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Food and water hygiene and diarrhoea in young Gambian children: a limited case control study
TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE
AND HYGIENE (1984) 78, 209-211
Food and water hygiene and diarrhoea in young Gambian limited case control study
209
children:
a
N. LLOYD-EVANS’, H. A. PICKERING~, S. G. J. GOH~ AND M. G. M. ROWLAND~* ‘The Gambia GovernmentiMRC Joint Health Research Unit, The Gambia; 2The Ross Institute of Tropical Hygiene, London School of Hygiene and Tropical Medicine, Keppel Street, London WCIE 7HT; 3Medical Research Council Laboratories, Fajara, The Gambia Summary During the annual rainy season epidemic of diarrhoea in The Gambia, two groups of urban children were identified, one of which remained completely free of diarrhoea and another in which diarrhoeal prevalence exceed 30% over a period of three months. Microbiological studies on the food and water consumed by these children during one day showed widely varying degrees of contamination in both groups. No difference was observed in levels of contamination, faecal or otherwise, between the two groups. The real problem seemed to lie in accounting for the freedom from diarrhoea of some children rather than explaining possible causes of morbidity in others. Introduction Diarrhoea is a major cause of morbidity and mortality in young children worldwide. Transmission is faeco-oral and endemicity is high in third world communities where environmental hygiene is poor. Faecal contamination of food and water has been demonstrated in association with high diarrhoeal rates in such communities (ROWLAND et al.. 1978: BLACK et al., 1982); food in p‘articular was thobght t6 play an important role in this respect (BARRELL & RowLAND, 1979). Only infrequently has this association between contamination of food and water with disease been sought at an individual level (BLACK et al., 1982). We have attempted to use the microbiological qualities of food and water consumed by individual infants and young children as an objective marker of environmental hygiene and to relate this to the widely varying pattern of diarrhoeal morbidity experienced by these individuals. Materials and Methods This study was carried out in The Gambia in Bakau, a settled community of 10,000 persons and the sixth largest township in the country. It is 10 km from the capital, Banjul. Male occupations vary from white-collar jobs to fishing, trading and manual labour, with unemployment fluctuating at around 10%. Most women are full-time housewives; some are petty traders and a few have salaried jobs. Bakau has a piped chlorinated water supply delivered to public standpFp& and some individual compounds (enclosed areas of land housing one or more extended families). Most families have access to sanitational facilities, mainly pit latrines, within their compounds and all adults defaecafe in these or in two public latrines. Though “potty-training” is widespread young children often defaecate indiscriminately in the dwelling areas. The community is the subject of a number of studies on morbidity, the main emphasis being on diarrhoea in early childhood. During the 1982 rainy season (July to October) the diarrhoeal morbidity of approximately 300 children aged 6 to 36 months was monitored using a weekly home questionnaire for a Deriod of 105 davs. The mean number of days of diarrhoea per child was 12’with a range of 0 to 56 days. Thus 30 children were completely free of diarrhoea through the annual epidemic whilst 25 had diarrhoea for more than 25% of the time, mainly due to repeated acute episodes. During the month of November 1982 food and water hygiene was studied through one day for 20 weaning children between the age of six and 18 months, ten of whom
had remained free of diarrhoea and 10 who had suffered diarrhoea for more than 30% of the observation period. An anthropologist (HAP) and field worker visited the subjects’ compounds at 0700 hours, before breakfast. Samnles for bacteriological analvsis were obtained of the child’s breakfast food and any other cooked cereal set aside for use later in the day. Any breakfast food that had been kept was again sampled at noon. The children ate a wide variety of snack foods during the morning, some of which were samuled randomlv. The child’s drinkine water obtained from the family storage jar was sampled”at 1100 hours and one “first flush” sample obtained from a communal standpipe. Whenever possible a fresh stool specimen was obtained from the child on the day of the visit. Five-gram aliquots of food were added to 45 ml of 0.1% peptone diluting fluid, homogenized and serial dilutions examined using routine methods (THATCHER & CLARK, 1968). From all samples vieldina Escherichia coli 10 colonies were’ pooled for to-tin testing: LT-toxin-producers were identified using a Vero cell assay (KONOWALCHUK et al., 1977), and ST-producers by the infant mouse assay (GIANNELLA, 1976). Aliquots of water were examined for total coliform counts and E. coli by the membrane filtration technique (Millipore Corporation, USA) using standard methods (DHSS, 1969). Faecal samples were examined by direct microscopy and after formol-ether concentration for intestinal helminths and other parasites. Specific bacterial pathogens including salmonellae, shigellae and Vibrio cholerae were also sought using standard methods (COWAN & STEEL, 1974), Campylobacter spp. (see SKIRROW, 1977) and Aeromonas hydrophilia by the method of SCHUBERT(1974) confirmed by API 20E (API System SA, France). These organisms were also sought in water specimens.
