Age-period-cohort analysis of 1990-2003 incidence time trends of childhood diabetes in Italy: the RIDI study.
OBJECTIVE
To investigate age-period-cohort effects on the temporal trend of type 1 diabetes in children age 0-14 years in Italian registries.


METHODS
This report is based on 5,180 incident cases in the period 1990-2003 from the Registry for Type 1 Diabetes Mellitus in Italy (RIDI). Multilevel (random intercept) Poisson regression models were used to model the effects of sex, age, calendar time, and birth cohorts on temporal trends, taking into account the registry-level variance component.


RESULTS
The incidence rate was 12.26 per 100,000 person-years and significantly higher in boys (13.13 [95% CI 12.66-13.62]) than in girls (11.35 [10.90-11.82]). Large geographical variations in incidence within Italy were evident; incidence was highest in Sardinia, intermediate in Central-Southern Italy, and high in Northern Italy, particularly in the Trento Province, where the incidence rate was 18.67 per 100,000 person-years. An increasing temporal trend was evident (2.94% per year [95% CI 2.22-3.67]). With respect to the calendar period 1990-1992, the incidence rates increased linearly by 15, 27, 35, and 40% in the following time periods (P for trend < 0.001). With respect to the 1987-1993 birth cohort, the incidence rate ratio increased approximately linearly from 0.63 (95% CI 0.54-0.73) in the 1975-1981 cohort to 1.38 (1.06-1.80) in the 1999-2003 cohort. The best model, however, included sex, age, and a linear time trend (drift).


CONCLUSIONS
Large geographical variations and an increasing temporal trend in diabetes incidence are evident among type 1 diabetic children in Italy. Age-period-cohort analysis shows that the variation over time has a linear component that cannot be ascribed to either the calendar period or the birth cohort.
Bruno
Graziella
G
Department of Internal Medicine, University of Turin, Turin, Italy. graziella.bruno@unito.it
Maule
Milena
M
Merletti
Franco
F
Novelli
Giulia
G
Falorni
Alberto
A
Iannilli
Antonio
A
Iughetti
Lorenzo
L
Altobelli
Emma
E
d'Annunzio
Giuseppe
G
Piffer
Silvano
S
Pozzilli
Paolo
P
Iafusco
Dario
D
Songini
Marco
M
Roncarolo
Federico
F
Toni
Sonia
S
Carle
Flavia
F
Cherubini
Valentino
V
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology*; D005260:Female; D005843:Geography; D006801:Humans; D015994:Incidence; D007223:Infant; D007558:Italy / Q000453:epidemiology; D016013:Likelihood Functions; D008297:Male; D016012:Poisson Distribution; D012042:Registries