  HIV increases the likelihood that a person will develop TB. Starting them on
anti-retroviral therapy (ART) reduces their risk of TB but not to the level in
HIV negative people. Since HIV-positive people who are on ART can expect to
live a normal life for several decades this raises the possibility that their
elevated risk of infection, lasting for a long time, could lead to an increase
in the population level incidence of TB. Here we investigate the conditions
under which this could happen and show that provided HIV-positive people start
ART when their CD4+ cell count is greater than 350/microL and that there is
high coverage, ART will not lead to a long-term increase in HIV. Only if people
start ART very late and there is low coverage of ART might starting people on
ART increase the population level incidence of TB.
