Informed consent will be sought as a condition for enrolment in the study. This will be in written form wherever literacy levels allow - which is expected to be in the great majority of cases. A written statement in the local dialect of shona will be provided explaining the purpose of the study and all aspects, benefits and risks of participation. The statement will make it clear that participants have the right to withdraw from the study at any time. Time will be allowed for prospective participants to read the statement, to ask questions and consider their decision. The statement will be read aloud to prospective participants who are unable to read themselves. Enumerators will be trained to do this in a balanced manner so as to avoid possible coercion.