Results 39 foods were examined, 17 from cases with high prevalence of diarrhoea (D) and 22 from children who had suffered no diarrhoea (C). Total
bacterial
counts ranged from 0-10*/g in both
groups. 17 foods (10 D, 7 C) contained no coliforms. The remainder
contained
from 10’ to more than lo7 per g.
Approximately half of all gruels whether sampled fresh or at four hours contained no E. coli (D 619, C 9117). In both groups counts of up to lo5 per g were
observed in the remainder indicating faecal contamination. Of the E. coli isolated only two were *Author
to whom correspondence
should be addressed.
210
FOOD
Table I-Numbers grouped according
AND
WATER
HYGIENE
AND
DIARRHOEA
Adult Foods Snacks All Foods
THE
GAMBIA
of samples and bacterial isolations from food samples consumed by young children to high (D) or zero (C) diarrhoea prevalence E. coli
Gruels
IN
Coliforms
Absent
Present (Range)
c”
t
5 ( 102-105) 8 ( 102-105)
c”
2 1
2 (102-10’) 2 (102-105)
ii?
3 1
1 (102) 1 (102)
c”
toxigenic, one producing heat-labile (LT) and the other heat-stable (ST) toxin. The LT-producing organism was isolated from freshly prepared gruel but could not be detected after four hours of storage. The ST-producer was also isolated in gruel; it was not detected in the fresh specimen but was isolated from the sample four hours after preparation. Gruels containing locally soured milk were particularly badly contaminated. In contrast no contamination was detected in one specimen to which tinned evaporated milk had been added during cooking. Seven adult cereal foods (steamed or boiled) were examined. Two from the diarrhoea (D) group and two from the control (C) group were contaminated with E. coli after overnight storage. Counts ranged up to lo5 and to greater than IO’ per g in the C and D groups respectively. The remaining three foods which were freshly prepared had no E. coli. Two snacks were examined from the C group and four from the D group. These were a variety of ice 1011~pops, sweetened liquid drinks, dry pastry and bread. Only the sweetened liquid drinks, one from each group, were contaminated with E. coli (up to 102/100 g). These food bacteriology results are summarized in Table I. The single standpipe water sample was sterile. Of the stored water samples tested only one from group C had E. coli (101/100 ml) but three of the D group were contaminated, one with a count greater than 103/100 ml. None of the E. coli isolated were toxigenie. Approximately half of the water samples in both groups had counts of greater than 10 coliforms/l00 ml; two samples from the C group remained sterile. Of 15 stools examined (nine from group C and six from group D), three yielded bacterial pathogens: one salmonella; one shigella plus campylobacter and one ST-toxigenic E. coli. Six contained Giardia lamblia and three yielded Ascaris lumbricoides also. There was no clear correlation between pathogens isolated and the diarrhoeal morbidity of the child. Discussion Discrete epidemics of diarrhoeal disease due to specific organisms have often been traced to contamination of food or water supplies.
