The epidemiology of enteric infections in agricultural communities exposed to wastewater irrigation: Perspectives for risk control

A cross-sectional survey was carried out in the irrigation districts of central Mexico, in which 9435 individuals participated. The health outcomes included diarrhoeal diseases and Ascaris lumbricoides infection. Water quality was assessed using faecal coliforms (FC) and nematode eggs as indicators of faecal pollution. Exposure groups were: 848 households irrigating with untreated wastewater; 544 households irrigating with the effluent from a series of interconnected reservoirs; and 928 households farming with natural rainfall. Children from households irrigating with untreated wastewater (108 FC/100 mL and 125 nematode eggs/L) had a 33% higher risk of diarrhoeal diseases than children from rainfall villages (OR = 1.33), whereas children from households exposed to the reservoirs effluent were not different from those in the rainfall group (OR = 1.17). No excess risk was found in older individuals from different exposure groups, but males had a 50% higher risk of disease than females (OR = 1.50). In the final analysis, drinking unboiled water and cultivating vegetables crops were associated with a higher risk of disease, both in children and older individuals, (OR = 1.45 and 2.00, respectively). Children from households exposed to untreated wastewater showed a fivefold increase in risk of A. lumbricoides infection (OR = 5.71), when compared to children from rain-farming villages. The observed difference in older individuals was even higher (OR = 13.18). Such risk, however, was substantially reduced in individuals exposed to the reservoirs effluent (OR = 1.29 and 1.94) with no detectable ova. The final analysis showed that most infected individuals came from landless households, poorer dwellings and low standards of sanitation, often purchasing vegetables in local shops (OR = 2.20, 2.23, 1.72 and 1.43, respectively). These results are discussed in the context of health protection measures and policy recommendations.     

Health impact evaluation of wastewater use in Mexico.

Wastewater from Mexico city is used to irrigate over 85 000 hectares, mainly of fodder and cereal crops in the Mezquital Valley. A cross-sectional study method is being used to test the impact of exposure to raw wastewater and wastewater from storage reservoirs on diarrhoeal disease and parasitic infections in farmworkers and their families. The study population in the rainy season survey included 1 900 households: 680 households where the farmworker is exposed to untreated wastewater (exposed group), 520 households exposed to reservoir water (semi exposed group), and 700 households where the farmworker practices rain-fed agriculture (control group). Preliminary analysis of the data from the rainy season study (dry season study in progress) has been carried out. Current information indicates that the risk of Ascaris lumbricoides infection is much higher in the exposed group than in the semi-exposed and the control groups. According to the procedures employed Entamoeba histolytica infection was more frequent in individuals aged 5 to 14 years exposed to wastewater, than in those in the control group. When diarrhoeal disease rates were analyzed, children under age 15 years from exposed households had a significantly higher prevalence than controls. The final results of this study are expected to aid decisions on low cost treatment options and other health protection measures within the National Wastewater Reuse Programme in Mexico. The implications for assessment of the WHO guidelines for the use of wastewater in agriculture are discussed.     

Estimation of norovirus and Ascaris infection risks to urban farmers in developing countries using wastewater for crop irrigation

A quantitative microbial risk analysis—Monte Carlo method was used to estimate norovirus and Ascaris infection risks to urban farmers in developing countries watering their crops with wastewater. For a tolerable additional disease burden of10^-4 DALY loss per person per year (pppy), equivalent to 1 percent of the diarrhoeal disease burden in developing countries, a norovirus reduction of 1–2 log units and an Ascaris egg reduction to 10–100 eggs per litre are required. These are easily achieved by minimal wastewater treatment—for example, a sequential batch-fed three tank/pond system. Hygiene improvement through education and regular deworming are essential complementary inputs to protect the health of urban farmers.     

