Background Cutaneous leishmaniasis is a neglected disease known to cause significant morbidity among the poor. We investigated a suspected outbreak to determine the magnitude of cases, characterize the cases and identify risk factors of cutaneous leishmaniasis in Gilgil, a peri-urban settlement in Central Kenya. Methods Hospital records for the period 2010-2016 were reviewed and additional cases were identified through active case search. Clinical diagnosis of cutaneous leishmaniasis was made based on presence of ulcerative, nodular or papular skin lesion. The study enrolled 58 cases matched by age and neighbourhood to 116 controls in a case control study. Data was collected using structured questionnaires and simple proportions, means and medians were computed, and logistic regression models were constructed for analysis of individual, indoor and outdoor risk factors. Results Of the 255 suspected cases of cutaneous leishmaniasis identified, females constituted 56% (142/255) and the median age was 7 years (IQR 7-21). Cases occurred in clusters and up to 43% of cases originated from Gitare (73/255) and Kambi-Turkana (36/255) villages. A continuous transmission pattern was depicted throughout the period under review. Individual risk factors included staying outside the residence in the evening after sunset (OR 4.1, CI 1.2-16.2) and visiting forests (OR 4.56, CI 2.04-10.22). Sharing residence with a case (OR 14.4, CI 3.8-79.3), residing in a thatched house (OR 7.9, CI 1.9-45.7) and cracked walls (OR 2.3, CI 1.0-4.9) were identified 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

14 Background 15 Cutaneous Leishmaniasis is a neglected tropical disease caused by a protozoan and 16 transmitted by sand-fly bite. Following reports of a possible outbreak of cutaneous 17 leishmaniasis in 2016, we conducted a review of hospital records and a follow up case control 18 study to determine the magnitude of the disease, characterize the cases and identify factors 19 associated with the disease in Gilgil, a peri-urban settlement in Central Kenya. 20 Methods 21 We reviewed hospital records, conducted active case search in the community and carried out 22 a case-control study. Medical officers in the study team made clinical diagnosis of cutaneous 23 leishmaniasis cases based on presence of a typical skin ulcer. We enrolled 58 cases matched by 24 age and residence to 116 controls in a case control study. We administered structured 25 questionnaires and recorded environmental observations around homes of cases and controls. 26 Simple proportions, means and medians were calculated for categorical data and continuous 27 data respectively. Logistic regression models were constructed for individual, indoor and 28 outdoor factors associated with the outbreak. 29 Results 30 We identified 255 suspected cases and one death; Females constituted 56% (142/255), 31 median age of the cases was 7 years (IQR 14). Cases were clustered around Gitare (28.6%, 32 73/255) and Kambi-Turkana (14%, 36/255) with seasonal peaks between June-November. 33 Among individual factors, staying outside the residence in the evening after sunset (OR 4.1, CI 34 1.2-16.2) and occupation involving visiting forests (OR 4.56, CI 2.04-10.22) had significant 35 associations with disease. Sharing residence with a cutaneous leishmaniasis patient (OR 14.4, 36 CI 3.8-79.3), a house with alternative roofing materials (OR 7.9, CI 1.9-45.7) and residing in a 3 37 house with cracked walls (OR 2.3, CI 1.0-4.9) were significant among indoor factors while 38 sighting rock hyraxes near residence (OR 5.3, CI 2.2-12.7), residing near a forest (OR 7.8, CI 2.8-39 26.4) and living close to a neighbour with cutaneous leishmaniasis (OR 6.8, CI 2.8-16.0) had 40 increased likelihood of disease. Having a cultivated crop farm surrounding the residence (OR41 0.1, CI 0.0-0.4) was protective. 42 Conclusions/Significance 43 This study reveals the large burden of cutaneous leishmaniasis in Gilgil. There is strong 44 evidence for both indoor and outdoor patterns of disease transmission. Occupations and 45 activities that involve visiting forests or residing near forests and sharing a house or 46 neighbourhood with a person with CL were identified as significant exposures of the disease. 47 The role of environmental factors and wild mammals in disease transmission should be 48 investigated further 49 Key Words: Cutaneous Leishmaniasis, Kenya, forests 50 Word Count: 389 Words 51 Author summary 52 Leishmaniasis is a group of diseases caused by a protozoa (Leishmania) and affects humans 53 and other mammals following the bite of an infected sand-fly. Cutaneous form of the diseas...