A protocol for heat treatment of four types of clay minerals used in French pelotherapy facilities.

In France, pelotherapy is mainly performed through the application of mud-packs that are conserved in heating cabinets and deposed on patient skin at a temperature between 40 and 45 °C. Repeated contacts with persons and storage conditions for their individual re-use are associated with microbiological risks. Currently, there are no quality standards or guidelines for the sanitary monitoring of this treatment. However, we used here the most stringent requirement proposed by the French National Academy of Medicine which recommends the heating of therapeutic muds up to 70 °C for at least 30 min in order to eliminate SARS-CoV-2 that may concentrate in sediments and is more resistant to heat inactivation than usual bacteria. To achieve this objective, operators lack information for scheduling a protocol regarding heat treatment duration and temperature because these parameters may vary according to the type of heating cabinet and composition/properties of extractive clays/mineral water. A series of heating/cooling scenarios using the most popular heating cabinet existing in French medical spas on four main types of extractive clays was tested. The target thermal conditions have been met with this chamber when scheduling the following data: 80 °C during 1h45 for a montmorillonite, illite and kaolinite mix, 2 h for a Ca-Montmorillonite and Na-Montmorillonite, and 1h30 for kaolinite. Due to very slow cooling kinetics, cycles duration was important (from 17 to 33 h), rendering necessary a reorganization in the daily scheduling of the procedure for therapeutic sessions. In addition, for application of these muds to the patient at 45 °C, a setting maintenance temperature at 50 °C (or at 45 °C for a 40 °C application temperature) is to be recommended. After validation by direct microbiological tests this protocol could be proposed as a methodological reference to the French medical spas using this type of heating material for pelotherapy.