Abstract:

Objective To understand the infection status of soil-transmitted nematodes at national surveillance sites in Guizhou Province from 2016 to 2019, and to provide a scientific basis for formulating prevention and control strategies. Methods From 2016 to 2019, the national surveillance sites of soil-transmitted nematodes were established in 9 cities (prefectures) of Guizhou Province, with 8 fixed surveillance sites and 5~7 mobile surveillance sites every year. Each surveillance site was county-based, and was divided into five areas according to the geographical location, including east, west, south, north, and mid areas. In each area, one administrative village was randomly selected from one township for conducting surveillance, No less than 200 permanent residents at 3 years of age and above were randomly selected from each administrative village, and no less than 1 000 residents were selected from each surveillance site. Fecal samples of residents were collected and examined for nematode eggs of intestinal with the modified Kato-Katz method(two slide-reading for each sample). Children aged 3~9 years were examined with cellophane anal swab to detect Enterobius vermicularis eggs. Five families were randomly selected from each village at three fixed surveillance sites every year. The modified saturated sodium nitrate floating method was used to detect the soil contamination of Ascaris eggs in fields or vegetable gardens near the residents’ houses, and the saltwater separation method was used for identification of hookworm larvae in the soil samples. Questionnaire survey was performed to collect the information of natural and social factors including geographical environment, economic level and health status of the surveillance sites. The infection rates of soil transmitted nematodes and the proportion of participant, gender, ages and occupations in different surveillance sites were analyzed and compared with Chi square test. Results From 2016 to 2019, Guizhou Province set up 13~15 national surveillance sites every year; the production mode of each surveillance site was mainly agriculture, and the drinking water was mainly tap water; the per capita annual income was 4 911-6 686 yuan; the coverage rates of sanitary toilets were 56.3% (36 861/65 520), 40.0% (21 327/53 285), 59.6% (37 992/63 802) and 59.5% (37 679/63 333), respectively. A total of 56 598 residents were investigated, and the overall infection rate of soil-transmitted nematodes was 4.9% (2 765/56 598). From 2016 to 2019, the infection rate by year was 8.6% (1 130/13 158), 5.2% (776/15 069), 3.9% (547/14 220) and 2.2% (312/14 151), respectively, showing a decreasing trend year by year, with the difference between years being statistically significant (χ² = 642.31, P < 0.01). The average infection rates of Ascaris lumbricoides, hookworm, Truchuris trichiura and Enterobius vermicularis in children were 2.5% (1 415/56 598), 1.2% (674/56 598), 1.7% (936/56 598) and 1.6% (130/8 158), respectively, maily of mild infection. Among the 9 cities (prefectures), the infection rate of soil-transmitted nematodes in Qiandongnan prefecture was highest, which was 8.2% (908/11 086) (χ² = 824.55, P < 0.01). The average infection rate of nematodes in males and females was 4.7% (1 322/28 286) and 5.1% (1 443/28 312), respectively, and the difference was significant (χ² = 5.45, P < 0.05). Among the age groups, the infection rate was highest in the group over 70 years old, at 6.3% (270/4 276) (χ² = 98.04, P < 0.01). The infection rate varied among ethnic groups, and minority ethnic groups had the highest infection rate, at 8.4% (267/3 182) (χ² = 441.19, P < 0.01). The occupation distribution showed that the infection rate was highest in students, at 5.6% (987/17 612) (χ² = 121.65, P < 0.01). Among educational groups, the infection rate was highest among illiterate people, at 7.0% (406/5 804) (χ² = 279.00, P < 0.01). The infection rate varied among ethnic groups, and minority ethnic groups had the highest infection rate, at 8.4% (267/3 182) (χ² = 441.19, P < 0.01). During the four years, 300 soil samples were collected from fields and vegetable gardens, among them 75 samples were positive of Ascaris eggs with a positive rate of 25.0% (75/300). The soil positive rates of Ascaris eggs in 2016—2019 were 36.0% (27/75), 26.7% (20/75), 25.3% (19/75) and 12.0% (9/75), respectively (χ² = 11.72, P < 0.01). No hookworm larva was detected. Conclusion From 2016 to 2019, the infection rate of soil-transmitted nematodes decreased in residents of national surveillance sites of Guizhou Province, maily the infection of Ascaris and Trichuris. Close attention should be paid to groups of females, over 70 years old, students, the illiteracy, other ethnic minorities and residents in southeast of Guizhou.

Key words: Soil-transmitted nematodes, Infection, Surveillance, Guizhou Province