Contribution to authorship
The manuscript has been read and approved by all authors. In addition,
all authors contributed to the preparation of the manuscript. I A, F A
and O K conceived and deigned he study, drafted and edited the
manuscript. H A and S A undertook data collection, data entry, prepared
tables and figures and edited the manuscript. T M revised the methods,
performed statistical analysis and edited the manuscript. I A supervised
all aspects of the study