JC93(Microbiology) - Infectious disease outbreak and infection control

Question 1

Purpose of infection control

Answer 1

protect health care workers, patients, and visitors from nosocomial/ hospital-acquired infections

Infection control cannot stop hospital-acquired infection, but
can delay it, reduce the incidence and prevent spread amongst
patients

Question 2

What is the most important measure of infection control

Answer 2

Hand hygiene

Question 3

Differentiate community-acquired and hospital acquired infections

Answer 3

1. Community-acquired infection (CAI): onset of symptoms before or within 48 hours of admission
2. Hospital-acquired infection (HAI), aka nosocomial infection: onset of symptoms after 48 hours of admission

Question 4

Examples of hospital-acquired infections

Answer 4

Common HAI includes:
 Catheter-associated bloodstream infections (CABSI)
 Pneumonia (ventilator-, tracheostomy-associated)
 Urinary tract infections (urinary bladder-, nephrostomy-, cystostomy-catheter associated)
 Surgical site infections
 Pressure sore related infections
 Antibiotic-associated Clostridium difficile colitis
 Infusion or blood product related infections

Question 5

Pathogens that commonly cause nosocomial infections

Answer 5

MRSA, VRSA

Multidrug-resistant Gram-negative bacilli:
 Extended-spectrum β-lactamases (ESBL) or carbapenemase producing
Enterobacteriaceae
 Carbapenem-resistant Acinetobacter baumannii or Pseudomonas
aeruginosa

Question 6

3 types of healthcare associated infections

Answer 6

o Infections acquired in healthcare institutions other than acute care facilities (e.g. longterm care facilities or nursing homes);

o Infections acquired during hospitalization but not identified until after discharge;

o Infections acquired through outpatient care, e.g. day surgery, dialysis, chemotherapy center, home parenteral therapy

Question 7

Define disease ourbreak

Answer 7

Outbreak = increase in occurrence of an infection above the background rate, e.g.:
o One episode of a rare occurrence (e.g. SARS); or
o Many episodes of a common occurrence (e.g. seasonal influenza)

Question 8

Define disease surveillance

Aim of surveillance

Answer 8

Surveillance = ongoing, systematic collection, analysis, and distribution of information regarding the occurrence of an infection in defined populations

Primary aim = determine the existing rates of infection and the risk factors

 When particular rate exceeds the pre-existing rate significantly on statistical calculation = outbreak

 By knowing the risk factors, we may find the common source and implement specific control measures

Question 9

Define pseudo-outbreaks

Answer 9

o Clusters of positive cultures in patients without evidence of disease, e.g. laboratory errors (e.g. equipment contamination with subsequent contamination of patient specimens); or

o Perceived increase in infections, e.g.:
 Surveillance was not previously conducted for that problem; or
 Surveillance definitions, intensity, or methods have changed

Question 10

7 Steps of carrying out an outbreak investigation

Answer 10

1. Case definition: to develop a working case definition based on known facts of the outbreak
2. Case finding: additional cases
3. Confirmation of an outbreak:
4. Epidemic curve (to describe the outbreak over time)
5. Line listing: Before reviewing medical records, determine the data that are important to collect for each case, and design a questionnaire and electronic file for data collection
6. Formulation of a hypothesis for source and transmission of infection
7. Case-control study: Univariate analysis to compare the exposure to potential risk factors in the affected patients with those in the control group
8. Collect environmental samples at source of outbreak for testing

Question 11

Metric to confirm a disease outbreak?

Answer 11

When the monthly rate for a particular infection exceeds the 95% confidence interval

based on the previous years’ rates for that particular month

Question 12

Assays for environmental samples collected at the site of outbreak

Answer 12

Compare microbe at environment and in patients infected,
perform microbiological typing to establish clonality, e.g.:

o Simple antibiogram, biotype

o Single or multilocus sequence genotyping, pulse field gel electrophoretic
genotyping

o Complete genome sequencing

Question 13

Line-listing for disease outbreak investigation

• Procedure
• Metrics

Answer 13

 Before reviewing medical records, determine the data that are important to collect for each case, and design a questionnaire and electronic file for data collection

 E.g. age, sex, underlying diseases, use of antimicrobial agents, invasive procedures,
operating room, surgeon, nurses, exposure to other health care workers, medications, intravenous fluid, placement in different cubicles or wards during hospitalization

 After reviewing the records, make a table with the data of the patients for statistical analysis

Question 14

Epidemic curve

• Function
• Implications of a curve with high initial peak vs long duration with no peaks

Answer 14

Epidemic curve (to describe the outbreak over time): Plot the number of cases (Y axis) against time (X-axis)

Function: Investigate possible source and mode of transmission

High initial peak = single, shared or ‘common’ source (e.g. a batch of contaminated food/ water supply)

Long duration with few/ no peaks = Person-to-person transmission or Poor infection control techniques or contaminated patient equipment

Question 15

Roles of infection control team

Answer 15

1. Develop an annual infection control plan
2. Train o health care workers on infection control
3. Surprise visits to monitor daily patient care practice to prevent infection
4. Implementation of infection control practice
5. Epidemiological surveillance for health care associated infections (e.g. surgical site infections, device-associated infections)
6. Monitor percutaneous exposure (needle stick injuries) or mucosal exposure to bloodborne pathogens (e.g. HBV, HIV)
7. Investigate outbreaks
8. Collaborate with pharmacy and other specialties for antibiotic stewardship program

