Water, trachoma and conjunctivitis.

Water, trachoma and conjunctivitis A. Prost1 & A.D. NegreJ2 The incidence of eye infections in a community is generally accepted as an indicator of the adequacy of water supply for their needs. However, discrepancies in the published results from various studies seem to challenge this view. We have reanalysed the published data on trachoma in relation to the most rele- vant indicators of water accessibility, using prevalence ratios as the single parameter for risk assessment. A definite trend emerges from this review: the incidence of infectious conjunctivitis is not sensitive to differences in water accessibility; on the other hand, a reduction in the risk of trachoma is consistently associated with better access to water. This conclusion may support the efforts of WHO and other multi- lateral and bilateral agencies to sustain the commitment towards the water supply sector beyond the International Drinking Water Supply and Sanitation Decade. Conjunctivitis and trachoma, two of the most common eye infections, appear to spread more easily if the quantity of water available for personal hygiene is limited. Most textbooks endorse the assumption made in East Africa by White et al. (24) that improvements resulting in sufficient quantities of water for individual use can reduce the incidence of trachoma by 60% and of other types of conjuncti- vitis by 70%. Very few studies, however, have report- ed on this impact of water availability and none has investigated the changes in the incidence of tra- choma induced by an improvement in water supply. This paper reviews the published data and conclu- sions concerning trachoma and also briefly discusses acute conjunctivitis, about which information is scarce because it is not a blinding condition. Trachoma and climate The geographical approach It is commonly stated in the epidemiological liter- ature (6) that the frequency of trachoma is greater in the drier parts of affected countries (e.g., India, South Africa, Australia and China, which have a variety of climatic zones). Observations in northern Africa suggest that the prevalence and the intensity of tra- choma increase with the distance from the sea. Thus, globally trachoma is associated with arid and dusty areas, and generally with a scarcity of water. However, trachoma has existed and still exists in many areas with different climatic conditions and was prevalent in most European countries up to this century. A special trachoma clinic used to be held in Amsterdam till 1940, and in Finland up to 1949. 1 Division of Environmental Health, World Health Organization, 1211 Geneva 27, Switzerland. Requests for reprints should be sent to this address. 2 Programme for the Prevention of Blindness, World Health Organization, Geneva, Switzerland. Trachoma is also present in the humid tropics, espe- cially in Africa and in the Pacific Islands. Mann (12) reported severe trachoma from the hot, humid, equa- torial islands of the Bismarck archipelago in New Guinea, and also prevalence rates as high as 46% in mainland Papua. The National Trachoma and Eye Health Program in Australia (16) has tested the association of trachoma with six climatic variables: humidity, rainfall, latitude, ultra-violet radiation, evaporation rate, and sunshine hours. Prevalence rates of follicu- lar trachoma are strongly related to humidity, evaporation, sunshine hours, and less strongly to latitude, UV radiation and rainfall. Increasing preva- lence is associated with climatic changes towards the brighter and more arid, from cool and moist to hot and dry. Detailed analysis indicates that the main determinant is the evaporation rate. Humidity and rainfall have less but significant force. Latitude has no significant role. These findings explain the current geographical distribution of trachoma and its association with arid areas. However, aridity is only the main environmental factor in the transmission of the disease. Lack of hygiene, low economic status, crowd- ing, density of contacts, presence of flies, and behavioural attitudes are key epidemiological deter- minants. Their interactions, for example, would explain observations in Africa, the Middle East, and Australia, that nomadic groups have less severe lesions than settled populations, despite the greater availability of water in the latter. In Western Aus- tralia (12), the aborigines who have settled in Kim- berley have the most severe form of the disease whereas nomadic aborigines in the same region, who have a very limited access to water sources and who never wash, tend to have a very mild trachoma. Similar observations have been reported from Saudi Arabia (3). 