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More than 1,400 disease-causing microorganisms are known to infect humans; pathogens include viruses, bacteria, fungi, and parasites.1 Additionally, new “emerging diseases” continue to materialize. In fact, the Centers for Disease Control and Prevention (CDC) dedicates an entire monthly publication, Emerging Infectious Diseases, exclusively to these new blights on humanity.
Oftentimes an outbreak of a disease might occur that initially many people have never heard of. West Nile, Ebola, Zika, severe acute respiratory syndrome (SARS), norovirus, and human immunodeficiency virus (HIV) have all dominated headlines over the past 30 years. Various influenza strains are also seemingly on the rise, such as Spanish, swine, and bird variants. What these organisms all have in common is that they are zoonoses.
A zoonosis (plural = zoonoses) is an infectious disease of animals (zoon = animal) that can be transmitted to humans. In fact, it is estimated that 60% of all human infections originated in an animal model.2 These can be spread by air, as with influenza; bites, as with rabies; or an intermediate species or vector such as Zika. The problem is that, with an animal host, these diseases are extremely difficult to eradicate.
A common thread among the aforementioned zoonoses is that they are all caused by ribonucleic acid (RNA) viruses.2 RNA is coded by a single-stranded molecule and there is no built-in repair mechanism to correct mistakes like in deoxyribonucleic acid (DNA) viruses. With DNA viruses, two strands of a double-stranded molecule fit together in a specific way. Thus, RNA viruses can mutate at a rate thousands of times faster than their DNA counterparts.2 New genetic variations mean new characteristics; therefore, RNA viruses probably evolve quicker than any other organisms on Earth.2 While most mutations are an evolutionary dead-end, occasionally a mutation will have an unprecedented boost in infectivity.
Chain of Infection
As humans encounter emerging pathogens for which we have no natural or innate immunity, these diseases present new challenges to our immune systems. We must be ever mindful of ways to prevent infection. The chain of infection is a conceptual way to envision the steps of disease transmission. Infection control efforts can be targeted toward five links in this chain: an adequate number of pathogens, a reservoir or source that allows these pathogens to live, a mode or method of transmission, a point of entry, and a susceptible host.3,4 Only one link in the sequence needs to be broken to destroy the integrity of the entire chain, halting the transmission of infectious organisms. When it comes to infection control efforts, finding avenues to prevent disease transmission is the key. The chain of infection provides a roadmap for areas to target.
Vaccines can break three of the five links in the chain of infection. First, they offer immune protection against a pathogen, thereby preventing an individual from becoming a reservoir or host. Also, a potentially susceptible host can become immune-protected. And, lastly, if enough people are vaccinated, the pathogen could potentially be eliminated. Immunization programs reduce the number of dental healthcare personnel susceptible to disease as well as the potential for disease transmission to patients. Vaccines offer simple, cost-effective tools to improve public health. For instance, smallpox killed up to half a billion people—up to 30% of those infected— worldwide in the 20th century.5 But through a World Health Organization vaccination initiative, this scourge has been eradicated.6 The smallpox program was so completely successful that because the infecting organism is not a zoonosis, further vaccination against the disease is no longer necessary.
According to the CDC’s Advisory Committee on Immunization Practices, dental practitioners are at a substantial risk for acquiring or transmitting hepatitis B (HBV), influenza, measles, mumps, rubella, varicella, and pertussis. Because these are all vaccine-preventable diseases, all practitioners should be vaccinated or have documented immunity.7 Other safeguards that should be strongly considered include vaccines for pneumococcal pneumonia, shingles, and human papilloma virus, and all adults should be immunized. To be licensed, a vaccine must be safe, invoke an immune system response, and, ultimately, prevent disease.8
Some people are not eligible for certain vaccines due to an allergy to a specific component or an inability to tolerate a live vaccine because of immunosuppression, pregnancy, or infancy.9 However, these susceptible individuals can still be indirectly protected through widespread immunization efforts. If a large enough portion of the population develops immunity through vaccination, even those who are not eligible for certain vaccines become protected through a lowered opportunity for an outbreak. This concept is called “community immunity” or “herd immunity.”10
Dental healthcare workers, however, may not uniformly heed the recommendations of public health officials and agencies. For instance, as many as 40% of dentists in New York state reported that they did not get a flu shot each year.11 Reasons for noncompliance include skepticism of disease risk and vaccine effectiveness, as well as fear of adverse reactions.12 Vaccine skeptics often site a link between vaccines and autism especially as it relates to a mercury-based preservative called thimerosal. However, the CDC has funded nine studies since 2003 that have uniformly found no link between thimerosal-containing vaccines and autism spectrum disorders.13 To allay continued concerns, all vaccines are now available without thimerosal.13
The world today is a much safer place because of vaccination efforts; for example, people do not worry about contracting polio at the neighborhood pool, dread the risk of birth defects from rubella, or fear tetanus if they step on a rusty nail. While there can be no argument against the overall disease prevention and life-saving capabilities associated with vaccines, vaccine-preventable diseases still contribute to significant mortality. A seemingly mundane illness such as the flu still accounts for numerous needless deaths, including the demise of 56,000 Americans in 2012-2013 alone.14
Personal Protective Equipment
Personal protective equipment (PPE) serves to limit the entry link of the chain of infection for disease-causing microorganisms. PPE refers to specialized clothing or equipment worn by dental personnel to protect specifically against infectious materials. As an essential element of standard precautions, it must be assumed that blood and body fluid from any patient can be infectious and exposure to patient body fluids must be limited by using PPE.4
Gloves should be used when touching blood or other potentially infectious patient materials, contaminated items, mucous membranes, and non-intact skin.4 If the patient’s skin is intact, it is perfectly acceptable to perform a head and neck examination without gloves. It is advisable to work from “clean to dirty” by touching clean body sites or surfaces before contacting heavily contaminated areas. Healthcare providers must be cognizant of “touch contamination” and limit behavior such as putting a gloved hand on their own face, adjusting PPE, or contacting operatory and clinic surfaces unless necessary for patient care. Gloves should be changed if torn or heavily soiled, and after use on each patient. Disposable latex gloves should never be washed or reused, as this can compromise glove integrity.15
Gowns protect a person’s skin and clothing from contamination with infectious agents. They should fully cover the torso and have long sleeves that fit snuggly at the wrists. Masks protect mucous membranes from splatter, sprays, and other aerosols; the fluid-resistant side must be on the outside in order for the mask to work properly. Finally, a person’s eyes must be protected against infectious materials and airborne debris. Regular prescription glasses are not a sufficient substitute for goggles, because they do not offer side protection unless side-shields are employed.
