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

BACKGROUND: 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. METHOD: 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. RESULTS: 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. CONCLUSIONS: 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.

Reducing the risk of unsafe injections in immunization programmes: financial and operational implications of various injection technologies.

The unsafe use and disposal of injection equipment continues to put patients, health care workers, and the general community at risk of infections such as hepatitis B virus and human immunodeficiency virus. Although the potential for unsafe injection practices varies substantially with the type of equipment that is used, technology alone cannot totally eliminate the risk. A knowledge of the cost, practicality and, most importantly, the potential for misuse, is critical for selecting the most appropriate injection equipment for each immunization setting. Four types of injection equipment are currently available for administering vaccines: sterilizable needles and syringes; standard disposable needles and syringes; autodestruct needles and syringes; and jet injectors. In general, the cost per injection is lowest with sterilizable equipment and highest with autodestruct. However, only autodestruct syringes virtually eliminate the risk of unsafe injection practices. Owing to differences in cost and programme factors, in some settings it may be appropriate to use a combination of equipment. For example, autodestruct syringes may be used in areas where it is difficult to ensure adequate supervision, while in medium-sized, fixed-site clinics with safe injection practices, sterilizable equipment will be the most cost-effective.

PIP: Every year, more than 550 million injections are administered in developing countries through the Expanded Program on Immunization. It is imperative that great care be given to providing these immunizations with only sterile injection equipment. Otherwise, children may be subjected during immunization to infections such as hepatitis B virus and HIV. Sterilizable needles and syringes, standard disposable needles and syringes, autodestruct needles and syringes, and jet injectors are currently available for administering vaccines. The design and operation of the former two types of needles and syringes are, by definition, evident. The design of autodestruct needles and syringes and jet injectors, however, is less directly apparent from their nomenclature. Autodestruct syringes have a device in the barrel which prevents the plunger from being redrawn after a single use, thereby automatically blocking the syringe and preventing it from being reused. Jet injectors deliver immunizations with a high pressure jet of fluid generated by either a hydraulic or mechanical compression system. This equipment was developed for high workload use and has been employed in immunization campaigns for many years. Low workload injectors are being developed for use in the small immunization clinic setting. In general, the cost per injection is lowest with sterilizable equipment and highest with the autodestruct device. Only autodestruct syringes, however, virtually eliminate the risk of unsafe injection practices. It must be emphasized that technology alone cannot eliminate the risk of accidental infection using unsterile injection equipment. The authors note that it may be appropriate in some settings to use a combination of equipment. For example, autodestruct syringes may be used in areas where it is difficult to ensure adequate supervision, while in medium-sized, fixed-site clinics with safe injection practices, sterilizable equipment will be the most cost-effective.