Rough determination of the cost-benefit balance point of sanitation programmes*

Rough determination of the cost-benefit balance point of sanitation programmes* B. CVJETANOVIC 1 & B. GRAB2 Resources for sanitation programmes in developing countries are limited and therefore must be used judiciously to obtain the best possible effect. Cost-benefit analysis is a tool that permits the better utilization of available resources. A simple method for rough determination of the cost-benefit balance point has been devised which requires little computation. To reduce the computations to a minimum, nomograms have been constructed which require little or no mathematical skill for their use. While the method falls short of perfection, its simplicity makes it usefulfor a rough evaluation ofthe benefitsfrom sanitation programmes aimed at disease control in countries whose resources are not available for more sophisticated analysis. Sanitary measures such as the provision of water supplies are an important tool in the control of water-borne communicable diseases. Financial limi- tations induce health administrators to renounce the use of sanitation as an anti-epidemic measure because it is considered to be too expensive. How- ever, very rarely is an evaluation made to see whether sanitation, if utilized, would represent a reasonable and effective use of available resources. The place of sanitation in disease control should be evaluated from a cost-benefit standpoint to ascertain its economic aspects. In the developing countries, with their many needs and restricted resources, selection of the most profitable disease control measures is particularly important. A simple aid for cost-benefit evaluation of control measures including sanitation is required for use in areas where expert knowledge and modern sophisticated computation facilities are not available. We have already developed a simple method for rough determination of the cost-benefit balance point of immunization programmes (1). A similar method could be utilized for cost-benefit evaluation of sanitation in the control of certain acute com- municable diseases, namely enteric infections of bacterial or viral origin, against which effective control can be achieved by safe water supplies and waste disposal. Cost-benefit analyses of control * From the World Health Organization, 1211 Geneva 27, Switzerland. 1 Chief Medical Officer, Bacterial Diseases. 2 Statistician, Health Statistical Methodology. measures against other communicable diseases for which various other types of sanitation are effective could be made in a similar way. Due attention should be paid to the particular epidemic behaviour of such infections and control methods should be modified accordingly in order to ensure their most effective use. METHODS Collection of essential information The following information should be available for each specific disease and the factors related to its control: 1. Incidence of the disease-e.g., of enteric infections (if possible, its distribution according to sex, age, ethnic and social group, geographical area, etc., in order to identify high-risk groups). 2. Cost of treatment per case (if possible, clas- sified by the severity of the cases and by type of therapeutic institution). 3. Cost of sanitation per individual per year. Sanitation comprises water supplies and/or waste disposal or similar measures, and its cost includes manpower and other expenses. 4. Effectiveness of a specific type of sanitation in preventing the disease. The data for items 1, 2, and 3 should be collected and assessed locally. Information on the effectiveness of sanitation (item 4) is obtained from the scientific evidence presented by studies carried out with that 3510 - 207 - BULL. WORLD HEALTH ORGAN., Vol. 54, 1976 208 B. CVJETANOVIC' & B. GRAB type of control. All the information should be as accurate as possible so that correct calculations can be made for each country, area, and population group. In our approach to the evaluation of costs and benefits, we have considered as input the overall cost of sanitation (manpower, equipment, etc.), and as benefits the savings on cases prevented through sanitation, expressed as savings on the expenses of treating such cases. We have not added savings on lost wages, since a large proportion of the population in developing countries (children and housewives) would not be engaged in gainful activities. This, of course, is an over-simplification and, in fact, the total social cost of the disease should be considered. The present method applies essentially to devel- oping countries in which the health authorities have to cover nearly all the cost of disease control, together with the cost of treatment. The simple technique for cost-benefit evaluation developed in this paper provides departments of health with a rough indication of the costs and benefits of sanita- tion programmes and allows them to compare these with the