The science of hand washing

Originally published in The Ottawa Citizen September 16, 2003
Original Title: The Matter at Hand: Share the love

Streptococcus, staphylococcus, E. coli, rhinovirus, Norwalk (gastroenteritis) and Coxsackie virus (Hand, Foot and Mouth disease) among others routinely contaminate our hands through the course of our daily activities. Our old soap standby does not eliminate germs as well as we think it does. Hand washing is a little more complicated than it seems.

Our skin harbours billions of bacteria. Most are harmless and indeed some help protect the skin from disease-causing organisms. There are two categories of skin bacteria: transient and resident.

Transient bacteria lie on the skin’s top layers. They are more amenable to removal with routine hand washing. These microbes tend to be caught through direct contact with other people or from contaminated objects. This is especially important in the health care institution or hospital setting.

Resident bacteria live within the deeper layers of the skin, are much harder to remove, but are less likely to cause infection.

Our first understanding of hand-borne infection goes back to 1822. A French pharmacist noted using chloride solutions of lime or soda eradicated the rotting smell emanating from corpses. He encouraged their use as an antiseptic and disinfectant formalizing this advice in a paper published in 1825.

In 1846 Vienna, Ignaz Semmelweis observed that women whose babies were delivered by students and physicians consistently had a higher mortality rate than those whose babies were delivered by midwives. He observed that the physicians who went from the autopsy room to the delivery room had odiferous hands despite using soap and water. Postulating that “cadaverous particles” were responsible for the greater death rates, he instituted mandatory hand washing with chlorine compounds. The infection rate tumbled thereafter and remained so thereon in.

This was the first evidence to demonstrate that plain soap and water could not disinfect contaminated hands as effectively as antiseptic agents could.

In 1843, the American lawyer, physician and researcher Oliver Wendell Holmes arrived at the same conclusion through an independent process. Although the medical profession was slow on the uptake, the work of these researchers remains one of the most important milestones of illness prevention through proper hygiene practices.

Studies continue to evaluate the effectiveness of various cleansing agents. Each new insight further hones the hand hygiene protocols in hospitals and other health care facilities right down to the physician’s office and your home.

Even though these protocols focus on the health care setting, it is nevertheless equally applicable to the public at large. Winter brings more incidences of cold and flu. People remain in closer proximity to one another increasing the risk of disease transmission through cough and hand-to-hand contact.

Ineffective hand washing after a bowel movement or sneezing into a tissue will leave viral/bacterial organisms on the hands. The hands will contaminate any object or person they touch. Anyone touching the contaminated object risks illness and potentially continues the contamination cycle.

What is known about the common hand cleansers? The perfect cleanser would completely eradicate all harmful microbes for an extended period of time obviating the need for repeat hand washing. It would not dry or irritate the skin, be portable, simple to use and remain on the skin after use to prevent future contamination.

The perfect cleanser does not exist. However, a combination of products will offer substantial protection.

Soaps are made of esterified fatty acids and sodium or potassium hydroxide. They are excellent detergents and remove grit, grime, dirt, soil, and other organic compounds. The non-antimicrobial soaps fail to remove resident disease-causing bacteria from the skin but do remove some transient bacteria. The more time taken to wash the hands, the more transient bacteria are removed (but not enough to prevent disease transmission). Sharing a plain soap bar has the potential to spread disease because it can become contaminated.

Hospitals now use alcohol gels as part of their hand hygiene protocols. In the laboratory studies, alcohols will kill multidrug-resistant bacteria such as MRSA (methicillin resistant staph aureus) and VRE (vancomycin resistant enterococcus), tuberculosis and some fungi. In vitro (in a test tube) evidence indicates that a 70 per cent solution of ethanol or isopropanol will destroy, herpes simplex virus, HIV, respiratory syncytial virus (a severe infant lung infection) and hepatitis B and C.

It is not effective against bacterial spores (clostridium difficile), some parasite’s reproductive cycle and certain other viruses.

Numerous studies indicate alcohol (ethanol) washes dramatically reduce hand bacteria counts after washing for 30 seconds. It is effective against common cold viruses and rotavirus (childhood gastroenteritis).

Ethanol cleansers do not have persistent activity. The bacteria will grow back after a while. However, the addition of chlorhexidine, triclosan, alkyl benzalkonium chlorides or octenidine to ethanol will inhibit bacterial regrowth on the skin surface.

The alcohol gels should be used for at least 20 to 30 seconds and cover the entire hand and under the nails. Apply about a nickel to quarter size blob in the palm. If the hands dry in less than 15 seconds, insufficient gel was used.

The bottom line: for visible dirt use soap and alcohol gel for routine decontamination. Speak to your pharmacist about combining products to increase persistent activity. For more information: http://www.health.gov.on.ca/english/public/pub/pubhealth/handwash.html


© Dr. Barry Dworkin 2003

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