It is possible that the figures for undiagnosed infection are slightly inflated by the phenomenon of people who, having had their HIV infection diagnosed and treated at one clinic, attend a second clinic for sexual health check-ups, without revealing their HIV status. Individuals may do this to benefit from more convenient services (e.g. opening times) and to avoid disclosing risky sexual behaviour. Recent research has shown that some GUM attendees with ‘undiagnosed HIV’ in fact have traces of antiretroviral drugs in their blood and that this occurs in all demographic groups. Public Health England will investigate the scale of the phenomenon and adjust future estimates accordingly.