Trachoma and water use; a case control study in a Gambian village

824

TIZAN~ACTIONS OFTHEROYALSOCIETY OFTROPICAL

Trachoma

MEDICINE

AND

85, 824-828

and water use; a case control study in a Gambian village

R. Bailey’, B. Dowries’, R. Dowries’ and D. Mabey’ Hygiene Gambia

HYGIENE (1991)

and Tropical

Medicine,

Keppel Street, London,

Abstract Trachoma is prevalent in many arid areas but data assessing the relationship between water use and trachoma are very scarce. This study compared 18 families having one or more active trachoma cases among the children with 16 trachoma-free families in the same village with respect to water use. Potential confounders such as family size, distance to water source, socio-economic indicators, and hygiene behaviour were assessedin the 2 groups. The families with trachoma were found to use significantly less water per person per day for washing children than did the control group (P=O*O33) with no evidence of confounding by the other measured variables. Low amounts of water for washing were also associated with unclean faces and impetigo in the children. If such a relationship can be substantiated it might provide the basis for effective and cheap interventions against trachoma. Introduction Trachoma, the most prevalent infectious cause of blindness, has long been recognized to be hyperendemic in many arid and dusty areas of the world (DAWSONet al:, 1981). This has led to the hypothesis that water availability, or behavioural factors related to water use, are important determinants of ocular infection with the causative organism, Chlamydia trachomatis. PROST & NEGREL (1989) reviewed published work

on trachoma and water availability and emphasized some of the technical difficulties inherent in investigating the relationship between the two. In published studies meeting their criteria the main confounding factor was the inability to separate water usage and availability from other variables associated with income and welfare. Several studies have shown an association between prevalence of active trachoma and distance to the water source (CAIRNCROSS & CLIFF, 1987; KUPKA et al., 1968; WEST et al., 1989), but in only 2 studies has water usage actually been measured. CAIRNCROSS & CLIFF (1987) in Mozambique assessedwater quantity and usage in detail but their assessmentof trachoma did not distinguish between active and healed trachoma lesions. KUPKA et al. (1968) assessedwater usage per caput by an interview .technique and observed no effect on trachoma mevalence in Morocco. WESTet al. (1989), in a &orough risk factor analysis of trachoma in Tanzania, investigated water-related and hygiene behaviour variables. They showed an association between trachoma prevalence and distance to the water source. However, the estimated amount of water brought into the household did not appear to influence either the prevalence of trachoma or the prevalence of unclean faces, and it was suggested that

‘Department of Clinical Sciences, London School of WClE 7HT, UK; ‘Dunn Nutrition Unit, Keneba, The

a behavioural factor influencing water use was implicated. BLUM & FEACHEM (1983), in their review of problems in the measurement of the effects of sanitation and water supply on health, argued that within-village studies can be useful in overcoming certain comparison problems and emphasized the utility of ‘opportunistic’ studies in this difficult area. The village of Keneba, the base of the Medical Research Council (MRC) Dunn Nutrition Unit in the Kiang West district of The Gambia, had a piped borehole water supply installed in 1986. As part of a seriesof investigations designed to evaluate its effect, water usage measurements and a cross-sectional trachoma survey were carried out there in 1987. We have used a casecontrol method to compare facilities with and without casesof active trachoma in respect of water usage and other socio-economic variables. Methods The geography and social environment of Keneba have been described elsewhere (MCGREGOR, 1976). The population is approximately 1300, mainly Muslims of the Mandinka tribe who live principally by subsistencefarming with groundnuts as the only cash crop. The piped water supply in Keneba comprises 3 sets of standpipes, situated in the main street which roughly bisects the village. Most of the village lives within 500 m of this facility and usage is virtually total. Before 1986, water was obtained from traditional deep wells and one protected well with a handpump. In August 1987 564 children under 15, representing well over 90% of the known population (from MRC records), were examined for signs of trachoma by an experienced observer (D.C.W.M.), using a ~4 illuminated monocular loupe. The subtarsal conjunctiva was examined after eversion of the eyelids. Active trachoma was diagnosed according to World Health Organization criteria (DAWSON et al., 1975). Water use was measured by field workers resident in the village. A field worker was assigned to one family unit from dawn (0645 h) to dusk (1930 h) on a single day. Observations were made on ‘typical’ weekdays, avoiding days of religious duty and other significant events. Collection of water outside these hours was observed to be unusual. Subjects were additionally asked to report if any water was collected while the field worker was absent and an estimate based on the container used was incorporated into the data; this occurred rarely. The amount of water collected by each family unit was determined directly by weighing the water carriers on leaving and returning to the household using a single set of scales, calibrated against an electronic balance and accurate

