lecture 7 Flashcards
Endemic
disease or health risk regularly found in a particular population or area. The baseline amount– has a predictable rate & spread
malaria
chickenpox
Outbreak
Sudden increase in #’s of a disease or health risk. More than would normally be expected in a
defined community, geography or season. Or a single case of a disease in an area where it never occurred before. If outbreak is not contained it becomes an epidemic
listeria
Epidemic:
The continued active spread of new cases of the outbreak disease. Levels far exceed what is normal for a community, population, or region. Is an outbreak that is out of control - if not contained becomes a pandemic
measles
obesity
opioid
Pandemic:
An epidemic that has spread over multiple countries or continents. #’s rise sharply each day - disease affects several countries and populations. An out of control epidemic
NOSOCOMIAL INFECTION (NI
-acquired within hospitals or other healthcare facilities; after >48 hours in the hospital
Iatrogenic infections: Infections that result from diagnostic or therapeutic procedures
sources - staff/patient with colonized orgs
-catheters or ventilators
-reuses of improperly cleaned surgical equipment /beds
-overcrowding of wards
-staff turn over- improper training
-antibiotic misuse
ANTIBIOTIC RESISTANT ORGANISMS (AROs)
-Resistance of a microorganism to several classes of antibiotics
-Consequence of, misuse of antimicrobial medicines. Develops when a microorganism mutates or acquires a resistance gene
-Clinical & Epidemiological concern because standard treatments become ineffective, infections persist, may spread to others
INFECTION CONTROL
- sub-discipline of epidemiology preventing healthcare-associated infection (HAI) & it’s spread in a hospital or medical facility
-Infection Control Practitioner (ICP) -RN or MLT
Prevention:
Standard Precautions & Transmission Based Precautions
Surveillance:
Keep track of HAI from specific wards with high- risk patients, medical device use, screen for AROs
Monitoring/Managing Outbreak:
Gather data from lab tests & microbiology reports, isolate patients, find the source of the infection, screen patients, ensure device sterility. Control by limiting patients or isolation
Education: Review proper hand washing, use of PPE or medical equipment & Ensure informative posters and signs available
Data Gathering - provide culture results and contamination rates
Report significant cases (communicable diseases) in and around the hospital community
Perform/report ARO screening results
Help investigate outbreaks by reporting the # of cases of a bacterial infection occurring in a specific time period in a given patient population
Also work up and report results from specimens taken to find mode of transmission or reservoir/carriers
Susceptibility reporting of ARO or unusual antibiotic resistance patterns - led by antibiotic pressures to limit use of antibiotics and prevent resistance
INFECTION & DISEASE
Infection: invasion & multiplication of a microorganism on/in a host only. Doesn’t mean person gets active disease, immune response may overcome organism.
Disease: The dysfunction of the body’s systems, or organs which result in specific symptoms -can be from an external or internal source
Can be communicable – contagious organism. Or non-communicable – heart disease, diabetes, cancer
Infectious Disease: Disease caused from the invasion & activity of a microorganism in/on a host that is not eliminated by the immune system –cause damage & symptoms
Can be a non-communicable disease caused by an organism- UTI. Or communicable like TB, Gonorrhea, or HIV
4 PHASES OF INFECTOUS DISEASE
Incubation Period: Time between “contact” or “exposure” with the microorganism and the appearance of symptoms
Prodromal Period: The period of days immediately before the appearance of specific symptoms
Generally, feel unwell (malaise), headache, muscle ache, fatigue. “I’m coming down with something”
Acute Period: Organisms are actively reproducing, & host experiences specific symptoms due to organ damage & immune response
Convalescent Period: Symptoms begin to subside- immune response has overcome the organisms – host feels better.