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N6grel Trachoma and domestic water Methodological lIues Although many reports assert that the provision of water supply has been instrumental in the control of trachoma, the published literature does not docu- ment precisely the effect of such intervention nor does it assess the magnitude of the contribution of the water component to the end result. Yet, in 1896, long before the agent of trachoma could be identified, Stephenson (19) in the USA noted that "epidemic ophthalmia had been shown to be often spread by imperfect washing arrangements". Much later, Bisley (2) reported from the northern frontier district of Kenya a 100% prevalence of tra- choma in children except in a small primary board- ing school where only 30% of the children were suffering from a mild degree of the disease. The striking difference was attributed to the school rule that every pupil should have his face washed in a nearby permanent stream every day before school inspection. However, very few authors have focused on environmental and social factors in eye diseases. Most papers acknowledge their role but seldom establish a relationship between detailed epidemio- logical observations and selected environmental determinants, among which water availability can be a qualitative (presence/absence) or a quantitative one. Two types of studies are available: intervention studies, in which the same population is examined before and after changes have been introduced in the water sector; and comparison studies using different populations which are presumed to be comparable except for their access to water. Intervention studies provide better clues since they are exempted from most of the biases and from many of the con- founding factors which affect comparison studies of the cross-sectional type. Unfortunately, intervention studies of an accept- able quality are rare. The introduction of hygiene practices in an Australian school (8) seems to be the only reliable one. A minimum of scrutiny is sufficient to discard all other studies in this category. Among them is the quotation, widespread in the literature, that in Barabanki, Uttar Pradesh, India, "trachoma morbidity dropped 90 percent following introduction of a piped water supply in 1965"; the original data indicate that the prevalence of trachoma was as low as 3.3 per thousand population even before the inter- vention, and that the above conclusion derived from a few single cases has no significance (26). A similar analysis calls for the rejection of another quotation that "an increase in the availability of water and the increased convenience of a piped supply failed to materially affect the prevalence of trachoma among American Indians living in Blackwater, Arizona"; the data indicate that in 1963, one year after each house had been provided with at least one tap deliv- ering safe water, the trachoma situation in the com- munity was more or less similar to that in 1928 (7). However, a sound comparison after 35 years does not seem possible. In both cases, the quotations made in the literature in support of either theory are interpretations which go far beyond the conclusions drawn by the authors themselves. The material for assessing the impact of water supply on trachoma consists almost exclusively (all but one) of comparison studies. Following an exten- sive literature search and a critical review of published information, fifteen studies (summarized in Table 1) met the following criteria: precise definition of the population sample; clear indicators for water supply, often allowing an analysis of quantitative relationships; and trachoma diagnosed by specialists. As regards the epidemiological interpretation of the results, no study was exempt from bias and often the validity of the conclusions could be questioned because of, for example, huge differences in the size of the clusters to be compared (323 and 58 480, or 50 and 2096) (13, 18), or in the age distribution within the clusters (18) or of cross-sectional surveys carried out in different places at different dates (13), lack of cross-checking for observer's variations (8), limited accuracy of the diagnosis of early stages of trachoma (4), and uncertainties concerning water utilization (18).a In all the studies, the main confounding factor was the impossibility to isolate water usage and water availability from other variables associated with income and welfare, those benefiting from greater availability of water tending to enjoy better housing conditions, higher incomes, a socially higher occupation for the head of the household, a higher level of education, and to exhibit better hygiene practices. For these reasons, the present review does not attempt to apportion a share of the benefits to the presence of water in the household environment; and because of differences in the design of the studies which make comparisons difficult, it only attempts to determine for each study the trends in trachoma endemicity in relation to the availability of water for domestic use of the different population subgroups. The use of a single parameter, whenever pos- sible, makes comparisons easier. In this review, the ratio of the prevalences of trachoma in population groups exposed to different conditions for water a Delon, P.J. Epidemiology and mass treatment of communicable eye diseases in Indonesia (unpublished document, WHO/SEARO/ TRACH/5, 1958). 