825

to 0.5 kg. The water used per person per day was calculated as the measured amount divided by the number of persons in the family unit using that water. The amount of water used for washing children was calculated from observations of the receptacles used combined with determinations of their volume. This total amount of water was then divided by the number of children washing or being washed with it. From census data the mothers of the trachoma survey children were identified. The case group consisted of 18 mothers whose children had one or more cases of active disease and from whom water data had been collected. In all. these mothers had 68 children, of whom 33 had active trachoma. A control group of 16 mothers for whom water data were available and whose children were free of active trachoma were selected so that they matched the case group as closely as possible in respect of the age distribution of their children; this group had 50 children in all. The case and control groups were then assessed with respect to a number of variables reflecting personal possessions, economic status and hygiene behaviour, using both interview and direct observation by one of the authors (B. D., a resident medical practitioner), with assistancefrom fieldworkers living in the village. Odds ratios were determined for individual discrete variables and an exact calculation of 95% confidence intervals was made using the EpiInfo software package (MEHTA et al., 1985). The water use measurements had negatively skewed distributions and were normalized by logarithmic transformation. Student’s t statistic was then used to compare case and control groups for the continuous variables. A null hypothesis of equality between case and control groups (twotailed criterion) was used throughout. Evidence of confounding was sought by stratification of potential confounding variables, analysed separately for case and control groups, and by the use of logistic regression analysis.

number

of children

16G 14

12

6

6-7

8-8

age(yrs)

Fig. 1. Age distribution and prevalence of trachoma in case family children; hatched bars indicate all children, solid bars indicate active cases only

number

of children

16

14 r

--

12t

Results

Seventy-one casesof active trachoma were found in children under 15 vears old from a total of 564 children examined (prevalence 13%). The age distribution and trachoma prevalence in the children of case and control families are shown in Figs 1 and 2. There was no significant difference in prevalence between the sexes. There was also no evidence of a trend in prevalence rates with increasing number of children per family, either in crude prevalence or after adjustment for age structure. The water data show considerable variability in amounts collected within the village and in volumes used for washing children. The amount collected ner person varied f;om 6 to 30 litresipersonid and
agetyrs)

Fig.

2. Age distribution

of control

family

children

group had slightly larger families and less sleeping area per person relative to the control group., but neither effect achieved significance. Three variables were significantly different between the case and control group. Less water was used per child for washing and fewer possessionswere owned by case group mothers; and impetigo in one or more of the

826 Table

1. Comparison

of case and control

families

Variable

Case families

Number of children Number of children per family: mean Age of children: mean (years) Sleeping area per person: mean (m’) Distance to tap: meanb (m) Water brought to household: mean (litresipersonid) Water for washing children: mean (litresichildid) Impetigo present in one or more children

Control

families

Significance”

50

68 3.78 5.68 2.8 (0.76)

-

3.13 5.66 3.2 (0.83) 1;; 9(101)

‘:o;fp (53) 4.2 5

6.4 0

E is P=!SO3 P=O*O4’

“NS=not significant; significance determined by Student’s t test except were indicated. The water use variables were transformed logarithmically because of non-normality. Non-parametric methods gave similar results. bStandard deviation in narentheses. ‘Fisher’s exact test. Table 2. Income, case and control

housing families

conditions,

and possessions

in

Odds ratiob Father having salary or income from trading Mother having income from salary, or sale of garden produce Cement floor Walls painted Walls plastered Latrine in compound Possessions Mosquito net cocci or metal trunk

0.29 (0.05 trading, 0.79 (0.12 3.0 (0.48 0.88 (0.06 0.91 (0.17 0.54 (0.04

0.71 0.33 0.38 Kerosene lamp 0.13 0.37 Cows (one or more) Sheep (one or more) 0.23 Four or more of the above items 0.09 “95% confidence interval in parentheses. zkb:;ei.

