Effects of microwave exposure and temperature on survival of mice infected with Streptococcus pneumoniae.

Female CD-1 mice were injected with an LD50 dose of Streptococcus pneumoniae and then exposed to 2.45 GHz (CW) microwave radiation at an incident power density of 10 mW/cm2 (SAR = 6.8 W/kg), 4 h/d for 5 d at ambient temperatures of 19 degrees C, 22 degrees C, 25 degrees C, 28 degrees C, 31 degrees C, 34 degrees C, 37 degrees C and 40 degrees C. Four groups of 25 animals were exposed at each temperature with an equal number of animals concurrently sham-exposed. Survival was observed for a 10-d period after infection. Survival of the sham-exposed animals increased as ambient temperature increased from 19 degrees C-34 degrees C. At ambient temperatures at or above 37 degrees C the heat induced in the body exceeded the thermoregulatory capacity of the animals and deaths from hyperthermia occurred. Survival of the microwave-exposed animals was significantly greater than the shams (approximately 20%) at each ambient temperature below 34 degrees C. Based on an analysis of the data it appears that the hyperthermia induced by microwave exposure may be more effective in increasing survival in infected mice than hyperthermia produced by conventional methods (ie, high ambient temperature). Microwave radiation may be beneficial to infected animals at low and moderate ambient temperatures, but it is detrimental when combined with high ambient temperatures.