Studies on interventions to prevent eltor cholera transmission in urban slums*

Bulletin of the World Health Organization, 64 (1): 127-131 (1986) © World Health Organization 1986 Studies on interventions to prevent eltor cholera transmission in urban slums* B. C. DEB,' B. K. SIRCAR,2 P. G. SENGUPTA,3 S. P. DE72 S. K. MONDAL,4 D. N. GUPTA," N. C. SAHA, S. GHOSH,5 U. MITRA,5 & S. C. PAL6 Transmission of eltor cholera infection in endemic communities continues without diminishing because of the absence of effective intervention measures. Two methods- chlorination of stored water and the use of a narrow-necked earthenware vessel (called a 'sorai') for storing the water- werefound to be effective in reducing the transmission of infection among the family contacts of cholera patients. The cholera carrier rates in the chlorination and 'sorai' intervention groups were 7.3% and 4.4%, respectively, compared with 17.3% in the control group. The 'sorai' is cheap and was well accepted by the local communities; its narrow neck prevented the introduction of the hand and contamination of the stored water. Since eltor cholera appears to have an endemic tendency, cases are regularly being reported from the city slums in many developing countries every year. Poverty, malnutrition, overcrowding, and unhygienic living conditions are important contributory factors, but persistence of the disease in these communities has been attributed to the large number of inapparent infections by the eltor organism and mild cases throughout the year (1). However, the exact mode of transmission of the disease is still poorly understood and the role of drinking-water in the transmission of cholera in highly endemic areas is still debated (2, 3). For example, the provision of tube-well water of pre- sumed good quality did not reduce the incidence of the disease (4-6). A number of hypotheses have been proposed to explain this failure, but have not satisfac- torily explained the relationship of water use to cholera transmission. The use of water for other purposes, especially bathing, has been incriminated in the transmission of cholera in some areas (7). Lack of a clear correlation between the water supply and the causation of the disease, as well as the pressure of a large number of inapparently infected persons in * From the National Institute of Cholera and Enteric Diseases (ICMR), P-33, C.I.T. Road, Scheme XM, Beliaghata, Calcutta-700 010, India. Requests for reprints should be addressed to Dr B. C. Deb. 1Deputy Director 2 Assistant Director 3Senior Research Officer 4Research Officer sAssistant Research Officer 6 Director the community, led us to the hypothesis that person- to-person transmission through contamination of domestic food and water, owing to poor hygienic practices, might be responsible for the maintenance of infection in endemic areas. In an earlier study (8), we investigated the modes of intrafamilial transmission of Vibrio cholerae bio- type eltor in cholera-affected houses in the Calcutta slums. The object was to determine the association between contamination of various items in the house- hold and the incidence of cholera infection. Our results showed statistically significant higher contam- ination rates of stored water and cooked food in the houses with hospitalized cholera patients, compared with the control group of houses without cholera. This difference in contamination rates was not noticed when other categories of domestic environ- mental samples were tested. It was concluded that V. cholerae-infected persons -without symptoms- were contaminating through their infected fingers the clean water which was stored unhygienically in wide- mouthed vessels (e.g., a bucket) in the house, thus leading to the transmission of infection to other persons. The present study was carried out to determine the effect of two hygienic measures to prevent trans- mission of infection through stored water. MATERIALS AND METHODS The study population was composed of the family contacts of bacteriologically proven, hospitalized 4646 -127- B. C. DEB ET AL. Fig. 1. The 'sorai', an earthenware vessel, with separate openings (shown by the arrows) for putting in and pouring out the water. cholera patients (index cases). As soon as a diarrhoea patient was admitted in the local Infectious Diseases Hospital, his or her stool sample was screened for the presence of V. cholerae. The house of the index case was visited within 18-24 hours and stool samples of all the family contacts were examined daily for 5 con- secutive days to determine the incidence of carriers among them. If any index case was not proved to be a case of cholera, further studies in this family were discontinued. Intervention measures The first group of 31 families was provided with chlorine tablets and instructed to put them (1.25 mg/ litre of water) in the buckets where the water was usually stored for drinking and other domestic use. The residual chlorine level in this stored water that had been treated with the chlorine tablets was estimated daily during