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Int J Epidemiol. 1995 Apr;24(2):446-52.

Model-based estimates of the risk of human immunodeficiency virus and hepatitis B virus transmission through unsafe injections.

Author information

Global Programme for Vaccines and Immunization, World Health Organization, Geneva, Switzerland.

Erratum in

  • Int J Epidemiol 1996 Jun;25(3):688.



Patient-to-patient transmission through contaminated medical equipment may be the principal route of nosocomial blood-borne infections globally. Quantifying cross infection risks could facilitate efforts to ensure safe injections in developing countries.


A mathematical model was developed to evaluate the risk of cross infection due to unsafe injections. The model was applied to immunization programmes with a fixed number of injections and in which unsterile needle and syringe reuse rates were specified. Risk estimates were generated using a range of human immunodeficiency virus (HIV) and hepatitis B (HBV) prevalences.


The risk of cross infection is zero when properly sterilized equipment is used. With unsafe injections, the risk of cross infection with HBV is consistently higher than HIV for comparable levels of endemicity. A single reuse of each needle and syringe in areas with an HBeAg prevalence of 4% results in 980 cases of HBV/100,000 infants; reuse four times results in 3740 cases. When the HIV prevalence is 1% and the reuse rate is 4, 14 to 35 cases of HIV/100,000 women could occur. Contamination of multidose vaccine vials could considerably increase these estimates.


Neither HIV nor HBV transmission has been reported with injections administered through the Expanded Programme on Immunization. However, ample evidence exists that reuse of unsterile needles and syringes is common in developing countries. Ongoing efforts to ensure safe practices and improve injection technologies are required to protect these populations from both medical and traditional skin-piercing procedures.

[Indexed for MEDLINE]

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