Guidelines for the microbiological quality of treated wastewater used in agriculture: recommendations for revising WHO guidelines

Three different approaches for establishing guidelines for the microbiological quality of treated wastewater that is reused for agriculture are reviewed. These approaches have different objectives as their outcomes: the absence of faecal indicator organisms in the wastewater, the absence of a measurable excess of cases of enteric disease in the exposed population and a model-generated estimated risk below a defined acceptable risk. If the second approach (using empirical epidemiological studies supplemented by microbiological studies of the transmission of pathogens) is used in conjunction with the third approach (using a model-based quantitative risk assessment for selected pathogens) a powerful tool is produced that aids the development of regulations. This combined approach is more cost-effective than the first approach and adequately protects public health. The guideline limit for faecal coliform bacteria in unrestricted irrigation (< or = 1000 faecal coliform bacteria/ 100 ml) is valid, but for restricted irrigation < or = 10(5) faecal coliform bacteria/100 ml is recommended when adult farmworkers are exposed to spray irrigation. A limit of < or = 10(3) faecal coliform bacteria/100 ml is recommended if flood irrigation is used or children are exposed. The guideline limit for nematode eggs for both types of irrigation is adequate except when conditions favour the survival of nematode eggs and where children are exposed; in these cases it should be reduced from < or = 1 egg/l to < or = 0.1 egg/l.     

Low risk for helminth infection in wastewater-fed rice cultivation in Vietnam

This study was done to assess the risk of helminth infection in association with wastewater-fed rice cultivation in an agricultural setting of Nam Dinh city, Vietnam. In a cross sectional survey data were collected for 202 households in a commune where wastewater was used for irrigation and for 201 households in a commune that used river water. Parasitological examination was conducted on single stool samples obtained from 1,088 individuals aged -15 years from the households. The irrigation water used in both communes was enumerated for helminth eggs and thermotolerant coliforms. The prevalence of infection with Ascaris spp., Trichuris spp., and hookworm was 42.2%, 19.9% and 10.5% respectively, with an overall prevalence of infection with any helminth of 53.4%. Surprisingly, the prevalence of infection with Ascaris and Trichuris was lower among people exposed to wastewater (containing 40-200 helminth eggs/l and 10(4) thermotolerant coliforms/100 ml) compared to people exposed to river water that contained lower worm egg and bacterial numbers. Poor sanitation and hygiene practices and not using protective measures were important independent risk factors for helminth infection. For hookworm infection, no significant difference was observed between the wastewater exposed and unexposed groups. Children living in the wastewater use area had a significantly better nutritional status than those in the area using river water. This suggests a generally higher welfare level of the wastewater use area. In conclusion, this study showed no evidence that rice cultivation with wastewater poses a risk for helminth infection. More detailed studies are needed on the reduction of fecal indicators and helminth eggs in peri-urban wastewater-irrigated rice culture systems and on the relative importance of wastewater irrigation compared to other risk factors for human helminth infection such as poor sanitation and poverty.     

Recent epidemiological studies to test microbiological quality guidelines for wastewater use in agriculture and aquaculture.

BACKGROUND: New guidelines for wastewater reuse (WHO 1989) are controversial. Epidemiological studies are needed to test their validity. Cross-sectional studies of the impact of excreta use in aquaculture in Indonesia, and of wastewater use in irrigation in Mexico have been carried out. METHODS: Each study involved an exposed group using wastewater/excreta with no treatment, a control group with no wastes use, and an intermediate group, where wastewater/excreta was used but some health protection measure existed. In Mexico, the intermediate group used wastewater from a storage reservoir which met the new WHO guideline for restricted irrigation. In Indonesia, the intermediate group did not have domestic exposure to pondwater, whose quality was around forty times higher than the tentative WHO bacterial guideline for fishpond water. RESULTS: In Indonesia, the prevalence of diarrhoeal disease was low in adults, and unrelated to exposure, but high in children under 5 years. Multiple logistic regression analysis gave odds ratios of 1.4 (p = .06) for consumer exposure, 1.9 (p = .01) for recreational or occupational exposure and 1.6 (p = .01) for domestic exposure, when allowance was made for all other exposures and several confounding factors. In Mexico, preliminary analysis of the wet season data suggests that the increased risks of Ascaris infection and diarrhoeal disease from the use of raw wastewater are removed when water of WHO guideline quality from storage reservoirs is used. CONCLUSION: WHO (1989) guidelines can be tested using cross-sectional epidemiological studies which indicate that guidelines for restricted irrigation and for aquaculture may be around the right level.     

