Abstract:

Objective To determine the nationwide epidemic status of soil-transmitted helminth (STH) infections and the prevalent risk factors in China, so as to provide scientific basis for evaluating the existing control efforts and formulating control strategies. Methods The surveillance for STH was carried out in 291 surveillance sites or counties in 30 provinces/municipalities/autonomous regions in China in 2017. Each surveillance site includes 5 villages evenly distributed geographically, and 200 permanent residents with age of over 3 years old were randomly enrolled from each village. The stool samples were collected from each enrolled villager and the eggs of STH were examined under microscope in duplicate using modified Kato-katz thick smear method. The prevalence for STH infections were then calculated. Chi-square test was used to compare the infection rates among different groups. In addition, the contamination of Ascaris eggs and hookworm larvae was also monitored in soil samples collected from 5 households in each village. Results Total 297 078 people were enrolled in the surveillance from the total 291 surveillance sites and the overall prevalence of STH infections was 1.78% (5 293/297 078)nationwide. The top three provinces with highest prevalence of STH infections include Yunnan (11.83%, 1 345/11 372), Hainan (10.91%, 220/2 017)and Chongqing (9.68%, 355/4 091). The prevalence of STH in female villagers (1.94%, 2 945/151 771)was significantly higher than male (1.62%, 2 348/145 307)(P < 0.01). Villagers with age of 60 years old and above had the highest infection rate of 2.78%(1 986/71 314), followed by 7-14 age group(1.71%)and 45-59 age group(1.69%), with statistical difference among the different age groups(P < 0.01). The overall prevalence of hookworm, Ascaris lumbricoides, and Trichuris trichiura within the investigated villagers were 1.00%, 0.50% and 0.41%, respectively. However, most of them were light infection, accounting for 93.85%(2 791/2 794)for hookworm, 82.89%(1 221/1 473)for A. lumbricoides and 90.20%（1 104/1 224）for T. trichiura. The moderate infection account for 3.33%(99/2 794) for hookworm, 16.50%（243/1 473）for A. lumbricoides and 9.6%(117/1 224) for T. trichiura. The heavy infections only accounted for 2.82%(84/2 794)for hookworm, 0.61%(9/1 473)for A. lumbricoides and 0.25%(3/1 224)for T. trichiura. The contamination rates of Ascaris eggs and hookworm larvae in collected soil were 5.59% (114/2 040) and 3.18% (64/2 040), respectively. Conclusion Based on the nationwide surveillance of STH from 291 surveillance sites in 2017 the overall prevalence of STH in China was low, however, the STH prevalence in some provinces with low economic development still remained high and the endemic risks still existed. It is needed to continue the surveillance and strengthen the control efforts especially in those areas with low economic growth.

Key words: Soil-transmitted helminth, Infection, Surveillance, Hookworm, Ascaris lumbricoides, Trichuris trichiura, Prevalence