surprise checks. A second group of 30 families was provided with narrow- necked earthenware pitchers (called 'sorais') and instructed to store water in them for drinking and domestic purposes. Since each 'sorai' (Fig. 1) had a narrow inlet and a spout, into which the hand could not be placed, this source of contamination of the water could be prevented. A third group of 30 families, where neither of the above interventions was applied, served as a control. The index case families were randomly assigned to the two intervention and the control groups. The families were advised to follow only the suggested method of intervention (chlorine tablets or 'sorai') in their respective groups, and were not instructed in the use of other hygienic measures so as to avoid the introduction of other intervention variables. RESULTS A total of 466 persons from among the 91 index- case families in the three groups were studied. Their age distribution shows that the three groups were comparable (Table 1); there was also hardly any difference between the groups regarding sex distribution. The study was conducted in the slums of the eastern part of Calcutta city where the incidence of diarrhoeal diseases including cholera is relatively higher than elsewhere. The study population in the three groups was more or less similar with regard to housing, religion, income, access to water supply and latrine facilities, and the literacy of the mothers (Table 2). Table 1. Age distribution of the study population in the three groups No. of family contacts of index cases Age group Chlorination 'Sorai' Control (years) group group group Total <1 9 7 5 21 (4.5)' 1-4 1 7 1 9 20 56 (12.0) 5-9 22 22 22 66 (14.2) 10-14 17 21 20 58 (12.5) > 1 5 86 90 89 265 (56.9) All ages 151 159 156 466 (100.0) a Figures in parentheses are percentages. 128 STUDIES ON ELTOR CHOLERA PREVENTION Table 2. Comparability of the three groups in economic and social terms Percentage of families Chlorination 'Sorai' Control Criteria for comparison group group group Housing: Slum 83.3 90.0 83.3 Non-slum 6.7 10.0 6.7 Religion: Hindus 90.3 90.0 86.7 Muslims 9.7 10.0 13.3 Monthly income (US$): <25 41.9 40.0 40.0 25-40 48.4 53.3 50.0 >40 9.7 6.7 10.0 Water supply: Tap + tubewell 90.3 93.3 90.0 Pond 3.2 3.3 3.3 Open well 6.5 3.3 6.7 Latrine facilities: Service type 29.0 36.7 40.0 Sanitary 58.1 56.7 50.0 Open 12.9 6.7 10.0 Mother's education: Primary school or below 35.5 30.0 33.3 Table 3 shows the rates of inapparent infections detected in families practising the two methods of intervention as compared to those in the control group. Out of the 151 persons in the chlorinated group, 11 (7.3%) were detected with cholera infec- tion; the mean residual chlorine level in the treated water was found to be 0.2 mg/l. Seven (4.4%) Table 3. Effect of the two intervention measures com- pared with the control group Family contacts of index cases No. No. +ve for studied V cholerae Chlorination group (31 families) 151 11 (7.3)b 'Sorai' group (30 families) 159 7c (4.4) Control group (30 families) 156 27 (17.3) a Chlorination vs control groups (P<0.01). b Figures in parentheses are percentages. c 'Sorai' vs control groups (P<0.001). infected persons were detected among the 159 persons in the 'sorai' group of families. In contrast, 27 (17.3%) inapparently infected persons were identi- fied among the 156 persons in the control group. The differences in the number of detected infections between the chlorination and control groups (P< 0.01) and between the 'sorai' and control groups (P<0.001) were found to be statistically significant. Fig. 2 shows the occurrence of asymptomatic infections among the contacts of index cholera patients in the three groups, on different days of follow-up. Two intervention measures were applied from day 0. On day 1 there was little difference in the number of infected individuals in the three groups, but the differences were considerable from day 2 on- wards between the study and the control groups. Use of the 'sorai' gave a slightly better result than chlorination. DISCUSSION The explosive outbreaks of classical cholera due to contamination of a water source are now rarely encountered in eltor infections. However, sporadic cases due to the latter biotype still continue in endemic areas, and scientists have been trying to elucidate the mechanism by which the eltor organism is transmitted from one person to another, thereby contributing towards the endemicity of an area. * CONTROL 0 CHLORINE [l 'SOR^A ,rr z 0 (/) S w 05 0 W~ 4 C LU4 U. z 2 0 zo0 1 2 3 4 5 D A Y S Fig. 2. Number of infected persons in the three groups during the first five days of the intervention. 