Estimation of Ascaris infection risks in children under 15 from the consumption of wastewater-irrigated carrots

Ascaris lumbricoides, the large human roundworm, infects ~1,200 million people, with children under the age of 15 being particularly at risk. Monte Carlo quantitative microbial risk analyses were undertaken to estimate median Ascaris infection risks in children under 15 from eating raw carrots irrigated with wastewater. For a tolerable additional disease burden of 10^-5 DALY (disability-adjusted life year) loss per person per year (pppy), the tolerable Ascaris infection risk is ~10^-3 pppy, which can be achieved in hyperendemic areas by a 4-log unit Ascaris reduction. This reduction can be easily achieved by wastewater treatment in a 1-day anaerobic pond and 5-day facultative pond (2 log units) and peeling prior to consumption (2 log units).     

Intestinal parasitism and Vibrio cholerae infection among diarrhoeal patients in Kolkata, India

In this study, we have analysed the epidemiological significance of the concurrent infections caused by Vibrio cholerae and intestinal parasites among different age groups of hospitalized diarrhoeal patients in Kolkata. A total of 3556 stool samples collected during 1996-2004 were screened for vibrios and parasites. The seasonality of V. cholerae and parasitic infections were studied in detail. The detection rates for Ascaris lumbricoides and Giardia lamblia infection were more than for the hookworm, Trichuris trichiura and Entamoeba histolytica. V. cholerae O1 was identified as the predominant serogroup among diarrhoeal patients. The highest rates for V. cholerae infection were in the 2-5 years age group and combined infection of V. cholerae and parasites was recorded among children aged between 2 and 10 years.     

Assessment of microbiological water quality and its relation to human health in Gaza Governorate, Gaza Strip

OBJECTIVE: To assess the contamination level of total and faecal coliforms in water wells and distribution networks, and their association with human health in Gaza Governorate, Gaza Strip. METHODS: Data were obtained from the Palestinian Ministry of Health on contamination of total and faecal coliforms in water wells and distribution networks, and on the incidence of water-related diseases in Gaza Governorate. An interview questionnaire was conducted with 150 residents of Gaza. RESULTS: The contamination level of total and faecal coliforms exceeded that of the World Health Organization (WHO) limit for water wells and networks. However, the contamination percentages in networks were higher than that in wells. Giardiasis was strongly correlated with faecal coliform contamination in water networks (r=0.7) compared with diarrhoeal diseases and hepatitis A (r=0.3 and 0.1, respectively). Diarrhoeal diseases were the highest self-reported diseases among interviewees in Gaza city. Such diseases were more prevalent among people using municipal water than people using desalinated water and water filtered at home for drinking (OR=1.6). Intermittent water supply and sewage flooding seemed to contribute largely to self-reported diseases. People in Gaza Strip have good knowledge on drinking water contamination, and this is reflected in good practice. CONCLUSIONS: Water quality has deteriorated in Gaza Strip. This may contribute to the prevalence of water-related diseases. Self-reported diseases among interviewees in Gaza City were associated with source of drinking water, intermittent water supply, sewage flooding and age of water, and wastewater networks.     

Risk factors for Fasciola hepatica infection in children: a case-control study

We conducted a case-control study to clarify the risk factors for human fascioliasis in the Northern Peruvian Altiplano. Cases (n=61) were individuals who were diagnosed as having chronic fascioliasis by faecal and/or serologic (Fas2-ELISA) studies. Controls (n=61) had negative serologic and coprological results for Fasciola hepatica. We identified an association between fascioliasis and four variables (40 analysed): the habit of drinking alfalfa juice (OR=4.5; 95% CI 1.8-11.1; P<0.001); familiarity with aquatic plants (OR=4.3; 95% CI 1.8-10.6; P<0.001); dog ownership (OR=5; 95% CI 1.7-15.1; P=0.002); and raising more than five sheep (OR=0.3; 95% CI 0.1-0.8; P=0.01). According to clinical presentation and laboratory studies, dizzy spells (P=0.01), history of jaundice (P=0.01), peripheral eosinophilia (P=0.005) and Ascaris lumbricoides in stools (P=0.001) were associated with fascioliasis. The principal exposure factor for F. hepatica infection was drinking alfalfa juice. In conclusion, we suggest that human fascioliasis in Peru should be suspected in patients from livestock-rearing areas, who present with recurrent episodes of jaundice and who have a history of consumption of alfalfa juice or aquatic plants, or who have eosinophilia.     

