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Abstract
Summary Bacillus spores resist inactivation, but the extent of their persistence on common surfaces is unclear. This work addresses knowledge gaps regarding biothreat agents in the environment to reduce uncertainty in risk assessment models. Studies were conducted to investigate the long‐term inactivation of Bacillus anthracis and three commonly used surrogate organisms – B. cereus, B. atrophaeus and B. thuringiensis on three materials: laminate countertop, stainless steel and polystyrene Petri dishes. Viable spores were measured at 1, 30, 90, 196, 304 and 1038 days. Twelve different persistence models were fit to the data using maximum likelihood estimation and compared. The study found that (1) spore inactivation was not log‐linear, as commonly modelled; (2) B. thuringiensis counts increased at 24 h on all materials, followed by a subsequent decline; (3) several experiments showed evidence of a ‘U’ shape, with spore counts apparently decreasing and then increasing between 1 and 304 days; (4) spores on polystyrene showed little inactivation; and (5) the maximum inactivation of 56% was observed for B. atrophaeus spores on steel at 196 days. Over the range of surfaces, time durations and conditions (humidity controlled vs. uncontrolled) examined, B. thuringiensis most closely matched the behaviour of B. anthracis.
Highlights
Bacillus anthracis spores have been used as bioweapons since World War I (Christopher et al, 1997)
Aerosolized B. anthracis spores are capable of remaining airborne after an attack for up to 48 h, settling on surfaces based on physical properties such as ambient wind velocity, aerodynamic properties of the spores and hydrophobicity of the surface and possibly re-aerosolizing (Sextro et al, 2002)
The objective of this study was to quantitatively evaluate the inactivation of Bacillus spores – B. anthracis Sterne, B. cereus, B. thuringiensis and B. atrophaeus – from commonly found indoor fomites such as laminate, stainless steel and polystyrene over 1038 days and compare them by fitting 12 different inactivation models published in the literature
Summary
Bacillus anthracis spores have been used as bioweapons since World War I (Christopher et al, 1997). It is important to consider the persistence of these spores in indoor environments after an attack, because spores can survive for decades. Redmond et al (1998) found viable B. anthracis spores in sugar samples used during World War I, even after 80 years of archiving. Because of numerous uncertainties about the persistence of spores, previous exposure assessments could not adequately consider the decay of spores over time (Canter, 2007; Hong et al, 2010). In these situations, extrapolation from short-term experiments may be problematic depending on the decay model selected. An understanding of long-term persistence will aid in decision-making about risk mitigation strategies (MitchellBlackwood et al, 2011; Hamilton et al, 2015)
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