Quantitative analysis of the limit of detection, sample recovery efficiency (SRE) and characterization of the microbial community are necessary parameters for accurate exposure assessment as part of the quantitative microbial risk assessment framework for indoor environments. To control and remediate an indoor environment from an outbreak, accidental or intentional release of pathogens can be a challenging task. Without understanding the situation in quantitative terms, determination of a site as safe or "clean" especially when a sample result is negative will be unachievable. The negative result may not establish zero risk and can be due to variability in the sampling or detection methods. The release of Bacillus anthracis in 2001, the numerous outbreaks from the food industry, hospital settings, and on university campuses have highlighted the lack of quantitative information. A review of the literature for the limits of detection of methods detecting B. anthracis provided a distribution to quantify the variability in the instrument limit of detection; however there were only a few articles on the environmental limit of detection. An exponential dose response model estimated the risk at the dose equal to the environmental limit of detection to determine the probability of death as high as 0.52. The SRE of bacteriophage P22 was evaluated at the environmental limit of detection and was most affected by sampling time, fomite surface area, wetting agent and relative humidity. After samples dried on the fomite (20 min), less than 3% was able to be recovered even though the bacteriophage P22 was still active on the fomite. Genetically characterizing the bacterial communities on touched and untouched fomites resulted in two unique bacterial communities. Touched fomites were more diverse and had a high presence of fecal indicators which demonstrated potential reservoirs for pathogens. This research will improve exposure assessment by indicating the risk and limitations at the environmental limit of detection, enhancement of sampling strategies and the role fomites have in the transmission of infectious diseases.
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