Subclinical infection
Infection that causes asymptomatic or very mild symptoms - the patient does not seek treatment because they don’t know they are infected – but they are still infectious
Latent infection
-After an acute or sub-clinical infection some organisms can remain dormant within host cell. Asymp carriers -Typhoid mary , the clap
-While dormant no symptoms & non- infectious – but can spontaneously & periodically re-activate to cause symptoms & are infectious while active
-Cold sore and genital herpes infections
-Tuberculosis, HIV (while latent) AIDs (when active)
Organism is not dividing but can be activated
Localized Infection
Systemic Infection
Localized Infection
An infection that is limited to a specific part of the body. ear infection
Systemic Infection
Infection in which the pathogen is distributed throughout the body rather than concentrated in one area. Many organs tissues - blood infection
Morbidity
Mortality
Morbidity: describe anything that causes ill health
Can be due to having a specific illness or condition or from having negative consequences from a medical procedure
It also refers to the amount of disease within a population.
use does not imply risk of death
Mortality
The number of deaths due to an illness
Usually expressed as a death rate : total deaths/population
LINKS IN THE CHAIN OF INFECTION
causative agent- BREAK THE LINK - prompt treatment, decontamination, rapid identification of organism
reservoir
portal of exit
mode of transmission
portal of entry
susceptible host
Reservoir:
Portal of Exit:
Reservoir: place of origin of the infectious organism – where it multiplies and lives
-Humans, animals, insects, inanimate objects, environment- plants, soil, water
BREAK THE LINK: sanitation, health and hygienic practices
Portal of Exit: path the organism uses to get out of the host
-place where it causes disease
Examples of portals of exit are blood, the respiratory, genitourinary, gastrointestinal tracts
BREAK THE LINK - PPE, proper disposal - occurs through wound care
Mode of Transmission:
How the organism gets from the reservoir to the host
direct and indirect
Direct contact: host comes into direct contact with the infectious agent.
3 types of direct contact:
Horizontal transmission: person to person, contact with contaminated material, such as mucous membranes, sputum or feces (sexual transmission is an example)
Vertical transmission: from mother to offspring during the perinatal period
Aerosol droplet transmission: person coughs or sneezes and pathogen in droplet of mucous – travels to host within 1 meter
Indirect contact: Pathogen first contaminate a surface, an object , food, water, an insect vector, or an animal and then the host.
-Air can also be a mode of indirect contact if the pathogen travels longer distances through the air to the host - > than 1 meter
BREAK THE LINK: airflow control, proper food handling, hand hygiene
Portal of Entry
Susceptible Host
Portal of Entry: How the infectious agent gets into the host
May or may not be the same as the portal of exit
Influenza: portal of exit & entry is the respiratory tract
Organisms of gastroenteritis: fecal – exit thru stool, enter mouth
BREAK THE LINK: Aseptic tech, wearing ppe , catheter care
Susceptible Host: Person who is next exposed to the pathogen & is at risk of being infected by the infectious agent
BREAK THE LINK - treatment of primary disease, recognize high risk patients
handwashing is the best way to break the chain of infection
Universal Precautions
Only concerned with patient, or patient blood specimens that may be positive for blood borne pathogens (like HIV, Hepatitis) not excretions or secretions
Body substance isolation procedures:
Outlined that precautions be taken when in contact with any moist body substances – applied to blood & sputum, feces, vomit, tears, urine, breastmilk and others.
Routine Practices & Additional Precautions
-all patients are possibly infectious even when asymptomatic
-Routine precautions start with assessing the risk that they may be exposed to the patient’s blood, mucous membranes or body fluids
IMMUNIZATION
Natural exposure
Artificial exposure:
The process by which an individual’s immune system becomes strengthened against an infectious agent
Natural exposure
Active immunity: exposure to infectious agent & your immune system makes antibodies against it.
Passive immunity: you are given the Ab’s to the infectious agent. Mother to fetus thru the placenta or if you are given Ab’s in blood product like immunoglobulin
Artificial exposure: Usually by Vaccines – a weakened artificial form of exposure to the infectious agent
2 Main Categories of Vaccines:
Live Attenuated
Inactivated – has some sub-categories
Live Attenuated Vaccine: Made weakened pathogenic organism
-grow in the person who receives the vaccine but does not cause disease – or very mild symptoms
-Immune response is excellent -same as natural exposure with memory cells being made
Examples: Measles, Mumps, Rubella & Shingles vaccines
Inactivated Vaccine:
-Made from the whole cell of the microorganism that has been killed through physical or chemical processes
-Does not cause any form of the disease
-Usually doesn’t have a strong enough immune response with 1 dose. Need boosters. Examples: Influenza, Pertussis, Polio
INACTIVATED SUBUNIT VACCINES
vaccine -has only a fragment of the killed pathogen rather than the whole organism.
