week 6: healthcare epidemiology & infection control

what is epidemiology?

epidemiology turns infection data into prevention action

what does epidemiology ask?

• how often is disease occurring?

• who is affected, where, and when?

• what factors increase or reduce risk?

• how can we prevent or control disease?

what are the basic measurements of epidemiology?

incidence, prevalence, morbidity, mortality

incidence: basic meaning + nursing/public health use

• new cases occurring in population during specified period

• track new infections and detect outbreaks

prevalence: basic meaning + nursing/public health use

• existing cases at point in time or during specified period

• describe current disease burden

morbidity: basic meaning + nursing/public health use

• illness in population due to disease

• track nonfatal disease impact

mortality: basic meaning + nursing/public health use

• deaths in population due to disease

• track fatal outcomes

incidence vs prevalence:

• incidence measures new disease occurrence

• prevalence measures existing disease burden

incidence: focus, question, time, and main use

• focus: new cases occurring over time

• q: how often are new cases occurring?

• time: requires specified period

• main use: track new disease occurrence

prevalence: focus, question, time, and main use

• focus: existing cases

• q: how much disease is present?

• time: at a point in time or over a period

• main use: describe disease burden

what are two ways to measure incidence?

• incidence risk and incidence rate

• risk describes probability over specified period

• rate describes how quickly new cases occur

incidence risk

probability of developing disease during a specified period

incidence rate

speed at which new cases occur

incidence risk: numerator, denominator, expression, and formula

• numerator: new cases during the period

• denominator: population at risk at start of period

• expression: proportion or %

• formula in photo

incidence rate: numerator, denominator, expression, and formula

• numerator: new cases during period

• denominator: person-time at risk during period

• expression: cases per person-time

• formula in photo

what is person-time?

• combines how many people are followed with how long each person is at risk

• ex:

  • patient a - 2 days at risk

  • patient b - 3 days at risk

  • patient c - 5 days at risk

  • total person-time = 10 patient-days

in healthcare surveillance, time may also be measured as:

patient-days or device-time such as catheter-days

formula for prevalence

• prevalence = existing cases/total population x 100%

• 4 of 20 patients have the infection

  • 4/20 × 100% = 20%

what are the four disease patterns?

sporadic, endemic, epidemic, pandemic

sporadic: meaning + example

• occurs occasionally or irregularly

• ex: a few scattered cases

endemic: meaning + example

• constantly present at an expected lvl

• ex: usually background lvl

epidemic/outbreak: meaning + example

• more cases than expected in a place/time

• ex: cluster above baseline

pandemic: meaning + example

• epidemic spread across many countries/regions

• ex: global spread

chain of infection

1. pathogen

2. reservoir

3. portal of exit

4. mode of transmission

5. portal of entry

6. susceptible host

• every nursing infection-prevention action targets at least one link in chain

what are the five modes of transmission?

contact, droplet, airborne, vehicle, vector

contact: basic idea + common prevention focus

• direct touch or indirect contact w/ contaminated objects

• hand hygiene, gloves/gown, cleaning

droplet: basic idea + common prevention focus

• respiratory particles transmitted mainly at close range

• medical mask, eye protection as indicated

airborne: basic idea + common prevention focus

• infectious particles that can remain suspended and travel through air

• N95 or higher-lvl respirator, airborne-infection isolation room

vehicle: basic idea + common prevention focus

• transmission through contaminated nonliving source, such as food, water, or blood

• safe food/water handling, safe blood and injections

vector: basic idea + common prevention focus

• transmission by arthropod, such as mosquito or tick

• bite prevention, vector control

what are the 3 classifications of infection?

• community-acquired infection

• healthcare-associated infection (HAI)

• latrogenic infection

community-acquired infection

acquired outside healthcare settings

healthcare-associated infection (HAI)

• associated w/ receiving healthcare

• may develop during care or become apparent afterward

• may arise from patients own microbiota or from pathogens acquired from other people or environment

• important targets for surveillance + infection prevention

latrogenic infection

results from medical or surgical intervention, and may also be healthcare-associated

what are 5 common types of HAIs?

• c.difficile infection (CDI)

• catheter-associated urinary tract infection (CAUTI)

• surgical site infection (SSI)

• ventilator-associated pneumonia (VAP)

• central line-associated bloodstream infection (CLABSI)

c.difficile infection (CDI): common risk factor + prevention

• antibiotic exposure

• contact precautions, sporicidal cleaning

catheter-associated UTI (CAUTI): common risk factor + prevention

• urinary catheter

• aseptic insertion, early removal

surgical site infection SSI: common risk factor + prevention

• surgery

• surgical asepsis, wound care, glucose control

ventilator-associated pneumonia (VAP): common risk factor + prevention

• mechanical ventilation

• aspiration prevention, oral care

central line-associated bloodstream infection (CLABSI): common risk factor + prevention

• central line

• aseptic access, dressing care

what increases risk for HAIs?

