Influence of exposure patterns of nitrogen dioxide and modifications by ozone on susceptibility to bacterial infectious disease in mice

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Abstract
The nitrogen dioxide (NO 2 ) diurnal cycle found in urban communities usually consists of a low basal concentration upon which are superimposed higher concentration peaks or spikes of short duration. Various components of this environmental exposure mode were examined to assess effects of urban exposure profiles on susceptibility to infectious pulmonary disease. Mice were exposed to NO 2 peaks of 4.5 ppm for 1, 3.5, or 7 h, challenged with Streptococcus sp. either immediately or 18 h postex‐posure, and then observed for mortality. When the streptococcal challenges were immediately after NO 2 exposure, the mortality rate was directly related to the length of peak exposure, whether or not a basal exposure was used, and all peak lengths significantly increased mortality. When the challenge was delayed for 18 h after the peak exposure, spiked exposures of 3.5 and 7 h increased mortality to the same degree. If a 1‐h peak exposure to 4.5 ppm was superimposed twice daily upon a continuous basal NO 2 concentration of 1.5 ppm, there was a suggestive trend toward increased mortality near the end of the second week of exposure when challenge occurred immediately after the morning spike. Studies were also conducted to examine interactions with ozone (O 3 ) and NO 2 , since urban air typically contains both of these oxidants. Using various combinations of basal and spiked exposure levels of NO 2 and O 3 , synergistic results were obtained for streptococcal‐induced mortality.