43. Control of Microorganisms Flashcards
Chain of infection
- means of transmission
- portal of entry
- susceptible host
- pathogen
- resevoir
- portal of exit
- back to means of transmission
How to control the chain of pathogens
- stop the connections
Explain targeted precautions
- use standard infection control precautions
- patient specific - medical history
- agent specific
- procedure specific - risk assessment, aerosol generating or not
- if you don’t leads to an outbreak scenario
Standard precautions in dentistry
- hand hygeine
- PPE
- sharps safety
- sterilization/disinfection
- surgery design
- dental unit waterlines
- waste management
- vaccines/screening
List infectious agents
- respiratory viruses
- blood borne viruses
- bacteria
- prions
Examples of respiratory viruses
- common colds (rhinovirus)
- influenza A
- SARS-CoV-2
Examples of blood borne viruses
- HBV
- HCV
- HIV
Examples of infectious bacteria
- mycobacterium tuberculosis
- MRSA
- pseudomonads
- Legionella pneumophilia
Major infectious concerns in dental clinic
- blood borne viruses
- respiratory viruses
- mycobacterium tuberculosis
- MRSA
- psuedomonas
- Legionella
- prions
- seasonal virus like norovirus, common cold
What do we have lesser resistance to?
- enveloped viruses the least
- gram positive bacteria
- large, non-enveloped viruses
- vegetative protozoa and helminths
- vegetative fungi a bit more
What do we have greater resistance to?
- prions the most
- bacterial spores
- protozoal cysts/helminth eggs
- mycobacteria
- small, non-enveloped viruses
- fungal spores
- gram negative bacteria
Routes of transmission for infectious agents
- patient to patient
- patient to dentist
- dentist to patient
What is nosocomial transmission?
- originating or taking place in hospital, acquired in hospital especially in reference to infection
- secondary to the original cause of treatment
What is iatrogenic transmission?
- due to action of physician or therapy
What is idiopathic transmission?
- of unknown cause
Examples of nosocomial infections
- UTIs
- pneumonia
- GI infections
- catheter-associated UTIs
Examples of iatrogenic transmission
- medical errors
- poor prescribing handwriting
- prescription drug interactions
- improper medical treatment
Transmission requires what 3 things?
- a source of infection like index case (person to person) or contamination
- a vehicle (like blood, saliva, contaminated instruments)
- a route (one of 6)
3 ways people can be a source of infection
- overtly infected
- incubating a disease
- healthy carriers
How is an overtly infected person a source of infection?
- large numbers of microbes or infectious agents can be liberated
- patients with serious acute infections are not common
- like COVID-19, influenza, HIV, colds
How is a person incubating a disease a source of infection?
- prodromal stage of infection (early onset symptoms)
- sometimes no signs of disease
- can be highly infectious (COVID-19, measles, mumps, chickenpox)
How can healthy carriers be a source of infection?
- convalescent carriers - past sufferers, persistant resevoirs of infection like strep sore throat, Hep B or diphtheria
- asymptomatic carriers with no past history maybe a sub-clinical infection like Hep B, COVID-19
Sources other than people of infection
- environmental micro-organisms
- normal commensal microflora
- issues like compromised patients, cutting tissue, overt pathogens like HIV, Hep B, opportunistic pathogens
How do environmental micro-organisms cause disease?
- environmental mycobacteria
- clostridioides spp. etc
- length of survival time in environment allows
Which kind of normal commensal microflora can cause infection?
- staph (epidermidis and aureus)
Give vehicles for infections
- blood
- saliva
- direct contact/skin
- objects/fomites
Blood is the vehicle for what infections?
- HIV
- Hep-B
Saliva is the vehicle for what infections?
- Glandular fever/infectious mononucleosis - Epstein Bar Virus
Direct contact is the vehicle for what infections?
- staphylococci
- non-commensal contamination
Objects such as … can be vehicles for infection
- instruments
- clothing
Give 6 routes of transmission
- in utero
- inhalation
- ingestion
- implantation
- inunction
- injection
Explain in utero transmission
- placenta is barrier for most microbes
- syphilis, cytomegalovirus, rubella
- low relevance to clinic
Explain inhalation transmission
- across most surfaces
- aerosols
- strep pyogenes, neisseria meningitidis, mycobacterium tuberculosis
- high relevance to clinic
Explain ingestion transmission
- usually food and drink but in dental clinic, objects introduced to mouth
- strep pyogenes, neisseria meningitidis, mycobacteium tuberculosis
- high relevance to clinic
Explain implantation transmission
- often via trauma to skin
- staph epidermidis and aureus
- C. tetani and perfringens
- strep pyogenes
- high relevance to clinic
Explain inunction transmission
- microbes driven into tissue by rubbing
- staph epidermidis and aureus
- neisseria gonorrhoeae
- moderate to low clinical relevance
Explain injection transmission
- often by biting insect
- malaria/plasmodium, typhus/rickettsia, yellow fever virus, HIV, hep
- high relevance to clinic wtih needlestick
How do inhalation infections become easy in dental clinics?
