Population risk of syringe reuse: estimating the probability of transmitting bloodborne disease

In 2008, the Medical Officer of Health at Alberta Health Services (Edmonton, Canada) was notified that, in some practice settings, a syringe was used to administer medication through the side port of an intravenous circuit and then the syringe, with residual drug, was used to administer medication to other patients in the same manner. This practice has been implicated in several outbreaks of bloodborne infection in hospital and clinic settings.

A risk assessment model was developed to predict the risk of a patient contracting a bloodborne viral infection from the practice. The risk of transmission was defined as the product of 5 factors: (1) the population prevalence of a specific bloodborne pathogen, (2) the probability of finding a viral bloodborne pathogen in an intravenous circuit, (3) the rate of syringe reuse, (4) the probability of causing disease given a bloodborne pathogen exposure, and (5) the susceptibility of the exposed person.

The risk was modeled first with consistent use of the proximal port of the intravenous circuit. The risk of transmission of hepatitis B virus was approximately 12-53 transmission events per 1,000,000 exposure events for a range of practice probabilities (ie, frequency of the risk practice) from 20% to 80%, respectively. The risk of transmission of hepatitis C virus was approximately 1.0-4.3 transmission events per 1,000,000 exposure events for the same practice probability range, and the risk of transmission of human immunodeficiency virus was approximately 0.03-0.15 transmission events per 1,000,000 exposure events for the same practice probability range. The use of the distal port was associated with a 10-fold decrease in the risk.

Practitioners must practice safe, aseptic injection techniques. The model presented here can be used to estimate the risk of disease transmission in situations where reuse has occurred and can serve as a framework for informing public health action.