costs and benefits of alternative control measures. Determination of the cost-benefit balance point of sanitation The calculations given below for the preparation of a simple nomogram have been made on the basis of a single sanitary measure being applied to the population group a against certain enteric diseases. Typhoid fever, cholera, and dysentery have been selected because, among other reasons, the costs and benefits of sanitation and other control measures have been studied for the first two of these diseases by epidemiological, mathematical models (2) bcC and a comparison of the results obtained by various methods may give further insight into the subject. The following parameters are used: P = population Ct = cost of treating one case a The population group is defined as the group actually protected by sanitation. The sanitation coverage is therefore theoretically 100 %. b WORLD HEALTH ORGANIZATION. Strategy of cholera control-health and economic considerations. Unpublished document BD/CHOLERA/71.5 Rev. 1 (1974). C UEMURA, K. ET AL. Epidemiological model of cholera and its use in cost-effectiveness and cost-benefit analyses. WHO unpublished document BD/CHOLERA/71.4 Rev. 1 (1974). Cs = cost of sanitation per individual per year Es = effectiveness of sanitation i = incidence of enteric infections per 10 000 population Sanitation effectiveness is defined as the propor- tional reduction in the original incidence of the disease due to the effect of sanitation. In the simple method described here it is assumed that the impact on disease incidence is directly proportional to sanitation effectiveness. There are no accurate data on the effectiveness of various types of sanitation. However, numerous studies and observations indicate the range of efficacy of sanitary measures such as safe water supplies on enteric diseases, cholera, and dysen- tery (3). The ranges of parameters shown in the following Table are supposed to cover practically all values actually encountered. Cost of Annual Cost of case sanitatton Disease incidence treatment per capita effectivenessper 10000 (in USS) and per annumefctvns (in US) Dysen- tery 1-10 000 5-50 0.15-10 0.10-0.50 Cholera 1-1000 11-100 0.15-10 0.30-0.90 Typhoid 1-200 20-500 0.15-10 0.30-0.70 Incidence is per epidemic period for cholera, and per year for other diseases. The cost varies considerably according to the level of therapeutic services, and the level and quality of various components of medical care, drugs, etc., as proved by enquiries made by WHO. The annual per capita cost of sanitation differs greatly according to the type of water supply, the method of waste disposal, the cost of manpower and supplies, etc. Numerous studies have been made confirming that the costs of water supplies can be calculated fairly exactly (4).d Details of the costing of water supplies, including calculation of the costs of construction, maintenance, and operation, dis- counting, etc., can be found in particular in recent publications of the International Bank for Recon- struction and Development.e With the available data, the annual per capita cost can be calculated. For example, as far as initial investment is concerned, d WORLD HEALTH ORGANIZATION. National rural water supply programme. Unpublished document CWS/70.5(1970). e SAUNDERS, R. J. & WARFORD, J. J. Village water supply and sanitation in less developed countries. IBRD unpublished document P.U. Report No. RES 2 (1974). COST-BENEFIT BALANCE POINT OF SANITATION PROGRAMMES 209 in South-East Asian countries a the provision of a simple rural water supply based on handpumps costs from US$ 1.0 per capita (Burma) to US$ 8.0 (Thailand), while piped water costs US$ 7.0- US$ 22.5, but in some places, for example the Philippines (5), it may cost less. In some other countries, because of difficult soil conditions, etc., the cost is much higher, as shown in a recent WHO review (4). The mean annual effectiveness of sanitation, measured by decrease in incidence, is derived from studies carried out on the effectiveness of various types of sanitation against cholera, e.g., in the Philippines (5), and elsewhere against cholera, typhoid, and bacillary dysentery (3, 6). The data on the effectiveness of sanitation in the control of cholera in rural areas (3, 5) show that the provision either of safe water or of privies decreases the inci- dence of cholera by 32-87%, while safe water and privies together may prove even more effective after several years in view of their cumulative effect. Studies on the effect of sanitation on bacillary dysentery (6) have shown that water supplies have little effect when located outside dwellings (in contrast with the high effect observed in cholera control in the Philippines) (5), but are over 50% effective when available indoors and even more so when supplemented by flush toilets. As for typhoid, it falls somewhere between cholera and dysentery (3) as far as the effectiveness of its