Objective To investigate the disease burden of acute gastroenteritis in the community population of Shenzhen. Methods A multi-stage stratified random sampling method was employed from April to September 2024 to survey the burden of acute gastroenteritis in the community. Four streets were selected from each of the seven administrative districts in Shenzhen, and from each street, four communities were chosen for the investigation. Results A total of 2 670 community members were surveyed. Within the preceding three months, 147 individuals reported 205 episodes of acute gastroenteritis, yielding a quarterly prevalence rate of 7.68% (95% CI: 6.67%-8.69%). Statistically significant differences in quarterly prevalence were observed across different occupations, per capita annual incomes, household sizes, and travel histories within the last three months (P<0.05 or P<0.01). After adjusting for population gender, the quarterly prevalence was 7.72% (95% CI: 6.71%-8.73%), leading to an extrapolated annual incidence rate of 0.31 episodes per person-year (95% CI: 0.30-0.33). Among the cases, 112 (76.19%) attributed their symptoms to food consumption and identified the suspected food items. The total estimated expenditure attributable to acute gastroenteritis in the Shenzhen community population for 2024 was 1.406 billion RMB, comprising 827 million RMB in direct costs and 579 million RMB in indirect costs. Conclusion Acute gastroenteritis imposes a substantial economic burden on both the community population and society in Shenzhen. Factors such as occupation, annual income, household size, and travel history may be associated with the occurrence of acute gastroenteritis. The suspected exposure history predominantly points towards the consumption of externally purchased food.

Objective To analyze the comorbidity of dental caries and overweight/obesity and its influencing factors among primary and secondary school students in key monitoring counties under the Henan Rural Compulsory Education Student Nutrition Improvement Plan in 2023, so as to provide a reference for promoting the healthy growth of students. Methods Using a stratified random cluster sampling method, primary and secondary school students in the third grade and above were selected as research subjects from four key monitoring counties implementing the "Rural Compulsory Education Student Nutrition Improvement Plan" in Henan Province in 2023. Examinations of their oral health status, height, and weight were conducted, along with a questionnaire survey. The χ² test was used for inter-group comparisons and univariate analysis, and logistic regression was employed for a multivariate analysis of the correlation between dental caries and the comorbidity of overweight/obesity. Results In 2023, a total of 4 291 primary and secondary school students of grade three and above were sampled from key monitoring counties under the Nutrition Improvement Plan in Henan Province, including 2 176 males and 2 115 females, with an average age of (11.96±2.04) years. The prevalence of dental caries was 42.30% (1 815 cases), the detection rate of overweight and obesity was 31.23% (1 340 cases), and the detection rate of the comorbidity of dental caries with overweight and obesity was 11.63% (499 cases). The detection rate of this comorbidity was higher in county towns (13.65%) than in rural areas (10.99%), higher in primary schools (14.91%) than in junior high schools (7.72%), and higher in non-boarding students (14.07%) than in boarding students (8.82%). The rate also increased with the educational level of both the father and mother (all P<0.05). Multivariate logistic regression results indicated that academic stage (junior high school OR=0.498, 95% CI: 0.406-0.609), picky eating behavior (non-picky eating OR=0.772, 95% CI: 0.636-0.935), maternal educational level (junior high school OR=1.649, 95% CI: 1.290-2.131; college and above OR=1.911, 95% CI: 1.288-2.807), and high-frequency consumption of fried foods (≥5 times/week OR=1.616, 95% CI: 1.023-2.462) were influencing factors for the comorbidity of dental caries and overweight/obesity (all P<0.05). Conclusion In 2023, the prevalence of dental caries, overweight/obesity, and their comorbidity were high among primary and secondary school students in the key monitoring counties of the Henan Rural Compulsory Education Student Nutrition Improvement Plan. The family dietary environment and children's eating habits are closely related to the detection of this comorbidity. It is recommended that health education be further strengthened to guide students in developing good living habits and to support the healthy growth of children.

