S206: A Retrospective Analysis of Sampling and Detection Issues Associated With Historical Anthrax Cases

It has been nearly 10 years since the U.S. anthrax letter attacks claimed the lives of 5 people and infected 17 others. An extensive cleanup operation was conducted costing hundreds of millions of dollars and considerable time.  In 2005, the Government Accountability Office critiqued the sampling efforts associated with the response, expressing concern about sampling efficiency and the confidence regarding whether the facilities were cleaned up to a safe level.  Since the letter attacks, there have been several incidents of anthrax exposures emanating from animal hides used for drum heads.  In all these cases, surface sampling was performed to understand the nature and extent of potential contamination.  Surface sampling results were also used as a means of establishing a cleanup threshold, which in all cases was “zero culturable growth” from the sampling media.  Sampling efficiency and the associated detection level were not factored into the decision criteria.  This study looks at the affects of sampling efficiency and detection levels on the interpretation of results from some of these past cases.  Sampling efficiency is dependent on the sampling method and the surfaces sampled. There could be considerable residual spores left on sampled surfaces that are not quantified due to the inefficiencies of surface sampling.  This paper also presents a notional risk assessment associated with the potential residual contamination not quantified by the surface sampling methods.