12 Water, trachoma and conjunctivitis Table 2: Prevalence ratios of trachoma cases from various studies, according to five different Indicators Nature of Prevalence ratio Country trachoma lesions (risk estimate) Definition of exposure variables 1. Distance from water sources India (14)' All stages China (1) Active cases Malawi (23) Morocco (9) Morocco (9) Tunisia (15): village 1 Tunisia (15): village 2 Inflammatory cases (age <6 years) Active cases Grave cases Scarring lesions Scarring lesions 1.4 1.2 1.3 1.4 1.5 1.2 1.4 1.7 1.07 1.14 1.0 3.6 2.1 2. Ouantity of water (per capita daily consumption) Mozambique (4) Stages II-IV Morocco (9) Active cases (all ages) Morocco (9) Morocco (9) 3. Water quality Indonesiac China (1) Malawi (23) Active cases (<15 years) Grave cases (>15 years) 3.2 1.1 1.2 1.2 1.0 1.1 1.1 1.1 1.2 1.3 All cases Active cases Inflammatory cases (age <6 years) 1.05 1.03 1.5 1.2 1.3 Distance >200 m vs <200 Mb Distant source vs home connection Distance >200 m vs <200 m Distance >500 m vs <500 m Distance >500 m vs home connection Distance covered in >5 min vs <5 min Distance covered in >30 min vs <5 min Distance covered in >60 min vs <5 min Distance >500 m vs <500 m Distance > 1500 m vs < 1500 m Two definitions (>500 m and >1500 m) Distant source vs home supply Distant source vs home supply Average 8 litres vs 14 litres < 5 1 vs > 51 daily <10 vs >10 1 < 51 vs >10 < 5 1 vs > 5 1 daily <10 vs >10 1 < 5 I vs >10 < 5 1 vs > 5 1 daily <10 1 vs >10 < 5 I vs >10 1 Households using wells vs piped water Households using canals vs piped water In-house supply from draw-well vs tap Supply from unprotected wells vs boreholes Supply from unprotected wells vs river Australia (21) Japan (13) All stages All stages (age 0-10 years) All stages (age 0-10 years) Inflammatory cases (age <6 years) Follicular Cicatricial Follicular Follicular Follicular Active cases (age 0-11 years) Active cases (age 0-21 years) All cases 2.2 1.8 2.0 1.06 11.5 8.2 8.5 12.8 10.8 3.1 2.9 5.9 12.5 Less than 1 bath daily vs daily bath Face washing <7 times a week vs >7 times Face washing <7 times a week vs >7 times Face washing < once/day vs 2 times Aborigines in the lowest water access grade vs the best Aborigines in the lowest water access grade vs the best Aborigines in the lowest category for waste disposal vs the best Aborigines in the lowest category for sewerage vs the best Aborigines in the lowest category for housing vs the best Aborigines in zone I vs zone Ilid Aborigines in zone vs zone lid Urban schoolchildren with limited water supply vs home pipe connection Rural schoolchildren with limited water supply vs home pipe connection a Figures in parentheses are the references to the studies concerned. b Actually 200 yards. c See footnote a, page 12. d See Table 1. 4. Personal hygiene Sudan (11) Mexico (20): Naranja Mexico (20): Chaonil Malawi (23) 5. Living standards Australia (16) 13 A. Prost & A.D. N6grel accessibility has been calculated from the original published data (Table 2). In many studies, the exami- nation for trachoma of population samples chosen on the basis of water indicators would allow for the determination of the relative risk associated with the relevant exposure. However, the estimation of the relative risk should be based on the incidence, whereas the available surveys report on prevalence rates. Thus, prevalence ratios have been preferred to relative risk estimates and to odds ratios for method- ological reasons. For the same reasons, confidence limits could not be calculated. Results and comments Four indicators are related to water accessibility: the distance between individual households and the source of water, the average quantity of water used per person daily, the quality of the water, and hygiene practices related to water (bathing, face washing). The prevalences of trachoma were com- pared in population groups with various degrees of exposure as measured by these indicators. In some cases, the influence of each indicator could not be separated from the overall social and economic con- ditions (13, 16), and the results are presented under the heading of living standards. Table 2 provides prevalence ratios of trachoma in countries with various exposure conditions. Distance. There is a clear advantage in having a water source at home compared with a distant source. The study in Tunisia did not estimate the distance between the water source and the house- holds with no pipe connection, but showed a striking difference in the prevalence of scarring lesions. A dis- tance of more than 500 m in China (Province of Taiwan) and any walking distance in excess of 30 minutes in Malawi seem to be serious risk factors for trachoma. Data also show that the further the water source, the higher the risk of trachoma. Ratios are not comparable for similar distances in different countries; a distance of 200 m seems to carry a greater risk in India than in Taiwan or Morocco. However, in any given situation the frequency of tra- choma rises with increasing distance from the water source. Longer distances are