Objective To investigate the epidemiological characteristics and associated risk factors of unintentional injuries among school-aged children and adolescents in the multi-ethnic regions of Yunnan Province, in order to provide a scientific basis for the formulation of effective prevention and control strategies. Methods A stratified random cluster sampling method was employed to conduct an epidemiological survey on unintentional injuries. The study population comprised students aged 8 to 16 years from ethnic minority areas in Yunnan Province, who were administered a self-designed questionnaire. Unconditional binary logistic regression analysis was utilized to identify the determinants of unintentional injuries. Results A total of 2 627 school-aged children and adolescents were recruited from the ethnic minority regions of Yunnan Province. The self-reported incidence rate of unintentional injuries was 71.22% (1 871 cases), with a male-to-female ratio of 1∶0.92. Students who had engaged in physical fighting in the past year (OR=1.71), those who frequently perceived high academic pressure (OR=1.55), those who had experienced persistent feelings of sadness and hopelessness in the past year (OR=1.30), those who frequently felt lonely (OR=1.53), as well as those whose mothers were engaged in non-agricultural occupations (OR=1.27) and left-behind children (OR=1.21) were identified as independent risk factors for unintentional injury among school-aged children and adolescents in ethnic minority areas of Yunnan Province (P<0.05). Conclusion The problem of unintentional injury among school-aged children and adolescents in multi-ethnic regions require urgent attention. The prevention and control of unintentional injuries among children in ethnic areas should recommend to implement health education on unintentional injury prevention, psychological health interventions be concurrently integrated, thereby effectively reducing the risk and burden of unintentional injuries among children and adolescents in ethnic areas.

Objective To investigate the impact of socioeconomic status (SES) on treatment-seeking delay behavior among hospitalized patients with heart failure (HF) and to explore the mediating mechanisms of health literacy, social support, and coping styles, thereby providing an evidence-based foundation for developing targeted intervention strategies. Methods A total of 232 patients diagnosed with HF and admitted to a hospital in Linquan Country between January 2024 and October 2025 were enrolled in this study. Data were collected on patients' SES (a composite index derived from principal component analysis), treatment-seeking delay time (dichotomized based on a median of 36.5 hours), general clinical characteristics, and prognostic outcomes. Health literacy, social support, and coping styles were assessed using the Health Literacy Scale for Chronic Patients (HLSCP), the Social Support Rating Scale (SSRS), and the Medical Coping Modes Questionnaire (MCMQ), respectively. A mediation analysis was conducted using PROCESS model 4, with the SES composite index as the independent variable, treatment-seeking delay as the dependent variable, and health literacy, social support, and coping styles as mediating variables. Results The final analysis included 229 HF patients. The median treatment-seeking delay time was 37.00 hours, with 112 patients (48.9%) classified into the delay group. The SES composite index was significantly lower in the delay group [-0.35 (-1.02, 0.21)] compared to the timely treatment group [0.18 (-0.41, 0.79)] (P<0.01). Multivariate analysis revealed that for each unit increase in the SES composite index, the risk of treatment-seeking delay decreased by 34.4% (OR=0.656, 95% CI: 0.527-0.818). The mediation analysis indicated a total effect of SES on treatment-seeking delay of -0.182, with a direct effect of -0.123 and a total indirect effect of -0.059, accounting for 32.4% of the total effect. Regarding prognosis, the delay group exhibited a longer length of hospital stay and significantly higher rates of 30-day all-cause readmission, HF-related readmission, and mortality compared to the timely treatment group (P<0.05 or P<0.01). Conclusion Lower socioeconomic status is associated with an increased risk of treatment-seeking delay in patients with heart failure. This relationship is both direct and indirect, with the indirect pathway being mediated by health literacy, social support, and a resignated coping style, which collectively account for 32.4% of the total effect. This delay subsequently contributes to prolonged hospitalization, elevated readmission rates, and higher mortality. Clinical practice should prioritize patients with low SES, implementing interventions aimed at enhancing health literacy, strengthening social support, and improving coping strategies to mitigate treatment-seeking delays and improve patient outcomes.

