How to calculate the log reduction?

·         "Log reduction" is a mathematical term (as is "log increase") used to show the relative number of live microbes eliminated from a surface by disinfecting or cleaning.

·         For example, a "5-log reduction" means lowering the number of microorganisms by 100,000-fold, that is, if a surface has 100,000 pathogenic microbes on it, a 5-log reduction would reduce the number of microorganisms to one.

Log Reductions

1 log reduction means the number of germs is 10 times smaller (10¹)

2 log reduction means the number of germs is 100 times smaller (10²)

3 log reduction means the number of germs is 1000 times smaller(10³)

4 log reduction means the number of germs is 10,000 times smaller(10⁴)

5 log reduction means the number of germs is 100,000 times smaller(10⁵)

6 log reduction means the number of germs is 1,000,000 times smaller(10⁶)

7 log reduction means the number of germs is 10,000,000 times smaller(10⁷)

v  Another way to look at it is: 1-Log Reduction would reduce the numberof bacteria 90%.

v   This means, for example, that 100 bacteria would bereduced to 10, or 10 reduced to 1.

Example:

1 log reduction = 100( bactreia) to 1log reduction = 100-10 =90 kill the bactria

 1000( bactreia)= 2log reduction = 1000-100 =900 kill the bactria

= Log =10 10 X10 =100

=log=10 10 X 100 =1000

EX:

Log Reduction (LR) = log10 (107) – log10 (105) =7-5 =2