Risk of infection

Published: 01 October 2011

A number of studies have calculated the risk of HIV infection from any single needlestick injury where HIV-contaminated blood is involved is around 0.32%.1 Some studies have also calculated the risk of HIV infection on the basis of person-years, and show a similarly low chance of infection.2

This is because the quantity of blood passed on from a needlestick injury is likely to be much smaller than that from an injection of blood when sharing injecting equipment. A 1991 study estimated that the volume of blood likely to be injected as a result of a needlestick injury was approximately one-seventh of the quantity passed on when sharing injecting equipment.3 Although deep injection has been suggested as another factor which increases the likelihood of infection, reports of documented seroconversions fail to show a consistent pattern of type of needlestick injury which leads to HIV infection.

In a CDC study, four factors were associated with increased risk of infection:4

  • Deep injury.
  • Visible blood on the device which caused the injury.
  •  Injury with a needle which had been placed in a source patient’s artery or vein.
  • Terminal HIV-related illness in a source patient who is not on therapy and has a high viral load.

The Department of Health’s guidance on PEP following needlestick injuries gives an estimate of the average risk for HIV transmission after percutaneous exposure to HIV-infected blood of 3 per 1000 injuries (0.3%), or of 1 per 1000 (0.1%) after mucocutaneous exposure. There is no risk of HIV transmission where intact skin is exposed to HIV-infected blood.5

A meta-analysis in 20066 assessed studies of transmission following needlestick injuries. Of 21 studies, 13 gave a transmission risk of 0%. The pooled infectivity estimate was 0.23%, and this was higher when the source of infection had AIDS (0.37%) and lower when studies had explicitly stated that the needlestick injury was the only risk factor (0.13%).

The authors commented that the risk of infection from needlestick injuries depends on factors that influence exposure to a greater volume of blood (e.g. visible blood on the device, procedures involving needle placement directly into a vein or artery, etc.); viral load of the source patient and post-exposure prophylaxis, which affect the 'effective' viral dose received; and the type of injection equipment (syringes with detachable needles retain – and probably transfer – substantially more blood than integral cannula syringes with a permanently attached needle). They also note that laboratory studies have suggested that a greater volume of blood is transferred by deeper injuries and by hollow-bore needles (especially those with larger gauges).

References

  1. Becker C et al. Occupational infection with human immunodeficiency virus (HIV). Risks and risk reduction. Ann Intern Med 110(8):653-6, 1989
  2. Leentvaar AK et al. Needlestick injuries, surgeons and HIV risks. Lancet 335: 546–547, 1990
  3. Gaughwin MD et al. Bloody needles: the volume of blood transferred in simulations of needlestick injuries. AIDS 5(8): 1025–1027, 1991
  4. Cardo D et al. A case control study of HIV seroconversion in health care workers after percutaneous exposure. N Engl J Med 337:1485–90, 1997
  5. Department of Health HIV post-exposure prophylaxis: Guidance from the UK Chief Medical Officers’ Expert Advisory Group on AIDS. London, 2008
  6. Baggaley RF et al. Risk of HIV-1 transmission for parenteral exposure and blood transfusion. AIDS 20: 805-812, 2006
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.
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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.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.