Comparison of data-fitting models for schistosomiasis: a case study in Xingzi, China.

When modelling prevalence data, epidemiological studies usually employ either Gaussian, binomial or Poisson models. However, reasons are seldom given in the literature why the chosen model was felt to be the most appropriate. In this study, we compared all three models for fitting schistosomiasis risk in Xingzi county, Jiangxi province, People's Republic of China. Parasitological data from conventional surveys were available for 36,208 individuals aged between 6 and 65 years from 42 sampled villages and used in combination with environmental data to map the spatial patterns of schistosomiasis risk. The results show that the Poisson model fitted the data best and this model identified the role of environmental risk factors in explaining the geographical variation of schistosomiasis risk. These factors were further used to develop a predictive map, which has important implications for the control and eventual elimination of schistosomiasis in the People's Republic of China.

[Relationship between snails and recent water level in different marshlands in Xingzi County, Jiangxi Province].

OBJECTIVE: To study the longitudinal change of data on Oncomelania hupensis surveillance in different marshlands and the impact of recent water level in Xingzi County, Jiangxi Province. METHODS: All information including water level of hydrometric station and the data of snails at the marshlands of Xiguanhu, Majiawan and Ximiaoqian was collected to explore the longitudinal change of snails and analyze the relationship between snail distribution and recent water level with Spearman rank correlation analysis. RESULTS: The highest proportion of frames with living snails and living snail densities at Majiawan and Ximiaoqian was 89.66% (442/493) in 2002 and 66.72% (872/1 307) in 2007, 8.33 in 2001 and 7.39 snails per frame in 2006, respectively, and the lowest was 13.26% (126/950) in 2010 and 4.60% (55/1 195) in 2005, 0.42 in 2010 and 0.22 snails per frame in 2002, respectively, and tended to decrease gradually after 2007. At Majiawan, infected snails were found in 2005 and 2009, the density and proportion of infected snails were 0.0033 and 0.0025 snails per frame, 0.09% (3/3 306) and 0.22% (3/1 389). Infected snails were found in Ximiaoqian in 2001, 2003, 2005 and 2009, the highest density and proportion of infected snails were 0.005 0 snails per frame and 0.88% (6/684) in 2005. Infected snails were found in Xiguanhu in 2002 and 2003 with a density and proportion of 0.0029 and 0.0027 snails per frame, 0.10% (1/974) and 0.32% (1/312), respectively. The correlation analysis between proportion of frames with living snails and density at Xiguanhu with the average water level of the first and second month before snail survey showed statistical significance, the correlation coefficient was 0.76, 0.71, 0.82 and 0.78 (P<0.05), respectively. The correlation between proportion of frames with living snails and density at Majiawan showed no statistical significance with the average water level of recent three months before snail survey. The proportion of frames with living snails and density at Xiguanhu were negatively correlated with the average water level of the first and second month before snail survey, the correlation coefficient was -0.67, -0.75, -0.79 and -0.72 (P<0.05), respectively. CONCLUSION: The change trend of snail indicators in different marshlands in the County and impact of water level in recent three months on snail population are both different, and the snail control strategy in marshlands should therefore be adjusted.

[Preliminary study on applying high resolution CBERS images to identify Oncomelania snail habitats in lake and marshland regions].

OBJECTIVE: To explore the preliminary application of high resolution CBERS-02B images in detecting the Oncomelania snail habitats in lake and marshland regions. METHODS: The images with high resolutions were first fused from CBERS-02B HR and CCD images, and then the potential snail habitats in Xingzi County of Jiangxi Province were extracted from high resolution CBERS images and CCD images, respectively. A total of 2 000 validation points were randomly selected for comparing the difference of distribution of these points inside and outside of the extracted two snail habitats with the McNemar chi-square test. RESULTS: The areas of the two snail habitats extracted from high resolution and CCD images were 98.23 km2 and 94.89 km2, respectively. The numbers of validation points in the two snail habitats were 255 and 248, respectively, and no significant difference was found (chi2 =177 9.52, P = 0.23). CONCLUSION: At large-scale studies, the ranges and areas of the two snail habitats extracted from high resolution and CCD images are not significantly different.

[Surveillance of schistosomiasis in Zhuxi Village, Xingzi County, 2005-2010].

OBJECTIVE: To understand the effect of schistosomiasis control in Zhuxi Village, Xingzi County, Jiangxi Province. METHODS: According to the national scheme of schistosomiasis surveillance, we investigated the schistosomiasis epidemic in Zhuxi Village from 2005-2010. The epidemic data of schistosomiasis on the humans, farm cattle, and Oncomelania snails were collected, respectively and analyzed by using the method of Cochran-Armitage test. RESULTS: Human infections and snail infections showed dynamic fluctuations (Z = 3.35, P = 0.000 8) and the density of alive snails tended to decrease gradually. The majority of the infections were peasants and students. The infection rates of farm cattle were 12.31%, 3.23%, 2.94%, 3.33%, 4.44% and 2.15%, respectively from 2005-2010. CONCLUSION: The effect of schistosomiasis control is very fine and schistosomiasis has been well controlled.

[Evaluation on application of common diagnosis methods for schistosomiasis japonica in endemic areas of China. III. Analysis and evaluation of underestimation of prevalence of Schistosoma japonicum infection by routine Kato-Katz technique].

OBJECTIVE: To understand the rates of underestimation of Schistosoma japonicum infection by Kato-Katz technique with different stool samples and different smears in field site. METHODS: With 27 Kato-Katz thick smears (3 stool samples with 9 thick smears each) for 3 consecutive years as a "gold standard", the rates of underestimation of schistosome infection by Kato-Katz technique with different stool samples and different smears were evaluated in a schistosomiasis endemic village. RESULTS: The examined rates of schistosome infection increased and the rates of underestimation decreased gradually with the increase of the number of Kato-Katz thick smears examined. The rates of underestimation of 3 smears were 40.98%-50.80% and the rates of underestimation of 6 smears were 25.48%-32.39%. The rates of schistosome infection based on the reading of 27 Kato-Katz thick smears were 10.96% in 2008, 8.54% in 2009 and 3.73% in 2010 respectively, but the rates of underestimation of various Kato-Katz thick smears were similar. There were no significant differences among the readings of 3, 6, and 9 smears of 1 stool sample, 3, 6 and 9 smears of 3 stool samples, 6 smears of 2 stool samples, 6 smears of 1 stool sample, and 6 smears of 3 stool samples. CONCLUSIONS: In a community with low-intensity of schistosome infection, the rate of underestimation is big by Kato-Katz technique with the reading of 3 smears of 1 stool sample. It suggested that it is better to increase smears rather than the number of stool samples examined.

A longitudinal study of comparison of the Kato-Katz technique and indirect hemagglutination assay (IHA) for the detection of schistosomiasis japonica in China, 2001-2006.

From 2001 to 2006, about one-third of the residents aged 5-65 years were selected as the subjects in a schistosome-endemic village located in Jiangxi Province, China. Every 1 year, all participants were analyzed by the Kato-Katz parasitologic examination and indirect hemagglutination assay (IHA). Statistical analysis of the results showed the k indices ranged from 0.250 to 0.347 between the two methods. Assuming the Kato-Katz results as the gold standard reference, the specificity of the IHA was from 60% to 77%, the positive predictive value of this method was from 19% to 30%, and its sensitivity and negative predictive value were more than 97%. The IHA method is unsuitable for individual screening in endemic community with relatively high prevalence (e.g. with >10% or more prevalence). A search for a better diagnostic test that can be applied in field situations in China is essential and should be given high priority.