Cases of Cutaneous Leishmaniasis in a peri-urban settlement in Kenya, 2016

Background Cutaneous Leishmaniasis is a neglected tropical disease caused by a protozoan and transmitted by sand-fly bite. Following reports of a possible outbreak of cutaneous leishmaniasis in 2016, we conducted a review of hospital records and a follow up case control study to determine the magnitude of the disease, characterize the cases and identify factors associated with the disease in Gilgil, a peri-urban settlement in Central Kenya. Methods We reviewed hospital records, conducted active case search in the community and carried out a case-control study. Medical officers in the study team made clinical diagnosis of cutaneous leishmaniasis cases based on presence of a typical skin ulcer. We enrolled 58 cases matched by age and residence to 116 controls in a case control study. We administered structured questionnaires and recorded environmental observations around homes of cases and controls. Simple proportions, means and medians were calculated for categorical data and continuous data respectively. Logistic regression models were constructed for individual, indoor and outdoor factors associated with the outbreak. Results We identified 255 suspected cases and one death; Females constituted 56% (142/255), median age of the cases was 7 years (IQR 14). Cases were clustered around Gitare (28.6%, 73/255) and Kambi-Turkana (14%, 36/255) with seasonal peaks between June-November. Among individual factors, staying outside the residence in the evening after sunset (OR 4.1, CI 1.2-16.2) and occupation involving visiting forests (OR 4.56, CI 2.04-10.22) had significant associations with disease. Sharing residence with a cutaneous leishmaniasis patient (OR 14.4, CI 3.8-79.3), a house with alternative roofing materials (OR 7.9, CI 1.9-45.7) and residing in a house with cracked walls (OR 2.3, CI 1.0-4.9) were significant among indoor factors while sighting rock hyraxes near residence (OR 5.3, CI 2.2-12.7), residing near a forest (OR 7.8, CI 2.8-26.4) and living close to a neighbour with cutaneous leishmaniasis (OR 6.8, CI 2.8-16.0) had increased likelihood of disease. Having a cultivated crop farm surrounding the residence (OR 0.1, CI 0.0-0.4) was protective. Conclusions/Significance This study reveals the large burden of cutaneous leishmaniasis in Gilgil. There is strong evidence for both indoor and outdoor patterns of disease transmission. Occupations and activities that involve visiting forests or residing near forests and sharing a house or neighbourhood with a person with CL were identified as significant exposures of the disease. The role of environmental factors and wild mammals in disease transmission should be investigated further Author summary Leishmaniasis is a group of diseases caused by a protozoa (Leishmania) and affects humans and other mammals following the bite of an infected sand-fly. Cutaneous form of the disease (cutaneous leishmaniasis) is considered a neglected tropical disease mainly affecting the poor destabilized or migrant populations in rural areas. Recently, the disease has expanded its geographical range and invaded previously non-endemic areas including areas surrounding large urban centres that are experiencing human population influx leading to multiple localised disease outbreaks. In this paper, we report findings of a study we conducted to determine the burden and factors promoting the spread of cutaneous leishmaniasis in a peri-urban settlement in Kenya. Our results indicate a high burden of cutaneous leishmaniasis in this area and an association of the disease with several groups of factors at individual, indoor and outdoor environments. Many cases of cutaneous leishmaniasis were linked to activities that involved visiting the forested areas around homes, underpinning the significance of human activity in forests in these areas in spread of the disease.