Bacterial indicators of risk of diarrhoeal disease from drinking-water in the Philippines

Inadequate measures of water quality have been used in many studies of the health effects associated with water supplies in developing countries. The present 1-year epidemiological-microbiological study evaluated four bacterial indicators of tropical drinking-water quality (faecal coliforms, Escherichia coli, enterococci and faecal streptococci) and their relationship to the prevalence of diarrhoeal disease in a population of 690 under-2-year-olds in Cebu, Philippines. E. coli and enterococci were better predictors than faecal coliforms of the risk of waterborne diarrhoeal disease. Methods to enumerate E. coli and enterococci were less subject to interference from the thermotolerant, non-faecal organisms that are indigenous to tropical waters. Little difference was observed between the illness rates of children drinking good quality water (less than 1 E. coli per 100 ml) and those drinking moderately contaminated water (2-100 E. coli per 100 ml). Children drinking water with greater than 1000 E. coli per 100 ml had significantly higher rates of diarrhoeal disease than those drinking less contaminated water. This threshold effect suggests that in developing countries where the quality of drinking-water is good or moderate other transmission routes of diarrhoeal disease may be more important; however, grossly contaminated water is a major source of exposure to faecal contamination and diarrhoeal pathogens.     

Quantitative variability of nematode egg counts in faeces: a study among rural Kenyans

As part of an investigation of intestinal parasitic infections of rural Kenyan people, a study was undertaken to examine variation in faecal egg counts and to assess the sensitivity of the ether sedimentation technique of faecal processing in the diagnosis of helminth infections. Three faecal samples a day were collected for five consecutive days from 10 men known to harbour a total of 23 nematode infections of Ascaris lumbricoides, Trichuris trichiura and hookworm. Considerable variation in egg counts was encountered among faecal samples collected from the same stool, as well as over the five day period. Some possible causes of this variation are discussed, especially in relation to a high fibre diet. The technique was found to be about 95% effective in detecting an infection.     

Prevalence of intestinal parasites in young Quichua children in the highlands of rural Ecuador

The prevalence of intestinal parasites in young Quichua children was assessed in 20 rural communities in the highlands of Ecuador in August 2005. The caregivers of 293 children aged 12-60 months were interviewed about the status of child health, household socioeconomic and environmental factors, and water-use practices and were requested to collect a faecal sample from the study child. Two hundred three (69.3%) of the 293 children provided faecal samples that were tested for parasites. The overall prevalences of infection for specific agents were Entamoeba histolytica or dispar 57.1%, Ascaris lumbricoides 35.5%, Entamoeba coli 34.0%, Giardia intestinalis (lamblia) 21.1%, Hymenolepis nana 11.3%, Cryptosporidium parvum 8.9%, Chilomastix mesnili 1.7%, Hymenolepis diminuta 1.0%, Strongyloides stercoralis 0.7%, and Trichuris trichiura 0.5%. The prevalence of parasites increased with age. Water storage, water treatment, consistent latrine-use, and participation in a community-based clean water project were not strongly associated with the prevalence of intestinal parasites, although having dirt floors was a risk factor for infection with E. histolytica or dispar and G. intestinalis.     

Application of Helminth ova infection dose curve to estimate the risks associated with biosolid application on soil

Helminth ova (HO) are the main biological concern when reusing sludge for agricultural production. Worldwide sludge regulations consider a permissible range of 0.25-1 HO/gTS. Such limits are unaffordable to most developing countries, due to high helminth ova content in sludge, and the lack of viable technology to inactivate them as needed. The quantitative microbial risk assessment (QMRA) is a useful tool to estimate the risk of treated sludge, considering feasible and viable limits. QMRA, however, has not been applied before for HO because no dose-infection curve was available. Therefore, the objectives of this paper are: to build up a risk-based model designed for untreated wastewater exposure (i.e., land irrigation) using Ascaris lumbricoides eggs as indicators for HO, and apply the results to assess health risk (i.e., Ascaris lumbricoides infection) associated with consumption of crops grown on biosolid-enriched soil. Data showed that it may be feasible to update HO threshold in biosolids from developing countries without significantly increasing risks. To reduce health risk from HO, it may be wiser to achieve feasible and evidence-based standards, than to set unaffordable limits in these countries. QMRA data suggested additional protection measures, such as biosolid application rates, crop restriction, and produce better washing practices.     