-No live components
-Causes a weak immune response - no guarantee that memory will form as there are no PAMPs
-Adjuvant (enhances ag immune response - mimic PAMPs) or a booster may be used to strengthen the immune response - mimic PAMPs
Peptide subunit vaccine: only a portion of protein from the original killed pathogen is used in the vaccine
Polysaccharide subunit vaccine: polysaccharide from the killed organism capsule is used in the vaccine
Toxoid vaccine: use only the inactivated toxin from the organism in the vaccine. tetanus , dipitheria
VECTOR VACCINES
-Use a weakened harmless virus that have the genetic code for production of the pathogen organism antigen in them.
-When injected into a person the carrier virus enters the host cell and injects the pathogen genetic material into the host cell nucleus
-Human host cell makes the antigen and presents it on its surface
-Immune system detects this antigen and mounts an immune response
Non-replicating vector viruses: do not make new viruses in the host – only cause host cells to make pathogen antigen
Replicating vector viruses: do produce new virus in host cells that infect new host cells and make the pathogen antigen
VACCINES MADE BY GENETIC ENGINNERING
Recombinant vaccine: DNA that codes for the production of pathogen antigen is inserted into a bacteria or yeast
-The bacteria or yeast make the antigen. This manufactured antigen is purified and used in a vaccine
mRNA vaccine: Vaccine includes mRNA from the pathogenic organism that is put into a lipid membrane to help it get into the host cells
Causes the host cell to make the pathogen antigen which elicits an immune response
DNA vaccines: Vaccine includes a plasmid that has a portion of the pathogen’s DNA – causes the host to make the antigen & an immune response
HERD IMMUNITY
-Resistance to the spread of an infectious disease in a population is based on the pre-existing immunity of a high proportion of individuals as a result of previous infection or vaccination.
-The % of people who need to be immune to achieve herd immunity is based on the reproduction number (R0) – R0 varies with each disease
-R0 = the average # of people that a single person with the virus can infect
Antimicrobial Agents
-drugs or chemicals that act against microorganisms
-kill the organism “cidal” at end of word
-slow the growth of the organism “static” at the end of the word
Disinfectant: kill wide range of organisms on non-living surfaces
Antiseptic: kill organisms on living tissue
Antibiotic/Antifungal/Antiparasitic: destroy bacteria, fungus or parasites within the body
Antibiotics
-Naturally produced by plants, molds & bacteria.
-Or synthetically by pharma
-Act against bacteria
-treat patients with active diseases
-help the patient to recover from the illness
-reduces the time during which the patient is infectious so limits spread
- eliminate potentially harmful microorganisms from “carriers” = healthy individuals who harbor organisms
Broad spectrum: Effective against a wide range of bacteria
Narrow spectrum: Active against a selected group of bacterial types
ribosome - inhibits protein syn
DNA- inhibit NA syn
Cell wall - inhibit cell wall syn
Cell membrane - disruption of membrane function
folic acid - block pathways and inhibit metabolism
Patient factors which affect antibiotic reporting are:
-Age, whether they are pregnant or immunosuppressed.