• HAI risk reflects both patient vulnerability, pathogen traits, and healthcare exposures and practices

• patient factors, pathogen factors, system factors

for increased risk for HAIs, what are examples of patient factors?

• very young or older age

• immunosuppression or serious illness

• wounds or burns

• antibiotic exposure

for increased risk for HAIs, what are examples of pathogen factors?

• antibiotic resistance

• spore formation, such as c.diff

for increased risk for HAIs, what are examples of pathogen factors?

• surgery and invasive devices

• lapses in hand hygiene

• aseptic technique or cleaning

antibiotic exposure can:

• disrupt normal gut microbiota

• reduce colonization resistance

• allow c.diff to overgrow

• takeaway: antibiotics can disrupt gut microbiota = allowing c.diff to overgrow

clinical connection to antibiotics, microbiota, and c.diff:

• monitor stool pattern and hydration

• implement contact precautions according to facility policy

• ensure appropriate cleaning of shared equipment and the environment

• support antimicrobial stewardship

clinical microbiology supports infection control since it:

• identifies pathogens from clinical specimens

• performs susceptibility testing when appropriate

• alerts infection-prevention teams to unusual patterns

• supports outbreak investigation through organism tracking and targeted testing

from one patient to a pattern:

• one patient’s results → helps guide patient’s care

• similar results in several patients → may signal transmission or outbreak

infection preventionists coordinate surveillance and outbreak response with the healthcare team, which consist of:

• tracking infections over time

• comparing patterns w/ expected baseline

• identifying unusual clusters that need investigation

• sharing findings to guide prevention

• takeaway: uses infection data to detect changes + guide prevention

standardized infection ratio (SIR)

SIR compares number of HAIs observed w/ number predicted using NHSN (national healthcare safety network) data

SIR formula

SIR = 1: observed = predicted

SIR > 1: more infections than predicted

SIR < 1: fewer infections than predicted

what are the standard precautions in all care settings?

• peform hand hygiene

• use PPE based on anticipated exposure

• use safe injection and shaprs practices

• use respiratory hygiene/cough etiquette

• clean and disinfect equipment

• treat blood, body fluids, secretions, excretions, nonintact skin, and mucous membranes as potentially infectious

anticipated exposure for gloves

touching blood/body fluids or contaminated surfaces

anticipated exposure for gown and gloves

splash or spray to clothing or skin

anticipated exposure for mask + eye protection/face shield

splash or spray to eyes, nose, or mouth

anticipated exposure for fit-tested N95 or higher-lvl respirator

airborne pathogen

transmission-based precautions are used:

• in addition to standard precautions (when they aren’t enough)

• contact, droplet, airborne

for contact, use when transmission risk is primarily… + examples:

• direct or indirect contact

• MRSA wounds, many multidrug-resistant organisms, varicella

for droplet, use when transmission risk is primarily… + examples:

• respiratory droplets transmitted at close range

• influenza, meningococcal disease

for airborne, use when transmission risk is primarily… + examples:

• small particles that remain suspended in air

• TB, measles, varicella

droplet precautions

• use a medical/procedure mask when entering the room or as policy requires

• use eye protection when splash or spray risk is present.

• place patient according to facility policy, limit transport when needed

• common examples: influenza, mumps, pertussis, meningococcal disease.

airborne precautions

• use an airborne infection isolation room (AIIR).

• wear fit-tested N95 or higher-level respirator.

• examples: TB, measles, and varicella.

protective environment/isolation

• protects selected severely immunocompromised patients (e.g., patients receiving a stem cell transplant from a donor)

• positive pressure helps keep outside air from entering.

asepsis: clean vs sterile

• both prevent infection, but different goals

• clean technique used to reduce pathogens

• sterile technique used when entering sterile body sites or maintaining sterile fields

medical asepsis: goal + examples

• reduce and prevent spread of pathogens

• ex: hand hygiene, cleaning equipment, gloves when needed

surgical asepsis: goal + examples

• exclude all microbes from sterile field or sterile body site

• ex: sterile gloves, sterile field, sterile instruments, invasive procedures

sequence of PPE:

• put PPE on before exposure risk begins

• remove PPE carefully to avoid contaminating hands, clothing, or the environment

• perform hand hygiene immediately after PPE removal and whenever hands become contaminated during removal

fomites

an inanimate object that can become contaminated and transmit pathogens

three considerations for fomites:

• clean and disinfect shared equipment between patients.

• use dedicated equipment when required by precautions.

• dispose of sharps and infectious waste safely according to policy.