Prolonged respiratory illness after single overnight continuous positive airway pressure humidification: endotoxin as the suspect.

A patient developed a prolonged respiratory illness after a single overnight use of tap water to humidify air supplied by a constant positive airway pressure (CPAP) device, which she had previously used for six years without difficulty. During those years, she used only distilled water for this purpose, as instructed by her sleep specialist. Analysis of the well water supplying her home showed no microorganisms, metals or other analytes likely to have caused her illness, but endotoxin was found at concentrations well above that recommended by the U.S. Pharmacopeia, as a maximum in water which may be inhaled as an aerosol.