-The body site where the organism was isolated
Antibiotic Resistance
-Natural even before antibiotics
Natural resistance- way for antibiotic producing bacteria to protect themselves from own antibiotic
-Recent resistance due to overuse of antibiotic agents
-Bacteria acquire mechanisms to withstand toxic effects & can pass these on to other bacteria
-Resistance passed on by physical movement of DNA & incorporation into recipient gene
-Transduction, conjugation, transformation
MDR = multidrug resistant organism
How are Resistant (R) Genes Acquired
Vertical gene transfer: Spontaneously produced R gene is passed through normal bacterial replication
Horizontal gene transfer: transposons, plasmids
Conjugation-plasmid with R gene passes it to another bacteria through pili
Transduction- bacteriophage incorporates bacterial R gene during repackaging of it’s own DNA & spreads it to other bacteria
Transformation-bacteria with R gene dies and lysis. Bits of genetic material is picked up by other bacteria & incorporated
Constitutive gene expression
Induced gene expression
Homogenous resistance expression
Hetero-resistant expression:
Intrinsic Resistance:
Acquired Resistance:
Constitutive gene expression:
gene expressed continuously
Induced gene expression - gene found on a plasmid-only produced after exposure to the antibiotic
Homogenous resistance expression; resistance expressed uniformly in all bacteria
Hetero-resistant expression: small bit of bacteria growing express resistant. Can be missed in lab
Intrinsic Resistance: inherent characteristic in a bacteria that allow antibiotic to be tolerated
Acquired Resistance: distinct from parent gene, horizontal transfer of pre existing gene
Intrinsic Mechanisms of Resistance
Impermeability
Impermeability -when bacteria decrease the ability of the antibiotic to enter the cell
Mutations in the o-antigens of the LPS in gram negative bacteria change the shape or overall charge of the cell wall = decrease in some antibiotic binding
Lack in #s of, or mutations in, antibiotic binding targets = a decrease in the ability of some antibiotics to bind to the cell wall
Porins (outer membrane channels) allow for movement of nutrients and waste in and out of cell. Decrease production of porins or a change in their structure reduce the ability of an antibiotic to go through into the cell
Efflux: Naturally occurring pumps in gram pos & gram neg bacteria
Transport proteins remove toxic substances & antibiotics from inside cell and pump them out
Enzymatic inactivation: Production of enzyme that inactivates the antibiotic before it reaches it target
Example = Production of beta lactamase: Most common intrinsic mechanism for beta lactam drugs
Acquired Methods of Resistance
Efflux: Acquire a gene for efflux mechanism
Target site modification/acquisition of new targets:
Chromosomal mutation that allows the bacteria to modify the antibiotic target site so antibiotic can’t bind
Example: beta lactam drugs target penicillin binding protein (PBP) in cell wall. If gene causes a change in the PBP the antibiotic can’t bind.
Mechanism used by MRSA - PBP altered to PBP 2a
Production of enzymes to inactivate antibiotic: Acquire a gene that causes the production of enzyme – beta lactamase
Methicillin Resistant Staphylococcus aureus (MRSA)
-S. aureus – is the most common cause of skin infections
-treated with oxacillin, methicillin or cloxacillin
-resistance due to acquired mec A or mec C gene
-These antibiotic target the PBP (penicillin binding protein) in bacterial cell wall
If resistant to one of these drugs is considered resistant to the whole group – Any penicillins, cephalosporins or carbapenems
SCREENING PATIENTS FOR MRSA/VRE
-Part of infection control in hospitals
-Screening determines if person is a carrier of methicillin-resistant Staphylococcus aureus (MRSA)
-Samples from at-risk patients even in the absence of signs or symptoms of infection
-Usually done on patients who are transferred from another hospital or to patients being admitted to critical care units like: ICU, surgery, burn units or who have been on a lot of antibiotics
-Nasal swab is taken and sent to the lab for MRSA and rectal for VRE
-Put on special chromogenic media that helps to isolate MRSA
Any Staphylococcus aureus isolated from a patient specimen is screened for methicillin resistance
-broth microdilution testing (Vitek Susceptibility test)
-S. aureus that is isolated is also put on MHA that contains 6 μg/ml of oxacillin & 4% NaCl
-confirm with latex agglutination or immunochromatographic membrane test which tests for PBP2a.
- test for the mec A gene
VANCOMYCIN RESISTANT ENTEROCOCCUS
-Normal flora of the intestine but can cause skin, surgical wound, blood and urine infections
-Intrinsically resistant to many antibiotics like penicillin & cephalosporins
-Acquired resistance to erythromycin, tetracycline, and high level aminoglycosides and now vancomycin
-Van A & Van B genes cause resistance
-Enterococcus faecium & Enterococcus faecalis acquire Van A or Van B via transposons to become vancomycin resistant
-Van C gives low level intrinsic resistance
WHY ITS IMPORTANT TO SPECIATE ENTEROCOCCUS
-aids in confirming whether an isolate has intrinsic (Van C) or acquired resistance (Van A or Van B)
-Van A and Van B genes are transferable
-Van C genes are not transferable
RELATIONSHIP BETWEEN VRE & MRSA
-Vancomycin first used to treat staphylococcal infections
-The VRE started spreading a plasmid-borne resistance genetic element to S. aureus
-Resulting in emergence of vancomycin intermediate S. aureus (VISA) or vancomycin resistant S. aureus (VRSA)
- reduced susceptibility of VISA, VRSA & VRE to vancomycin leaves few options for treatment
