Bulletin 122

UVC and infectious diseases

The odds of contracting a life threatening infectious disease are comparatively low in developed countries.  However, the threat of terrorist attacks makes it a real and frightening scenario.  To understand the rudiments of infection control, it is necessary to understand certain basic microbial terminology.  A review of some microbiological terms follows:  

  1.   Micro      Means tiny

  2.   Biology     Is a study of physical life

  3.   Microorganism (also microbe)      Animals or plants that can be seen with a microscope

  4.   Vegetative Forms     These are microorganisms that are less resistant to disinfection or sterilization.

  5.   Spore Forms    Spores are inactive microorganisms, more highly resistant to disinfection or sterilization than vegetative forms.  Spores usually have a thick wall enabling the cell to withstand unfavorable environmental conditions.  (Much like a pea in a pod)

  6.   Bacterial Types

      a.     Spherical (or ovid):  Singly, they are called micrococci.  In pairs, they are called diplococci.  In irregular clusters, they are called staphylococci.  In chains, they are streptococci.

b.     Rod Type:  Known as bacilli.  In oval form, they are called coccobacilli.  In end to end forming a chain, they are strepobacilli.

c.     Spiral Type:  In rigid form, they are called spirilla.  If flexible, they are called spirochetes.  If curved, they are known as vibrios.

  7.   Virus Forms

A minute organism not visible with a standard microscope.  Viruses can be seen with an electron microscope.  They consist of a strand of DNA or RNA (but not both) separated by a capsid (a covering of protein).  Viruses cause a variety of important infectious diseases including the common cold, smallpox, yellow fever, most childhood diseases, and the majority of upper respiratory problems.  

  8.   Pathogenic       A term meaning disease-producing in man.

  9.   Sterilization       The total destruction of all life.

  10.  Disinfection       The destruction of most microorganisms, but not all.

  11.  Sanitizing    Pertains to conditions that are clean and free of dirt, but does not include disinfection.

  12.  Autogenous (also Endogenous) Infection        This type of infection originates from within ones own body.

  13.  Exogenous Infection        This is an infection originating from an external source.

  14.  Cross Contamination        This is a term for infection passed from one person to another.

  15.  Asceptic (also Sterile)        This is a condition that is free from germs, from infection and any form of life.

  16.  Septic        A contaminated or putrefied condition.

  17.  Carrier         A person who disseminates a microorganism capable of causing disease in another person.  A carrier  may be immune to the primary disease.

  18.  Mode of Transmission     This is the method device or vehicle by which microbes are transmitted from one place or person to another place or person.

  19.  Route of Transmission        The opening through which, or by which, microbes enter or are carried to the body.

  20.  Disease        Interruption of vital functions of a human, plant or animal by an infective agent.

  21.  Infection   The condition in which the body or part of it is invaded by a pathogenic agent (microorganism or virus) that multiplies under favorable conditions and produces effects that are injurious

  22.  Symptoms of Infection     The five classical symptoms are pain, heat, redness, swelling and disordered function.

    23.  Droplet Infection      Infection conveyed by means of invective particles, such as when carried in a sneeze, cough or spray from the nose or mouth.  This is the usual mode of infection for the common cold.

Many bacterial pathogens can be airborne and until the discovery of antibiotics, they were often deadly.  Antibiotics changed the approach to infectious disease treatment, and it became possible to stop infections before they got a foothold.

  Unfortunately, bacteria are clever little beasts and they make strange bedfellows.  Like us, they are trying to survive and reproduce.  They can easily mutate to new forms of self-defense and the disaster they cause to humans is an unfortunate by-product.  Bacteria have learned to adapt to almost every environmental condition and it didn’t take long for them to find a resistance to the antibiotics.  Frightening???  Certainly, and of course, that brings up the case for UVC germicidal light.

  UVC germicidal light remains lethal to microbial contaminants including bacteria, virus and mold.  But, UVC is not a panacea.  It has drawbacks in that the UV light rays must directly strike the microorganism, and its lethality depends upon a specific amount of energy absorbed by the microorganisms.  The UV level of germicidal light emitted at 253.7 nanometers required for destruction of various organisms varies.  Refer to Fuller UV Bulletin FG66 for a listing of organisms and the levels necessary for destruction.  Proper design is necessary to provide the UV dosage necessary to inactivate a microorganism, this being a function of exposure time and intensity.

  Transmission of infectious diseases can occur through contact with aerosol droplets from a cough, a sneeze, from body fluids containing organisms, from contaminated appliances and devices, the food we ingest, or the water we drink.  Some of the more prominent infectious bacterial contaminants are listed as follows:

                                                                                                                                                                                                           The answer to protection against infectious diseases is not a complex issue once the marketing hype is separated from the facts.  There are many marketing schemes purporting the uses of filters in capturing and/or destroying airborne infectious microorganisms.  The recent Anthrax situation can serve as a model for other types of terrorist attacks.  As mentioned earlier in this treatise, Bacillus anthracis is a bacteria that is spread by spores of the bacteria.  Typically, the Anthrax spore is in the 1 to 5 micron size range.  Anthrax spores can be dormant and survive for years before re-emerging as a deadly bacteria.

  Anthrax bacilli or spores can enter human beings by either of two routes – cutaneous or inhalation.  This is important because the mode of transfer can be airborne as well as direct contact.

  Distribution of spores in HVAC systems includes injecting spores into the air intake, which is often accessible from outside the building.  Another possibility is the introduction of spores inside a building near an air intake.

  The use of filters can be an efficient collection source.  But who wants to replace a germ-laden used filter?  The contaminated filter poses a very serious health hazard and possible hazardous waste because of the possible release of spores during filter changing.  The most efficient filter is a HEPA filter which provides excellent filtration for the Anthrax spore size range.  However, many HVAC systems are not designed to handle higher airflow resistance created by the HEPA filter.  The inlet and exit faces of the HEPA filter can harbor the spores and this is a threat to respiratory invasion.  This can be avoided by the use of ultraviolet germicidal lamps adjacent to both faces of the filter.  Stand-alone HEPA units with UV on both faces are a possible acceptable alternative.

  Is there a better solution?  Yes,  The use of duct mounted UV lamps, correctly sized for airflow rate, duct size and other environmental conditions is excellent protection against airborne microorganisms in the HVAC system.

The Infectious Process

Microbes have existed on planet earth longer than man. Unfortunately, they show no signs of being conquered. Billions of microbes exist harmoniously amongst us; but some will be disruptive and become mysteriously virulent.

There are hundreds of various types of microbes:

What happens when microbes attack and invade our amazing system? The body readily reacts by resisting the infection through  a series of natural defense processes, including:

• An elevated temperature (fever) helps control microbial growth by making the body an uncomfortable host.

• Certain body cells called macrophages try to capture and destroy the microbial invaders by activating a process called phagcytosis, ( The ability to ingest and destroy particulate substances such as bacteria, protozoa, cells and cell debris, dust particles and colloids).

• Body tissues will try to wall off the microbial invaders to localized areas (abscesses) to give the other body processes time to come to the defense of the host.

• Body fluids will try to wash away the invading microbes, as with "sniffles" that accompany a common cold.

• Conserving strength and resting to build up energy to fight the infection. 

No question that infection control is an evolving rigorous field of technology and the process is continuous. There are always new emerging virulent diseases. Infection control practices are of paramount importance, which requires constant attention in an evolving process.

Not all micro- organisms are alike. But every micro- organism can be classified according to size, structure, and mode of transmission.
The chart below describes seven of these major classifications. Common examples and their effects in man are included.

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