Transactions of the Royal Society of Tropical Medicine and Hygiene (2007) 101, 996—1003 available at www.sciencedirect.com journal homepage: www.elsevierhealth.com/journals/trst Trichiasis and geoclimatic factors in Mali Jean-Franc ¸ois Sch´ emann a,e,* , Dominique Laffly b , Doulaye Sacko c , Germain Zephak d , Denis Malvy e a Institut de Recherche pour le D´ eveloppement, UR 24, BP 1386, Dakar, S´ en´ egal b Universit´ e de Pau et des Pays de l’Adour (SET UMR 5 603 CNRS), Pau, France c Organisation Ouest Africaine de la Sant´ e, Bobo Dioulasso, Burkina Faso d Institute of African Tropical Ophthalmology, BP 248, Bamako, Mali e Universit´ e Bordeaux 2 (EA 3677 et Centre Ren´ e Labusqui` ere), Bordeaux, France Received 13 November 2006; received in revised form 15 May 2007; accepted 16 May 2007 Available online 20 July 2007 KEYWORDS Trachoma; Trichiasis; Environment; Risk factors; Climate; Mali Summary Several trachoma surveys conducted in sub-Saharan countries showed different geographical distributions of active trachoma and trichiasis. Trichiasis is more common in south- ern regions. We analysed the role of geoclimatic factors in determining the distributions of active trachoma and trichiasis in Mali. In each region a random sample of 30 clusters was examined. The prevalence of active trachoma among children and of trichiasis among women was compared, and geographical, environmental and social risk factors were assessed. Logistic regression models were constructed. Multiple regression analysis was applied and models were used to map the probability of active trachoma and trichiasis. The highest prevalence rates of active trachoma (TF/TI) were found in the northern part of Mali reaching 41.1% among chil- dren living north of the 15th parallel. Surprisingly, prevalence rates of trichiasis (TT) among women regularly increased from north to south (1.0% north of the 15th parallel vs. 2.8% south; OR = 2.91, 95% CI 2.01—4.24). The two related predictive maps showed a gradient SSE/NNW for TF/TI very different from the gradient NS/SW for TT. These opposite spatial distributions could be explained by differences in the pathogenic agent, the natural history of the disease, population susceptibility, grading process or vulnerable group behaviour. © 2007 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. 1. Introduction Trachoma remains the major preventable cause of blind- ness and is responsible for six million cases of blindness ∗ Corresponding author. Tel.: +221 849 35 40; fax: +221 832 43 07. E-mail address: jfschemann@wanadoo.fr (J.-F. Sch´ emann). worldwide (Resnikoff et al., 2004). The relationship between active trachoma and environmental risk factors, such as water availability, facial cleanliness, cattle involvement, and domestic flies as vectors for transmission of Chlamy- dia, has not been definitively clarified. National prevalence surveys have been conducted in some sub-Saharan African countries, including Burkina Faso (Sch´ emann et al., 2003), Mali (Sch´ emann et al., 1998), Mauritania (WHO, 2000) and Senegal (Sall et al., 2003). Active trachoma was found in 0035-9203/$ — see front matter © 2007 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.trstmh.2007.05.015