Application of Helminth ova infection dose curve to estimate the risks associated with biosolid application on soil

Helminth ova (HO) are the main biological concern when reusing sludge for agricultural production. Worldwide sludge regulations consider a permissible range of 0.25–1 HO/gTS. Such limits are unaffordable to most developing countries, due to high helminth ova content in sludge, and the lack of viable technology to inactivate them as needed. The quantitative microbial risk assessment (QMRA) is a useful tool to estimate the risk of treated sludge, considering feasible and viable limits. QMRA, however, has not been applied before for HO because no dose-infection curve was available. Therefore, the objectives of this paper are: to build up a risk-based model designed for untreated wastewater exposure (i.e., land irrigation) using Ascaris lumbricoides eggs as indicators for HO, and apply the results to assess health risk (i.e., Ascaris lumbricoides infection) associated with consumption of crops grown on biosolid-enriched soil. Data showed that it may be feasible to update HO threshold in biosolids from developing countries without significantly increasing risks. To reduce health risk from HO, it may be wiser to achieve feasible and evidence-based standards, than to set unaffordable limits in these countries. QMRA data suggested additional protection measures, such as biosolid application rates, crop restriction, and produce better washing practices.     

High risk of hookworm infection among wastewater farmers in Pakistan

The health risks of wastewater use in agriculture were investigated in the city of Faisalabad, Pakistan, by means of a cross-sectional study. The study showed an increased risk of intestinal nematode infection and hookworm infection, in particular, in wastewater farmers (OR = 31.4, 95% CI 4.1-243) and their children (OR = 5.7, 95% CI 2.1-16) when compared with farming households using regular (non-wastewater) irrigation water. Textile labourers living in the same village as the wastewater farmers showed a lower risk of hookworm infection than wastewater farmers but an increased risk compared with farming households using regular irrigation water. Many urban and peri-urban farmers make a living by using untreated wastewater in the production of fresh produce for the urban market. Banning the use of untreated wastewater would deprive these farmers of their livelihood and affect food supply for the urban population. If treatment of wastewater is not a feasible option, the promotion of footwear and improved hygiene, the construction of toilets, in combination with regular anthelminthic treatment, would be suitable alternatives to safeguard the health of wastewater farmers and their children.     

学龄儿童生长发育迟缓及其与土源性线虫感染的关系

【目的】 了解学龄儿童生长发育迟缓现状及其相关影响因素。 【方法】 在广西、海南两地农村地区,对3个乡15个学校的1 031名9~12岁儿童生长发育进行现况调查,调查内容包括:填写问卷、病原学检测、体格测量以及实验室检测等。问卷涉及儿童、家长及家庭经济状况等信息。病原学粪便检测采用Kato-Katz涂片法一送三检查三种主要土源性线虫 (钩虫、蛔虫和鞭虫) 虫卵并感染度分级为轻、中、重度感染。测量儿童身高体重并采用WHO标准计算年龄别身高(Height-for-age, HA)的Z评分值,作为评定儿童生长发育迟缓的指标。检测血红蛋白评价儿童是否贫血。使用EpiData3.0软件建立数据库,SPSS16.0软件进行统计分析。 【结果】 儿童生长发育迟缓(HAZ<2)264人,占25.6%。生长发育迟缓的危险因素:1)中重度土源性线虫感染(OR=1.927,95%CI:1.194~3.110);2)贫血(OR=3.26,95%CI:2.02~5.27),母亲的文化程度(OR=2.13,95%CI:1.39~3.25)。土源性线虫感染378例,感染率为36.7%;中、重度感染173例,感染率为16.8%。单纯蛔虫、钩虫和鞭虫感染的感染率为11.2%(115/1 031)、11.5%(119/1 031)和4.9%(51/1 031),混合感染的感染率为9.1%(93/1 031)。贫血(Hb<120 g/L)135人,患病率为13.1%。 【结论】 生长发育迟缓在研究地区患病率高,且土源性线虫感染,尤其是中重度感染是生长发育迟缓的重要危险因素。     