also associated with infec- tion at younger ages. In China, the peak prevalence of active cases was observed in the 10-14-year age group in families using a water source at a distance of 100 m or more; the peak prevalence occurred in the 15-19-year group in families where the water source was less than 100 m. In Tunisia, the intensity was greater in children under 5 years and com- plications occurred more frequently in the 6-14-year age group in households which had no pipe connec- tion. It is likely that an increased consumption of water, especially for personal hygiene, is the factor limiting the transmission of trachoma. It appears that when the water source is far away, there may be only a single collection of water per day whereas several trips are likely when the source is closer. However, several studies in our series have failed to demonstrate a relationship between distance and daily consumption (9). When water is a limited commodity, mothers may value it too much to use it liberally for hygiene, especially in children. This attitude may persist even though water is provided in sufficient quantities in the vicin- ity of households, thus reducing the expected impact of water intervention studies. An investigation into this complex relationship in rural Africa (28) has shown that water consumption tends to increase when the journey time decreases. However, a plateau is reached when the distance to the water source is covered in less than 30 minutes, which is equivalent to a maximum of about one kilometre. Only when water is supplied in the household does consumption increase further, but then it rises by a factor of three or more. Quantity. Here the evidence for an impact is not so clear. The differences in water consumption do not induce dramatic changes in the prevalence of tra- choma, but the prevalence ratio is consistently greater than unity when the effect of low consump- tion levels is compared to high levels. In addition, the authors of the Moroccan study concluded that a higher prevalence of severe cases was associated with the lowest water consumption in all age groups (9). The data from Mozambique (4) also should not be regarded as conclusive as there was no homo- geneity in the samples; the per capita consumption was an average value for the village, including the whole range of consumption patterns. In addition, late stages of trachoma, which could have resulted from infections acquired before the test village was supplied with a new water system 18 months before the survey, were included in the study and may have distorted the conclusions. A most interesting finding of the study is that the water utilization for children's hygiene was most sensitive to changes in the per capita daily availability of water; when the water collection journey time was reduced from five hours to 15 minutes, the total per capita daily consumption of water increased four times, out of which the amount used for bathing children increased 30 times. Quality. Results from Indonesia and Mexico indicate that the quality of water had no effect on the preva- lence of trachoma. The higher risk in China 14 Water, trachoma and conjunctivitIs (Province of Taiwan) and to a lesser extent in Malawi, associated with the use of wells, would require additional supporting evidence that it was independent of the effect of quantity. Hygiene. There is no doubt that bathing, among other individual hygiene practices, plays a significant role in reducing the incidence of trachoma. Bisley (2) suggested in Kenya that daily face washing could reduce both prevalence and intensity in children. Results from Mexico show that this impact was associated with face washing and not with washing of other parts of the body, and that daily washing was necessary to manifest an impact on trachoma. In Australia (8), the daily bath of schoolchildren also showed a significant improvement in trachoma assessed by the examination of conjunctival smears. In the Mozambique study (4), it is not possible to determine the prevalence of trachoma associated with different bathing frequencies, but the prevalence of trachoma in the village where only one third of the children had a daily bath was two times higher than that in the village where all the children had a daily bath. On the other hand, the Malawi study failed to demonstrate a significant impact from face washing. Living andards. Water, as one element in an overall welfare situation, is not a discriminant factor for tra- choma. Sewerage, housing, and waste disposal seem equally important; income, education, and occupation of the head of the household lead to similar results. In these studies, access to large quan- tities of water, or even unlimited access to water, is linked to the improvement of a whole set of socio- economic conditions, all of which contribute to a reduction in the transmission of trachoma. Similar observations in India (14) showed a regular decline in trachoma associated with rising household per capita income. However, the same study indicated that the impact of