Is spread of HIV by medical injection being ignored?

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The rate of HIV transmission in Africa through contaminated needles, syringes and medical equipment has been underestimated, according to a review published in this month’s edition of the International Journal of STD & AIDS. The authors argue that “the current tenets on which HIV prevention programmes are based need reassessment”.

In 1999 the World Health Organisation estimated that 80,000 to 160,000 HIV infections occurred each year due to unsafe injections in medical settings, but Dr Gisselquist argues that these estimates “may be an order of magnitude too low”.

Dr David Gisselquist points to a number of factors which suggest that contaminated needles, syringes and medical instruments may be responsible for a higher proportion of infections than previously thought:


sexually transmitted diseases (STDs)

Although HIV can be sexually transmitted, the term is most often used to refer to chlamydia, gonorrhoea, syphilis, herpes, scabies, trichomonas vaginalis, etc.


The period of time from conception up to birth.

case-control study

An observational study in which a group of people with an infection or condition (called ‘cases’) are compared with a group of people without the infection or condition (called ‘controls’). The past events and behaviour of the two groups are compared. Case-control studies can help us understand the risk factors for having an infection or a condition. However, it is difficult both to accurately collect information about past events and to eliminate bias from case-control studies.

prospective study

A type of longitudinal study in which people join the study and information is then collected on them for several weeks, months or years. 


The surgical removal of the foreskin of the penis (the retractable fold of tissue that covers the head of the penis) to reduce the risk of HIV infection in men.

  • Studies which have found big increases in the risk of HIV transmission in individuals with sexually transmitted infections ignore the fact that prospective cohorts are recruited from STD clinics, where treatment is given by injection, in itself a source of risk.
  • Studies in serodiscordant African couples with low condom use have not reported a substantial difference in transmission probability compared to European and North American studies, but computer models of epidemic growth in the US and Africa contain radically different assumptions about the number of onward infections generated by each HIV case, leading epidemiologists to ignore the contribution of unsafe injecting in medical settings.
  • HIV-positive children with HIV-negative mothers have been identified in several studies (the most recently cited dating from 1994).
  • Incidence in some antenatal studies is higher than could be calculated from the number of HIV-negative women with known HIV-positive partners.
  • The length of time receiving antenatal care was correlated with increased risk of HIV infection in several large antenatal studies, and medically assisted delivery was associated with a higher risk of HIV infection postpartum than delivery involving traditional birth assistants.
  • Some antenatal studies show that incidence suddenly falls despite rising rates of sexual transmission year on year, suggesting that changes in medical practice may be responsible. For example, antenatal and postpartum incidence in a Malawi study fell from 21.3 per 100 patient years in 1990 to 1.1 per 100 patient years in 1994/95.

Injections tend to be more common in pregnant women, commercial sex workers and STD clinic patients – precisely the groups, argues Dr Gisselquist, in which HIV infection is most often measured (the so-called `sentinel’ populations). Studies which have calculated the effect of ulcerative genital infections on infectivity may be biased by the fact that STD treatment is given by injection, the populations studied were commercial sex workers, and the partners in whom incidence was assessed were male clients of commercial sex workers attending STD clinics (Hayes 1995).


Whilst this article is an important contribution to thinking about factors driving the ongoing epidemic in Africa and Asia, several key assertions underlying the argument are open to challenge.

The assertion that WHO estimates may be an order of magnitude too low is based on the argument that the risk of transmission through contaminated needles is closer to the level seen for deep needlestick injuries and wounds caused by medical instruments (estimated in two case control studies at around 4 – 5%) rather than the 0.3% transmission rate estimated in a 1993 study of occupational needlestick injuries. However, nowhere in the review do the authors produce evidence to support the view that the volumes of blood transferred by contaminated needles and syringes in routine medical settings correspond with the volumes typically transferred in deep injuries reported in studies of occupational exposure.

The review also asserts that different epidemic trajectories in various African cities cannot be explained by behavioural characteristics, ignoring the significant differences that were correlated with HIV prevalence in a recent comparative study of African cities: age of sexual debut in women, circumcision in men, and genital herpes in both sexes (Buve; Weiss).

To read the full text of this review, click here


Buve A et al. The multicentre study on factors determining the differential spread of HIV in four African cities: summary and conclusions. AIDS Suppl 4:S127-31, 2001.

Gisselquist D et al. HIV infections in sub-Saharan Africa not explained by sexual or vertical transmission. International Journal of STD & AIDS 13: 657-666, 2002.

Hayes RJ et al. The cofactor effect of genital ulcers on the per-exposure risk of HIV transmission in sub-Saharan Africa.

J Trop Med Hyg 98(1):1-8, 1995.

Weiss HA et al. The epidemiology of HSV-2 infection and its association with HIV infection in four urban African populations.

AIDS Suppl 4: S97-108, 2001.