Using a Markov decision analysis model and a model of the flow of IDUs through prison the work here estimates the cost effectiveness of a number of alternative case-finding strategies including verbal screening for ever injecting drug use and for previous HCV testing. Results indicate that verbally screening for ever injecting illicit drugs and for ever having received a past positive HCV test was the most cost effective approach to establishing prisoners eligible for serological testing, while sensitivity analysis found that the proportion of eligible prisoners that accept ELISA testing had a significant impact on the cost-effectiveness of the case-finding scenarios.
It has been found that the case-finding scenarios described here all become less cost-effective over time, this being due to the impact of previously screened individuals returning to prison that do not need re-screening and the time taken to identify these prisoners. Although a reduction in annual costs were noted over time in some of the case-finding scenarios due to prisoners that had already received a positive serological test being identified on prison reception. For each scenario when the proportion of prison receptions covered by HCV case-finding had been assumed to have reached a constant the costs and benefits over time display only relatively small variation.
It is possible for an individual to become HCV RNA positive during a spell of imprisonment. This may occur for two reasons; either the individual was infected while in prison or the individual was infected outside prison but due to the natural history of HCV, HCV RNA was not detectable on reception into prison. HCV RNA can be detected within 1 to 2 weeks after exposure to the virus although HCV RNA positivity may appear much later at 30 to 40 days[19
]. As two further PCR tests are administered to those individuals that are anti-HCV positive but negative for HCV RNA it is unlikely that individuals infected just prior to reception will remain undetected. If however it is felt that there is a significant risk of some prisoners becoming HCV RNA positive while in prison, then to allow these individuals to be offered treatment or counselling it may be necessary to administer some HCV testing during an individuals prison sentence or perhaps on discharge from prison.
The work has not given any consideration to the subject of treatment although it is acknowledged that the inclusion of the costs and benefits associated with treating individuals that have been identified with HCV in prison will play an important role in judging whether to implement an HCV case-finding programme on reception into prison. This study examines the best approach to identifying individuals that may be eligible for treatment and this can be taken forward when considering the implementation of treatment.
Results from sensitivity analysis showed the importance of encouraging eligible prisoners to accept the offer of an ELISA test, with a reduction in uptake having a large impact on cost-effectiveness. Intervention measures outside prison such as testing and diagnosis in the community or those that target IDUs aimed at reducing their at risk behaviour (and therefore the FOI) can have a negative impact on the cost-effectiveness of a prison based case-finding programme even though a prison based programme may well be more cost-effective than a programme based in the community. This shows the importance of coordinating intervention measures inside and outside prison to ensure the maximum effectiveness of both.
The work here has focused on identifying those individuals that may be at risk from HCV infection and then offering them an HCV test as appropriate, however it is possible that an individual may encounter further problems if they admit to injecting drug use, this in many instances may take the form of the social stigma associated with injecting drug use. It is hoped that admitting to previous injecting drug use will be seen in a positive light as individuals can then be targeted for drug related intervention measures or HCV treatment if necessary. To allow for the possibility that individuals may not give reliable answers to questions regarding injecting drug use or HCV status a range of values describing the sensitivity and specificity to individuals answers related to previous HCV testing and injecting drug use were considered. It was found that of importance to model results were the answers that individuals gave to the issue of previous injecting behaviour. However it is hoped that the one hour health awareness lecture described at the start of the screening pathway will provide a good opportunity in which to address individuals concerns regarding the revealing of potentially sensitive information.
A further account of screening for HCV in the prison population in England and Wales is described in a previous study considering the experience of screening in the Dartmoor prison[21
]. In this study the authors describe data collected from a cohort of prisoners screened from 1 January 1998 to 30 June 2001 describing progress from test result to treatment. A key difference between the screening pathway described in Dartmoor compared to the Isle of Wight appears to be the additional two PCR tests administered at the Isle of Wight for those individuals that test anti-HCV positive but HCV RNA negative after a first PCR test. This means that the costs of the scenarios reported here may be less cost-effective than if the requirement to implement these two additional PCR tests was removed.
The approach to staff costs in this work has considered only the role of a doctor and nurse in implementing the alternative case-finding scenarios, while the estimates of the length of time taken to undertake the individual tasks along the case-finding pathways are inevitably subject to much variation. Considering only doctors and nurses is an obvious over simplification, with other members of staff such as prison chaplains and guards playing a role in the implementation of a prison based case-finding programme, However in mitigation the results from the sensitivity analysis have shown that staff costs and length of time required to accomplish each task play only a small part in variation in the estimates of the cost-effectiveness of the case-finding scenarios.
While treatment has not been considered here, there are still advantages in identifying those individuals that are anti-HCV positive. Any individual that is anti-HCV positive obviously has the potential to transmit infection particularly if the person is an IDU and continues to inject illicit drugs. An awareness of the infected status of these individuals is useful to services as they can then be targeted for intervention measures aimed at reducing the behaviour that leads to further HCV transmission. This may take the form of encouraging injecting cessation or the supplying of clean needles to reduce the risk of transmission due to the sharing of syringes. A further advantage of case-finding is that HCV positive individuals can be monitored so that they can be treated when treatment criteria have been met, which in the case of IDUs will be when the individual has ended their injecting career[22
]. Finally the identification of HCV positive individuals on prison reception may also assist in identifying further positive individuals in the community through contact tracing exercises.
Future work should consider the cost-effectiveness of HCV treatment in a prison setting, including the possibility that some individuals may require a treatment pathway that involves continued treatment in the community following discharge from prison. The model here has not considered infection in the non-IDU population, and has assumed that all infection is as a result of injecting illicit drugs. While it is acknowledged that there is some HCV infection in the non-IDU population this is likely to be insignificant compared to injection related infection[4
]. However it would be beneficial if FOI estimates could be obtained that consider the possibility of HCV infection due to risk factors not associated with injecting drug use, and the possibility of increased risk of infection in a prison setting. The model here could then be re-parameterised to reflect this new information.