Objective To investigate the characteristics and determinants of electrocardiographic ST-T segment alterations in middle-aged and older adult populations diagnosed with dyslipidemia. Methods Individuals aged ≥45 years who were identified with dyslipidemia during routine community health examinations between January 2022 and December 2025 were enrolled in this study. Electrocardiography (ECG) was performed to ascertain the epidemiological characteristics of dyslipidemia and the incidence rate of ST-T alterations. A multivariate logistic regression model was employed to evaluate the influencing factors of ST-T changes, utilizing sex, age, body mass index (BMI), hypertension, diabetes mellitus, and dyslipidemia subtype as independent variables. Results Among the 1 200 screened individuals, the detection rate of dyslipidemia was 41.00% (492/1 200), which comprised 73 cases of isolated hypercholesterolemia, 88 cases of isolated hypertriglyceridemia, 208 cases of mixed hyperlipidemia, and 123 cases of low high-density lipoprotein cholesterol (HDL-C). Within the cohort of 492 patients with dyslipidemia, ST-T segment alterations were observed in 189 cases (38.41%). Multivariate logistic regression analysis revealed that female sex (OR=2.186), age ≥60 years (OR=2.906), BMI>24.0 kg/m² (OR=6.401), hypertension (OR=2.797), diabetes mellitus (OR=2.250), and mixed hyperlipidemia (OR=19.237) were independent risk factors for ST-T alterations (all P<0.05). Notably, the risk associated with mixed hyperlipidemia was the most pronounced, demonstrating an odds ratio significantly superior to those of low HDL-C, hypertriglyceridemia, and hypercholesterolemia. Conclusion The prevalence of dyslipidemia among community-dwelling middle-aged and older adults remains substantial, with mixed hyperlipidemia emerging as the predominant subtype. Female sex, advanced age, overweight, comorbid hypertension and/or diabetes mellitus, and mixed hyperlipidemia significantly elevate the susceptibility to electrocardiographic ST-T alterations. Clinical practice should prioritize the screening of these high-risk factors and the implementation of targeted interventions to mitigate the potential incidence of adverse cardiovascular events.

Objective To investigate the dose-response relationship between the non-high-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio (NHHR) and the risk of hypertension among middle-aged and older adults in China, utilizing data from the China Health and Retirement Longitudinal Study (CHARLS). Methods A cross-sectional study design was employed. Participants meeting the predetermined inclusion and exclusion criteria were selected from the 2011 CHARLS database and stratified into hypertensive and non-hypertensive cohorts. The NHHR was calculated, and its association with the risk of hypertension was systematically analyzed. Results A total of 9 838 participants were included, of whom 4 350 (44.22%) had hypertension. Significant differences were observed between the two groups in age, smoking, alcohol consumption, physical activity, BMI, waist circumference, and NHHR (all P<0.05). Restricted cubic spline analysis revealed a non-linear curvilinear dose-response relationship between NHHR and hypertension risk. Multivariate logistic regression identified age ≥60 years (OR=1.320), smoking (former OR=1.138, current OR=1.111), alcohol consumption>15 g/day (OR=1.162), insufficient physical activity (OR=1.157), overweight (OR=1.169), obesity (OR=1.249), waist circumference (OR=1.024), and NHHR ≥2.64 (OR=1.733) as independent risk factors for hypertension (all P<0.05).Subgroup analyses showed that NHHR ≥2.64 consistently increased the risk of hypertension across all subgroups (all P<0.05). Significant interactions were found between age and NHHR (P<0.001), as well as between BMI and NHHR (P<0.001), whereas no significant interaction was observed between gender and NHHR. Sensitivity analyses confirmed consistency with the primary findings. Conclusion A non-linear dose-response relationship exists between NHHR and the risk of hypertension among the middle-aged and older Chinese population. This robust association persists across disparate age, sex, and BMI stratifications, indicating that age and BMI may synergistically modulate the pathogenesis and risk profile of hypertension.

