Avoid raw freshwater fish and shrimp dishes, including sashimi, raw-fish congee, and drunken shrimp; if you have eaten them regularly, get tested for liver flukes and take praziquantel as prescribed if infection is found

Avoiding raw fish costs nothing; the hard part is changing long-standing tastes and declining it at group meals. If you have eaten it regularly, have a hospital stool test for parasite eggs; prices vary by location. If infection is found, take praziquantel at the dose prescribed by a doctor, usually for 1–2 days.

Clonorchis sinensis is commonly called the Chinese liver fluke. At a 2009 meeting, the WHO's International Agency for Research on Cancer classified chronic infection as carcinogenic to humans: it causes bile duct cancer and belongs in Group 1. Its 1994 assessment had classified it only as Group 2A, probably carcinogenic. Pooled published studies found about 4.8 times the bile duct cancer risk in people infected with liver flukes (relative risk 4.8, 95% CI 2.8–8.4, the confidence interval). This estimate also included another liver fluke found in Southeast Asia. In the same review, hepatitis B had a risk ratio of 2.6 and hepatitis C 1.8, making liver flukes the strongest of these factors. Another review pooled 36 studies. For bile duct cancer, the odds ratio was about 4.37 in case-control studies (OR 4.37, 2.84–6.72) and the relative risk was about 10.43 in follow-up studies (RR 10.43, 2.90–37.47). Cholangitis and cholecystitis had an estimated 7.80-fold risk (RR 7.80), gallstones 2.42-fold (RR 2.42), and hepatocellular carcinoma an odds ratio of about 4.69 (OR 4.69). Bile duct cancer and hepatocellular carcinoma are rare, so odds ratios are close to relative risks. No significant association was found with cirrhosis. Heavier infection was associated with more disease. China's 2014–2015 national survey found 0.47% prevalence, about 6 million people. Prevalence exceeded 1% in Guangdong, Guangxi, Heilongjiang, and Jilin. Modeling from 2016–2021 surveillance estimated national prevalence in 2020 at about 0.67%, or 9.46 million people, including about 8.92% in Guangxi and 2.99% in Guangdong. In 2024, China's National Disease Control and Prevention Administration and 14 other departments issued a prevention and control plan using mean surveillance-site prevalence from 2018–2022 as the baseline: 8.75% in Guangxi, 4.38% in Jilin, 3.16% in Heilongjiang, and 2.95% in Guangdong. China's National Center for Food Safety Risk Assessment warned in 2026 that seasonings such as alcohol, vinegar, and mustard cannot effectively kill liver flukes. Freezing requires at least 7 continuous days at or below −20°C. Heating requires the food's center to remain at or above 70°C for at least 10 minutes. IARC also states that pickled or smoked freshwater fish can transmit infection. For treatment, a 2022 review included 26 trials and 3340 people. The WHO-recommended praziquantel regimen is 25 milligrams per kilogram of body weight per dose, 3 times daily for 2 days. The predicted cure rate for Clonorchis sinensis was 98.5% (85.4%–99.9%).

IARC Working Group on the Evaluation of Carcinogenic Risks to Humans (2012). Opisthorchis viverrini and Clonorchis sinensis. In: Biological Agents. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 100B, 341-370. https://publications.iarc.who.int/119；Shin HR, Oh JK, Masuyer E, 等 (2010). Epidemiology of cholangiocarcinoma: an update focusing on risk factors. Cancer Science, 101(3), 579-585. https://doi.org/10.1111/j.1349-7006.2009.01458.x；Xia J, Jiang SC, Peng HJ (2015). Association between liver fluke infection and hepatobiliary pathological changes: a systematic review and meta-analysis. PLoS ONE, 10(7), e0132673. https://doi.org/10.1371/journal.pone.0132673；Qian MB, Chen J, Bergquist R, 等 (2019). Neglected tropical diseases in the People's Republic of China: progress towards elimination. Infectious Diseases of Poverty, 8, 86. https://doi.org/10.1186/s40249-019-0599-4；Qian MB, Huang JL, Wang L, 等 (2025). Clonorchiasis in China: geospatial modeling of the population infected and at risk, based on national surveillance. Journal of Infection, 91(1), 106528. https://doi.org/10.1016/j.jinf.2025.106528；国家疾控局等 15 部门 (2024). 关于印发全国包虫病等重点寄生虫病综合防治实施方案（2024—2030 年）的通知，附表 7. https://www.gov.cn/zhengce/zhengceku/202405/content_6950309.htm；国家食品安全风险评估中心 (2026). 关于慎食淡水生鲜食品预防肝吸虫病的风险提示（重庆市疾病预防控制中心转载）. https://www.cqcdc.org/index.php?a=shows&catid=179&id=3861；Qian MB, Patel C, Palmeirim MS, 等 (2022). Efficacy of drugs against clonorchiasis and opisthorchiasis: a systematic review and network meta-analysis. The Lancet Microbe, 3(8), e616-e624. https://doi.org/10.1016/S2666-5247(22)00026-X；中国疾病预防控制中心寄生虫病预防控制所 (2020). 华支睾吸虫病（肝吸虫病）防治知识（广东省疾病预防控制中心转载）. https://cdcp.gd.gov.cn/jkjy/jkzt/jscbfz/content/post_3439516.html；广东省疾病预防控制中心 (2023). 吃鱼生没余生？警惕潜伏在鱼生中的“凶手”肝吸虫！ https://cdcp.gd.gov.cn/jkjy/jkts/content/post_4274108.html；香港食物安全中心. 淡水鱼刺身的食物安全. https://www.cfs.gov.hk/sc_chi/multimedia/multimedia_pub/multimedia_pub_fsf_148_01.html

The risk figures above all come from case-control and observational follow-up studies, without randomized controlled groups. No study directly compared whether testing followed by treatment reduces bile duct cancer either. Bile duct cancer is uncommon, so a large relative increase does not mean a large absolute increase for each person. The evidence grade is therefore B. The roughly 4.8-fold figure compares infected with uninfected people, rather than quantifying disease prevented by this action; the benefit is judged medium, as in Item 46 in this section (discard the whole package when food goes moldy). Guangdong CDC says liver flukes can survive in humans for 20–30 years. Light infections often cause no symptoms, so people who regularly eat raw fish should not wait to feel ill before testing. Stool examination for eggs establishes the diagnosis; ultrasound, CT, and blood tests are only supportive. A doctor must determine praziquantel dosage based on body weight and infection severity. The parasitic diseases institute says that, in areas with cysticercosis, medical history should be checked before high-dose treatment. Continuing to eat raw fish after cure can lead to reinfection. Keep knives and chopping boards used for raw fish separate from those for cooked food. Marine fish sashimi commonly carries other parasites, such as Anisakis. Hong Kong's Centre for Food Safety advises buying from licensed shops and says older people, children, and pregnant women should avoid raw fish. Infection can affect children's growth. Hepatitis B and C also damage the liver and cause cancer; see Section 1, Item 14 (get the five-marker hepatitis B panel) and Section 1, Item 45 (get a hepatitis C antibody test once). The main beneficiaries are you and family members sharing your meals.