Hygiene

and eye

care

among

(0.05 (0.06 (0.07 (0.03 (0.03 (0.04 (0.01 case

- 1.54) -

6.28) 20) 14.2) 4.76) 5.56)

-

7.1) 1.49) 1.96) 1.47) 3.23) 1.16) 0.57)

and control

Odds ratio” Children Apparently unclean 2.96 Washed more than twice per dav 1.14 Faces washed more than twice 1.14 per day Soap always used 0.34 Faces dried with shared cloth 1.33 Shared cloth or fingers used to wipe sticky eyes 0.81 “95% confidence interval in parentheses. Table 4. Correlation apparently unclean

between children

amount

(0.47 - 19.98) (0.19 - 7.1) (0.19 - 7.1) (0.06 - 2.0) (0.78 - 6.58) (0.10 -

5.86)

Table 5. Trend in odds ratio for trachoma in families with decreasing amounts of water used for washing children

Water used Case Control Odds families families ratio” (litresichildld) >6.8 3 1.0 3.4-6.8 2 1.67 ti 5 3.0 <3.4 ‘x2 test for trend was not significant. Odds ratios are relative to the top stratum. children was seen more frequently in the case group relative to the control group. Variables relating to housing conditions, income, and other aspects of hygiene behaviour could not be shown to vary either individually or collectively between cases and controls. Low amounts of water used for washing children were correlated not only with trachoma in families but, in the combined data set, were also significantly associated with unclean faces and impetigo in those children (Table 4). Stratification of the washing water variable showed an increase in odds ratio for trachoma in the family with decreasing amounts of water used per child for washing (Table 5). Confounding effects were sought in the data. The case and control group did not differ significantly in terms of distance to the water source. There were slightly larger families in the case group, and large families are more likely to contain a trachoma case, but there was no trend in the amount of water used for washing per child with family size in either case or control group. The case group had less sleeping area

of water used for washing

and prevalence

of trachoma,

impetigo,

and

Mean volume of water for washing (litresichildld) Significance” Trachoma Trachoma Impetigo Impetigo Children Children

4.23 6.43 2.68 5.71 3.64 5.94

present in one or more children (n=18) absent (n= 16) present in one or more children (n=S) absent (n=29) apparently unclean (n= 10) apparently clean (n=24)

YSigSig~ance determined

by Student’s

t test on log-transformed

variables;

non-parametric

P=O.O337 P=O.O149 P=O-05 methods gave similar

827

per person, but this was not correlated with water use. The age structure of the families was comparable between case and control groups. The control group owned more possessions than the case group, but analysis showed that possessions considered individually or collectively did not confound the association between trachoma and low amounts of water used for washing children. Discussion

The small size of this study makes firm conclusions inadvisable but nevertheless some interesting features deserve comment. The study demonstrated a lo-fold variation in the amount of water used for washing children within the village. Some day to day variation was likely; however, the association of impetigo cases and observation of unclean faces with low amounts of water for washing supported the validity of the observations, as did the negative trend in water collected per person with distance to the water source. There was a suggestion of a ‘dose response’ relationship between low amounts of water used for washing children and trachoma in those children. It is thus likely that the significant association between trachoma and low amounts of water for washing children did indeed represent a real effect. HOQUE et al. (1989) studied determinants of water consumption in rural Bangladesh and found a similar distribution of water consumption per caput. They also noted a negative associatibn with distance to thi water source. MERTENS et al. (1990) in Sri Lanka found no relationship between ‘the time needed to obtain water and consumption per caput but did not directly measure water consumption, using an interview technique combined with measurements of containers. This study has not demonstrated an effect of water availability on trachoma prevalence. However, the power of the study to demonstrate such an effect was not great. WEST et al. (1989) reported an effect which became manifest at more than 30 min from the water source. In Keneba almost everyone was within 5 min walk of the water source and it-seems likely that water availability was much less critical there than in the much drier Tanzanian environment. TAYLOR et al. (1985) in Mexico described an effect of face washing, distinct from washing other parts of the body, on trachoma prevalence. In Australia a daily bath for schoolchildren was associated with a lower C. trachomutis detection rate (HARDY et al., 1967), and in a comparison in Mozambique more trachoma was found in a village where fewer children had a daily bath (CAIRNCROSS & CLIFF, 1987). In our study all subjects washed or were washed at least daily. Questions relating to how many times the face or whole body was washed each day produced identical answers and no further analysis-w& therefore possible. In common with the larger studv of TIELSCH et al. (1988) in Malawi, we -have not shown any difference in the number of daily washes between case and control groups. Data derived from the comparison between Keneba and other nearby Dunn Nutrition Unit study villages which use traditional wells (R. Downes, unpublished information) suggest that the provision of a piped water supply has not significantly affected the amount of water collected, and it has been shown elsewhere