Objective To evaluate the cumulative effect of clustered unhealthy lifestyle factors on the risk of readmission for patients with chronic heart failure (CHF) within one year. Methods A prospective cohort was established consisting of 355 CHF patients admitted to the Department of Cardiology at Linquan County People's Hospital between May 2023 and April 2024. Unhealthy lifestyle factors were categorized into five dimensions: diet, physical activity, sleep, emotional status, and smoking/alcohol consumption. Based on these dimensions, a Unhealthy Lifestyle Syndrome Index (ULSI) was constructed, dividing patients into three groups according to the number of unhealthy behaviors: Low (0-1 item), moderate (2-3 items), and high (4-5 items). Patients were followed up for one year to record readmission events. The relationship between ULSI and readmission risk was analyzed using χ² tests, logistic regression, and trend analysis. Results A total of 355 patients were enrolled (13 lost to follow-up), and 63 (17.75%) were rehospitalized within 1 year. The readmission rates among the low, moderate, and high ULSI groups were 9.59% (7/73), 15.15% (30/198), and 30.95% (26/84), respectively, with statistically significant differences (χ²=14.277, P=0.001). Multivariate logistic regression analysis revealed that, after controlling for New York Heart Association (NYHA) functional class and medication adherence, patients in the high ULSI group had a significantly increased risk of readmission compared to those in the low group (OR=2.744, 95% CI: 1.025-7.346, P=0.045), while no significant difference was observed between the moderate group and the low group (OR=1.087, 95% CI: 0.426-2.771, P=0.862). Trend analysis further indicated that each increment in ULSI level was associated with an 81.5% increase in readmission risk(OR=1.815, 95% CI: 1.130-2.918, P=0.014). Conclusion The clustering of unhealthy lifestyle factors independently contributes to the risk of readmission in CHF patients within one year, with higher clustering levels corresponding to greater readmission risks. Multi-dimensional lifestyle assessment and comprehensive intervention should be emphasized in clinical practice.

Objective To investigate the association between the dietary diversity score (DDS) and cardiometabolic multimorbidity (CMM) among middle-aged and older populations in China, utilizing data from the China Health and Retirement Longitudinal Study (CHARLS). Methods A cross-sectional study design was employed using data from the 2020 wave of CHARLS. A total of 8 174 middle-aged and older adults were included and subsequently categorized into a CMM group (n=3 268) and a non-CMM group (n=4 906) based on the presence of cardiometabolic multimorbidity. The association between DDS and CMM was evaluated using multivariable logistic regression, restricted cubic splines (RCS), and urban-rural stratified regression analyses. Results The mean DDS among the 8 174 participants was 8.50 ± 4.56. The cohort was stratified by DDS into low (2 297 individuals, 28.10%), moderate (4 165 individuals, 50.95%), and high (1 712 individuals, 20.94%) dietary diversity categories. Multivariable logistic regression analysis demonstrated that age, sex, educational attainment, lifestyle patterns, physical activity levels, family history of cardiovascular disease, nocturnal sleep duration, and DDS were significantly associated with the prevalence of CMM (all P<0.01). RCS analysis revealed a nonlinear dose-response relationship between DDS and the risk of CMM. Urban-rural stratified analyses indicated that a low DDS was associated with an elevated risk of CMM among rural populations (OR=1.144, 95% CI: 1.014-1.290, P=0.029). Conversely, this association was attenuated in urban populations, where only a high DDS exhibited a marginal protective effect (OR=1.151, 95% CI: 1.003-1.321, P=0.046). Conclusion The dietary diversity score is significantly and nonlinearly associated with cardiometabolic multimorbidity among middle-aged and older adults in China. Furthermore, substantial urban-rural heterogeneity exists in this association, with the risk of CMM being particularly pronounced among rural populations exhibiting low dietary diversity.

Objective To analyze the epidemiological characteristics and forecast the incidence trends of other infectious diarrhea (OID) in the Shapingba District of Chongqing, in order to provide an empirical basis for evidence-based prevention and control strategies. Methods Utilizing OID surveillance data from 2014 to 2023 in Shapingba District, this study employed descriptive epidemiological and spatial autocorrelation methods to characterize the disease patterns. Joinpoint regression analysis was conducted to assess temporal trends. Furthermore, a Seasonal Autoregressive Integrated Moving Average (SARIMA) model and a Back Propagation Neural Network (BPNN) model were developed and compared for forecasting future incidence. Results A cumulative total of 40 377 OID cases were reported in Shapingba District from 2014 to 2023, corresponding to an average annual incidence rate of 331.78 per 100 000 population. The overall reported incidence exhibited an increasing trend from 2014 to 2018 (APC=10.30%, P=0.14), followed by a significant decreasing trend from 2018 to 2023 (APC=-11.88%, P=0.02). The disease displayed a distinct bimodal seasonal distribution, with a primary peak from November to February and a secondary peak from June to August. The average annual reported incidence was significantly higher in males (361.45/100 000) than in females (312.71/100 000) (χ²=6 740, P<0.05). Children under five years of age constituted the most affected population group, and rotavirus was the predominant etiological agent. In a comparative evaluation of predictive models, the BPNN model demonstrated superior performance, with lower MAE and RMSE values than the SARIMA model. The BPNN model forecasts an epidemic peak between November 2024 and January 2025, with projected monthly incidence rates ranging from 26.54 to 31.73 per 100 000 population. Conclusion The epidemiological burden of OID in Shapingba District remains substantial, warranting sustained implementation of surveillance, early warning systems, risk assessment, and health education initiatives. The BPNN model proves to be a more effective tool for forecasting OID incidence compared to the SARIMA model.