Etiquette and Hand Hygiene
The final link of the chain of infection can be destroyed by eliminating the mode of transmission from the source to a susceptible host. “Typhoid Mary” was an actual person who carried the pathogen associated with typhoid fever. Simply put, people should stay home from work if they are sick. A strong sneeze can launch mucous over 30 miles per hour to a distance of more than 10 feet.16 People should appropriately cover their coughs and sneezes using a tissue so that oral secretions and respiratory droplets are not allowed to fill the air.
The CDC indicates that hand hygiene is the “single most critical measure for reducing the risk of transmitting organisms to patients.”4 There is an obvious benefit to people by reducing pathogens on their bodies. Hands need to be cleaned when they are visibly dirty, after bare hand touching of contaminated objects, before glove placement, and after glove removal. If hands are visibly soiled, soap and water must be employed.4 Otherwise, alcohol-based hand rubs can be used, which offer tangible benefits that include more effective killing of bacteria, reduced damage to skin, and less time required compared to handwashing.17 These hand rubs can also be conveniently placed at the point of care.
Hand lotions can prevent skin dryness, which helps maintain the integrity of the integumentary system and reduces a person’s own risk of contracting an infectious disease.18 Lotions must be compatible with the gloves being used. For the sake of maintaining glove integrity, fingernails should be kept short and artificial nails avoided. Also avoid wearing hand jewelry that might cause tears, harbor organisms, or perhaps make glove donning and/or removal more difficult.
Bacterial species such as Clostridium difficile spores and methicillin-resistant Staphylococcus aureus can survive for months on dry surfaces.19 While viruses tend to be more fragile, norovirus and hepatitis B can still be transmitted for up to a week.19 It is, therefore, imperative that surfaces are properly cleaned and disinfected. Clinical contact surfaces are areas that have been contaminated by instruments, aerosols, or dirty gloves/hands. These surfaces can include virtually anything in or around the operatory, including light handles, radiograph equipment, chair controls, faucet knobs, and drawer handles. Door knobs, telephone receivers, computers, and cell phones can also potentially become contaminated.
Two separate steps to the surface disinfection process are cleaning and disinfecting. Cleaning involves removing visible contamination from a device or surface; it serves to physically remove pathogens. Disinfection destroys pathogens by chemical means. If using disposable towelettes, for example, one would be used to clean the surface of all gross debris and then thrown away, while a second towelette would then be used to thoroughly wet the surface following manufacturer guidelines for disinfection. Manufacturer directions need to be followed. If a product has cleared a claim as a one-step cleaner/disinfectant then the user should be able to follow the label directions for one-step cleaning/disinfection. If the disinfectant isn’t cleared to clean it may require the use of two separate products.
The CDC advises dental healthcare professionals to use an Environmental Protection Agency-registered, hospital-grade disinfectant with low-level (HIV/HBV) to intermediate-level (tuberculosis) claim to ensure effectiveness. Additionally, an intermediate-level disinfectant must be used if an area is visibly contaminated with blood or other potentially infectious material.4
It is vital to read the product label and material data sheet, paying particular attention to the pathogen kill times, appropriate PPE during use, and suitable surfaces for usage. Kill times vary greatly between products, ranging from approximately 1 or 2 minutes to 15 minutes.20 Chair setup protocols must allow for adequate time for disinfection. Because risks are associated with working with chemicals and contaminated surfaces, product-compatible PPE should always be used, and, again, reading the manufacturer instructions is essential.
Barriers are an effective means of preventing cross-contamination, especially for difficult-to-clean noncritical areas.4 If, however, the protected area becomes contaminated during treatment or when removing the barrier, the area should be cleaned and disinfected as well.
To combat the ever-growing list of pathogens, dental professionals must protect themselves, their patients, and, in doing so, their families to the best of their abilities. This can be aided by becoming educated in the hazards that can be controlled. Disease transmission can be minimized by following immunization guidelines, properly using PPE, and eliminating transmission of diseases through proper hygiene and disinfection. These principles work in the dental environment for both established pathogens and emerging diseases.
About the Author
Ken Tilashalski, DMD
University of Alabama at Birmingham School of Dentistry
American Board of Oral and Maxillofacial Pathology
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