# What is disinfection efficiency and log reduction?

What does it mean when a device is said to have a certain disinfection efficiency in a single pass through the unit? Suppose we allow a certain amount of air enter the disinfection unit, in which there are, for example, 1,000,000 live viruses. There will be 10,000 live viruses in the same volume of air coming through the disinfection unit. This means that the number of live viruses has been reduced by 100 times (100 = 102). Expressing the reduction using the decimal logarithm, we get log102 = 2. The number of live viruses decreased by 100-fold, which is expressed as 2 log reductions. If 1,000,000 viruses entered the unit and 10,000 viruses survived, it means that 1,000,000 – 10,000 = 990,000 viruses were eliminated by passing through the disinfection unit. This corresponds to a disinfection efficiency (990,000 / 1,000,000) x100% = 99%. If we eliminated all the viruses, the disinfection efficiency would be 100%.