Total bacteria
Absent
Present (Range)
Absent
Present (Range)
10 7
7 (102-10’) 15 (lo’-10’)
:
16 (lo’-10’) 21 (loi-108)
In endemic situations, particularly where young children are concerned, a clear understanding of diarrhoeal epidemiology rarely exists. Certainly faecal contamination of food and water has been shown to be commonplace in developing countries. Some studies have shown that the highest levels of food contamination are associated with seasonal peaks in diarrhoea prevalence and are worst in the food presented to young children, the age group in which diarrhoeal morbidity is highest (ROWLAND, 1983; BLACK et al:, 1982). In addition to the agents of gastroenterms many other organisms found in such foods may produce enterotoxins (JIWA et al., 1981). Such evidence relating food to diarrhoeal illness is of course circumstantial, though a causal relationship has been suggested by the Bangladesh studies already referred to (BLACK et al., 1982). If, as seem likely, “food occupies a central and important position” in the epidemiology of diarrhoeal disease (LUCAS & GILLES, 1973) one might expect the standard of food and water hygiene of a community to be reflected in its diarrhoeal rates and the same factors within a family to affect the diarrhoeal rates of the individual members. In Bakau township the provision of an accessible, efficiently chlorinated water supply, the customary use of latrines and the much greater time which mothers are able to devote to normal domestic duties including child-care, contribute to an environment in which poor food and water hygiene and the faeco-oral spread of disease could be less common than in the strongly contrasting circumstances observed in Keneba (ROWLAND, 1983). In fact many of the water and food samples obtained in Bakau were completely clean but the range of contamination, disturbingly, was as high as found in the earlier study in Keneba (BARRELL & ROWLAND, 1979). Interestingly the least hygienic foods were again stored gruels, particularly those to which unprocessed cows’ milk had been added. The relatively good bacteriological quality of the gruels sold by the street vendors illustrated the virtues of fresh production and high turn-over though clearly such a system if mishandled could equally well generate an epidemic. In Bakau we would recommend improved water storage within the homes and, as in Keneba, the consumption of food as soon as possible after cooking; the addition of supplements such as
N.
LLOYD-EVANS
milk or sugar should be made immediately before consumption. Would such conventional advice be expected to help? Our results in this respect were unpromising. There was no obvious correlation between our measurement of water and weaning food contamination and the diarrhoeal morbidity of the child. Though numbers were small the pattern of morbidity in the two groups contrasted so strongly that some differences could have been expected had the bacteriological examinations we were making been of fundamental enidemioloaical imnortance. This lack of correlation was not an Isolated phenomenon in our experience. In the much larger comprehensive environmental study in Bakau (Pickering, 1984) no single, nor indeed combined factors were significantly related to diarrhoeal morbidity in children. In any such community gastro-intestinal infection and consequent disease will be determined by a complex interaction between the general environment, personal practice and individual “immunity”. Infants and toddlers avidly exploring their contaminated surroundings, transferring a variety of objects from hand to mouth, often allowed to defaecate indiscriminately and with incompletely developed or impaired immune defence systems are obviously the most susceptible group and this is clearly reflected in the age distribution of diarrhoeal disease. Only widespread multifactorial improvements in hygiene at a civic and personal level are likely to have a measurable impact on this situation (BLACK et al., 1983) unless we can learn why some children manage to escape disease so successfully. These reasons are not at present known. A change in emphasis away from investigating why children get diarrhoea (often all too obvious) to an examination of why others remain relatively free of symptoms despite their environment might point us in the direction of more effective strategies. Acknowledgements The authors thank Dr. A. M. Tomkins for helping to initiate the morbidity surveillance system. References Barrell, R. E. A. & Rowland, M. G. M. (1979). Infant foods as a potential source of diarrhoeal illness in rural West Africa. Transactions of the Royal Society of Tropical Medicine and Hygiene, 73, G-90. Black, R. E., Brown, K. H., Becker, S., Alim, A. R. M. A. & Merson, M. H. (1982). Contamination of weaning
et al.
