The spatial epidemiology of leprosy in Kenya: A retrospective study

Background: Leprosy elimination defined as a registered prevalence rate of less than 1 case per 10,000 persons was achieved in Kenya at the national level in 1989. However, there are still pockets of leprosy in some counties where late diagnosis and consequent physical disability persist. The epidemiology of leprosy in Kenya for the period 2012 through to 2015 was defined using spatial methods. Methods: This was a retrospective ecological correlational study that utilized leprosy case based data extracted from the National Leprosy Control Program database. Geographic information system and demographic data were obtained from Kenya National Bureau of Statistics (KNBS). Chi square tests were carried out to check for association between sociodemographic factors and disease indicators. Two Spatial Poisson Conditional Autoregressive (CAR) models were fitted in WinBUGS 1.4 software. The first model included all leprosy cases (new, retreatment, transfers from another health facility) and the second one included only new leprosy cases. These models were used to estimate leprosy relative risks per county as compared to the whole country i.e. the risk of presenting with leprosy given the geographical location. Principal findings: Children aged less than 15 years accounted for 7.5% of all leprosy cases indicating active leprosy transmission in Kenya. The risk of leprosy notification increased by about 5% for every 1 year increase in age, whereas a 1% increase in the proportion of MB cases increased the chances of new leprosy case notification by 4%. When compared to the whole country, counties with the highest risk of leprosy include Kwale (relative risk of 15), Kilifi (RR;8.9) and Homabay (RR;4.1), whereas Turkana had the lowest relative risk of 0.005. Conclusion: Leprosy incidence exhibits geographical variation and there is need to institute tailored local control measures in these areas to reduce the burden of disability. Author summary: Leprosy is a chronic bacterial disease that mainly affects the nerves. If untreated, it may cause progressive and permanent damage to the skin, nerves, limbs, and eyes leading to physical disability. Through use of a combination of drugs, Kenya was able to declare the disease as eliminated in the year 1989. However, there are still pockets of leprosy in some Kenyan counties where physical disability persists, mainly due to late diagnosis. To be able to curb this disease, control measures must be intensified, especially in the counties reporting more cases. We used data of the leprosy cases reported in Kenya for the period 2012 through to 2015 in order to describe geographical variation and factors influencing this variation. More than half of the registered cases had visible physical disability. The risk of leprosy notification increased with an increase in age as well as the severity of disease. We estimated that people living in Kwale, Kilifi and Homabay counties are 15, 9, and 5 times respectively more at risk of leprosy as compared to the whole country. Given the limited resources, it’s therefore paramount that high risk counties be initially targeted for control, with a focus on early diagnosis.