Others:
 Environmental cleaning, disinfection, sterilization of equipment, disposal of infectious waste
 Oversight on the use of new products that directly or indirectly relate to the risk of nosocomial infections

Question 16

Standard infection control measures

• 5 methods
• Purpose

Answer 16

Purpose: reduce the risk of transmission of bloodborne and other pathogens from blood, all body fluids, broken skin and mucosa

Methods:

• Hand hygiene before and after every patient contact
• Use gloves, gowns (disposable 100% polypropylene) and eye protection when exposure to body secretions or blood is possible (e.g. diarrhea, bleeding)
• Dispose sharp instruments and needles in impervious sharp box (no recap)
• Safe injection practices
• Soiled linen or contaminated materials in impervious bags

Question 17

Safe injection practices

Answer 17

o Hand hygiene, use gloves

o Maintain an aseptic field

o Prepare injection site properly

o Use sterile, single-use, disposable needle and syringe for each injection

o Prefer single-dose vials over multiple-dose vials whenever possible

Question 18

Types of contact infection

Answer 18

Direct:
o Finger skin to skin: skin colonization/infection
o Finger skin to mucosa of eye, nose & mouth: colonization or infection
(acute viral respiratory diseases)
o Ingested into gastrointestinal tract: GI colonization/infectious diarrhea

Indirect contact:
catch the microbe from environment (e.g. fomites) which has been
contaminated by hands or secretions of others

Question 19

Pathogens that transmit by contact

Answer 19

Selected multidrug-resistant bacteria, e.g.:
o Vancomycin-resistant enterococci (VRE)
o Methicillin-resistant Staphylococcus aureus (MRSA)

Various pathogens:
o Enteric (norovirus, rotavirus, Clostridium difficile), enterovirus
o Parasitic (scabies)
o Respiratory syncytial virus (RSV), parainfluenza
o HSV

Question 20

Contact precaution methods

Answer 20

1. Hand hygiene and gloves upon room entry
2. Nonsterile gloves for all patient contact
3. Gown if substantial direct contact
4. Remove gowns and gloves prior to exiting isolation rooms
5. Dedicate medical equipment to a single patient; single room/ cubicle

Question 21

Pathogens that transmit by droplets

Answer 21

 Neisseria meningitidis

 Respiratory viruses (e.g. influenza, adenovirus) and bacteria: Bordetella
pertussis, Haemophilus influenzae type b, Mycoplasma pneumoniae, diphtheria
(pharyngeal), streptococcal pharyngitis/ pneumonia/ scarlet fever in infants and young children

 Rubella, mumps, parvovirus B19 etc.

Question 22

Pathogens that transmit by air

Answer 22

 Tuberculosis (TB)
 Measles
 Varicella (chickenpox)
 Smallpox
 SARS

Question 23

Droplet precaution methods

Answer 23

1. Hand hygiene
2. Healthcare workers within 2m of patients on droplet precautions should wear a surgical mask
3. May give a surgical mask to patient (if tolerated) as
   source control to reduce the shedding of respiratory droplets

Question 24

Airborne precaution methods

Answer 24

Nurse patients in an airborne infection isolation room:
 Negative air pressure (pressure differential of 2.5Pa between patient room and anteroom)

 >12 air changes/hr

 Doors must remain closed

 All persons entering must wear a respirator (N95) with a filtering capacity of 95% that allows a tight seal over the nose and mouth

Question 25

Pathogens with parenteral transmission

Prevention of parenteral transmission and treatment for accidental exposure

Answer 25

Parenteral transmission (injection, infusion, transplantation or needle stick):
o HIV, AIDS, Hepatitis virus

o Never recap the needle; put in sharp box

o Prevention of infections due to sharps injuries:
 Vaccination: HBV
 First aid (squeeze as much blood out as possible under running water)
 Source and victim serological testing
 Post-exposure prophylaxis
 HIV: antiretroviral for 4 weeks
 HBV: HBIG + vaccination

Question 26

Indications of hand washing with chlorhexidine soap

Answer 26

1. Your hand is visibly soiled
2. Dealing with the spores of Clostridium
   difficile
3. After using the restroom

Question 27

Composition of alcohol-based hand wash

Answer 27

Requires alcohol + water todenature proteins
 Ethanol: 2-carbon compounds with better in vitro virucidal activity

 Isopropanol, npropanol: 3-carbon compounds with better in vitro bactericidal activity

 Concentrations of 75- 80% most commonly used (usually measured
by vol/vol)

Question 28

3 advantages of alcohol-based soap vs other compositions

Answer 28

1. More effective in bactericidal and virucidal activity
2. More convenient and not limited by the availability of washing basins
3. Better skin care (glycerol is present in WHO formulations I and II of alcohol-based handrub)

Question 29

Indication for gloves for contact precaution

Answer 29

1. Anticipating direct contact with blood/ body fluids, mucous membranes, non-intact skin, and other potentially infectious material;
2. Having direct contact with patients who are colonized/ infected with pathogens transmitted by the contact route e.g. VRE, MRSA; or
3. Handling or touching visibly/ potentially contaminated patient care equipment and environmental surfaces

Question 30

Respiratory protection methods

Answer 30

respirator with N95 or higher filtration to prevent inhalation of infectious particles

Perform hand hygiene before putting on a respirator

Perform fit test to identify an appropriate model of N95 for all users