211
foods and transmission of enterotoxigenic Escherichia coli diarrhoea in children in rural Bangladesh. Transactions of the Royal Society of Tropical Medicine and Hygiene, 76, 259-264. Black, R. E., Chen, L. C., Harkavy, O., Rahaman, M. M. & Rowland, M. G. M. (1983). Prevention and control of the diarrhoeal diseases. In: Diarrhea and Malnutrition: Interactions, Mechanisms and Interventions. Chen. L. C. & Scrimshaw, N. S. (Editors). New York: Plenum Publishing Corporation, pp. 297-303. Cowan, S. T. & Steel, K. J. (1974). Characters of gram-negative bacteria, The enterobacteria. In: Manual for the identification of medical bacteria. (2nd edit.). Cambridge: Cambridge University Press, pp. 103-117. Department of Health & Social Security (DHSS) (1969). The bacteriological examination of water supplies. Reports on Public Health and Medical Subjects, No. 71, 4th edition, London: HMSO. Giannella, R. A. (1976). Suckling mouse model for the detection of heat-stable Escherichia coli enterotoxin: characteristics of the model. Infection and Immunity, 14, 95-99. Jiwa, S. F., Krovacek, K. & Wadstrom, T. (1981). Enterotoxigenic bacteria in food and water from an Ethiopian community. Applied Environmental Microbiology, 41, 1010-1019. Konowalchuk, J., Speirs,, J. I. & Stavric, S. (1977). Vero response to a cytotoxm of Escherichia coli. Infection and Immunity, 18, 775-779. Lucas, A. 0. & Gilles, H. M. (1973). Infections through the gastrointestinal tract. In: Preventive Medicine for the Tropics. London: English Universities Press, pp. 38-94. Pickering, H. A. (1984). Social and environmental factors associated with high rates of diarrhoea in young children. University of London, Doctoral Dissertation (unpublished). Rowland. M. G. M.. Barrell. R. A. E. & Whitehead. R. G. (1978). Bacterial’contamination in traditional Gambian weaning foods. Lancet, i, 136-138. Rowland, M. G. M. (1983). Epidemiology of childhood diarrhea in The Gambia. In: Diarrhea and Malnutrition: Interactions, Mechanisms and Interventions. Chen, L. C. & Scrimshaw, N. S. (Editors), New York: Plenum Publishing Corporation, pp. 87-99. Schubert, R. H. W. (1974). In: Bergq’s Manual of Determinative Bacteriology (8th edit.) Buchanan, R. E. & Gibbons, N. E. (Editors). Baltimore: Williams & Wilkins, p. 345. Skirrow, M. B. (1977). Campylobacter enteritis-a new disease. British Medical Journal, ii, 9-11. Thatcher. F. S. & Clark. D. S. 11968). Micro-organisms in foods.‘Vol. 1. Their signt$cance and methods 07 enumeration. Canada: University of Toronto Press.
Accepted for publication
8th July,
1983.
AND HYGIENE (1984) 78, 209-211
Food and water hygiene and diarrhoea in young Gambian limited case control study
209
children:
a
N. LLOYD-EVANS’, H. A. PICKERING~, S. G. J. GOH~ AND M. G. M. ROWLAND~* ‘The Gambia GovernmentiMRC Joint Health Research Unit, The Gambia; 2The Ross Institute of Tropical Hygiene, London School of Hygiene and Tropical Medicine, Keppel Street, London WCIE 7HT; 3Medical Research Council Laboratories, Fajara, The Gambia Summary During the annual rainy season epidemic of diarrhoea in The Gambia, two groups of urban children were identified, one of which remained completely free of diarrhoea and another in which diarrhoeal prevalence exceed 30% over a period of three months. Microbiological studies on the food and water consumed by these children during one day showed widely varying degrees of contamination in both groups. No difference was observed in levels of contamination, faecal or otherwise, between the two groups. The real problem seemed to lie in accounting for the freedom from diarrhoea of some children rather than explaining possible causes of morbidity in others. Introduction Diarrhoea is a major cause of morbidity and mortality in young children worldwide. Transmission is faeco-oral and endemicity is high in third world communities where environmental hygiene is poor. Faecal contamination of food and water has been demonstrated in association with high diarrhoeal rates in such communities (ROWLAND et al.. 1978: BLACK et al., 1982); food in p‘articular was thobght t6 play an important role in this respect (BARRELL & RowLAND, 1979). Only infrequently has this association between contamination of food and water with disease been sought at an individual level (BLACK et al., 1982). We have attempted to use the microbiological qualities of food and water consumed by individual infants and young children as an objective marker of environmental hygiene