Permeability of the thermometer sheath when taking oral temperatures

Oral mercury-in-glass thermometers are contaminated with each use and must be decontaminated prior to reuse. It has been shown that the application of a thermometer sheath prevents contamination of the rectal thermometer. The purpose of the present study is to evaluate sheathed thermometers for contamination after oral use on dentulous patients. One hundred sterile sheathed thermometers were distributed into four groups and subjected to in vitro and in vivo conditions. After clinical use 80% of the sheathed thermometers became contaminated, while not one of those exposed to microorganisms in vitro was contaminated. The cause for contamination was shown to be perforation of the sheath by the dentition. Thus the thermometer sheath is ineffective in preventing contamination of the mercury-in-glass thermometer when used for obtaining oral temperatures from dentulous patients. Sheathed mercury-in-glass thermometers should be decontaminated after each oral use.