Assessment of the health hazards associated with wastewater reuse: transmission of geohelminthic infections (Marrakech, Morocco)

To address the problem of water scarcity, wastewater has long been used for agricultural purposes in Marrakech (Morocco) and its benefits have long been recognized. However, the benefits of urban wastewater reuse may be limited by its potential health hazards associated essentially to the danger of transmission of pathogenic organisms to human beings. The current study aimed to evaluate the risks associated with raw wastewater reuse for agricultural purposes, and the incidence of geohelminthic infections among the children of the wastewater spreading area of Marrakech as compared to a control group. Faecal samples from 610 individuals were examined for Ascaris spp. ova and Trichuris spp. ova (323 children for the exposed group and 287 for the control group). The study duration was two months and a half, and was carried out in the summer period. A questionnaire-interview with children and parents was used to collect data on possible demographic, hygiene and behavioural-contact factors such as gender, age, family size, source of water supply, parental occupation. The investigations resulted in the detection of Ascaris spp. ova in 43 samples indicating a point-prevalence of 13.3% in the exposed group versus 1.7% for the control group. Trichuris spp. ova was detected in 43 faecal samples indicating a point-prevalence of 13.3% in the exposed group, and 3.8% in the control group. The Chi-square test showed that the differences observed between the exposed and control group are statistically significant (p < 0.01). Males are more infected with ascariasis and trichuriasis than females and children of 2-8 years of age are heavily infected as compared to 9 - 14-year-old children. Based upon the findings of this study, it is concluded that wastewater reuse for agricultural purposes presents an increased risk of infection in the exposed group.     

Evaluation of the efficacy of pyrantel-oxantel for the treatment of soil-transmitted nematode infections

A randomized controlled trial comparing the efficacy of pyrantel-oxantel (10 mg/kg) with mebendazole (500 mg) was performed on 1329 schoolchildren aged 6-9 years on Pemba Island in September-October 2000 to evaluate alternative single-dose drugs for regular treatment of intestinal nematode infections. Both mebendazole and pyrantel-oxantel were very effective in eliminating Ascaris lumbricoides infection, inducing cure rates of more than 96% and reducing the mean egg counts by more than 95%. Both drugs had a moderate efficacy against Trichuris trichiura infection, but pyrantel-oxantel had a higher cure rate (31.5% vs. 23.3%, P < 0.01), though the reductions in egg counts did not differ significantly and were more than 80%. Pyrantel-oxantel and mebendazole had a similar, poor efficacy in curing hookworm infections and had a moderate effect in reducing the egg counts by 67% and 68%, respectively. Pyrantel-oxantel (10 mg/kg) offers a valuable alternative to mebendazole as a single-dose treatment for the control of intestinal nematode infections in children in endemic areas of sub-Saharan Africa, due to its comparable efficacy, its low cost and its suitability for use in young children.     

The impact of intestinal parasitic infections on the nutritional status of primary school children in Alexandria, Egypt

In order to investigate the relationship between intestinal parasitism and nutritional status, stool specimens obtained from 1674 school children aged 6-13 years, enrolled in primary governmental schools in the Eastern zone of Alexandria, Egypt were examined for helminth and protozoan parasites. The findings were collated with anthropometric data (weight and height) on the same children. The prevalence of parasitic infections was found to be 31.5%. The most common infections were found to be with Giardia lamblia (15.4%) and Ascaris lumbricoides (10.2%). Children infected with both helminths and protozoa showed an increased but insignificant risk of underweight relative to those without infections. The risk of stunting was found among all types of parasites as compared to children with no parasites. Also there was a higher non significant risk of wasting among those with protozoal infection especially Giardia lamblia. Children infected with three species or more of intestinal parasitic infections were significantly underweight than non infected children (OR = 4.68, 95% confidence limit = 1.04-18.03). Using stepwise logistic regression analysis, number of parasites appeared to be the most effective variable of the nutritional status of children indicated by weight for age Z score, followed by education of the mother.