Objective To understand the prevalence of clonorchiasis in Sichuan Province for scientific guidance to prevention and control of Clonorchis sinensis infection in Sichuan area. Methods By the national and Sichuan provincial monitoring plans for clonorchiasis and soil-transmitted nematodes,we selected certain mobile monitoring sites annually from the counties (cities/ districts) without standardized surveillance,and Wutongqiao District of Leshan City as regular monitoring sites. Modified Kato-Katz thick smear technique (two slides/ one sample) was used to detect the eggs of Clonorchis sinensis in population. In 2017—2020,the metacercariae in fresh water fish and shrimp were detected by compression method,and the feces of the reservoir host,including cat,dog or pig was detected by modified Kato-Katz thick smear method. A question-naire survey on health knowledge and behavior was carried out among the population undergone fecal examination. Results From 2016 to 2020,a total of 143 311 people in the mobile surveillance sites underwent investigation,which revealed infection with Clonorchis sinensis in 28,with an infection rate of 0. 02%. The infection rate in population remained relative lower,ranging in 0. 01% (5/34 967),0. 02% (6/33 507),0. 04%(7/19 326),0. 02% (7/30 256) and 0. 01% (3/25 255)between 2016 and 2020,respectively. There was no significant difference in infection rate in different years(χ 2 =4. 249,P =0. 373). The highest infection rate of Clonorchis sinensis was seen in the plain(0. 03%,6/20 217) and hilly area(0. 03%,19/ 64 989) of Western Sichuan,yet clonorchiasis was not detected in the Northwest Sichuan Plateau. The difference was insignificant converging diverse terrain(χ 2 = 9. 949,P = 0. 028). Clonorchis sinensis was detected in 18 counties,accounting for 14. 06% of the total number of mobile surveillance sites. The infection rate of clonorchiasis was 0. 02% (13/68 316) in males and 0. 02% (15/74 995) in females,without significant difference between genders(χ 2 =0. 017,P =0. 895). The infection was 0. 02% (12/48 446) and 0. 02% (12/48 873),respectively for 40-59 years old group and ≥ 60 years old group,yet was not detected in 0-9 years old group. There was no significant difference among different age groups(χ 2 =4. 721,P =0. 291). The infection rate of Clonorchis sinensis was 0. 03% (12/35 401) and 0. 03% (2/7 772),respectively for junior school group and senior high school,technical secondary school/ polytechnic school group,however,the infection was not found in population with college degree or above. The difference was insignificant among population with different educational background (χ 2 = 5. 155,P = 0. 326) . Farmers and population with other occupations had infection rate of Clonorchis sinensis by 0. 02% (24/107 679) and 0. 02% (2/9 525),respectively,yet there was no infection detected in children in the kindergartens,children at home and medical professionals,and no difference among different occupation groups(χ 2 =1. 794,P =0. 805). The infection rate from 2016 to 2020 in regular surveillance sites was 0. 49% (5/1 018),0. 10% (1/1 013),0% (0/1 000),0. 10% (1/1 026) and 0% (0/1 009),respectively,without difference among years (χ 2 =7. 131,P =0. 008). Detection of the 256 freshwater fishes and shrimps out of 270 revealed infection with metacercariae of Clonorchis sinensis in 53,with a positive rate of 20. 70%. The highest positive rate(48. 15%) was seen in Pseudorasbora parva among the intermediate hosts. No Clonorchis sinensis eggs were detected in the 95 aliquots of feces collected,including 59 aliquots of dog feces and 36 cat feces. Of the 604 people surveyed by questionnaire,423 people(70. 03%) had the knowledge of clonorchiasis,and 92. 38% of the respondents had no history of intake of raw or semi-cooked freshwater fish and shrimp,while only 26. 66% of the respondents had the habit of using separate chopping board for raw and cooked dishes. Conclusion The infection rate of Clonorchis sinensis in population in Sichuan Province remains at a low level. Nevertheless,the positive rate is relatively higher in the intermediate host of Pseudorasbora parva,which suggests that risk of clonorchiasis transmission still exists,and further strengthened comprehensive prevention and control measures are necessary in order to reduce the infection rate of Clonorchis sinensis and its disease burden.