and to relate this to the widely varying pattern of diarrhoeal morbidity experienced by these individuals. Materials and Methods This study was carried out in The Gambia in Bakau, a settled community of 10,000 persons and the sixth largest township in the country. It is 10 km from the capital, Banjul. Male occupations vary from white-collar jobs to fishing, trading and manual labour, with unemployment fluctuating at around 10%. Most women are full-time housewives; some are petty traders and a few have salaried jobs. Bakau has a piped chlorinated water supply delivered to public standpFp& and some individual compounds (enclosed areas of land housing one or more extended families). Most families have access to sanitational facilities, mainly pit latrines, within their compounds and all adults defaecafe in these or in two public latrines. Though “potty-training” is widespread young children often defaecate indiscriminately in the dwelling areas. The community is the subject of a number of studies on morbidity, the main emphasis being on diarrhoea in early childhood. During the 1982 rainy season (July to October) the diarrhoeal morbidity of approximately 300 children aged 6 to 36 months was monitored using a weekly home questionnaire for a Deriod of 105 davs. The mean number of days of diarrhoea per child was 12’with a range of 0 to 56 days. Thus 30 children were completely free of diarrhoea through the annual epidemic whilst 25 had diarrhoea for more than 25% of the time, mainly due to repeated acute episodes. During the month of November 1982 food and water hygiene was studied through one day for 20 weaning children between the age of six and 18 months, ten of whom
had remained free of diarrhoea and 10 who had suffered diarrhoea for more than 30% of the observation period. An anthropologist (HAP) and field worker visited the subjects’ compounds at 0700 hours, before breakfast. Samnles for bacteriological analvsis were obtained of the child’s breakfast food and any other cooked cereal set aside for use later in the day. Any breakfast food that had been kept was again sampled at noon. The children ate a wide variety of snack foods during the morning, some of which were samuled randomlv. The child’s drinkine water obtained from the family storage jar was sampled”at 1100 hours and one “first flush” sample obtained from a communal standpipe. Whenever possible a fresh stool specimen was obtained from the child on the day of the visit. Five-gram aliquots of food were added to 45 ml of 0.1% peptone diluting fluid, homogenized and serial dilutions examined using routine methods (THATCHER & CLARK, 1968). From all samples vieldina Escherichia coli 10 colonies were’ pooled for to-tin testing: LT-toxin-producers were identified using a Vero cell assay (KONOWALCHUK et al., 1977), and ST-producers by the infant mouse assay (GIANNELLA, 1976). Aliquots of water were examined for total coliform counts and E. coli by the membrane filtration technique (Millipore Corporation, USA) using standard methods (DHSS, 1969). Faecal samples were examined by direct microscopy and after formol-ether concentration for intestinal helminths and other parasites. Specific bacterial pathogens including salmonellae, shigellae and Vibrio cholerae were also sought using standard methods (COWAN & STEEL, 1974), Campylobacter spp. (see SKIRROW, 1977) and Aeromonas hydrophilia by the method of SCHUBERT(1974) confirmed by API 20E (API System SA, France). These organisms were also sought in water specimens.
Results 39 foods were examined, 17 from cases with high prevalence of diarrhoea (D) and 22 from children who had suffered no diarrhoea (C). Total
bacterial
counts ranged from 0-10*/g in both
groups. 17 foods (10 D, 7 C) contained no coliforms. The remainder
contained
from 10’ to more than lo7 per g.
Approximately half of all gruels whether sampled fresh or at four hours contained no E. coli (D 619, C 9117). In both groups counts of up to lo5 per g were
observed in the remainder indicating faecal contamination. Of the E. coli isolated only two were *Author
to whom correspondence
should be addressed.
210
FOOD
Table I-Numbers grouped according
AND
WATER
HYGIENE
AND
DIARRHOEA
Adult Foods Snacks All Foods
THE
GAMBIA
of samples and bacterial isolations from food samples consumed by young children to high (D) or zero (C) diarrhoea prevalence E. coli
Gruels
IN
Coliforms
Absent
Present (Range)
c”
t
5 ( 102-105) 8 ( 102-105)
c”
2 1
2 (102-10’) 2 (102-105)
ii?
