The incidence of childhood IDDM was associated with environmental factors including population density and overcrowded homes. A possible inference from these data is that patterns of infection are involved in the occurrence of IDDM. Analytical epidemiological studies will be needed to investigate these ideas further.

Summary. A register of the incidence of Type 1 (insulin-dependent) diabetes mellitus in the Yorkshire region of the United Kingdom has been completed. A total of 1,490 subjects aged between 0 and 16 years were identified from 1978 to 1990, giving an incidence of 13.7 per 100,000 (ages 0-14) or 13.6 per 100,000 (ages 0-16), comparable to other recent studies in the United Kingdom. An age-period-cohort analysis shows evidence for a modest drift effect of 1.75 % per year (95% confidence interval 0.28 to 3.25%). There is a marked epidemic pattern with peaks at 4-year intervals. The age-incidence curve is similar to that reported elsewhere, having peaks in early childhood and puberty. Girls have an earlier pubertal peak than boys. There is substantial seasonal variation in incidence confined to those over 5 years of age. Ascertainment is believed to be very complete, and is estimated to be 97.6% (95% confidence interval 97.2% to 98.1%).Key words: Type 1 (insulin-dependent) diabetes mellitus, epidemiology, aetiology, disease registry, childhood, ascertainment estimates.Type 1 (insulin-dependent) diabetes mellitus is an increasingly common disorder in many European populations [1,2]. Neither the causes of the condition, nor the causes of the increased incidence are known. Although a genetic predisposition is clearly of great importance, direct epidemiological evidence from case-control studies [3,4] and indirect epidemiological evidence from migrant studies [5,6] indicate that environmental agents are also very important.The descriptive epidemiology of Type i diabetes is an important source of information for the framing of aetiological hypotheses. Several prominent features require explanation. There is great geographical variation in incidence, with as much as a 40-fold variation between countries; Finland and Sardinia have the highest incidence rates (over 30 per 100,000 per year); Japan, Africa and Korea have the lowest (0.3 to 2.5 per 100,000 per year) [7][8][9][10][11][12][13]. The age incidence curve typically shows a peak in early adolescence, and may have a secondary peak earlier in childhood. There is marked seasonality of onset in many (though not all) studies [12,[14][15][16][17], although this may relate more to infections precipitating a metabolic decompensation in prediabetic persons, than to any aetiological agent [8]. The incidence in a population may change rapidly during short periods of time, whether in the indigenous population [18], or in migrant populations [5].A necessary first step in any series of investigations of the aetiology of Type 1 diabetes is to establish a good, well-validated register. This was the aim of the Yorkshire project.

1054 females of child-bearing age in Kuwait were screened for rubella antibodies. 56 or 5.4% were found seronegative. In view of this relatively low rate of susceptibility, a large-scale rubella vaccination campaign in Kuwait may not be necessary. An alternative vaccination policy is suggested.

SUMMARY The modification of the standard rubella haemagglutination-inhibition (HAl) test using trypsin-treated human group 0 erythrocytes instead of chick erythrocytes was evaluated. In a comparative study we found that, of 816 samples tested by both methods, the titres of 807 (98-9 %) sera were in close agreement within an acceptable twofold difference. Trypsin-treated human group 0 erythrocytes usually provided titres that were twofold higher than those obtained with chick erythrocytes. In general, a very good correlation between the two methods was obtained. Data are presented that emphasise the importance of trypsin treatment of human group 0 erythrocytes before use in the HAI method. Furthermore, we found that trypsin-treated human group 0 erythrocytes can be stored for periods of up to 30 days and used in the HAI test without any appreciable loss of sensitivity or specificity. Moreover, we replaced chick erythrocytes with trypsintreated human group 0 erythrocytes in the sucrose density gradient/HAl method used for the detection of rubella virus-specific IgM and found it to be a very satisfactory method. In view of these findings we recommend that trypsin-treated human group 0 erythrocytes should replace chick erythrocytes in the standard rubella HAl test since the former provided not only a more sensitive, more economic, and less time-consuming method but also a technique which is as specific as that using chick erythrocytes.The rubella haemagglutination-inhibition (HAI) test using day-old chick erythrocytes is the most widely used technique for both diagnostic and epidemiological studies on rubella. However, in most developing countries, such as Kuwait, a continuous supply of day-old chick cells from a commercial source is not usually available, and the use of this technique for such purposes is therefore limited.Quirin et al. (1972) andIwakata et al. (1974) provided preliminary data, which suggested that day-old chick erythrocytes could effectively be replaced by trypsin-treated human group 0 erythrocytes in the HAI method without affecting the sensitivity or specificity of the test. This encouraged us to investigate this possibility further, and in this paper we report our results. Furthermore, we have extended our investigation to show that trypsin-