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Undiagnosed HIV infection

Roger Pebody

This briefing paper covers undiagnosed HIV infection and late diagnosis of HIV in the UK. One in five people living with HIV are unaware of their infection, while half of all diagnoses are made ‘late’; in other words, when HIV treatment should already have been started (after the CD4 cell count has fallen below 350 cells/mm3).

Undiagnosed HIV infection has two major consequences. Individuals are at greater risk of transmitting HIV to others as they cannot take HIV treatment (which suppresses the virus and greatly reduces the risk of onward transmission) and cannot make informed decisions about their sexual behaviour. Secondly, individuals who are diagnosed late are at risk of serious clinical illness. All people with HIV are undiagnosed for a period of time, while some individuals’ infections remain undetected for so long that they are diagnosed late. This briefing begins by addressing the issue in terms of undiagnosed infection, before turning to late diagnosis.

The briefing focuses on the two populations most affected by HIV in England, men who have sex with men (MSM) and black African communities. More research has been done on this issue in relation to MSM. The briefing describes the scale, characteristics and consequences of the problem; it does not address interventions to tackle it.

Thanks to Valerie Delpech (Public Health England), Fiona Burns (University College London), Joanna Moss (MBARC), Jabulani Chwaula (BHA) and Cary James (Terrence Higgins Trust) for their comments and feedback.

This briefing paper, produced by NAM for HIV Prevention England, covers undiagnosed HIV infection and late diagnosis of HIV in the UK.

  • What proportion of infections are undiagnosed?

    By its nature, information on undiagnosed infection is challenging to produce accurately. Public Health England produces estimates based on anonymised blood samples which have been...

  • The impact of undiagnosed infection on HIV transmission

    Reducing undiagnosed infection is vital because an individual can only take HIV treatment if HIV has been diagnosed. Effective HIV treatment reduces HIV viral load,...

  • How accurate are the figures on undiagnosed infection?

    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...

  • HIV diagnosis and sexual risk taking

    Earlier diagnosis would also give people the opportunity to make informed decisions about their sexual behaviour. Research suggests that most people diagnosed with HIV reduce...

  • Undiagnosed primary infection

    It is useful to consider specifically the impact of undiagnosed primary infection. Primary infection refers to the first few months of infection, when individuals have...

  • Late diagnosis of infection

    A ‘late’ diagnosis is one which is made at a point in time after which HIV treatment should have been started. In 2012, among those...

  • Facilitators and barriers to testing

    Research has identified a range of factors that affect people’s motivation to take an HIV test. Studies conducted with men who have sex with men...

  • How often should people test?

    Regular and frequent testing is a good way for HIV infection to be identified before a substantial decline in CD4 count. While there has been...

  • Key points

    One in five people living with HIV are unaware of their infection.Half of all diagnoses are made ‘late’; in other words, when HIV treatment should...

  • Further reading

    Public Health England HIV in the United Kingdom: 2013 Report.Cairns G Tales of the Late Diagnosed. HIV treatment update, winter 2013.Phillips AN et al. Increased...

Undiagnosed HIV infection

Published November 2013

Last reviewed November 2013

Next review November 2016

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.