Methods of Decontamination

As per estimates, around 46.5 million surgical and medical procedures are performed in the US every year. All the procedures are performed using sterile medical devices or equipment to eliminate any sort of contamination. For ensuring the safety of such devices/instruments, procedures like disinfection and sterilization are essential prior to use.

In the past, many studies have reported lack of compliance in terms of established guidelines for disinfection and sterilization, resulting in devastating outbreaks. In this regard, it is important that the healthcare, clinical and hospital authorities establish clear guidelines related to the decontamination mechanism of medical instruments, and whether they need to be cleaned, disinfected or sterilized. These terms, although similar, differ from each other in certain ways. Below is a summary of some key differences.

Decontamination

It is an umbrella term used to describe an item or an environment, which is free from micro-organisms, and therefore safe to handle and use. The terms sterilization, disinfection and cleaning are different forms of decontamination.

1) Sterilization: The process involves killing of all living micro-organisms including spores. However, toxic substances (pyrogens) and dead microorganisms may continue to persist on the surface of the object. In addition, it is important to note that sterilization is not effective against prions.

Degree of sterilization is calculated using the Sterility Assurance Level, which is the probability of survival of a microorganism after the treatment, which should be less than one in one million.

In a laboratory environment, steam sterilization (also known as autoclaving) is often used to achieve optimal levels of sterilization. Autoclaving is performed with saturated steam under pressure of around 15 psi and at least a temperature of 121°C for a certain period of time. This temperature and pressure setting can rapidly destroy microorganisms and decontaminate any other infectious waste. It is often employed to sterilize laboratory glassware and reagents. For an effective heat transfer using autoclaving, the following points must be considered:

• The steam should be able to flush out the air present in the autoclave chamber.
• One needs to check and clean the drain screen present at the bottom of the autoclave chamber. If the drain is blocked, it might result in entrapment of air, which would prevent optimum functioning, and is therefore, critical to achieving sterility.
• In addition, one needs to ensure that the material to be sterilized is in contact with the steam.
• Chemical indicators, such as an autoclave tape should also be used with each batch, which can be a useful indicator of efficacy. Autoclave’s sterility levels must also be monitored on a regular basis through suitable biological indicators, such as B. stearothermophilus spore strips, which are placed at different locations inside the autoclave.
• As spores are highly resistant to heat, each autoclaved container should be spore tested before use.

2) Disinfection

Disinfection is a process of eliminating or destroying the majority, but not all viable organisms. The objective is to minimize the number of microbes to a degree at which they render harmless. However, unlike sterilization, disinfection does not necessarily eliminate spores. Although chemical sterilants have the ability to kill spores with prolonged exposure (3-12 hours).

On the other hand, certain kinds of disinfectants, also known as high-level disinfectants are able to kill all kinds of microorganisms except bacterial spores at a similar concentration as chemical sterilants but with shorter exposure time. In addition, low-level disinfectants are able to kill most vegetative bacteria, certain fungi and viruses, and intermediate-level disinfectants can kill vegetative bacteria, mycobacteria, most fungi and viruses, but not necessarily bacterial spores.

Classification of Disinfection

1. High Level Disinfection

• This level of disinfection requires high concentrations of chemical germicides, such as concentrated sodium hypochlorite.
• High level disinfectants are usually used for shorter periods of time (10-30 min) for disinfection, however, they are able to achieve sterilization if they are in contact with the surface for longer periods of time (7-10 hours).
• This level of disinfection eliminates vegetative microorganisms and inactivates viruses.
• It should not be used on environmental surfaces, such as lab benches or floors.

1.  Intermediate Level Disinfection

• EPA-approved tuberculocidal hospital disinfectants fall into this category.
• It kills vegetative microorganisms and fungi and renders most viruses inactive.
• It can be used for disinfecting lab benches, as well as housekeeping. 

1. Low Level Disinfection

• It does not kill M. tuberculosis
• Eliminates most vegetative bacteria, certain fungi, and inactivates some viruses.
• They are also called ‘hospital disinfectants’ or ‘sanitizers’.

Certain factors, such as prior cleaning of the item, existing organic and inorganic load, type and degree of microbial contamination, physical attributes of the item, biofilm concentration, temperature and pH of the process are crucial to the efficacy of both disinfection and sterilization. These factors must be monitored and evaluated periodically to attain optimal levels of decontamination.