that water needs to be supplied directly into the household before consumption increases significantly (CAIRNCROSS, 1987). It seems likely that the main effect of the provision of the piped water supply has been an imnrovement in the quality of water rather than an in&ease in the quar&y used for washing. These data support the suggestion of WEST er al. (1989) that behavioural factors acting: at the level of water’ use are important in trachgma. The wide variation in observed amounts of water used for washing children does appear to influence trachoma prevalence. A larger detailed study of the influences on water use in this environment would clarify this relationship which might be amenable to intervention, perhaps via a health education campaign. Such campaigns may be an appropriate way to maximize the effect of improved water resources on waterrelated disease. Trachoma is a disease of poverty which has disappeared where substantial improvements in socioeconomic conditions have occurred. Sadly, in many environments such changes are unlikely, so that interventions aimed at modifiable aspects of hygiene and water use behaviour may be an important method of trachoma control. Acknowledgements

We are grateful to the people of Keneba for their unfailing patience during many studies, and to the field staff Momodu Lamin Colley, Nuah Sanneh, Lamin Sanyang and Bakary Dibba. who assisted with this studv. We are most erareful to Dr Sandv Cairncross for his review-of the manus&& and his helpful iomments. This work was in part supported by a grant from the Edna McConnell Clark Foundation. R.B. was supported by a Medical Research Council Training Fellowship. References

Blum, D. & Feachem, R. G. (1983). Measuring the impact of water supply and sanitation investments on diarrhoeal diseases: problems of methodology. InternationalJournal of Edidemiolow.

12. 357-365.

Cair~crdss, S. (1%7). ‘The benefits of water supply. In: Developing World Water, Pickford, J. (editor), volume 2. London: Grosvenor Press, pp. 30-34. Cairncross, S. & Cliff, J. L. (1987). Water use and health in Mueda, Mozambique. Transactions of the Royal Society of Tropical

Medicine

and Hygiene,

81,

51-54.

Dawson, C. R., Jones, B. R. & Darougar, S. (1975). Blinding and non-blinding trachoma: assessment of intensity of upper tarsal inflammatory disease and disabling lesions. Bulletin of the World Health Organization.

52. 279-281.

Dawson, C.‘R., Jones, B. R. & Tarizzo, M. L. (1981). Guide IO Trachoma Control. Geneva: World Health Organization.

Hardy, D., Surman, P. G. & Howarth, W. H. (1967). The cytology of conjunctival smears from aboriginal schoolchildren at Yalata, South Australia after improved hygiene conditions and treatment. American Journal of Ophthalmology, 63, 1538-1540. Hoque, B. A., Hultly, S. R. A., Aziz, K. M. A., Patwary, M. Y. & Feachem, R. G. (1989). Tubewell water consumption and its determinants in a rural area of Bangladesh. Journal of Tropical Medicine and Hygiene, 92, 197-202. Kupka, K., Nizetic, B. & Reinhards, J. (1968). Sampling

studies on the epidemiology and control of trachoma in southern Morocco. Bulletin of the World Health tion, 39, 547-566. McGregor, I. A. (1976). Health and communicable in a rural African environment. Oikos, 27,

Organizadisease 180-192.

828 Mehta, C. R., Patel, N. R. & Gray, R. (1985). Computing an exact confidence interval for the common odds ratio in several 2x2 tables. Journal of the American Statistical Association,

78,

969-973.

Mertens, T. E., Fernanda, M. A., Marshall, T. F. de C., Kirkwood, B. R., Cairncross, S. & Radalowicz, A. (1990). Determinants of water quality, availability and use in Kurunegala, Sri Lanka. Troprcal Medicine and Parasitology, 41, 89-97. Prost, A. & Negrel, A. B. (1989). Water, trachoma and conjunctivitis. Bulletin of the World Health Organization, 67, 9-18. Taylor, H. R., Velasco, F. M. & Sommer, A. (1985). The ecology of trachoma: an epidemiological study in south-

ern Mexico. Bulletin of the World Health Organization, 63, 559-567. Tielsch, J. M., West, K. P., Katz, J., Keyvan-Larijani, E., Tizazu, T., Schwab, L., Johnson, G. J., Chirambo, M. C. & Taylor, H. R. (1988). The epidemiology of trachoma in southern Malawi. American Journal of Tropical

Medicine

and Hygiene,

38,

393-399.

West, S., Lynch, M., Turner, V., Munoz, B., Rapoza, I’., Mmbaga, B. B. 0. & Taylor, H. R. (1989). Water availability and trachoma. Bulletin of the World Health Organizarion,

Received accepted

67,

71-75.

18 February for publication

1991; revised 10 June 19 June

1991

1991;