Is HIV out of control in the UK? An example of analysing patterns of HIV spreading using incidence-to-prevalence ratios

The incidence of diagnosed HIV in the UK is increasing. We calculated the incidence-to-prevalence ratio, IPR(t), which must exceed an 'epidemic threshold', the reciprocal of the mean infectious period, for sustained transmission to occur. For heterosexuals the IPR(t) is too low for a self-sustained UK epidemic, and incidence is driven by increasing prevalence, mostly from imported cases. For men who have sex with men the IPR(t) is around the epidemic threshold, suggesting that spread is not yet under control.