27 Moreover, for control of the above-mentioned diseases to be effective, all the ministries and agencies working in this field in a given country must ensure that they coordinate their efforts in the best possible way. In this respect the CPT wishes to stress that the continuation of treatment after release from prison must be guaranteed. 1 High security units 32. In every country there will be a certain number of prisoners considered to present a particularly high security risk and hence to require special conditions of detention. The perceived high security risk of such prisoners may result from the nature of the offences they have committed, the manner in which they react to the constraints of life in prison, or their psychological/psychiatric profile. This group of prisoners will (or at least should, if the classification system is operating satisfactorily) represent a very small proportion of the overall prison population. However, it is a group that is of particular concern to the CPT, as the need to take exceptional measures vis-à-vis such prisoners brings with it a greater risk of inhuman treatment. Prisoners who present a particularly high security risk should, within the confines of their detention units, enjoy a relatively relaxed regime by way of compensation for their severe custodial situation. In particular, they should be able to meet their fellow prisoners in the unit and be granted a good deal of choice about activities. Special efforts should be made to develop a good internal atmosphere within high-security units. The aim should be to build positive relations between staff and prisoners. This is in the interests not only of the humane treatment of the unit's occupants but also of the maintenance of effective control and security and of staff safety. The existence of a satisfactory programme of activities is just as important - if not more so - in a high security unit than on normal location. It can do much to counter the deleterious effects upon a prisoner's personality of living in the bubble-like atmosphere of such a unit. The activities provided should be as diverse as possible (education, sport, work of vocational value, etc.). As regards, in particular, work activities, it is clear that security considerations may preclude many types of work which are found on normal prison location. Nevertheless, this should not mean that only work of a tedious nature is provided for prisoners. 1 See also "Health care services in prisons", section "transmittable diseases".