Sterilization lethality metric (Δ): if the microbial count is reduced from 10^10 to 1, what is the corresponding del factor (Δ), defined as the number of decimal (log10) reductions achieved?

Introduction:
Microbial lethality during sterilization is often quantified in terms of decimal reductions, also called log reductions. Each decimal reduction reduces the survivor count by a factor of 10. Expressing performance as Δ log reductions provides a clear, scalable measure across methods such as steam, radiation, or chemical sterilants.

Given Data / Assumptions:

• Initial population N0 = 10^10.
• Final population N = 1.
• Δ is defined as log10(N0/N).

Concept / Approach:
By definition, Δ = log10(N0/N). A reduction from 10^10 to 1 corresponds to 10 powers of ten eliminated. This directly counts the number of decimal (one-log) reductions and is commonly used in sterility assurance calculations alongside D- and z-values.

Step-by-Step Solution:
Write the formula: Δ = log10(N0/N).Substitute values: Δ = log10(10^10 / 1) = log10(10^10).Evaluate: log10(10^10) = 10.Conclude Δ = 10 decimal reductions.

Verification / Alternative check:
Each one-log reduction multiplies by 0.1. Applying ten sequential one-log steps takes 10^10 down to 1, verifying the calculation.

Why Other Options Are Wrong:

• 1: Only one log reduction (10^10 → 10^9), far from the target.
• 23: No basis in the given numbers.
• 10^3: Not a count of log reductions; it is a number, not Δ.
• 0.5: Fractional log reductions are possible but not here.

Common Pitfalls:
Confusing log reduction count with percentage reduction; ten logs equals 99.99999999% reduction.

Final Answer:
10