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.

We conducted the study in Gilgil Sub-county, a rapidly growing peri-urban settlement located 105 in south-eastern part of the Great Rift Valley in Kenya, between 20 th January and 3 rd February 129 plaque (typical raised edges and depressed centre) ascertained by a medical officer in the 130 study team during the study period. Due to logistical challenges, no laboratory confirmation 131 for cutaneous leishmaniasis was done on the suspected or the probable cases. All entries that 132 matched suspected, probable or confirmed case definitions were included in the study line list. 133 We also abstracted information such as name, sex, age, date seen at the facility, residence, 134 signs and symptoms, diagnosis and treatment given.

Enrolment of cases and controls into a Case Control study
136 To determine the risk factors of cutaneous leishmaniasis infection in the study population, we 137 conducted a follow-up case-control study. Cases and controls consisted of eligible residents 138 found in the study area during the study period (20 th January-3 rd February).
139 Sample size: Using OpenEpi, we calculated a sample size of 174 (2 controls per case) to be able 140 to achieve a power of at least 80% at the 5% significance level, able to detect an odds ratio 141 (OR) of ≤0.3 for an exposure present in 31% of controls (17-19). The exposure chosen was use 142 of mosquito nets.
143 Case and control recruitment: We recruited 59 cases for the case control study: 41 cases were 144 selected from the line list developed in the records review and a further 18 cases were 145 identified during active house-to-house survey (Fig. 2). The investigation team comprising a 146 field epidemiologist, 2 medical doctors, a laboratory scientist and 2 public health specialists, 147 worked with community-based locators who included community health volunteers and local 148 chiefs to locate and identify cases for inclusion in the study. In each village, the number of 149 cases that were recruited in the case control study was allocated by probability proportional to 150 size sampling based on the proportion of residents from that village with suspected cutaneous 151 leishmaniasis from the line list. 8 152 Figure 2: Flow diagram of selection of cases and controls before and after field work 153 We attempted to match each case to two community-based controls by age using the 154 following criteria: Cases less than two years of age were matched to controls within two years, 155 cases 2−4 years old were matched to controls within 3 years, cases 5−19 years to controls 156 within 5 years, cases 20−59 year's old to controls within10 years, and cases more than 60 157 years old to controls within 20 years. One case was dropped in the final analysis owing to lack 158 of suitable controls (Fig. 2).
159 Controls were selected from among residents of the same age group and living in the same or 160 neighbouring village(s) as the case patients, and had no typical ulcer, wound or scar upon     254 remained significant with a reduced odds ratio of 3.8. Activities such as charcoal burning, 255 hunting, herding, stone masonry and mining were included among the occupations involving 256 forest visits. When assessed separately, these occupations had significantly large odds ratios, 257 but this analysis is not reported here due to possible close link between each of these 258 occupations with forest visits. Other individual attributes such as sex, level of education, 259 history of travel or use of mosquito nets did not have any significant association with disease.
260 Table 3.   324 Our finding of increased risk of CL in households with 5 or less inhabitants marks a departure 325 from what has been observed in most studies since a large house-hold size (number of regular 326 residents of a household) and high population density is considered a proxy indicators of 327 poverty which has been associated with CL (2). One possible explanation for this relationship