Abstract:

Objective To investigate the prevalence and transmission of soil-transmitted helminth (STH) in Liaoning Province, in order to provide scientific evidence for development of control plans, strategies and measures aagainst these diseases in Liaoning Province. Methods The surveillance was performed during 2016—2020 in Liaoning Province according to the National Surveillance Program and Implementation Guideline for Chlonorchiasis and Soil-transmitted Helminthiasis. One county (city or district) per provincial city was selected annually as a surveillance site. Each surveillance site was further divided 5 regions as geographical east, west, south, north and centre. One village was chosen from each region to conduct surveillance, and 200 permanent residents over 3 years old were randomly enrolled from each village. Fecal samples ( > 30 g) from enrolled residents were collected and were examined for STH eggs (two slide-reading for each sample) using the modified Kato-Katz thick smear method to estimate infection rate and intensity. The samples that are positive for hookworm eggs were further examined by test-tube filter paper incubation for the larva to identify the species. Cellophane anal swab method was used to detect Enterobius vermicularis eggs in children aged 3-9 years. The contamination of Ascaris eggs and hookworm larvae was also monitored in soil samples collected from 5 households in each village. Chi-square test was used to compare the infection rates. Results Total 69 909 people were recruited from 70 surveillance sites in Liaoning Province during 2016—2020, including 4 659 children aged 3-9, and the overall infection rate of STH infection was 0.26% (184/69 909), and the infection rate of A. lumbricoides and Trichuris trichiura were 0.25% (178/69 909) and 0.01% (6/69 909), respectively. Hookworm and E. vermicularis were not detected. The STH infection rate in the residents from 2016—2020 respectively were 0.59% (89/15 097), 0.19% (28/14 554), 0.27% (33/12 044)）, 0.13%(19/14 103), and 0.11%(15/14 111) (χ² = 59.44, P < 0.01). The top three cities with the highest infection rate of STH include Dandong (1.77%, 89/5 042), Dalian (0.56%, 28/5 004) and Benxi (0.42%, 23/5 451). The STH infection rate in females was 0.27% (94/35 057) and in males was 0.26% (90/34 852). The difference was not statistically significant (χ² = 0.07, P > 0.05). The infection rate in the 60-69 age group was the highest (0.36%, 50/13 803), followed by the 40-49 age group (0.32%, 34/10 788) and the age group over 70 years old (0.31%, 23/7 396). The differences were statistically significant among the different age groups (χ² = 18.30, P < 0.01). The infection rate in Man ethnicity (0.55%, 97/17 643) was statistical-significantly higher than that in Han ethnicity (0.17%, 87/51 154) (χ² = 75.04, P < 0.01). The STH infection rate among medical personnel, farmers and workers were 0.67% (2/298), 0.31% (158/50 631) and 0.28% (7/2 542), respectively. The differences were statistically significant (χ² = 26.90, P < 0.01). The infection rate among participants with primary school, education, middle school education and college education or higher were 0.32% (76/24 019), 0.26% (93/36 406) and 0.28% (5/1 815), respectively. The difference was not statistically significant (χ² = 10.12, P > 0.05). Among 69 909 people surveyed, only 232 people (0.33%) had taken deworming medications within 3 months prior to the examination. A total of 1 757 soil samples were examined in Liaoning Province during 2016—2020, and the result indicated the positive rate of A. lumbricoides eggs of 2.22% (39/1 757), while hookworm larvae not found. Conclusion The STH infection rate showed a declining trend and remained at a low level in Liaoning Province during 2016—2020, with mainly Ascaris infection. Attention should be paid to the 60-69 age group, farmers, people with primary school education, Man ethnicity, and the residents in southern Liaoning Province in the control practice.

Key words: Soil-transmitted helminth, Infection, Surveillance, Liaoning Province