Simply put, Log Kill–also known as Log Reduction–is a common logarithm metric describing how well a process of decontamination eliminates a contaminant. It is determined by measuring the relative number of living microbes eliminated when the decontamination process is complete. The higher the Log Reduction, the more thorough the decontamination. By eliminating 99.999% of living microbes, Cleanbox products achieve a Log Kill of 5.
The table below shows the level of contaminant reduction in each level of Log Reduction.
|5 (Cleanbox Products)
We understand. The log kill rate is confusing…because there are two ways that “log kill” is used in the world.
Microbe Labs: What they do is they count how many bacteria they put into the sample. They put hundreds of thousands of bacteria, fungi or viruses into a single sample. Because those numbers are unwieldly to put on a form, they shorthand the numbers. For example, 1.42E+05 pathogens = 142,000 pathogens. The logarithm of 142,000 = Log 5.15. So, because it’s shorter and easier to type (especially when they get to very large numbers), they use the Log notation for pathogen count.
Let’s make up an example contagion testing. Say we start with 5.59 log of fungi and reduced it to 5.15 log after 120 seconds. Thus, we reduced the pathogen by Log 0.44 in total count (5.59 – 5.15 = 0.44). But if we want to calculate the percentage of kill, we take the bacterial burden of the treated sample (1.42E5 or 142,000) and divide it by the bacterial burden of the control (3.93E5 or 393,000) and subtract 1. That gives us the percentage reduction of 63.87%.
In another example of this kind of notation, let’s say we start with Log 4.3 count of pathogens in the sample, and we kill every last one of them (100% kill). This would still be notated as “Log 4.3 reduction” because there were only Log 4.3 of the pathogens to kill in the first place, but our “percent reduction vs control” would be 100%.
And then there’s everyone else: Log 1 = 99%, Log 2 = 99.9%, Log 3 = 99.99%, etc. This is acceptable nomenclature everywhere except in microbe lab reports.
We can convert “microbe lab” notation to the “everyone else” notation by simply paying attention only to the “percent reduction vs control” statistic and placing it in the scale above.
Clear as mud? We know, so feel free to send us an email with any questions.