  At present, the best hope for eliminating HIV transmission and bringing the
epidemic of HIV to an end lies in the use of anti-retroviral therapy for
prevention, a strategy referred to variously as Test and Treat (T&T), Treatment
as Prevention (TasP) or Treatment centred Prevention (TcP). One of the key
objections to the use of T&T to stop transmission concerns the role of the
acute phase in HIV transmission. The acute phase of infection lasts for one to
three months after HIV-seroconversion during which time the risk of
transmission may be ten to twenty times higher, per sexual encounter, than it
is during the chronic phase which lasts for the next ten years. Regular testing
for HIV is more likely to miss people who are in the acute phase than in the
chronic phase and it is essential to determine the extent to which this might
compromise the impact of T&T on HIV-transmission.
  Here we show that 1) provided the initial epidemic doubling time is about 1.0
to 1.5 years, as observed in South Africa, random testing with an average test
interval of one year will still bring the epidemic close to elimination even if
the acute phase lasts for 3 months during which time transmission is 26 times
higher than in the chronic phase; 2) testing people regularly at yearly
intervals is significantly more effective then testing them randomly; 3)
testing people regularly at six monthly intervals and starting them on ART
immediately, will almost certainly guarantee elimination.
  In general it seems unlikely that elevated transmission during the acute
phase is likely to change predictions of the impact of treatment on
transmission significantly. Other factors, in particular age structure, the
structure of sexual networks and variation in set-point viral load are likely
to be more important and should be given priority in further analyses.
