A case for PDAs is disclosed. The case is particularly suitable for maintaining mobile telephones free of infectious agents. The case includes a barrier material defining a body configured to enclose a PDA, and at least one fastener, wherein: (a) the case is configured to convert between a relaxed configuration which facilitates transfer of the PDA into and out of the case, and a fitted configuration which conforms more closely to the PDA enclosed therein, (b) the at least one fastener is configured to reversibly retain the case in the fitted configuration, and (c) the barrier material is effective to prevent viruses and bacteria from penetrating therethrough.