The difference between killing 99.99% and 99.9999 % of bacteria
Many disinfectant products on the market claim that they kill 99.99% of bacteria, but what exactly does this mean and how effective is it compared to 99.9999%?
Bacteria are microscopic single-celled organisms that can be found almost anywhere, and are an essential part of the planet’s ecosystems. Bacteria can also be found in the human body, and there are types of good commensal bacteria, many of which are gram-positive bacteria, that work hard in and on the body to outcompete the bad bacteria for resources, keeping them in check. By doing so, they help to keep people healthy by supporting the immune system, controlling inflammation and enabling a more healthy biome and digestion in the gut.
Whilst there are good and helpful types of bacteria, there are even more types of harmful bacteria and many of these are gram-negative bacteria. These can cause diseases in humans such as cholera and pneumonia, so it is important to take pre-emptive measures to keep spaces as clean as possible.
When it comes to how effective a disinfectant is, there is a major difference between killing 99.99% and 99.9999% of bacteria. This is measured using log reduction, which is a mathematical term used to express the relative number of living microbes eliminated by a disinfectant. The below table shows different log-reductions, the percentage kill rate and the amount of microbes left after disinfecting with the corresponding kill rate %. 
Essentially, a disinfectant that claims to kill 99.99% of bacteria will, out of 1 million bacteria, leave behind 1,000 bacteria to grow, multiply and re-contaminate the area.
There is, however, a type of disinfectant solution that is 99.9999% effective and this is Hypochlorous Acid, or HOCL. This means that it is safer and effective because out of 1 million bacteria microbes, only 1 microbe will be left behind to grow, multiply and re-contaminate an area.
The log kill rate, and the likely residual number of bacteria remaining, matters because it is the infectivity of the type of disease causing bacteria and their ability to multiply rapidly that is important when preventing infections. Therefore, maximizing the delay in the regrowth of pathogenic microbes is an important factor in this result. For example, 1,000 bacteria will grow and multiply at a much faster rate than a single microbe of bacteria, meaning the area will be re-contaminated very quickly - so the higher the kill rate, the longer it will take the colony of microbes to grow and multiply to its original number before the disinfection took place.
HOCL obliterates both gram-positive and gram-negative bacteria, including MRSA and E-Coli and it is proven to kill enveloped viruses. It is also close to being a pH neutral solution, free from other additives that can be found in most other cleaning and disinfectant solutions, such as:
Quaternary compounds which are potent disinfectant chemicals that can be extremely harmful to humans and the environment
Surfactants which are used to lower the surface tension of a liquid, but can be harmful to humans and the environment
HOCL addresses the need for a universal disinfectant solution that is safe for both people and the environment. HOCl is naturally manufactured within the body for most mammals because the white blood cells of their immune systems produce it. Not surprisingly, nature has worked out the best approach to the required disinfection and Pathisol is simply copying nature, but on a more industrial scale. As a consequence, HOCl has no COSHH implications, which is the law that requires employers to control substances that are hazardous to health.
As cases rise in COVID-19 and influenza it is more important now, more than ever, to use disinfectant products such as HOCl that are effective, harmless to people and animals and don’t raise the incidence of antibiotic resistance.
Pathisol Disinfectant is proven to kill 99.9999% of bacteria, and is a highly effective solution in keeping environments safe.
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This article has been approved by our lead scientist and producer of Pathisol, Barrington Burles