Health & Medical Public Health

Epidemiology of Type 1 Diabetes in Young Adults and Adults

Epidemiology of Type 1 Diabetes in Young Adults and Adults

Results

Description of the Information Obtained From the Systematic Review on Adult T1D


Seventy articles reporting incidence of T1D in young adults and adults aged over than 15 years concerned one country, and one article concerning two countries were retrieved in this systematic review, resulting in a total of 71 studies covering 35 countries (Table 1). Twenty-four of the 71 studies were nationwide; 43 papers provided information on the T1D incidence in the age class 15–29 years, 26 in the age class 30–59 years, and 6 in the persons aged >60 years.

A primary source of information was reported in 99% (70 of 71) of the studies: among these reported sources, 60% (42 of 70) were from medical/hospital records, 36% (25 of 70) from national or regional registers, and 4% (3 of 70) from other sources, such as community-based surveys; a secondary source of information was reported in 90% (64 of 71) of the studies: among these reported sources, 58% (37 of 64) were from medical/hospital records, 16% (10 of 64) from associations of patients, 14% (9 of 64) from drug or supplies prescription registers, 8% (5 of 64) from national or regional registers, and 5% (3 of 64) from death certificates and schools registers; finally, a tertiary source of information was reported in 21% (15 of 71) of the studies: among these reported sources, 27% (4 of 15) were from national or regional registers, 27% (4 of 15) from associations of patients, 20% (3 of 15) from death certificates, 20% (3 of 15) from drug or supplies prescription registers, and 7% (1 of 15) from medical registers; see details in Table 1. Percentage of ascertainment (completeness) between sources of information was evaluated in 53 of 71 (75%) studies. The mean percentage of ascertainment of these 53 studies was 94% (Table 1).

In the group of young adults (15–19), the lowest incidence of T1D was reported in Mauritius, (1.1/100.000 persons/year), and the highest in Estonia (39.9/100.000 persons/year). In the 70–79 year age group, the lowest incidence was reported in Navarra, Spain (0.8/100.000 persons/year) and the highest in Kronoberg, Sweden (55/100.000 persons/year). The details of all retrieved incidence by study and age classes are in Additional file 4: Table S1 http://www.biomedcentral.com/1471-2458/15/255/additional.

Diagnostic Criteria Used to Define T1D in Adults Reported in 71 Epidemiological Studies


Autoantibodies against beta-cell antigens or the C-peptide were included in the T1D diagnostic criteria in 14 studies, detection of ICAs was reported in 9 studies, IAA in 4 studies, IA2 in 5 studies, and GAD in 11 studies. The C-peptide was measured in 7 studies. In one paper difference of auto-antibodies by age group (0–19) was explored but no significant differences were detected. The other reported diagnostic criteria for T1D were the need for insulin therapy (reported in 70 of 71 studies), clinical symptoms of diabetes (reported in 56 of 71 studies), low or normal body weight (14 of 71 studies), and ketosis or ketonuria (26 of 71 studies). The details are shown in Table 1.

Comparison of Adult and Children T1D Incidences


The variations of incidence of T1D in adults with country and age were studied in each area for which we retrieved information on a geographically defined population. This concerned 35 countries.

Variation of T1D Incidence With Age in Adults. In 23 out of 35 (66%) countries (55 of 71 studies), the incidence of T1D was higher in the age range of 0–14 compared with 15–19 years. When restricted to the 14 reports for which the criteria of diagnosis of T1D were auto-antibodies against beta-cells or C-peptide detection, the variation of adult incidence with age showed a consistent decrease after the age of 14 years (Figure 2 and Additional file 4: Table S1 http://www.biomedcentral.com/1471-2458/15/255/additional).



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Figure 2.



Age variation of incidence from childhood to adult age. On this figure, the adult estimates of incidence were taken from the 14 reports of the systematic review using the autoantibodies/C-peptide as diagnostic criteria. Full lines correspond to articles from which both child as well as adult information could be retrieved. The dotted lines are those for which the child information was searched in the same country as in the adult paper, but was from a different paper (seep Additional file 3 for details on this literature search). The corresponding countries are shown as: BE1: Belgium (2007) [30]; BE2: Belgium (2002) [31]; BE3: Belgium (1997) [32]; DK: Denmark [34]; ES1: Spain, Catalonia [54]; ES2: Spain, Navarra (2014) [56]; ES3: Spain, Navarra (2013) [57]; FI: Finland [35]; IR: Iran (Islamic Republic of) [15]; IT: Italy [45,46]; SE: Sweden [63], TW: Taiwan [81]; US: United States of America [74].





Geographical Correlation of Adult and Child T1D Incidence. A significant geographical correlation, as measured by the Spearman correlation coefficient, was found between adult T1D incidence and 0–14 incidence in the age classes 15–19 years, 20–24 years, 25–29 years, 30–34 years and overall in the entire 15–60 group (r = 0.75, p-value: 5.7 × 10). The correlation was not significant in the oldest class where sparse data were available, but the relation was similar (Figure 3).



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Figure 3.



Geographical correlation of T1D incidence between individuals aged 0–14 years and adults. Studies using autoantibodies/C-Peptide for T1D case definition are identified by Red diamonds. The corresponding countries are shown as: BE1: Belgium (2007) [30]; BE2: Belgium (2002) [31]; BE3: Belgium (1997) [32]; DK: Denmark [34]; ES1: Spain, Catalonia [54]; ES2: Spain, Navarra (2014) [56]; ES3: Spain, Navarra (2013) [57]; FI: Finland [35]; IR: Iran (Islamic Republic of) [15]; IT: Italy [45,46]; SE: Sweden [63], TW: Taiwan [81]; US: United States of America [74]. Sp. Cor: Spearman correlation.




Comparison of Male and Female T1D Adult Incidences


T1D incidence was larger in males aged 15 to 39 years than in females in 44 (81%) of the 54 studies reporting incidence by sex (Additional file 5: Table S2 http://www.biomedcentral.com/1471-2458/15/255/additional). The mean male-to-female ratio in our review was 1.47 (95% CI for mean 1.33–1.60, SD = 0.49, n = 54, p = < 0.0001).



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