control through sanitation is concerned. The following computations are on an annual basis for typhoid fever and dysentery and per epidemic period for cholera. The total cost of treatment when the population is not protected by sanitation is: i xP 10 000 The total annual cost of sanitation is: Cs x P The total cost of treatment when the population is protected by sanitation is: i xPCtX o x (1-Es)10 000 The critical balance point between the annual cost of treatment saved by preventive measures and the a WORLD HEALTH ORGANIZATION. Provision of safe water supplies to rural communities in South-East Asia. Un- published document SEA/Env. San./141 (1974). annual cost of the sanitation programme is reached when: Ct x 10 = Cs x P+ Ct x 10 x (l-Es) (1)10 000 10 000 This equation can be simplified as follows: Ct x 10 xE8E= Cs8xP (2)b10 000 andhence Ct= 10000xC x- (3) Calling R the ratio Cs/Es, equation (3) becomes: Ct = ROOOOx (4) The mathematical relationships between Cs, Es, i, and Ct are presented in the nomogram discussed below. Nomogram for cost-benefit balance determination The nomogram for determining the cost-benefit balance point of sanitation, presented in Fig. 1, is based on formula (4). The scale for the incidence of the diseases concerned is given on the abscissa (logarithmic scale) and covers the full range envi- saged in the above Table (from 1 to 10 000 cases per 10 000 population). Similarly, the logarithmic scale for the cost of treatment per case is shown on the ordinate for values ranging from US$ 1 to 1000. The minus 450 slope lines across the nomo- gram represent the value of R, defined as the ratio of the annual sanitation cost per individual over the mean sanitation effectiveness. These lines show a balance or indifference. They divide the nomogram into two areas: the lower left portion corresponds to financial loss and the upper right portion to gain. The levels of disease incidence and treatment cost for a specific population group can easily be plotted on the nomogram. The location of the point so determined with respect to the relevant indifference line will give the position of the sanitation pro- b Equation (2) can also be written Ct x i x Eg = 10 000 x C8, the left hand side expressing the savings in treatment costs and the right hand side the cost of sanitation for a population group of 10 000 individuals. Benefit will of course result from the sanitation programme if the left hand side exceeds the right hand side. Such a presentation of the basic equation has the advantage of permitting extension on the left hand side to take into account several diseases with differing treatment costs, incidences, and responses to various prevention programmes, and also on the right hand side to include the cost of the additional control measures envisaged. It is, however, beyond the scope of this paper to build the more comprehensive model that could be derived from this approach. B. CVJETANOVIC & B. GRAB o o) o o0Co o o 0 0(c (0 0 00 0 00 0OR (0 ltCN v- ($sn) aseo jad 1uawieaji lo Jso3 210 a5 E E 0 CLQ 0 CoC o Q .0 a) a) .0 C, 0 -0 a) 0. c a) a) 0 Co0 0) -Ei z .- 0 0 CN 000 00CD 0 0 oq: C 0 o 0O O-00 C_, Co a)*0 0 C C.) C La) 0.0 ,,T n(A 0(N _qT CN COST-BENEFIT BALANCE POINT OF SANITATION PROGRAMMES 211 gramme in terms of financial loss or gain. The dis- tance from the point to the indifference line reflects the magnitude of the loss or gain. The determination of the value of R, which defines the indifference line, is facilitated by means of the nomogram given in Fig. 2. It suffices to plot Cs 50 40 30 R 500 20 400 300 15 200 - ~~~~Es 10 100 0.10 80 8.0 60 6.0 40 0.1530 5.0- 0.20 ~~~~~20 4.0 - 0.30- 3.0103.0 28.0 7 6.0 0.40 - 2.0 4.0 1.00. 3.0 -0.60- 1.5 2.0- 0.80 1.0 1.0 1.00 0.8 0.80 0.6 - WHO 76795 0.60 0.40.30.50- 0.2- 0.40 _ 0.30 -0.1L 0.20 0.15 Fig. 2. Nomogram for calculating the ratio of sanitation cost to sanitation effectiveness. C8 = sanitation cost per individual per year;0.10 Es = sanitation effectiveness; R = Cs/Es. the annual cost of sanitation per individual on the left scale and the sanitation effectiveness on the right scale of the nomogram, and to draw a straight line through these two points: the corresponding R value can be read at the intersection of this line with the middle scale. There may be several sanitation measures available with different rates of effectiveness and costs. The cost-benefit relationship of various measures applied singly or in combination can also be assessed by the nomogram presented in Fig. 1. Examples of use Cholera. In a given population group the usual seasonal cholera incidence rate is 150 cases per 10 000 population, and the cost of treatment of one case is US$ 25. These two parametric values define point A on Fig. 3. It is planned to provide the population with water supplies that have been shown to be 50% effective (Eg = 0.50). The annual cost of sanitation will correspond to 15 US cents per individual (C8 = 