Case 3 : HAIs Flashcards
1
Q
What are hospital acquired infections ?
A
- Infections patients get while receiving treatment for medical or surgical conditions.
- Many are preventable.
- Infections can be associated with procedures (like surgery) and the devices used in medical procedures, such as catheters or ventilators.
- Healthcare associated infection: diff between the two, this is a more general term than hospital acq inf, because healthcarre encompasses healthcare facilities not just hospitals
2
Q
What is a central line-associated bloodstream infection (CLABSI)
A
Serious HAI that occurs when germs (e.g., bacteria) enter the bloodstream through the central line (a long flexible tube placed in a large vein that empties out near the heart).
3
Q
What is Methicillin-resistant Staphylococcus aureus (MRSA)
A
A type of bacteria that is resistant to many antibiotics. In medical facilities, MRSA causes life-threatening bloodstream infections, pneumonia, and surgical site infections.
4
Q
Sources of HAIs :
A
- CLABSI
- MRSA
- Catheter-associated urinary tract infections
- Surgical site infections
- Bloodstream infections
- Pneumonia
- Clostridium difficile
5
Q
Why Are Healthcare-Associated Infections Important?
A
- Source of complications
- Transmission between different health care facilities
- Medical cost saving
- Education and training of health care workers increases compliance with and adoption of best practices (e.g., infection control, hand hygiene, attention to safety culture, and antibiotic stewardship) eg careful insertion, maintenance, and prompt removal of catheters, and careful use of antibiotics and getting rid of MRSA in patients with an evidence-based method to reduce transmission of MRSA in hospitals.
6
Q
Chain of infection
A
- Infectious agent
- Reservoir
- Portal of exit
- Mode of transmission
- Portal of entry
- Susceptible host
7
Q
Reservoir meaning
A
- The habitat in which the infectious agent normally lives, grows, and multiplies.
- Can be humans, animals, and the environment.
- The reservoir may or may not be the source from which an agent is transferred to a host eg reservoir of Clostridium botulinum is soil, but the source of most botulism infections is improperly canned food containing C. botulinum spores.
8
Q
Human reservoirs
A
- include the sexually transmitted diseases, measles, mumps, streptococcal infection, and many respiratory pathogens.
- Because humans were the only reservoir for the smallpox virus, naturally occurring smallpox was eradicated after the last human case was identified and isolated.
9
Q
Types of human reservoir
A
- A carrier : person with inapparent infection who is capable of transmitting the pathogen to others.
- Asymptomatic or passive or healthy carriers : never experience symptoms despite being infected.
- Incubatory carriers : can transmit the agent during the incubation period before clinical illness begins.
- Convalescent carriers : recovered from their illness but remain capable of transmitting to others.
- Chronic carriers : continue to harbor a pathogen such as hepatitis B virus or Salmonella Typhi, the causative agent of typhoid fever, for months or even years after their initial infection.
- Carriers commonly transmit disease because they do not realize they are infected, and consequently take no special precautions to prevent transmission.
- Symptomatic persons who are aware of their illness, on the other hand, may be less likely to transmit infection because they are either too sick to be out and about, take precautions to reduce transmission, or receive treatment that limits the disease.
10
Q
Animal reservoirs and zoonosis
A
Zoonosis refers to an infectious disease that is transmissible under natural conditions from vertebrate animals to humans.
Long recognized zoonotic diseases include brucellosis (cows and pigs), anthrax (sheep), plague (rodents), trichinellosis/trichinosis (swine), tularemia (rabbits), and rabies (bats, raccoons, dogs, and other mammals).
11
Q
Environmental reservoirs
A
- Plants, soil, and water
- Many fungal agents eg those that cause histoplasmosis, live and multiply in the soil.
- Outbreaks of Legionnaires disease often traced to water supplies in cooling towers and evaporative condensers, reservoirs for the causative organism Legionella pneumophila.
12
Q
Portal of exit
A
- influenza viruses and Mycobacterium tuberculosis exit the respiratory tract, schistosomes through urine, cholera vibrios in feces, Sarcoptes scabiei in scabies skin lesions, and enterovirus 70, a cause of hemorrhagic conjunctivitis, in conjunctival secretions.
- Some bloodborne agents can exit by crossing the placenta from mother to fetus (rubella, syphilis, toxoplasmosis), while others exit through cuts or needles in the skin (hepatitis B) or blood-sucking arthropods (malaria).
13
Q
Modes of transmission
A
Direct
- Direct contact
- Droplet spread
Indirect
- Airborne
- Vehicleborne
- Vectorborne (mechanical or biologic)
14
Q
Direct contact
A
- skin-to-skin contact, kissing, sexual intercourse, contact with soil or vegetation harboring infectious organisms.
- Thus, infectious mononucleosis (“kissing disease”) and gonorrhea are spread from person to person by direct contact.
- Hookworm is spread by direct contact with contaminated soil.
15
Q
Droplet spread
A
- spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking.
- Droplet spread is classified as direct because transmission is by direct spray over a few feet, before the droplets fall to the ground.
- Pertussis and meningococcal infection are examples of diseases transmitted from an infectious patient to a susceptible host by droplet spread.
16
Q
Airborne transmission
A
- when infectious agents are carried by dust or droplet nuclei suspended in air.
- Airborne dust includes material that has settled on surfaces and become resuspended by air currents as well as infectious particles blown from the soil by the wind.
- Droplet nuclei are dried residue of less than 5 microns in size.
