From your new strain piece.

Transmission in heterosexuals also progressed at a much slower rate than in homosexuals, the study finds, with only 2% occurring within the first 6 months of infection (25% in homosexuals).
(Why might that be Royston?)

While in the 1990s genetic characterisation of the virus in heterosexuals showed a predominance of subtype B - the most common form in the Americas, Australia, Europe, Japan, and Thailand - more recent studies find that there has been a shift. Most HIV cases these days in the heterosexual risk group in the UK are of the non-B subtype, 'indicating viruses originating among immigrants from sub-Saharan Africa,' the scientists state.