0.15) (5).a R (the ratio Cs/Es) is therefore-according to the above formula R or to the nomogram in Fig. 2-equal to 0.30. The cor- responding indifference line is called L1 on Fig. 3. It can be seen that point A falls in the upper right field of the nomogram (Fig. 3), which means that a financial gain is expected from sanitation. It can also be noted that if the cost of treatment per case were less than US$ 20 or if the incidence were less than 120 cases per 10 000 population, point A could fall in the nomogram area corresponding to an economic loss. Typhoid. The annual incidence of typhoid is 60 cases per 10 000 population in a certain com- munity. The treatment of a case costs, on average, US$ 165. These two values are the coordinates of point B on Fig. 3. Assuming that the annual cost of sanitation per individual is US$ 2 b and that the mean annual effectiveness of sanitation is 50%, the resulting value for R will be 4.0. This value can also be read directly from the nomogram in Fig. 2: the straight line joining points C8 and Es gives R, which in turn defines the indifference line L2 on Fig. 3. It is seen that sanitation under the present conditions will lead to a financial loss. A benefit a WORLD HEALTH ORGANIZATION. Strategy of cholera control-health and economic considerations. Unpublished document BD/CHOLERA/71.5 Rev. 1 (1974). b WORLD HEALTH ORGANIZATION. Provision of safe water supplies to rural communities in South-East Asia. Unpublished document SEA/Env. San./141 (1974). B. CVJETANOVIC & B. GRAB ILUW PaM 60a _Z7 W -V nL as E m VW \ _ _ \% \N1 \1 _ I2'N T]11><| \\<ll 100 8 2 600 40~~~~~~~~~~~~~~~~~~~~~~. 4~~~~~~~~~~~~~~~~~~4 2-I 1 24 68 10 20 40 60 80 100 200 400 600 1000 2000 4000 6000 100(0 Case incidence per 10000 population 0 Fig. 3. Nomogram for determining the cost-benefit balance of a sanitation programme: theoretical examples of use. might result from the sanitation programme if the cost of treatment were higher than US$ 700 or, alternatively, if the incidence were higher than 250 per 10000. The above are theoretical examples of the use of the method. When using it in practice there are other aspects to be taken into consideration such as, for instance, estimate of the true incidence, the real cost in view of shadow pricing, other benefits of sanitation besides the control of a single disease, etc. Examples of use in an actual situation In order to demonstrate the use of the nomograms in an actual situation, we present data obtained during a study of typhoid control in Tonga through immunization and sanitation. The control of typhoid in Tonga, as in other countries in the South Pacific where the national income depends largely on tourism, is essential for improvement of the economy and therefore highly desirable (2). The problem was to evaluate which of the possible strategies-immunization or sanitation-was more effective and financially beneficial. Tonga has about 90 000 inhabitants. The health services are the responsibility of the Government, which provides for the treatment of infectious diseases and their prevention. Typhoid is a major health problem but other diarrhoeal diseases (dysentery, gastroenteritis, and infantile diarrhoea) are common. Mild diarrhoeas, however, are under- reported. For the years 1965-72 the average annual morbidity rates per 10 000 were: typhoid, 20; diarrhoeal disease, 582; and both together, 602. It was estimated that the cost of treatment of one case of typhoid was, on average, T$ 72, or about US$ 100. The cost of treatment of other diarrhoeal \ xi x\ - x _ x c 212 \1Xi5LL \ \\ COST-BENEFIT BALANCE POINT OF SANITATION PROGRAMMES diseases was considered, on average, to be USS 9. This gave a weighted mean cost of US$ 12 per case of these diseases. The per capita cost of the construction of rural water supplies was US$ 11.5, of which two-thirds (i.e., $8) was provided by the Government, the rest being contributed by the population. With this figure on hand and after having taken into considera- tion discount rates, maintenance and operation costs, etc. (4), we arrived at an estimated annual per capita cost for water supplies of $0.80 (C8 = 0.80). It was assumed from experimental evidence and various studies that the effectiveness of water supplies in the control of enteric diseases was 50% (Eg = 0.50). The above values (Cs = 0.80 and Es = 0.50) give R = 1.6; this could also be read directly from the nomogram in Fig. 2. If this ratio is used to define 10oo 800 to En 0 0 the indifference line on the nomogram (see Fig. 4), and the costs of treatment per case and the incidence are plotted, then corresponding points are obtained for typhoid (Ty) and diarrhoeal diseases (DD), or both (Ty + DD). They are found in the loss area but the last two are not far from the balance line. However, if the effectiveness were to increase to 700 and the cost of sanitation drop to half, then the ratio R would be at 0.6 and the indifference line would