129 B. C. DEB ET AL. Urban slums in most developing countries are now provided with a filtered and chlorinated water supply as the only source of water for most of the people living in these communities, alternative sources being rare or not accessible. Because of the irregular com- mon water supply, however, the water has to be stored, and when this is done in an unhygienic fashion, the consequence is often secondary contam- ination of the water by already infected persons in the house. This fact was amply demonstrated by our earlier study (8). The results of the present study on interrupting the transmission of V. cholerae infection within the household strongly suggest a causal relationship between contamination of the stored water and the high infection rate in the family as observed during the intrafamilial transmission study (8). Other factors capable of interrupting the transmission of cholera infection remaining the same in our three groups, it can be reasonably concluded that the two inter- vention measures in our two study groups were responsible for lowering the transmission of V. cholerae from an infected to other persons in the household. A notable feature of this study was that a simple and cheap earthenware pitcher with a narrow neck (the 'sorai'), which was well accepted by the local community, was effective in reducing the transmission of infection. The results given in Table 3 show that by using either of our two interventions it was possible to reduce the spread of V.cholerae infection among household contacts to the extent of 74.6% and 57.8% in the 'sorai' and chlorinated groups, respectively. This suggests that in our study groups the exposure to infection outside the home was relatively less important so far as spread of eltor cholera infection was concerned. ACKNOWLEDGEMENTS The authors are thankful to the field and laboratory staff of the National Institute of Cholera and Enteric Diseases, Calcutta, for valuable support in this study. The statistical help provided by Mr S. N. Sikdar, Research Officer (Statistics), and Mr B. Manna, Assistant Statistician, are also gratefully acknowledged. RISUMt ETUDES SUR LES MESURES DESTINtES A PRtVENIR LA TRANSMISSION DU CHOLtERA ELTOR DANS LES TAUDIS URBAINS Pauvrete, malnutrition, surpeuplement et manque d'hygiene dans les taudis urbains sont autant de facteurs qui contribuent a la persistance du cholera dans les pays en developpement d'Asie et d'Afrique. On ne connait pas exactement les modes de transmission de la maladie dans ces collectivit6s. Des etudes ont montre que la fourniture d'eau de bonne qualite n'entrainait aucune reduction de l'incidence du cholera. Une etude que nous avons faite anterieurement a Calcutta a revele que, malgre l'existence de puits tubes et d'un reseau de canalisations d'eau, le fait de conserver l'eau a domicile dans de mauvaises conditions d'hygiene entrainait une contamination par Vibrio cholerae, d'oui une incidence plus elevee des infections inapparentes dans ces familles par rapport a un groupe temoin. La pr6sente 6tude a e faite en vue de determiner l'impact de mesures d'hygiene simples- fourniture de jarres de terre cuite a goulot etroit (appel6es "sorai") pour garder l'eau destin6e a la boisson et a d'autres usages domestiques, prevention de la contamination due au contact manuel de personnes infect6es et enfin chloration de l'eau conserv6e traditionnellement dans des seaux non fermes- destin&es a empecher la transmission de l'infection a V. cholerae. Trente et une familles, comptant chacune un premier cas de cholera, composaient le groupe oui l'eau etait chlor&e et 30 autres le groupe auquel on a fourni des "sorai". Trente autres familles dans lesquelles aucune mesure n'a e appliqu&e ont servi de groupe temoin. Dans le groupe oui la chloration etait pratiquee, 1'eau conserv6e dans des seaux a e traitee a l'aide de comprimes de chlore (1,25 mg/litre d'eau) tandis que des "sorai" ont ete fournies aux familles du deuxieme groupe en echange des seaux dans lesquels elles conservaient habituellement l'eau provenant d'un puit tube ou du robinet. On a examine quotidiennement pendant cinqjours consecutifs 466 contacts familiaux dans les trois groupes (151 dans le groupe ou l'eau a e chlor6e, 159 dans le groupe auquel des "sorai" ont e fournies et 156 dans le groupe temoin) afin de rechercher la presence de V. cholerae dans les selles. On a constate que les taux d'infection inapparente a V. cholerae dans le groupe oii l'eau etait chlor6e et le groupe auquel des "sorai" ont e fournies 6taient de 7,3% et de 4,4%, respectivement, contre 17,3% dans le groupe temoin. Ces differences entre chacun des deux groupes cibles et le groupe temoin etaient statistiquement significatives. Ces mesures simples, en particulier l'utilisation des "sorai", cofitent peu cher et ont e tres bien accept&es par les communautes locales. 130 STUDIES ON ELTOR CHOLERA PREVENTION 131 REFERENCES 1. SINHA, R. ET AL. Role of carriers in the epidemiology of cholera in Calcutta. Indian journal ofmedical research, 56: 964-978 (1968). 2. FEACHEM, R. Is cholera primarily water-borne? Lancet, 2: 957 (1976). 3. LEVINE, R. & NALIN, D. Cholera is primarily water- borne in Bangladesh. Lancet, 2: 1305 (1976). 4. SOMMER, A. &. WOODWARD W. The influence of pro- tected water supplies on the spread of classical/Inaba and Eltor/Ogawa cholera in rural East Bengal. 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