3 1
1 (102) 1 (102)
c”
toxigenic, one producing heat-labile (LT) and the other heat-stable (ST) toxin. The LT-producing organism was isolated from freshly prepared gruel but could not be detected after four hours of storage. The ST-producer was also isolated in gruel; it was not detected in the fresh specimen but was isolated from the sample four hours after preparation. Gruels containing locally soured milk were particularly badly contaminated. In contrast no contamination was detected in one specimen to which tinned evaporated milk had been added during cooking. Seven adult cereal foods (steamed or boiled) were examined. Two from the diarrhoea (D) group and two from the control (C) group were contaminated with E. coli after overnight storage. Counts ranged up to lo5 and to greater than IO’ per g in the C and D groups respectively. The remaining three foods which were freshly prepared had no E. coli. Two snacks were examined from the C group and four from the D group. These were a variety of ice 1011~pops, sweetened liquid drinks, dry pastry and bread. Only the sweetened liquid drinks, one from each group, were contaminated with E. coli (up to 102/100 g). These food bacteriology results are summarized in Table I. The single standpipe water sample was sterile. Of the stored water samples tested only one from group C had E. coli (101/100 ml) but three of the D group were contaminated, one with a count greater than 103/100 ml. None of the E. coli isolated were toxigenie. Approximately half of the water samples in both groups had counts of greater than 10 coliforms/l00 ml; two samples from the C group remained sterile. Of 15 stools examined (nine from group C and six from group D), three yielded bacterial pathogens: one salmonella; one shigella plus campylobacter and one ST-toxigenic E. coli. Six contained Giardia lamblia and three yielded Ascaris lumbricoides also. There was no clear correlation between pathogens isolated and the diarrhoeal morbidity of the child. Discussion Discrete epidemics of diarrhoeal disease due to specific organisms have often been traced to contamination of food or water supplies.
Total bacteria
Absent
Present (Range)
Absent
Present (Range)
10 7
7 (102-10’) 15 (lo’-10’)
:
16 (lo’-10’) 21 (loi-108)
In endemic situations, particularly where young children are concerned, a clear understanding of diarrhoeal epidemiology rarely exists. Certainly faecal contamination of food and water has been shown to be commonplace in developing countries. Some studies have shown that the highest levels of food contamination are associated with seasonal peaks in diarrhoea prevalence and are worst in the food presented to young children, the age group in which diarrhoeal morbidity is highest (ROWLAND, 1983; BLACK et al:, 1982). In addition to the agents of gastroenterms many other organisms found in such foods may produce enterotoxins (JIWA et al., 1981). Such evidence relating food to diarrhoeal illness is of course circumstantial, though a causal relationship has been suggested by the Bangladesh studies already referred to (BLACK et al., 1982). If, as seem likely, “food occupies a central and important position” in the epidemiology of diarrhoeal disease (LUCAS & GILLES, 1973) one might expect the standard of food and water hygiene of a community to be reflected in its diarrhoeal rates and the same factors within a family to affect the diarrhoeal rates of the individual members. In Bakau township the provision of an accessible, efficiently chlorinated water supply, the customary use of latrines and the much greater time which mothers are able to devote to normal domestic duties including child-care, contribute to an environment in which poor food and water hygiene and the faeco-oral spread of disease could be less common than in the strongly contrasting circumstances observed in Keneba (ROWLAND, 1983). In fact many of the water and food samples obtained in Bakau were completely clean but the range of contamination, disturbingly, was as high as found in the earlier study in Keneba (BARRELL & ROWLAND, 1979). Interestingly the least hygienic foods were again stored gruels, particularly those to which unprocessed cows’ milk had been added. The relatively good bacteriological quality of the gruels sold by the street vendors illustrated the virtues of fresh production and high turn-over though clearly such a system if mishandled could equally well generate an epidemic. In Bakau we would recommend improved water storage within the homes and, as in Keneba, the consumption of food as soon as possible after cooking; the addition of supplements such as
N.
