HIV infection prevention has been largely unsuccessful in many sub-Saharan countries including Malawi, where HIV prevalence remains high despite prevention activities [1, 2]. In Malawi the current estimate for 2008 is 12% in 15-49 year olds . Any reassessment of a prevention strategy as is happening in Malawi requires knowledge of where new HIV infections are arising . Sources of new HIV infections can be identified in places where community based incidence studies have been carried out . None such study has been carried out in Malawi. Estimating incidence in difference groups of the population can be done using mathematical models such as the "Mode of Transmission" model distributed by UNAIDS and recommended by their Reference Group on Estimates, Modeling and Projections [6, 7].
Three things make it timely to review national HIV prevention strategies. Firstly, epidemiologists have belatedly come to realise the importance of concurrent sex partners in the spread of HIV infection. Until recently transmission models, while taking the importance of multiple partnerships into account, failed to include the magnitude of the spread within concurrent partnerships in the early stages of infection. An example of this failure is in a paper written in 1989 which wrongly anticipated a heterosexually spread epidemic in the UK because the difference between serial monogamous multiple partnerships and concurrent partnerships was not realised .
Secondly, the very high transmission risk in the early infection period was not fully realised until the paper from Rakai in 2005 . The study showed the ten fold increase of risk of infection in early infection as compared to the base line rate which occurred from about five months after infection until the development of AIDS.
Thirdly, the belief that deep seated cultural practice of polygamy and concurrent sexual partnerships in Africa could not be changed was disproved . The profound effect of a hard hitting (zero-grazing) campaign in Uganda has been compared to trends in Malawi. Given the similar (but different) cultures of Uganda and Malawi there is no reason why a hard hitting campaign would not work here .
The Mode of Transmission spreadsheet provides a simple means of assessing the impact of HIV prevention measures singly and in combination. This paper assesses the impact using a set of input variables to accurately reflect what is likely to be happening in Malawi. For this exercise absolute numbers are not as important as relative ones because the exercise is looking at the relative not the absolute value of different interventions.