Diabetes incidence and projections from prevalence surveys in Fiji

Background: Type 2 diabetes mellitus (T2DM) incidence is traditionally derived from cohort studies that are not
always feasible, representative, or available. The present study estimates T2DM incidence in Fijian adults from T2DM
prevalence estimates assembled from surveys of 25–64 year old adults conducted over 30 years (n = 14,288).
Methods: T2DM prevalence by five-year age group from five population-based risk factor surveys conducted over
1980–2011 were variously adjusted for urban-rural residency, ethnicity, and sex to previous censuses (1976, 1986, 1996,
2009) to improve representativeness. Prevalence estimates were then used to calculate T2DM incidence based on birth
cohorts from the age-period (Lexis) matrix following the Styblo technique, first used to estimate annual risk of
tuberculosis infection (incidence) from sequential Mantoux population surveys. Poisson regression of year, age,
sex, and ethnicity strata (n = 160) was used to develop projections of T2DM prevalence and incidence to 2020
based on various scenarios of population weight measured by body mass index (BMI) change.
Results: T2DM prevalence and annual incidence increased in Fiji over 1980–2011. Prevalence was higher in Indians
and men than i-Taukei and women. Incidence was higher in Indians and women. From regression analyses, absolute
reductions of 2.6 to 5.1% in T2DM prevalence (13–26% lower), and 0.5–0.9 per 1000 person-years in incidence (8–14%
lower), could be expected in 2020 in adults if mean population weight could be reduced by 1–4 kg, compared to the
current period trend in weight gain.
Conclusions: This is the first application of the Styblo technique to calculate T2DM incidence from population-based
prevalence surveys over time. Reductions in population BMI are predicted to reduce T2DM incidence and prevalence in
Fiji among adults aged 25–64 years.