Liver Fluke Infections Strike Nearly a Third of Patients in Hengzhou, China

In a hospital-based survey that has startled parasitologists, nearly one in three patients admitted to a hospital in Hengzhou City, in China’s Guangxi Zhuang Autonomous Region, turned out to be infected with the liver fluke Clonorchis sinensis. The cross-sectional study, published in the journal Parasites & Vectors, screened 1,220 hospitalized patients between April and May 2025 and found 362 individuals, or 29.7 percent, carrying the parasite according to the reference diagnostic method. The finding underscores that clonorchiasis, a foodborne trematode infection acquired by eating raw or undercooked freshwater fish, remains a formidable public health problem in this corner of southern China, decades after national control programs began pushing the disease downward elsewhere in the country.

The infection is caused by a trematode worm that settles in the bile ducts after humans ingest larvae encysted in fish tissues. Once established, adult flukes can live for years, shedding eggs into the feces and provoking chronic inflammation of the biliary system. Long-standing infection is associated with cholangitis, gallstones, bile duct hyperplasia and, most seriously, cholangiocarcinoma, a cancer of the bile ducts that has earned C. sinensis a place among the biological agents classified as carcinogenic to humans. Because early infection is often asymptomatic or produces only vague abdominal complaints, reliable diagnosis is the linchpin of any control strategy, and it is precisely where the new study makes its most practical contribution.

The research team, led by scientists from Guangxi Medical University Cancer Hospital, the First Affiliated Hospital of Guangxi Medical University and Hengzhou People’s Hospital, set out to answer two questions at once: how common is the infection in this high-burden area, and which of the diagnostic tools actually available to laboratories detects it best. To do so, they collected both fecal and serum samples from every enrolled patient and ran four tests in parallel. The reference standard was hydrochloric acid-ether centrifugal sedimentation, or HCl-EC, a concentration technique that separates parasite eggs from fecal debris by density. Alongside it they tested the KU-F40 automated feces analyzer, a machine-based egg-detection platform; the traditional direct smear, in which a small amount of feces is examined microscopically without concentration; and an enzyme-linked immunosorbent assay, or ELISA, which detects antibodies against the parasite in serum.

The demographic pattern that emerged was striking. Infection was far more common in men than in women, with 44.2 percent of male patients testing positive compared with just 11.6 percent of female patients, a difference the authors report as highly statistically significant. Age mattered as well: 99.2 percent of all detected infections occurred in patients aged 30 years or older. The explanation likely lies in dining habits, since raw freshwater fish dishes are a traditional delicacy in Guangxi and are consumed far more frequently by adult men at social gatherings and banquets. Whatever the behavioral driver, the data give health authorities a clear target: screening campaigns in Hengzhou should concentrate on men and on people past their twenties, rather than treating the whole population as uniformly at risk.

The comparison of diagnostic techniques produced results that will resonate with laboratory directors far beyond Guangxi. The positive detection rates of the four methods diverged dramatically: HCl-EC found infections in 29.7 percent of patients, the KU-F40 analyzer in 25.3 percent, the direct smear in only 13.3 percent, and the ELISA in a remarkable 65.0 percent. Agreement between methods, quantified with statistical measures of concordance, was highest between the sedimentation reference and the automated analyzer, at 80.3 percent overall agreement, and lowest between the direct smear and the ELISA, at 47.1 percent. In other words, the choice of test alone can determine whether a patient is labeled infected or healthy, a discrepancy with direct consequences for treatment and follow-up.

When the researchers used HCl-EC as the reference standard and calculated classical diagnostic performance metrics from two-by-two contingency tables, each test revealed a distinct personality. The ELISA achieved the highest sensitivity, correctly identifying 90.9 percent of truly infected patients, which reflects its ability to pick up antibody signals even when eggs are scarce in the stool. The direct smear, by contrast, showed the highest specificity at 93.7 percent, meaning it rarely produced false positives, but its sensitivity was so poor that it missed roughly two-thirds of infections, a predictable consequence of examining only a tiny fraction of the sample without concentration. The KU-F40 automated analyzer landed in between, with a sensitivity of 59.4 percent and a specificity of 89.2 percent, detecting most moderate and heavy infections while occasionally missing light ones.