be L (Fig. 4). An interesting finding is that sanitation considered separately for typhoid or diarrhoeal diseases control will in neither case be financially beneficial, both points (Ty and DD) being on the loss side of the indifference line. When typhoid and diarrhoeal diseases (Ty + DD) are taken together, however, the benefit of sanitation becomes evident. \ E,\S E\iN<sa\ X\f I11,NN q400 NX9 \ _ \\ _\ II 200 Ty~~~~~~C a t 2 C00 -- 100 Ty 80IN 60 I (6 40 SC 20 TDD 10 8~~~~~~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ X Ty =Typhoid 2 DOD Diarrhoeal diseasesI SC Social cost 2000 4000 6000 10000 Fig. 4. Nomogram for determining the cost-benefit balance of sanitation programmes in the control of enteric diseases in Tonga and Colombia. 2 4 6 8 10 20 40 60 80 100 200 400 600 1000 Case incidence per 10000 population w I _5 3 213 B. CVJETANOVIC & B. GRAB Looking at the nomogram one can then reconsider the various cost values and correct or change them, according to the needs and possibilities. If one were to add to the cost of case treatment lost wages, the cost of various indirect expenses due to illness (e.g., the costs of epidemiological investigation, destruc- tion of contaminated food, closure of incriminated restaurants, etc.), and the costs of deaths (that do occur), one would arrive at the total social cost of the disease, which might come to a value three times as high as the cost of treatment alone, i.e., $36. In that case, with the global rate of enteric infections of 602 per 10 000, the point corresponding to the total social costs (SC) will fall clearly on the benefit side of the original indifference line (see Fig. 4). Further, since reporting is far from complete and since only cases reported to health centres and hospitals are accounted for, a thorough survey may reveal, as has been demonstrated in many places, that the true incidence rates are up to ten times higher. Perhaps the cost per case would be somewhat lower, but nevertheless the resulting points would fall on the benefit side. Last but not least, any decrease in the cost of water supply would favourably change the position of the balance line and increase the benefit. If a thorough study were made to list all the costs incurred through illnesses due to water-borne diseases, certainly the total cost per case would be much higher than that of treatment alone. If, in addition, a thorough survey of the water-borne diseases were carried out, incidence could be deter- mined with greater precision. These two operations- a thorough and complete costing and a survey of incidence-improve the effectiveness of the above method and should be carried out in order to arrive at more accurate results. Bryant, in a study of health problems in Colom- bia (7), estimated that clean water in rural areas costs US$ 2.25 per capita per annum. One can use the nomogram to examine under what conditions such expenditure would be offset by benefits in health, namely by benefits derived from the prevention of enteric and diarrhoeal diseases through the provision of water to the population. With the above cost of sanitation (Cs = US$ 2.25) and assuming the effectiveness of water supplies in diarrhoeal diseases control to be 500% (Es = 0.50), one obtains R = 4.5 (Fig. 4). Accordingly, one can see that at an incidence of 600 per 10 000 (equal to that on Tonga) there would be a benefit only if the treatment cost per case were about $75. At the cost per case of $36 the incidence would have to be double to reach the benefit area. Such, and similar, cal- culations can be done in many ways. It is, however, recognized that there are many other benefits besides those of health to be derived from water supplies, but some are " hidden " and difficult to account for. There are also factors that increase the effectiveness of water supplies but are difficult to quantify. These are mainly in the sphere of human attitudes and often stay hidden to so-called objective quantification. DISCUSSION AND CONCLUSIONS For diseases that attack equally both sexes and all ages and social strata, it is logical to utilize a yearly average of incidence in the total population. For enteric infections affecting mainly children, the incidence in children of a susceptible age should be taken into account. For example, in diarrhoea the incidence in infants and young children is important while diarrhoea in adults is rather rare. In such a case sanitation covering young age-groups, e.g., at home and in school, would be more beneficial and would be more likely to fall on the benefit side of the balance line than sanitation among older groups. One has, therefore, to consider the age composition which in developing countries is usually characterized by larger young-age groups. When estimating the possible effect, one should see that high-risk groups are covered in order to obtain the desired results. The financial benefit of sanitation is related to the cost of disease