26 Transmissible diseases 31. The spread of transmissible diseases and, in particular, of tuberculosis, hepatitis and HIV/AIDS has become a major public health concern in a number of European countries. Although affecting the population at large, these diseases have emerged as a dramatic problem in certain prison systems. In this connection the CPT has, on a number of occasions, been obliged to express serious concerns about the inadequacy of the measures taken to tackle this problem. Further, material conditions under which prisoners are held have often been found to be such that they can only favour the spread of these diseases. The CPT is aware that in periods of economic difficulties - such as those encountered today in many countries visited by the CPT - sacrifices have to be made, including in penitentiary establishments. However, regardless of the difficulties faced at any given time, the act of depriving a person of his liberty always entails a duty of care which calls for effective methods of prevention, screening, and treatment. Compliance with this duty by public authorities is all the more important when it is a question of care required to treat life-threatening diseases. The use of up-to date methods for screening, the regular supply of medication and related materials, the availability of staff ensuring that prisoners take the prescribed medicines in the right doses and at the right intervals, and the provision when appropriate of special diets, constitute essential elements of an effective strategy to combat the above-mentioned diseases and to provide appropriate care to the prisoners concerned. Similarly, material conditions in accommodation for prisoners with transmissible diseases must be conducive to the improvement of their health; in addition to natural light and good ventilation, there must be satisfactory hygiene as well as an absence of overcrowding. Further, the prisoners concerned should not be segregated from the rest of the prison population unless this is strictly necessary on medical or other grounds. In this connection, the CPT wishes to stress in particular that there is no medical justification for the segregation of prisoners solely on the grounds that they are HIV-positive. In order to dispel misconceptions on these matters, it is incumbent on national authorities to ensure that there is a full educational programme about transmissible diseases for both prisoners and prison staff. Such a programme should address methods of transmission and means of protection as well as the application of adequate preventive measures. More particularly, the risks of HIV or hepatitis B/C infection through sexual contacts and intravenous drug use should be highlighted and the role of body fluids as the carriers of HIV and hepatitis viruses explained. It must also be stressed that appropriate information and counselling should be provided before and - in the case of a positive result - after any screening test. Further, it is axiomatic that patient-related information should be protected by medical confidentiality. As a matter of principle, any interventions in this area should be based on the informed consent of the persons concerned.