|Blood Transfusion Services Impact Model and Manual (UNAIDS, 1999, 29 p.)|
|1. Introduction to Blood 3.0 and project|
A collaborative research project between UNAIDS and London School of Hygiene and Tropical Medicine, has been working since 1994 to develop methodologies to determine the costs and likely impact of a range HIV prevention strategies - the strengthening of blood transfusion services, the strengthened distribution of condoms, school education, the strengthening of sexually transmitted disease (STD) treatment services, interventions working with sex workers and their clients, and interventions working with injecting drug users.
HIVTools: a cost-effectiveness toolkit for HIV prevention is currently being developed. HIVTools consists of 1) a set of five simulation models that estimate the impact on HIV and STD transmission of different HIV prevention activities, and 2) guidelines for costing different HIV prevention activities. HIVTools can be used to estimate the impact, cost and cost-effectiveness of different HIV prevention strategies in different settings.
Blood 3.0 is one of the models within HIVTools. It has been developed to estimate the impact of different HIV prevention activities. Blood 3.0 can be used, within a particular setting, to obtain estimates of the impact of interventions to strengthen the delivery of blood transfusion services. It can also be used to explore what may be the likely impact of different policy options. Estimates of the extent to which the strengthening of blood transfusion services may avert HIV infection among the main recipients of blood products are obtained by comparing the projected number of HIV infections estimated to have occurred in a particular year, if the intervention had not been implemented, with the projected number of HIV infections estimated to have occurred in the presence of the intervention. Comparisons are made using information on the pre and post intervention patterns of blood collection, testing and transfusion.
From conception, the aim was to develop a simple tool that could be used to provide applied intervention specific insights of use to Program Managers and policy makers at the national and local level. For this reason, the structure of Blood 3.0 has been geared towards using the routine forms of monitoring and evaluation data currently being collected by blood transfusion services. It is hoped that this approach can be used to improve understanding of the impact blood transfusion services, and the potential impact of different forms of possible changes in blood collection, testing and transfusion practice.
· A model of the impact of the strengthening of blood transfusion products that can be used to obtain:
- Estimates of the number of HIV infections averted and surviving to discharge among under fives
- Estimates of the number of HIV infections averted and surviving to discharge among women
- Estimates of the number of HIV infections averted and surviving to discharge among men.
· Blood 3.0 incorporates a range of intervention specific inputs, which enable the user to explore the impact of different forms of intervention activity related to blood collection, testing and transfusion, on the number of HIV infections averted.
· Blood 3.0 aims to use the forms of epidemiological and intervention process and outcome data that are commonly collected by blood transfusion services.
· Blood 3.0 is a self-contained piece of computer software, that aims to be sufficiently user-friendly for it to be used by broad range of individuals concerned about the transmission of HIV infection through the provision of infected blood products.
The model considers ways in which an intervention may alter patterns of HIV transmission by:
· Reducing the volume of blood required, (by reducing un-necessary transfusions, or using alternatives to blood products);
· Reduce the prevalence HIV infection in the blood collected - by collecting blood from lower risk donors;
· Increase and improve HIV testing facilities - by possibly increasing the proportion of blood that is HIV tested, and increasing the sensitivity and specificity of the blood transfused;
· Reduce blood wastage - by increasing the flow of blood within the system.
The initial structure of the model developed is the result of a series of consultations with staff at UNAIDS, and following a review of the literature on HIV and blood transfusion services. Simple flow charts were used to describe the initial model structure and underlying assumptions. These were used to enable a range of groups to guide the structure of the model developed.
The model and its underlying assumptions were field tested in Zambia in 1995, in collaboration with the Zambia National Blood Transfusion Services and the Zambia National AIDS Control Programme. Further field-testing will be required to assess the more general applicability of the model, and to refine its format to the needs of specific users.
Version 3.0 was finalised in February 2000, and can be obtained free of charge from UNAIDS. It is likely that further revisions to the model will be made once further feedback on its use has been obtained. Anyone who would like to receive up-dated copies of the model should write to London School of Hygiene and Tropical Medicine giving their contact details, and describing how they plan to use the model. They will then be sent the latest version of the model and an accompanying manual. Copies of any reports or publications arising from use of the model should be sent to UNAIDS, and to Dr. C. Watts at the London School of Hygiene and Tropical medicine. Feedback on the model would also be greatly appreciated, and will be used to guide the future development of the package.
Figures A, and B (on the following pages) outline the conceptual framework and the main inputs of the model. These are described in more detail in Section 2.2 of the manual.
Figure A outlines the inputs used to describe how the patterns of HIV collection and testing that occur within a particular setting, how this has changed as a result of the intervention, and how this may influence the prevalence of HIV infection among blood transfused. In the figure, text written in italics represents inputs required by Blood 3.0. Text that is not in italics represents information that is calculated from these inputs. For example, the number of units of blood available for transfusion in any year will be dependent upon the total number of units collected; the proportion of blood collected from low risk compared with random donors; the percentage of each that is HIV tested; and the percentage of blood tested that tests HIV negative, and does not test positive for other diseases (such as syphilis or hepatitis).
Figure B outlines the inputs used to estimate the numbers of HIV infections averted among the main groups receiving blood products, and surviving to discharge. Again, text written in italics represents inputs required by Blood 3.0. Text that is not in italics represents information that is calculated from these inputs. Estimates of the prevalence of HIV infection in blood transfused, HIV prevalence among the main recipient groups, and estimates of the distribution of numbers of units provided to the different recipient groups are used to estimate the numbers receiving blood products, and the numbers of HIV infections that may occur. Comparisons between the estimates made in the presence and absence of the intervention are used to estimate the total number of HIV infections averted from the provision of safe blood products. This is combined with inputs describing the percentage of individuals within the main recipient groups surviving to discharge to obtain the final estimates of the total number of HIV infections averted by the intervention.
Sheet A: Blood collection & testing
Sheet A: Blood transfusion