Sterilisation and COVID-19 testing

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Anil Anand
Anil Anand
Anil K Anand is currently the Director Technical, MICROTROL Sterilisation Services Pvt. Ltd. Former  Director Reactor Projects Group BARC. Scientific Consultant, Academy Industry Interaction in the office of the Principal Scientific Advisor to the Govt. He has authored books including The Second Strike, Submarine Propulsion - Muscle Power to Nuclear; Probating the Will and Testament. He can be contacted at [email protected] *views are Personal.

Image: Top: General view of Gamma Sterilization Plant, Bottom: General view of Ethylene Oxide sterilization Chambers

Should you test just to check? Not advised, because the probability of being falsely identified as Covid-19- positive is quite high. When no test is 100% accurate…

The above article in the Indian Express on August 1 by Mr Tushar Gore is probably the best on the subject. He clearly brings out the definition of sensitivity and specificity with examples for a common person to understand. He brings out the high probability of the test being a false positive or a false negative; most of the medical fraternity, knowingly or unknowingly, did not consider this aspect. There are a number of cases where the patients were admitted to the hospital due to cough, cold fever etc. and a test is carried out and declared positive. After 4 to 5 days of rest, turmeric milk, lemon and paracetamol, a re-test is done which is negative and an announcement is made that the patient is cured and discharged. It is quite likely that the first test may have been a false positive. Of course in the process, hospitals make money and the explanation by the Doctor or the Hospital is that the patient has built up antibodies, in simple language, immunity during those 4 or 5 days. A case was narrated to me about a person going to a hospital; he was asked to make an option of the packages of boarding and lodging and an advance was taken. After 5 days he was discharged and some amount was refunded as he was cured only in 5 days. A WhatsApp message is going around in which, the beds are shown in a hospital with two medicos talking to each other and the caption is ‘Not medical reports, we have to check their bank statements before starting treatment’

I share some more information as the subject is of importance and there are concerns; being in the profession I am, several enquire about the cleanliness of the equipment and devices used for conducting these tests. During the Corona pandemic, there has been a noticeable spurt in demand for sterilisation of some disposable medical devices (Gloves, PPE, other Personnel protection gear, Catheters, IV sets, syringes…) all used by Doctors, our front-line warriors and other paramedical workers.

By way of background, the medical profession, until the late 1800s was practised in a fairly primitive manner and it was only once the germ theory of diseases gained (that explained the increased cases of diseases in a hospital environment), credibility antiseptic surgical dressings and the importance of disinfection and sterilisation processes came into vogue around the last few decades of the 1800s. Ernst von Bergmann introduced the autoclave in the 1870s, a device used to sterilize surgical instruments and in the 1920s the wide-scale production and use of sterile syringes and needles began.

Subsequently, hygienic practices and sterilisation methods are being used and developed further to decrease the spread of disease and infection. Further development in technology led to the first use of Ethylene oxide gas as a hospital sterilant in 1940, radiation sterilisation in 1956 and gamma radiation sterilisation in 1964.

Sterilisation is a process used to render a product free from viable micro-organisms such as bacteria, fungi & their spore forms and viruses. It is thus the most effective means of reducing the risk of infection, complication and mortality.

The two popular methods or processes for sterilisation are Ethylene Oxide gas or Gamma Radiation, and the choice depends upon the material of construction of the device. There are challenges such as ensuring no residual gases remain in the product and the minimum required radiation dose has been imparted; of course, the product does not pick up any radioactivity

Inactivation or Sterilisation of micro-organisms follows an exponential law i.e. no matter how high the irradiation dose (or concentration of Ethylene Oxide gas) is, there is always a chance that a micro-organism has survived irradiation. Thus, evidence that a product is sterile is proved only in terms of probability. Sterility of a product is defined in terms of probability of the existence of an unsterile product in a population. The term used to indicate this probability is Sterility Assurance Level (SAL). SAL is a function of the number and types of micro-organisms on the product, the sterilization process lethality and sometimes environment in which the micro-organisms exist during treatment.

Each log reduction represents 90% reduction in the population of micro-organisms. Thus a 6-log reduction indicates that the microbial population has been reduced by a million which is theoretically close to zero. SAL is normally expressed as 10-n. Most of the countries mandate a maximum SAL of 10-6 in sterilized medical devices which means only one, in a million pieces, can remain non-sterile. Different values of SAL may also be selected; however, these matters are usually regulated by National Licensing or Approving Authorities.


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