Objective To investigate the modifiable risk factors associated with prehospital delay (PHD) among patients with acute ischemic stroke (AIS) and to perform population attributable fraction (PAF) analysis. Methods A retrospective analysis was conducted on 397 AIS patients admitted to the Neurology Department of a tertiary hospital in Fuyang from January 2023 to December 2025. These patients were divided into the PHD group (n=268) and non‑PHD group (n=129). Clinical data were compared, and PAF analysis was performed to assess the proportion of PHD attributable to specific factors. Results The proportions of age ≥65 years, male sex, experience awakenings after stroke onset, fail to call 120, have insufficient stroke knowledge, lack family accompaniment at the time of symptom onset, suffer from stroke during non-working hours, and reside in rural areas were significantly higher in the PHD group than in the non‑PHD group, while the admission NIHSS score was lower in the PHD group (all P<0.05). Multivariate logistic regression showed that failure to call 120 (OR=1.873), insufficient stroke knowledge (OR=2.345), lack of family accompaniment at symptom onset (OR=2.781), stroke occurrence during non-working hours (OR=2.089), and rural residence (OR=2.217) were independent influencing factors for PHD (all P<0.05). The overall PAF for the five modifiable factors was 38.614 (95% CI: 26.410%-51.705%). Based on PAF ranking, the most significant contributors were insufficient stroke knowledge, failure to call 120, lack of family accompaniment, rural residence, and stroke occurrence during non-working hours. Sensitivity analysis, with PHD thresholds adjusted to 3.0 and 6.0 h, revealed no substantial change in the ranking of PAF contributors. Conclusion These five factors are independent modifiable risk factors for PHD among AIS patients. Insufficient stroke knowledge and failure to call 120 were identified as core population-level targets for prevention.

Objective To investigate the characteristics of alcohol consumption among residents aged 18 and over in Guangdong Province, providing a scientific basis for the formulation of relevant intervention measures. Methods Relying on the 2023 China Chronic Disease and Risk Factor Surveillance project, a multi-stage cluster random sampling method was employed to select permanent residents aged ≥18 years from 14 counties and districts in Guangdong Province for a questionnaire survey on drinking behavior. A complex sampling weighting method was utilized to analyze drinking rates, frequency, volume, and hazardous and harmful drinking patterns, thereby exploring the characteristics of alcohol consumption across different demographic groups. Results A total of 8 844 permanent residents aged 18 and above in Guangdong Province were included. In 2023, the 12-month prevalence of alcohol consumption among residents aged ≥18 years in Guangdong Province was 46.3%. The drinking rate was significantly higher in males (61.5%) than in females (29.3%), with the highest prevalence (52.2%) observed in the 18-<45 age group. The rates of hazardous and harmful drinking were 5.7% and 4.5%, respectively. The average daily alcohol intake among drinkers was 12.6 g. Among drinkers, the frequencies of consuming alcohol ≥5 days a week, 1-4 days a week, and <1 day a week were 8.7%, 19.4%, and 71.9%, respectively. Key indicators such as the male drinking rate, hazardous drinking rate, average daily alcohol intake, rate of heavy episodic drinking, and all drinking frequencies other than <1 day a week were significantly higher for males than for females (all P<0.01). Mid-to-high frequency drinking (≥5 and 1-4 days/week) was more prevalent in rural areas, whereas low-frequency drinking (<1 day/week) was more common in urban areas. Although the 60 years and older age group had the lowest overall drinking rate, they exhibited the highest average daily alcohol intake, highest frequency of heavy drinking (≥5 days/week), and the highest rate of harmful drinking among all age groups. Conversely, while the 18-44 age group demonstrated lower drinking frequency and average daily consumption compared to other groups, they reported a higher prevalence of both overall drinking and heavy episodic drinking. Conclusion The prevalence of alcohol consumption among residents aged 18 and over in Guangdong Province remains at a high level, particularly within the male population. To prevent and reduce the incidence of alcohol-related diseases, it is imperative to develop targeted health education and behavioral intervention models that address the distinct drinking habits of urban versus rural residents, as well as those of young to middle-aged adults and the elderly.

