The incidence of diabetes mellitus and diabetic retinopathy in a population-based cohort study of people age 50 years and over in Nakuru, Kenya.
BACKGROUND
The epidemic rise of diabetes carries major negative public health and economic consequences particularly for low and middle-income countries. The highest predicted percentage growth in diabetes is in the sub-Saharan Africa (SSA) region where to date there has been no data on the incidence of diabetic retinopathy from population-based cohort studies and minimal data on incident diabetes. The primary aims of this study were to estimate the cumulative six-year incidence of Diabetes Mellitus (DM) and DR (Diabetic Retinopathy), respectively, among people aged ≥50 years in Kenya.


METHODS
Random cluster sampling with probability proportionate to size were used to select a representative cross-sectional sample of adults aged ≥50 years in 2007-8 in Nakuru District, Kenya. A six-year follow-up was undertaken in 2013-14. On both occasions a comprehensive ophthalmic examination was performed including LogMAR visual acuity, digital retinal photography and independent grading of images. Data were collected on general health and risk factors. The primary outcomes were the incidence of diabetes mellitus and the incidence of diabetic retinopathy, which were calculated by dividing the number of events identified at 6-year follow-up by the number of people at risk at the beginning of follow-up. Age-adjusted risk ratios of the outcomes (DM and DR respectively) were estimated for each covariate using a Poisson regression model with robust error variance to allow for the clustered design and including inverse-probability weighting.


RESULTS
At baseline, 4414 participants aged ≥50 years underwent complete examination. Of the 4104 non-diabetic participants, 2059 were followed-up at six-years (50 · 2%). The cumulative incidence of DM was estimated at 61 · 0 per 1000 (95% CI: 50 · 3-73 · 7) in people aged ≥50 years. The cumulative incidence of DR in the sample population was estimated at 15 · 8 per 1000 (95% CI: 9 · 5-26 · 3) among those without DM at baseline, and 224 · 7 per 1000 (116.9-388.2) among participants with known DM at baseline. A multivariable risk factor analysis demonstrated increasing age and higher body mass index to be associated with incident DM. DR incidence was strongly associated with increasing age, and with higher BMI, urban dwelling and higher socioeconomic status.


CONCLUSIONS
Diabetes Mellitus is a growing public health concern with a major complication of diabetic retinopathy. In a population of 1 · 6 million, of whom 150,000 are ≥50 years, we estimated that 1650 people aged ≥50 develop DM per year, and 450 develop DR. Strengthening of health systems is necessary to reduce incident diabetes and its complications in this and similar settings.
International Centre for Eye Health, Clinical Research Department, London School of Hygiene & Tropical Medicine, London, UK. andrew.bastawrous@lshtm.ac.uk.
Andrew
http://orcid.org/0000-0001-8179-556X
A
Bastawrous
Rwanda International Institute of Ophthalmology and Dr Agarwal's Eye Hospital, London, Rwanda.
Wanjiku
W
Mathenge
Department of Non-Communicable Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Kevin
K
Wing
Nuffield Department of Primary Care, University of Oxford, Oxford, UK.
Madeleine
M
Bastawrous
International Centre for Eye Health, Clinical Research Department, London School of Hygiene & Tropical Medicine, London, UK.|Kitale Eye Unit and Trans Nzoia County, London, Kenya.
Hillary
H
Rono
MRC Tropical Epidemiology Group, Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
Helen A
HA
Weiss
MRC Tropical Epidemiology Group, Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, UK.
David
D
Macleod
International Centre for Eye Health, Clinical Research Department, London School of Hygiene & Tropical Medicine, London, UK.
Allen
A
Foster
NIHR BMRC at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.|Centre for Public Health, Queen's University Belfast, London, UK.
Tunde
T
Peto
NIHR BMRC at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.
Peter
P
Blows
International Centre for Eye Health, Clinical Research Department, London School of Hygiene & Tropical Medicine, London, UK.|Moorfields Eye Hospital NHS Foundation Trust, London, UK.
Matthew
M
Burton
International Centre for Eye Health, Clinical Research Department, London School of Hygiene & Tropical Medicine, London, UK.
Hannah
H
Kuper
D015331:Cohort Studies; D003430:Cross-Sectional Studies; D003920:Diabetes Mellitus / Q000175:diagnosis* / Q000453:epidemiology*; D003930:Diabetic Retinopathy / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007630:Kenya / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods; D011897:Random Allocation