|Food and Nutrition Bulletin Volume 17, Number 3, 1996 (UNU Food and Nutrition Bulletin, 1996, 104 pages)|
|Public health nutrition|
|Vitamin A deficiency and the prevalence of xerophthalmia in southern Rwanda|
Data were collected in November and December 1987 in the prefecture of Gikongoro, a rural region of Rwanda located between 1,500 and 2,000 meters above sea level. The population is 500,000, approximately one-tenth of the national population. It is one of the poorest prefectures of Rwanda. Gikongoro is divided into 13 communes, 12 of which were studied. The thirteenth commune was not included because it was assessed using a different method and had already received vitamin A supplementation . A sample size of approximately 6,000 children was required for an estimated prevalence of Bitot's spots of 1 % with a precision of 0.25 % (95 % confidence interval). After stratification by commune (n = 12), a random sample of 52 clusters from a complete list containing 752 clusters was used. Each cluster represented an administrative region with a population of approximately 115 children aged five years or less. All children were eligible for the study, and a complete census of five randomly selected clusters (among the 52) indicated a population coverage of 98.1%.
A total of 5,629 children underwent an ophthalmological examination. Three groups were defined, as shown in table 1. Group 1, cases, consisted of children diagnosed with Bitot's spots. Group 2, controls, were matched with cases of Bitot's spots for gender and age (within one year) and appearing next on the list in the same or neighbouring cluster. Group 3 was a systematic sample (10%) from the total population that received an ophthalmological examination. Group 3 was used to assess the level of vitamin A deficiency among the entire population of Gikongoro prefecture because the matched controls were not representative of the entire region but rather of the areas where cases occurred. Group 3 also served to assess the overall nutritional status of children from the region .
TABLE 1. Screening, sub-sampling, and measurements for children 0 to s years old examined in Gikongoro (N =5,629)
|Bitot's spots cases||Matched controls||Representative sample|
|n = 74||n = 74||n = 592|
|Food frequency questionnaire||67||67||300|
All children examined received 200,000 IU of retinol and 50 mg of levamisol. Children with Bitot's spots and those with more advanced xerophthalmia were treated according to Sommer's guidelines [1, 5]. Common childhood diseases were treated on the spot.
Bitot's spots were classified as unilateral when they were located in one eye, bilateral-temporal when they were located temporally in both eyes, and bilateral temporo-nasal when they were located in the temporal and nasal conjunctive in both eyes. Corneal scars were attributed to vitamin A deficiency only after exclusion of other causes of corneal scars by history and physical examination, as suggested by Sommer . Signs of corneal ulcers, xerosis, and scars were noted, but because of their low frequencies, the sample size was not sufficiently large to obtain reliable estimates of their prevalence.
Table 1 shows the measurements taken for each case and matched control in the study population: anthropometric measurements (including the presence of clinical signs of malnutrition, such as oedema, lunar facies, uncurled hair), serum retinol, and the frequency of consumption of foods containing vitamin A or its precursors. Because of delays in receiving proper test tubes, only 56 pairs of cases and controls had serum retinol determinations. All children in the representative sample had anthropometric measurements taken, but serum retinol and food frequency data were obtained randomly in half the sample.
Children weighing less than 25 kg were weighed with a Salter's scale; heavier children were weighed with an ordinary bathroom scale. Height was measured with an AHRTAG apparatus ; taller children were measured using a standing yardstick. Venous blood was drawn for retinol determination. Samples were centrifuged the same day, and serum was frozen until processing six months later. Retinol was analysed by high-pressure liquid chromatography at the Landbouwuniversiteit, Wageningen, Netherlands.
The food frequency questionnaire measured the frequency of consumption of 20 sources of vitamin A or beta-carotene, as suggested by Sommer . Data were summarized into three frequency categories (see table 5 footnote). A food diversity score was developed by cumulating the frequency of consumption of the foods listed (1 if consumed, 0 if not consumed).
The Centers for Disease Control Anthropometric Software Package (CASP) was used to obtain the anthropometric indices weight-for-age, height-forage, and weight-for-height. All children with visible oedema were classified as wasted [weight/height (w/h) < 80%] according to the Waterlow criteria, as the presence of oedema elevates the w/h ratio. Analysis of variance, paired t tests, and McNemar c2 tests were used in the analyses (SPSS ).