the distance to the water source on trachoma persisted when the results were con- trolled for income. Conjunctivitis and domestic water The assessment of the impact of water supply on acute conjunctivitis is difficult because of the epi- demic character of outbreaks resulting from the high infectivity of the bacterial and viral agents, and because of the seasonal pattern of the epidemics. Moreover, epidemiological information is scarce because the absence of debilitating complications makes it a "mild disease". However, conjunctivitis is a disease of public health importance owing to its frequency, the burden on the resources of the health services (representing up to 15% of total outpatient visits in health facilities in rural Africa), and the associated cost to individual patients and the com- munity. Several studies on the impact of water supply failed to document changes in the incidence of con- junctivitis because of the small number of cases during the study period (4) or because of seasonal outbreaks (10). Other studies provide results which may appear conflicting. Majcuk (11) in Sudan observed that the prevalence of conjunctivitis was significantly lower in people bathing daily compared with people bathing occasionally. Other authors reported no change in the incidence of eye infections during the year following the introduction of water supply systems (10, 25). On the other hand, in Port- au-Prince, Haiti, families faced with an accidental 10-week acute shortage of water did not suffer a higher incidence of conjunctivitis than families un- affected by this breakdown (22). Table 3 summarizes the available information from these studies. In general, the studies seem to show a trend towards a reduced incidence of conjunctivitis when water is available in unlimited quantity. However, this trend never reaches the level of statistical signifi- cance. There is also no indication that an improved quality of water can reduce the incidence of conjunc- tivitis.b Although water-borne transmission is known to occur in places such as hospitals and nurseries (27), it does not seem to play a major role in the open environment. A provisional conclusion is that there is no scientific evidence that change in water supply influ- ences the incidence of conjunctivitis. There is no evi- dence supporting the 70% reduction attributable to water improvements, as reported in textbooks. The nature of the agents, their high infectivity through interhuman contacts, and the epidemiological pattern of these infections make such a reduction unlikely. Thus, the broad category of conjunctivitis cannot be used as an indicator to assess the impact of water in a population. Conclusions This review of field studies shows that a decrease in the risk of trachoma is associated with the following: a reduction in the distance between households and water sources, an increase in water consumption (which often depends on the distance to the water source), improvement in personal hygiene (such as face washing), and possibly improvement in water quality. The extent to which trachoma is reduced depends on local circumstances including behav- b See footnote a, page 12. 1s 0 0 VE 0c0 0 0 0O o *- E 0 CoOO :C j~~~C E) E o~ ~ ~ ~ ~ ~~~o o.2V 0.~ ~ ~ ~ ~ ~ 0~~ ~ ~C . I- Z~~~~~~~~~~~ 0 ~~~~~CC 0. 0 EC ~~~~~~ o. Ct- = 0 00CD 2L0 . o- E CC U 0.C ~0 co ~ E a) o - 0 o . E cm04) O L 0. C 0) ~~~~~~~~~~0. o.o)%- =.E E. ~ 00 U)~~~~ S3. M -0. CL, E - CO0 * 0 cjo 0 59-O 00.E CL coV1a 0 0 0 0C V o E E ro- cmC 0 -4E 0 T0 a -a0 0 C0 C 0 ._ x Y 0¢._C - 0 S. o - r 00 0 Co >, Q. r 0Coo . 0 e F OCO 0) 0~~~C 0 O *- co 2- co 2) ,.- o j>EE E a0 c S00 CV o 0 A. Prost & A.D. N6grel 0 C EE E 00) 0 V 0 0 0 C 0 a, 0. C C 0 C C 0. - .Y.. 0 o CL I 0S 0 C 0 8 C 31 cS a a5 30 C .2 0 C 0 a E 1. 09 0 0 ._ 0 0 011 c 0 C) 0- 0.a D 4-0Q ._C (a0 0 LLU @- .C 16 Water, trachoma and conjunctivitIs ioural patterns and overall environmental condi- tions. The extent to which this reduction is measurable depends on selection of appropriate indi- cators and analysis of confounding factors. The type of trachoma lesion used by authors as an epidemiological indicator varies, some referring to all cases, i.e., the overall prevalence in the study population, and others to active cases, follicular tra- choma and inflammatory cases, as opposed to grave cases or scarring lesions. Some studies refer to the entire population; others use age-specific prevalence rates. These variations in the definition of indicators may be responsible for the discrepancies in impact assessment. Several studies suggest that a more sensitive indicator relating to water consumption is the inten- sity of the eye infection, especially the inflammatory reaction (2, 5, 8, 9, 15, 23), and not the overall preva- lence of infection. The accuracy of the analysis is therefore greater if it is based on only the intensity of trachomatous inflammation. This observation also provides a better under- standing of the benefits of water availability. It is unlikely that the provision of water in any quantity can result in