From zero-spore expectations to risk-based decision-making: Lessons from the Cambridge workshop

The workshop concluded that environmental conditions, spore characteristics, and surface types all influence how Bacillus anthracis behaves after decontamination. Factors such as UV exposure, humidity, pH, weathering, and soil type affect spore survival and adhesion, while particle size and attachment to dust or fibres shape inhalation risk. Porous materials, carpets, and busy environments increase the chance of resuspension. Although engineering controls can reduce the movement of residual spores, major knowledge gaps remain, especially regarding the infectious dose, post‑decontamination aerosol formation, and how exposure varies with height and population vulnerability.
Effective recovery requires targeted, multi‑step decontamination using non‑persistent chemicals, with potential support from biological tools such as germinants or bacteriophages. Agricultural areas may need long‑term land‑use planning where complete removal is unrealistic. Access control, proportionate security, and reliable monitoring, particularly methods that distinguish viable spores from DNA, are essential. Clear, consistent communication is critical: The public must understand that zero spores cannot be guaranteed, and acceptable residual risk depends on context, land use, and operational practicality. Policies must balance scientific uncertainty, resource limits, population needs, and coordinated messaging while managing misinformation risks.

Overall, the workshop urged a shift from unrealistic zero‑spore expectations toward flexible, evidence‑based approaches that balance science, practicality, and public expectations.