- aerosols!
- easily produced with ultrasonic scalers, high speed handpieces, sneezing, coughing, talking, stirring liquid
How do reduce impact of aerosils?
- evacuate aerosol and splatter after dental procedures
- masks
Influenza is associated with coughing but may need …
direct contact
TB was once considered what for dentists?
occupational disease
How is the pneumonic plague transmitted?
- inhalation
- no insect vector needed
- high mortality, rapid onset
How can things infect you in a dental appointment?
- inhalation of aerosols or droplets
- inoculation - like sharps injuries or surgical procedures
- absroption through mucous membranes inc. eyes
- absorption through intact or broken skin
- ingestion
What masks do dentists use?
- type IIR fluid-repellent surgical masks
- disposable filtering facepiece (FFP) respirators - FFP2 and FFP3, highest level of protection from 3
Why is sharps safety needed in dentistry?
- sharps injuries most common type but preventable
- puncturing of skin is major route of blood borne virus transmission
What is sterilisation?
- killing or removal of all viable organisms
- inactivation or removal of all self-propagating biological entities (to include prions)
What is disinfection?
- more vague than sterilising
- killing or removal of most viable organisms
- reduction in viable organisms to the point where risk of infection is acceptable
Equation for efficiency of sterilisation/disinfection
N = k/CT
N is number of surviving organisms
C is concentration of agent/temp
T is time applied
K is constant
Value of K in efficiency equation depends on what?
- species of microbes present
- physiological state of microbe
- presence of organic material (blood, saliva)
- means absolute sterility can’t be guaranteed
Due to k being dependent on different things, sterile means …
less than 1 in 10 to the 6 chance of single viable organism being present
Methods of disinfection - reducing the microbial load
- heat - boiling water or pasteurisation
- chemical disinfection
How does heat cause disinfection?
- boiling water kills most bacteria but not spores
- 2 types of pasteurisation - heat to 66 degrees or 71 degrees - kills mycobacterium TB but not some heat resistant bacteria or spores
How does chemical disinfection occur?
- glutaraldehyde, chlorine compounds, phenolics, alcohol, chlorhexidine
- activitty affected by conc, temp, pH, protein conc
- problems with toxicity and corrosion of equipment
Methods of sterilisation
- dry heat/oven
- moist heat
- radiation sterilisation
- sterilising gases/chemicals
- filtration
How does moist heat sterilise?
- autoclave
- tyndalisation (3 times through heating to 100 degrees, cooling, incubating cycle)
How does radiation sterilisation occur?
- cobalt 60
- specialised environment
- used for disposables (syringes, needles, catheters)
- effective but may damage article
Give 2 sterilising gases/chemicals
- sulphur dioxide
- ethylene oxide
2 methods of filtration for sterilisation
- physical removal
- IV fluids
Reusable surgical instrument cycle
- acquistion (purchase or loan) enters cycle
- cleaning
- disinfection
- inspection
- packaging to disposal in bad
- sterilization
- transport
- storage
- use
- transport
- to cleaning
3 ways to decontaminate dental instruments
- manual washing
- ultrasonics
- washer disinfectors
Is manual washing good?
- least efficient
- difficult to validate
What do ultrasonics do?
- instruments placed in bath with detergent
- ultrasonic generator creates vacuum within liquid
Washer disinfectors do what?
- clean and disinfect to high and reproducible standard
Autoclaving process
- high pressure saturated steam
- 121 degrees for 15 minutes or 134 degrees for 3-4 minutes
Types of transmissible spongiform encephalopathies
- Kuru
- BSE (mad cow) and scrapie
- CJD (Creutzfeldt-Jakob-disease)
How are prions transmitted?
- through infected nervous tissue
- thought to be misfolded forms of normal protein, no nucleic acid
- capable of propagation but not culturing
- extreme resistance to heat, radiation and disinfectant
- very long incubation of many years
Dental safeguards against prions and TSEs
- endodontic reamers and files are single use
- highest standard of decontamination for all dental instruments
- manufacturers instructions are followed and where difficult to clean single use
High risk patients include …
- symptomatic and asymptomatic
- general control is enough unless procedures exposes neurovascular tissue
How can the surgery be designed to control infection?
- zoning - clean and dirty zones
- good ventilation
- dental unit cleaned after each patie and surfaces cleaned
- dental unit and all surfaces cleaned down at end of session
How to control infection through dental unit waterlines?
- dental units contaminated with a range of microbes
- waterlines harbour pathogens such as Pseudomonas and Legionella species
- water static for long periods of time and heated to temps between 22 (room temp) and 37 (body temp) also encourages microbial growth
How to control infection through safe waste disposal?
- separation of clinical and domestic waste
- yellow bags for clinical waste
- black for general
- sharps bin
How to control infection by boosting host defences - immunisations?
- behaviour change and immunisation
- occupational health
- HIV/HCV screening
- Hep B - vaccination and sero-conversion check
- stay up to date with diphtheria, tetanus, polio, MMR
- reccommended an annual flu vaccine, SARS-CoV-2 vaccination/booster