LLOYD-EVANS
milk or sugar should be made immediately before consumption. Would such conventional advice be expected to help? Our results in this respect were unpromising. There was no obvious correlation between our measurement of water and weaning food contamination and the diarrhoeal morbidity of the child. Though numbers were small the pattern of morbidity in the two groups contrasted so strongly that some differences could have been expected had the bacteriological examinations we were making been of fundamental enidemioloaical imnortance. This lack of correlation was not an Isolated phenomenon in our experience. In the much larger comprehensive environmental study in Bakau (Pickering, 1984) no single, nor indeed combined factors were significantly related to diarrhoeal morbidity in children. In any such community gastro-intestinal infection and consequent disease will be determined by a complex interaction between the general environment, personal practice and individual “immunity”. Infants and toddlers avidly exploring their contaminated surroundings, transferring a variety of objects from hand to mouth, often allowed to defaecate indiscriminately and with incompletely developed or impaired immune defence systems are obviously the most susceptible group and this is clearly reflected in the age distribution of diarrhoeal disease. Only widespread multifactorial improvements in hygiene at a civic and personal level are likely to have a measurable impact on this situation (BLACK et al., 1983) unless we can learn why some children manage to escape disease so successfully. These reasons are not at present known. A change in emphasis away from investigating why children get diarrhoea (often all too obvious) to an examination of why others remain relatively free of symptoms despite their environment might point us in the direction of more effective strategies. Acknowledgements The authors thank Dr. A. M. Tomkins for helping to initiate the morbidity surveillance system. References Barrell, R. E. A. & Rowland, M. G. M. (1979). Infant foods as a potential source of diarrhoeal illness in rural West Africa. Transactions of the Royal Society of Tropical Medicine and Hygiene, 73, G-90. Black, R. E., Brown, K. H., Becker, S., Alim, A. R. M. A. & Merson, M. H. (1982). Contamination of weaning
et al.
211
foods and transmission of enterotoxigenic Escherichia coli diarrhoea in children in rural Bangladesh. Transactions of the Royal Society of Tropical Medicine and Hygiene, 76, 259-264. Black, R. E., Chen, L. C., Harkavy, O., Rahaman, M. M. & Rowland, M. G. M. (1983). Prevention and control of the diarrhoeal diseases. In: Diarrhea and Malnutrition: Interactions, Mechanisms and Interventions. Chen. L. C. & Scrimshaw, N. S. (Editors). New York: Plenum Publishing Corporation, pp. 297-303. Cowan, S. T. & Steel, K. J. (1974). Characters of gram-negative bacteria, The enterobacteria. In: Manual for the identification of medical bacteria. (2nd edit.). Cambridge: Cambridge University Press, pp. 103-117. Department of Health & Social Security (DHSS) (1969). The bacteriological examination of water supplies. Reports on Public Health and Medical Subjects, No. 71, 4th edition, London: HMSO. Giannella, R. A. (1976). Suckling mouse model for the detection of heat-stable Escherichia coli enterotoxin: characteristics of the model. Infection and Immunity, 14, 95-99. Jiwa, S. F., Krovacek, K. & Wadstrom, T. (1981). Enterotoxigenic bacteria in food and water from an Ethiopian community. Applied Environmental Microbiology, 41, 1010-1019. Konowalchuk, J., Speirs,, J. I. & Stavric, S. (1977). Vero response to a cytotoxm of Escherichia coli. Infection and Immunity, 18, 775-779. Lucas, A. 0. & Gilles, H. M. (1973). Infections through the gastrointestinal tract. In: Preventive Medicine for the Tropics. London: English Universities Press, pp. 38-94. Pickering, H. A. (1984). Social and environmental factors associated with high rates of diarrhoea in young children. University of London, Doctoral Dissertation (unpublished). Rowland. M. G. M.. Barrell. R. A. E. & Whitehead. R. G. (1978). Bacterial’contamination in traditional Gambian weaning foods. Lancet, i, 136-138. Rowland, M. G. M. (1983). Epidemiology of childhood diarrhea in The Gambia. In: Diarrhea and Malnutrition: Interactions, Mechanisms and Interventions. Chen, L. C. & Scrimshaw, N. S. (Editors), New York: Plenum Publishing Corporation, pp. 87-99. Schubert, R. H. W. (1974). In: Bergq’s Manual of Determinative Bacteriology (8th edit.) Buchanan, R. E. & Gibbons, N. E. (Editors). Baltimore: Williams & Wilkins, p. 345. Skirrow, M. B. (1977). Campylobacter enteritis-a new disease. British Medical Journal, ii, 9-11. Thatcher. F. S. & Clark. D. S. 11968). Micro-organisms in foods.‘Vol. 1. Their signt$cance and methods 07 enumeration. Canada: University of Toronto Press.
Accepted for publication
8th July,
1983.