- In contrast to droplets that fall to the ground within a few feet, droplet nuclei may remain suspended in the air for long periods of time and may be blown over great distances.
- Eg measles
17
Q
Vectors
A
- mosquitoes, fleas, and ticks may carry an infectious agent through purely mechanical means or may support growth or changes in the agent.
- Eg of mechanical transmission are flies carrying Shigella on their appendages and fleas carrying Yersinia pestis, the causative agent of plague, in their gut.
- in biologic transmission, the causative agent of malaria or guinea worm disease undergoes maturation in an intermediate host before it can be transmitted to humans.
18
Q
Portals of entry examples
A
- skin (hookworm),
- mucous membranes (syphilis),
- blood (hepatitis B, human immunodeficiency virus).
19
Q
Susceptibilty
A
- Depends on genetic or constitutional factors, specific immunity, and nonspecific factors that affect an individual’s ability to resist infection or to limit pathogenicity
- persons with sickle cell trait seem to be at least partially protected from a particular type of malaria.
- Specific immunity : protective antibodies that are directed against a specific agent; may develop in response to infection, vaccine, or toxoid (toxin that has been deactivated but retains its capacity to stimulate production of toxin antibodies) or mtransplacental transfer from mother to fetus or by injection of antitoxin or immune globulin.
- Nonspecific factors that defend against infection include the skin, mucous membranes, gastric acidity, cilia in the respiratory tract, the cough reflex, and nonspecific immune response.
- Factors that may increase susceptibility to infection by disrupting host defenses include malnutrition, alcoholism, and disease or therapy that impairs the nonspecific immune response.
20
Q
Interventions
A
- Controlling or eliminating agent at source of transmission
- Protecting portals of entry
- Increasing host’s defenses
21
Q
What is given to protect against malaria
A
prophylactic use of antimalarial drugs, recommended for visitors to malaria-endemic areas, does not prevent exposure through mosquito bites, but does prevent infection from taking root.
22
Q
Difference between vector and carrier
A
a vector carries the infection but is not affected by it, a carrier actually has the disease.
23
Q
How do altered target sites arise in resistant bacteria?
A
- Bact gets alternative gene or a gene that encodes a target-modifying enzyme.
- MRSA encodes an alternative PBP (PBP2a) with low affinity for beta-lactams, enables bacterium to resist them.
- Streptococcus pneumoniae resistance to erythromycin becasue it acquires erm gene, which encodes an enzyme that methylates the AB target site in the 50S ribosomal subunit.
24
Q
How do resistant bacteria inactivate antibiotics?
A
- Enzymatic degradation or alteration : renders antibiotic ineffective.
- Examples include beta-lactamase (bla) and chloramphenicol acetyl-transferase (cat).
- ESBL and NDM-1 are examples of broad-spectrum beta-lactamases (can degrade a wide range of beta-lactams abs, including newest).
25
Q
How does penicillin resistance come about
A
- B-lactamase breaks a bond in the b lactam ring of penicillin to disable the molecule -
- Bact with this enz can resist effects of penicillin and other B lactam ab
26
Q
How do bacteria alter their metabolism to resist the effects of antibiotics?
A
- Increased production of enzyme substrate can out-compete antibiotic inhibitor (e.g. increased production of PABA confers resistance to sulfonamides).
- Alternatively, bacteria switch to other metabolic pathways, reducing requirement for PABA. Eg bact that have access to thymidine are not inhibited by trimethoprim because bact can bypass the inherited metabolic pathway.
27
Q
How do resistant bacteria decrease drug accumulation?
A
Reduced penetration of AB into bacterial cell (permeability) and/or increased efflux of AB out of the cell – drug does not reach concentration required to be effective.
28
Q
How is resistance conferred
A
- The cell wall consists of peptidoglycan
- Gram positive build thick sheath of this but gram neg has thin sheath of this sandwiched between two membranes.
- Osmosis - peptid prevents pressure build-up
- Penicillin weakens this, prevents bact building the peptid layer so that overcomes to pressure
- two Sugars assembled into chains with amino acids, crosslinked via peptide bridge to - tough matrix
- Penicillin assembling protein assembles chain , Enzyme D - alanyl-Dalanine Carboxypeptidase / transpeptidase, also known as penicillin - Binding protein, assists with peptid matrix assembly by creating the crosslinks between the chains.
- Penicillin blocksthis enzyme by making a direct bond to key serine amino acid in its active site. Active portion of penicillin is a beta lactam ring, chemically reactive and opens up to form a bond to active site serine.
- Inactivates enzyme and prevents proper formation of peptid matrix
- some bact have developed resistance mechanisms to pen.
- For example MRSA - expresses penicillin binding protein 2a which has an altered active site that doesn’t bind beta lactam antibiotics.
- Bact can also express special Beta lactamase enzymes which bind to beta lactam antibiotics and break the beta lactam ring making antibiotic ineffective
- New drugs block beta lactamases so that ab can break down the bact.
- some block beta lactamase directly leaving antibiotic free to inhibit penicillin binding proteins, other beta lactam drugs are either not recognized or not broken down by some beta lactamases.
- Many genes crucial in ab resistance are encoded on small circular pieces of DNA called plasmids - these plasmids can be passed on from one generation of bact to another.
- One particularly dangerous gene is NDM-1, bact possessing this gene can build the New Delhi metallo beta lactamase enzyme - these types of enzymes can break down almost all known beta lactam drugs posing a major global threat
