Disease Transmission and Hand Hygiene

I get asked a lot of questions about the cross-transmission of pathogens.  Generally people understand that we spread germs by contacting each other, and by contacting inanimate objects that others have contacted.  But beyond that, there are gaps in our common knowledge about the transmission process.  Some of the confusion comes from the vast diversity of microorganisms, each with unique characteristics.  That said, there are some general guidelines to be aware of.

Hand transmission is hands-down (pun intended) the number one route for spreading germs.  Microorganisms frequently colonize in our nasal, perineal, inguinal, and axillae regions and are easily spread to our upper extremities (including hands).  In addition, we shed nearly 106 microorganism-containing skin flakes daily into our surrounding environment.  In laboratory studies, many bacteria including Pseudomonas aeruginosa have been shown to survive on hands for up to 60 minutes, with a few species persisting up to 180 minutes.  Some bacteria such as Clostridium difficile produce spores that are incredibly hardy and can survive for as long as five months without nutrients.  Certain viruses can also spread via hand contact for up to 60 minutes after exposure.  Furthermore, gloves have been shown to demonstrate the same potential for cross contamination as ungloved hands if the gloved surface becomes infected.

While hand washing is a good preventative measure for controlling the spread of pathogens, ineffective techniques can produce inadequate results.  According to the CDC, there are five key steps to proper hand washing practice: (1) wet your hands with clean running (not standing) water; (2) lather with 3 mL of soap; (3) scrub for at least 20 seconds including the backs of your hands and your fingernails; (4) rinse well under running water; and (5) dry with a clean towel or air dry.  Note that wearing rings and false fingernails can increase the chances of residual pathogens.

Hand gels are a popular and convenient product for hand decontamination, particularly when soap and water are not available.  In order to be effective, the CDC recommends using an alcohol-based sanitizer that contains at least 60% alcohol to achieve the most effective results and to avoid increasing antimicrobial resistance.  Note that alcohol typically takes up to 30 seconds for complete deactivation, and some types of germs including Cryptosporidium, norovirus, and Clostridium difficile are less susceptible to alcohols.

For environmental decontamination, chlorine compounds (e.g., bleach) can’t be beat.  The CDC recognizes the importance of bleach due to it’s fast-acting and broad spectrum of antimicrobial activity, lack of toxic residues, low incidence of toxicity, and low cost.

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