Over the last five years, Buruli ulcer (BU) care has been greatly improved by implementation of antimicrobial therapy and more effective diagnosis methods. However, much about the transmission of this devastating skin disease remains to be learnt. The incidence of BU disease is still on the rise (e.g. in Ghana, Togo and Gabon), and its emergence or increasing incidence have been linked with environmental modifications in rural areas, such as construction of dams or irrigation systems 
. The main control strategy, based on early detection and early treatment, is hampered in many places by the lack of awareness of the disease and limited access to health services. So far, no primary prevention strategy has been proposed for the population of rural regions where the disease is endemic.
Studies aimed at identifying BU risk factors have repeatedly shown an association between the disease and activities such as wading 
or washing clothes 
in marshy areas of stagnant or slow-flowing waters. Farming in short clothes was also found to increase the risk of disease 
. Using a protected water source was associated with a decreased risk in some settings 
. Proper care of wounds, such as using alcohol to cleanse wounds, and hygienic practices, such as using soap for bathing, were also repeatedly found protective 
In 2006, a case-control study performed in Akonolinga, in the endemic region of the Nyong valley in central Cameroon, showed for the first time that the use of a bed net was associated with protection against BU 
. This association was strong and independent of the socio-economic level of individuals, as it was found when comparing cases to both village and family controls.
This finding is consistent with a possible role of insects in the transmission of Mycobacterium ulcerans
. Several water bugs (aquatic Hemipterans) species 
, as well as mosquitoes 
, have been shown to carry M. ulcerans
in endemic areas. Furthermore, saliva of Hemipterans captured in the environment has been shown to harbor M. ulcerans
, and the first M. ulcerans
culture from an environmental sample was obtained from a semi-aquatic Hemipteran 
Laboratory experimental infection of mice bitten by infected water bugs provides important biological support for their involvement 
, and mosquitoes-related risk factors have been associated with the disease in Australian epidemiologic studies 
Protection against insect bites using a bed net could present a simple, easily implementable means of BU prevention.
We designed this replication study 
to investigate the association between bed net use and protection against BU in the health district of Bankim, in north-western Cameroon (Figure S1
). BU disease was first identified in this region in 2004 
The Bankim BU focus shows several specificities compared to the endemic region of the Nyong river basin in central Cameroon. First, the disease was unknown in the area until recent years (Boussinesq, M. personnal communication). It was reported 15 years after construction of a dam on the Mape River which caused major modifications in the environment and relocations of populations and activities after submersion of villages and farmland. Secondly, the region's geographic, climatic and demographic context differs from that of the forested Nyong River basin. Bankim is located in a transitional zone between forest and savanna and at the foot of the Mambila Mountains; its tropical seasonality is more contrasted than in the equatorial south; and the region is populated by a rich diversity of ethnic groups with specific cultural features. Due to its ecological, demographic and ethnic heterogeneity, Bankim district represented an adequate setting to challenge the hypothesis of bed net use as a protective factor against BU.
Realizing a study in Bankim provided an opportunity to document the other risk factors for BU in this newly discovered focus. It also contributed to raising awareness of BU among Bankim's diverse populations, who considered the disease to result from occult origins and who frequently under-report it.