One of the study’s more elegant analyses examined how infection intensity shapes test agreement. The team counted eggs per gram of feces, a standard measure of worm burden, and found that agreement between the different tests’ positive results was significantly higher in heavily infected patients than in lightly infected ones. This makes intuitive biological sense: the more eggs a patient sheds, the more likely any egg-detecting method, whether a centrifugation tube or an automated scanner, is to encounter one. Consistent with this, ELISA optical density values showed only a weak positive correlation with egg counts, and the antibody levels differed significantly between mild and moderate infection groups but not between other intensity categories. Antibody tests, in short, are imperfect mirrors of the actual worm burden living in the bile ducts.

The statistical machinery behind these conclusions was appropriately rigorous for a method-comparison study. Qualitative results across the four tests were compared with Cochran’s Q test, followed by pairwise McNemar tests corrected with the Bonferroni procedure to guard against false positives from multiple comparisons. Subgroup analyses by sex and age employed McNemar or exact McNemar tests, concordance of positive results was assessed with Pearson’s chi-square test, and the relationship between ELISA optical density and egg counts was explored with Spearman’s rank correlation, supplemented by Kruskal-Wallis testing with Dunn’s post hoc comparisons across infection-intensity groups. This layered approach matters because naive comparisons of test positivity rates can mislead; only paired, corrected analyses can say whether one test genuinely outperforms another on the same patients.

So which test should a busy hospital laboratory in an endemic area actually use? The authors come down in favor of the KU-F40 automated feces analyzer. While the HCl-EC sedimentation method remains the gold standard for accuracy, it is labor-intensive, requires trained microscopists, and involves handling hazardous chemicals including ether. The automated analyzer achieved accuracy comparable to the reference method while offering clear advantages in cost, speed and standardization, freeing technicians from repetitive manual microscopy and reducing operator-to-operator variability. The ELISA, despite its excellent sensitivity, detects exposure rather than active patent infection and produced a positivity rate far above the reference standard, making it better suited as a supplementary or epidemiological tool than as a stand-alone diagnostic. The humble direct smear, meanwhile, is simply too insensitive for a region where light infections are common and would miss most cases if used alone.

The broader message of the study extends past the laboratory bench. Hengzhou’s nearly 30 percent prevalence among hospitalized patients signals that clonorchiasis transmission continues unabated in parts of Guangxi, sustained by culinary traditions that resist change and by the parasite’s long lifespan in the human host. The authors argue that targeted screening should be prioritized for high-risk populations, particularly males and individuals aged 30 and above, an approach that concentrates resources where they will detect the most infections. Combined with the availability of an automated, affordable diagnostic platform, such targeted strategies offer a realistic path toward bending the curve of a disease that quietly damages livers and sets the stage for bile duct cancer. For a parasite that most of the world has never heard of, C. sinensis is clearly still a force to be reckoned with in the fish-eating heart of southern China.

Subject of Research: Prevalence and diagnosis of Clonorchis sinensis infection in Hengzhou, China

Article Title: High prevalence of Clonorchis sinensis infection with sex and age related patterns and comparative evaluation of four diagnostic techniques in Hengzhou, China

Article References: Xu, Y., Lao, Y., Zhou, L., Jiang, Y., Huang, T., Wei, C., Lin, Q., Qin, Y., Tang, Z., & Fang, M. (2026). High prevalence of Clonorchis sinensis infection with sex and age related patterns and comparative evaluation of four diagnostic techniques in Hengzhou, China. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07658-w

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07658-w

Keywords: Clonorchis sinensis, clonorchiasis, Guangxi, diagnostic techniques, HCl-ether sedimentation, automated feces analyzer, ELISA, direct smear, foodborne parasites, parasitology, screening, China