the elimination of trachoma from a community because the infection is mainly spread through interhuman contacts, flies, contaminated clothes, etc. Water used for personal hygiene reduces the spread of Chlamydia. Therefore, it is possible to assume that providing water to a community will reduce the intensity of the infection, thus leading to fewer complications including blindness. Improving the water supply can therefore change the epidemio- logical pattern of trachoma from a severe blinding endemic disease constituting a major public health problem to a relatively mild non-blinding infection. Another important outcome is the evidence that the overall socioeconomic situation of the com- munity (i.e., the living standards) is a much more important risk factor for trachoma than water itself. It means that water is a necessary condition to reduce the risk, but that it is not sufficient to induce marked differences. Changes result from the com- pounded effect of behavioural and environmental determinants (such as housing conditions, waste dis- posal, hygiene practices, literacy, income level, etc.), among which water availability is a key factor which interacts positively with all the other elements. Acknowledgements We thank Mr Sandy Cairncross, London School of Hygiene and Tropical Medicine, and Dr B. Thylefors, Programme for the Prevention of Blindness in WHO, for their in-depth and critical review of the manuscript. Resume L'eau, le trachome et la conionctivite 11 est devenu banal de dire que dans une collecti- vite affectee par le trachome, la maladie decrottra spontanement si l'eau lui est fournie en quantite suffisante. Cet article tente de retrouver les fonde- ments bibliographiques d'une telle assertion. A cette fin, quinze etudes concernant le trachome et cinq autres concernant les conjonctivites ont ete selectionnees dans la litterature comme repondant aux trois criteres suivants: d6finition precise de la population etudiee; utilisation de parametres per- mettant I'analyse quantitative de la disponibilite et de l'utilisation de l'eau; fiabilite du diagnostic des maladies oculaires. Le facteur climatique qui associerait trachome et zones arides n'est pas entierement verifie. Ni la latitude, ni le nombre de journees d'enso- leillement, ni les radiations ultra-violettes, ni la pluviosite ne sont des determinants du trachome. Seul le coefficient d'evaporation paratt directe- ment associe a l'extension de l'endemie. L'etude des relations entre l'usage domes- tique de l'eau et l'incidence du trachome a necessi- te une re-analyse des donnees publiees. Pour rendre la lecture homogene et faciliter la con- paraison, un rapport de prevalence du trachome (donnant une estimation du risque) a ete calcule pour une serie de sous-echantillons de population qu'il a ete possible d'isoler a posteriori en fonction de leur degre de relation avec l'eau. Ainsi, 1'effet de l'eau ete evalue selon trois variables quantit- atives caracterisant l'accessibilite de l'eau (distance, quantite, qualite), une variable semi- quantifiable d'utilisation de l'eau (hygiene individuelle), et un indicateur composite plus diffi- cile a cerner (qualite de la vie). Par-dela la disparite des resultats, une ten- dance tres nette se dessine: il y a un moindre risque de trachome quand la distance aux sources d'approvisionnement en eau se reduit, quand les quantites utilisees augmentent, quand certaines pratiques d'hygiene sont plus frequentes. 11 y a surtout une tres forte reduction de l'incidence du trachome quand les niveaux de vie s'elevent et que non seulement l'acces a l'eau s'ameliore, mais que l'habitat, I'evacuation des dechets, I'assainissement, le niveau d'education etc... sont meilleurs. Toutefois, I'eau reste un element pri- mordial de cet ensemble puisqu'a revenu egal une moindre consommation d'eau est un facteur de risque pour le trachome. En revanche, pour les conjonctivites non tra- chomateuses, aucune influence nette de la dis- A. Prost & A.D. N6grel ponibilit6 en eau ne peut 6tre mise en evidence. Cette revue de la litt6rature n'apporte pas de preuve irr6futable confortant l'argument souvent avance qu'un approvisionnement illimite en eau r6duirait de 60% la prevalence du trachome dans les communautes qui en sont atteintes. Si l'on peut dire que la disponibilite de quantit6s suffisantes d'eau r6duit l'incidence du trachome, les observa- tions de terrain ne permettent pas de chiffrer cet impact. Cela pourrait etre imputable A I'absence d'un indicateur a la fois fiable et sensible utilisable dans les enqu6tes de terrain. La prevalence du trachome dans l'ensemble de la population n'est a l'evidence pas cet indicateur. Les auteurs sug- gerent d'utiliser de pr6f6rence l'intensite de la reaction inflammatoire dans un groupe cible, dont l'age est a definir selon le contexte epidemiolo- gique. L'experience a montre que cet indicateur 6tait le plus sensible pour mesurer l'impact de l'eau comme celui d'autres programmes d'intervention. References 1. Assaad, F.A. et al. 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