024 (Table 1). No significant sex differences were observed in either year (P>0.05), while age differences were statistically significant in both years (P<0.0001) (Table 2).

Over 85% and 93% of hookworm, Ascaris lumbricoides, and Trichuris trichiura infections were mild in 2023 and 2024, respectively. Moderate and severe cases were observed in all three species in both years (Table 3).

The detection rates of Ascaris eggs were 1.93% (52/2700) and 1.37% (37/2,691) in soil samples, and positive samples were identified in nine and four PLADs in 2023 and 2024, respectively. The highest detection rates were found in Qinghai and Sichuan in both years, and contamination was found in both farmland and vegetable garden soils.

The detection rates of hookworm larvae were 2.44% (66/2,700) and 2.27% (61/2,691) in the soil samples, respectively, and positive samples were identified in seven and five PLADs in 2023 and 2024, respectively. The highest detection rates were observed in Jiangxi and Anhui in 2023 and in Yunnan and Chongqing in 2024, and larvae were present in both farmland and vegetable garden soils.

Soil-transmitted helminthiasis remains a persistent public health challenge that has long been endemic to China (14). Since the 20th century, nationwide control efforts have made substantial progress. Successive national parasite surveys demonstrated a marked decline in STH infection rates from 53.58% in 1990 (4) to 4.49% in 2015 (6). Despite this reduction, transmission continues, with pockets of hyper-endemicity highlighting control complexity (15). The National Implementation Plan for Comprehensive Control of Key Parasitic Diseases (2024–2030) calls for enhanced and control targets: highly endemic PLADs should reduce infection rates by >10% by 2025 and by >30% by 2030, while other PLADs maintain low prevalence. Sustained, intensive interventions are crucial to improve STH control in China.

A national STH surveillance system currently covers over 400 monitoring counties across all 31 PLADs and XPCC (7). Surveillance data from 2016 to 2022 indicate a steady infection rate decline from 2.46% to 0.64% (7–13). New data show rates of 0.53% (2023) and 0.47% (2024), continuing the downward trend, highlighting persistent epidemiological patterns. Infections were clustered regionally, with higher prevalence in warm, humid southern PLADs (Sichuan, Yunnan, and Chongqing), where climate and agricultural practices favor transmission, particularly of hookworm (15). Lower rates occurred in cooler, more developed eastern and northeastern regions (Beijing, Shanghai, and Heilongjiang). Demographically, infection rates were higher in women and peaked among adults ≥60 years, followed by children aged 7–14 years and adults 45–59 years, consistent with known at-risk populations (7–13). Older adults frequently face farming; children face risks from outdoor activities and hygiene practices. Given hookworm dominance, future strategies should prioritize this species while maintaining comprehensive efforts against all major STH.

Surveillance data showed persistent Ascaris egg contamination in PLADs (Qinghai and Sichuan), and with hookworm larvae in various regions (Jiangxi and Yunnan), indicating ongoing environmental transmission risk. Future STH control should prioritize sanitation improvements, such as expanding access to hygienic toilets and enhancing environmental management, to disrupt transmission and lower infection rates.

Given geographical disparities, regionally targeted strategies are required. In highly endemic areas, focused interventions should aim to reduce infection rates, and a comprehensive strategy of health education as the precursor and source control as the mainstay should be implemented. In low-endemic areas, efforts should shift toward transmission control and eventual elimination. Currently, STH infection rates exceed 1.00% in only four PLADs, whereas all others remain below this threshold. Specific provincial objectives for transmission control and interruption were set in line with the National Implementation Plan for Comprehensive Control of Key Parasitic Diseases (2024–2030). PLADs are advised to align activities with the national standard Control and Interruption of Soil-transmitted Helminth Transmission (WS/T629-2018) and to utilize the forthcoming Measures of Evaluation for Soil-transmitted Helminth Transmission Control and Interruption to systematically advance toward STH control and eventual interruption in China.

China has made significant strides in soil-transmitted helminthiasis prevention and control, where the National Surveillance System plays a key role. Currently, the national prevalence is low. However, considerable disparities persist across regions and population groups, with some areas reporting elevated infection rates. Therefore, implementing targeted interventions in high-prevalence regions guided by national surveillance results is essential. In areas where conditions allow, efforts should be made to control and eliminate soil-transmitted helminthiasis, advancing China’s efforts towards a new phase of parasitic disease control.

Appreciation goes to all surveillance personnel at provincial, municipal, and county levels of the Disease control agencies across all 31 provinces (autonomous regions, municipalities) and the Xinjiang Production and Construction Corps for their dedicated efforts in the National Soil-transmitted Helminth Surveillance Program.

This study used surveillance data from the National Institute of Parasitic Diseases (NIPD), Chinese Center for Disease Control and Prevention (China CDC). Ethical approval was granted by the Institutional Ethical Review Committee of NIPD, China CDC (Nos. 2021006 in 2023 and 2022001 in 2024). No personally identifiable information is disclosed. Oral informed consent was obtained from all participants and their guardians provided consent for those under 18 years of age.