and its incidence; as the incidence and/or cost of treatment rises, so the benefits of sanitation increase. When the general state of health and standards of living improve, the incidence of most (particularly endemic) bacterial enteric infec- tions declines. However, the financial benefit of sanitation does not necessarily decline propor- tionately, since treatment becomes widely available, more sophisticated, and more expensive. At very low incidence rates no ;ancial benefit is derived from control measures. but when that stage is reached the community i isually sufficiently wealthy to provide the necessary nieans to fight the infection purely on humanitarian grounds and to improve the quality of life. Our rather over-simplified and rough method of determining the cost-benefit balance point was developed to provide a simple technique for those who do not have the facilities for complex studies and work in the planning of health programmes and 214 COST-BENEFIT BALANCE POINT OF SANITATION PROGRAMMES 215 community development. The method described has many imperfections and is not highly accurate. It gives only limited guidance as regards cost-effective- ness, and it is not suitable for cost-benefit analyses over a period of years. The effects, costs, and benefits of long-term sanitation programmes can be pro- jected only with the use of epidemiological models. Difficulties in evaluating and quantifying the epi- demiological impact and health benefit that are expected to result from prevention programmes have frequently been mentioned. It is hoped that the method described here will to some extent help the public health administrator or the epidemiologist on the one hand, and the sanitary engineer or the econo- mist on the other, to work in concert to solve the multifaceted problem that challenges them. The method can be considered as an attempt to bring together the disciplines involved by avoiding the use of concepts and techniques highly specific to each of them. Such an approach is a compromise and it is recognized that the proposed simplified technique can give only approximate results. It is believed, however, that it can provide the information needed by the decision-maker for a comparison of alternative sanitation programmes at the initial screening stage. As already mentioned, the treatment of complex situations requires the use of appropriate sanitary and epidemiological techniques and econometric methods which have yet to be developed and which will be more accurate than the method described here. ACKNOWLEDGEMENT The assistance and advice of the staff of Community Water Supply, WHO, Geneva, and of Dr R. C. Ballance in particular, in reviewing the manuscript are appreciated. RESUME DETERMINATION APPROXIMATIVE DU POINT D'EIQUILIBRE COUtTS-AVANTAGES DANS LES PROGRAMMES D'ASSAINISSEMENT Dans les pays en developpement, les ressources que l'on peut consacrer aux programmes d'assainissement sont limitees et doivent par cons6quent etre utilisees de fa$on judicieuse pour que l'on en tire les meilleurs resultats possibles. L'analyse couits-avantages est un instrument qui permet de mieux utiliser les ressources disponibles. Une methode simple, exigeant peu de calculs, a ete mise au point pour la determination approximative du point d'equilibre couits-avantages. Pour ramener les calculs a un minimum, on a construit des nomogrammes qui n'exigent a peu pres aucune connaissance math& matique. Pour 1'emploi de cette methode, il est indispensable d'avoir des donnees fiables sur le cout des differents e1lments du programme d'assainissement ainsi que sur l'incidence et le couit des maladies que l'on peut maitriser au moyen de mesures sanitaires. II est necessaire aussi de connaitre 1'efficacit6 des diff6rentes mesures d'assai- nissement a employer pour maitriser ces maladies. Si les donnees precitees sont exactes, elles permettent de deter- miner approximativement le point d'equilibre couts- avantages du programme d'assainissement et de savoir si ce programme a des chances d'etre ou non financierement avantageux. La methode n'est certes pas parfaite mais, grace a sa simplicit6, elle est utile pour evaluer approximativement les avantages des programmes d'assainissement visant A maitriser les maladies dans les pays oui l'on ne dispose pas de ressources suffisantes pour proceder a une analyse plus perfectionnee. REFERENCES 1. GRAB, B. & CVJETANOVIC, B. Bulletin of the World Health Organization, 45: 536-541 (1971). 2. CVJETANOVIC, B. ET AL. Bulletin of the World Health Organization, 45: 53-75 (1971). 3. ZAHEER, M. ET AL. Journal of the Indian Medical Association, 38: 177-182 (1962). 4. World health statistics report, 26: 732 (1973). 5. AZURIN, J. C. & ALVERO, M. Bulletin of the World Health Organization, 51: 19-26 (1974). 6. SCHLIESSMANN, D. J. Bulletin of the World Health Organization, 21: 381-386 (1959). 7. BRYANT, J. Health in the developing world. Cornell University Press, 1969. 4