Objective To investigate the molecular mechanisms underlying the deletion of the Furin Cleavage Site (FCS) during in vitro culturing of SARS-CoV-2 and to analyze the biological significance of this phenomenon for the virus's origin and evolution. Methods The prototype strain and various mutant strains of SARS-CoV-2 were serially passaged in Vero E6 and 293T-hACE2 cell lines. High-throughput sequencing of multiplex PCR amplicons was employed to dynamically monitor the variation characteristics of the FCS region and its flanking sequences. The association between FCS deletion, the viral entry pathway, and specific genomic loci was analyzed by pharmacologically inhibiting the Transmembrane Serine Protease 2 (TMPRSS2) pathway. Phylogenetic analysis was conducted in conjunction with sequences from global public databases. Results The in vitro serial passage experiments demonstrated that, with the exception of B.1、Alpha, Omicron, and their sublineages, all other tested SARS-CoV-2 evolutionary branches underwent rapid deletion of the FCS sequence. Although direct FCS deletion was not detected after six passages (P6) of plaque-purified B.1 virus in both cell lines, a mixed T/C quasispecies emerged at position 23525 of the spike (S) protein gene, with its mutation frequency increasing with successive passages. Following the blockade of the TMPRSS2-dependent cell surface entry pathway, mutant strains with FCS deletions rapidly appeared and were enriched, becoming the dominant population (reaching an abundance of 57.9%) by P6. Sequence analysis confirmed a strict co-occurrence of the FCS deletion with synergistic T>C mutations at upstream positions 23422 and 23525, indicating that a cytosine (C) genotype at this dual-locus is possibly a prerequisite molecular event for the FCS deletion. Database analysis further revealed that position 23422 is highly conserved in human populations, whereas position 23525 exhibits lineage-specificity: early epidemic strains (e.g., Delta) predominantly carried 23525C and were prone to FCS deletion, while later strains (e.g., Omicron) predominantly featured 23525T with a relatively stable FCS, observations that are highly consistent with the in vitro experimental phenotypes. Conclusion The deletion of the FCS during in vitro replication of SARS-CoV-2 exhibits marked sequence specificity. The concurrent presence of a cytosine (C) genotype at the upstream 23422 and 23525 loci is possibly a critical molecular precondition that induces the deletion in this region. This study elucidates the molecular determinants of FCS stability, providing a significant basis for clarifying the adaptive mechanisms of SARS-CoV-2 in cross-species transmission and its molecular evolutionary patterns.

Objective To develop a machine learning model based on the Adverse Outcome Pathway (AOP) framework, integrating Molecular Initiating Events (MIE) and Adverse Outcomes (AO) , for the efficient prediction of endocrine-disrupting toxicity of chemical ingredients in personal care product. Methods Employing binding affinity to estrogen receptor (ERα, ERβ) and androgen receptor (AR) as the MIEs, molecular features of chemical compounds were extracted. Five machine learning algorithms: Random Forest (RF), Support Vector Machine (SVM), Logistic Regression (LR), Extreme Gradient Boosting (XGBoost), and K-Nearest Neighbors (KNN) were utilized to establish predictive models.. The optimal model was applied to virtually screen 2 267 chemical ingredients found in personal care products. High-risk constituents were selected based on prediction scores, and their estrogenic activity was further authenticated via in vivo assays using transgenic medaka (Oryzias latipes). Results For the ER and AR binding endpoints, the LR and SVM models demonstrated the highest predictive performance, with balanced accuracies of 0.934 7 and 0.831 6, respectively. For the AO endpoint, the RF model exhibited superior performance, with a balanced accuracy of 0.828 5. In vivo experiments revealed that p-hydroxyacetophenone and o-cymen-5-ol exhibited significant estrogenic activity and the capacity to potentiate endogenous estrogen effects. Conclusion The establishment of an integrated framework of ' computational prediction → risk prioritization → experimental validation' enables the effective identification of endocrine-disrupting chemicals in personal care products. This methodology offers a robust and novel strategy for high-throughput safety screening of chemicals.