OBJECTIVES (38 QUESTIONS)

• Design of Surveillance Systems

• Collection and Compilation of Surveillance Data

• Interpretation of Surveillance Data

• Outbreak Investigation

• Healthcare Associated Infections

DESIGN OF SURVEILLANCE SYSTEMS

Definition:• The purpose is to understand the causes of

disease by knowing distribution, natural history and determinants in terms of person, place and time

EPIDEMIOLOGY

Relationship between host, environment, and agent

EPIDEMIOLOGICAL TRIANGLE

A causal association is one that evidence indicates one factor is clearly implicated.

An Indirect association is a mixing effect and may be a confounding variable.

Statistics do not prove causality only suggest and association

ASSOCIATION AND CAUSATION

Incidence number of new cases of disease in a given time period

Prevalence number of cases occurring in a population

INCIDENCE AND PREVALENCE

EPIDEMIOLOGICAL STUDY DESIGN

Observational (descriptive and analytic)

Experimental (clinical community trials)

Used for theory verification

Persons are studied as a whole, not independent of their environment

Quantitative Qualitative

COLLECTION AND COMPILATION OF SURVEILLANCE DATA

DESCRIPTIVE STATISTICS

Rate: frequency of an event in a defined population per unit of time

Prevalence rate: numerator is the number of existing cases of disease in a population; denominator is the population at risk

Incidence rate: numerator is the number of new cases in a defined population; denominator is the defined time period for the population at risk

Incidence density: new cases/exposure time

MEASURES OF ASSOCIATION, 2X2 TABLE

Disease No disease Total

Factor present a b a+b

Factor absent c d c+d

a+c b+d N

RELATIVE VS. ODDS RATIO

Relative ratio (risk ratio) a ÷ c a + b c + d probability of developing disease if risk factor is

present probability of developing disease if risk factor is not

present

Odds ratio (a x d) ÷ (c x b) probability of having a risk factor if disease is

present probability of having a risk factor if disease is not

present

SENSITIVITY VS. SPECIFICITY

Sensitivity a ÷ (a + c) x 100 true positive test

Specificity d ÷ (b + d) x 100 true negative test

Positive predictive value a ÷ (a + b) x 100 % tests positive when disease present

Negative predictive value d ÷ (c + d) x 100 % tests negative when disease not present

POSITIVE VS. NEGATIVE PREDICTIVE VALUE

STATISTICAL TERMS TO KNOW

Mean average of the set of values

Median point in a series that divides that numbers in half

(middle)

Mode value in the data that occurs most frequently

Range difference from lowest to highest

STATISTICAL TERMS TO KNOW

Standard deviation variability around the mean

Variance square of standard deviation (similar to SD)

Frequency distribution normal ( 68.2% is 1 SD, 95.5% is 2 SD, 99.7% is

3 SD)

INTERPRETATION OF SURVEILLANCE DATA

HYPOTHESIS Hypothesis testing

estimates the likelihood that the result did not occur by chance

Null Hypothesis (Ho) it is stated to be rejected; hypothesis testing will

either accept or reject the null hypothesis

INFERENTIAL STATISTICS P value

a probability that your test is true; this is based on the level of significance

assigned by the investigator ( <.05)

Confidence interval the range of values that is likely to be included

data set

DATA PRESENTATION

Tables: show frequency

Graphs : epidemiologic informationshould be displayed in a histogram

because it depicts disease over time

Bar charts: use for only one coordinate

Pie charts: to show the percentage of the whole

CONTROL CHARTS Interpretation (out of control)1. One data point above UCL or below UCL2. 2 of 3 consecutive points are -2SD but -3 SD

on one side of the mean3. 4 of 5 consecutive points are –SD but -2 SD

on one side of the mean4. 9 consecutive points on one side of mean5. 6 consecutive points increasing or decreasing6. 14 consecutive points alternating up or

down7. 15 consecutive points within 1 SD above or

below the mean

OUTBREAK INVESTIGATION

OUTBREAK INVESTIGATIONo Outbreak

o an increase over the expected occurrence of an event;

o exception – one case of an unusual disease (e.g., botulism) may constitute an epidemic.

o “pseudo-outbreak” is generally applied to situations in which there is a rise in test results (e.g., positive microbiology cultures) without actual clinical disease.

INITIAL OUTBREAK INVESTIGATION

o Confirm presence of an outbreako Alert key partners about the investigationo Perform a literature reviewo Establish an initial case definitiono Develop a methodology for case findingo Prepare an initial line list and epidemic curveo Observe and review potentially implicated

patient care activitieso Consider whether environmental sampling

should be performedo Implement initial control measures

o Refine the case definitiono Continue case finding and surveillanceo Regularly review control measureso Considering whether an analytical study

should be performedo Prepare and disseminate reports

FOLLOW UP INVESTIGATION

Graph in which the cases of a disease that occurred during an epidemic (outbreak) are plotted according to the time of onset of illness in the cases.

The shape of the curve is determined by the epidemic pattern.

The epidemic curve is used to:o Determine whether the source of the infection was

common, propogated (continuing) ,or botho Identify the probable time of exposure of the cases to

the source(s) of infectiono Identify the probable incubation periodo Determine if the problem is ongoing

THE EPIDEMIC CURVE

THE EPIDEMIC CURVE

THE EPIDEMIC CURVE

THE EPIDEMIC CURVE

THE EPIDEMIC CURVE

HEALTHCARE ASSOCIATED INFECTIONS

CDC DEFINITION OF HAI An infection meeting the following criteria:

a. Not present or incubating on admissionb. Develops during the course of receiving treatment

for other conditionsc. Incubating at the time of admission that is related to

previous hospitalization at the same facility or identified in an admission following performance of a procedure during a previous admission

d. Healthcare workers acquire while performing their duties within a healthcare setting

e. HAIs include those that occur in the course of care in acute care hospitals, long-term care, behavioral health, correction facilities, dental care, home health, outpatient medical and surgical clinics, dialysis centers, radiology centers, etc.

COMMUNITY-ASSOCIATED VS. IATROGENIC

Community-associated infections present or incubating on admission to the

healthcare facility and not associated with previous treatment/procedures at that healthcare facility

Iatrogenic infection infection arising from the actions or treatments

of a physician or healthcare provider or a secondary condition arising from treatment of a primary condition

URINARY TRACT INFECTION

SUTI – Symptomatic Urinary Tract Infection

ABUTI – Asymptomatic Bacteremic UTI

OUTI – Other Infections of the Urinary Tract (Kidney, Ureter, Bladder, Urethra or Tissues Surrounding the Retroperineal or Perinephric Spaces)

SURGICAL SITE INFECTION

Superficial (Primary/Secondary) – Superficial Incisional Surgical Site Infection

Deep (Primary/Secondary) – Deep Incisional Infection

Organ/Space – SSI (organ/space)

ORGAN/SPACE – SSI (ORGAN/SPACE) Osteomyelitis Breast abscess or mastitis Myocarditis or pericarditis Disc space Ear, mastoid Emdometritis Endocarditis Eye, other than

conjunctivitis Gastrointestinal (GI) tract Intra-abdominal, no

specified elsewhere Intracranial, brain abscess

or dura Joint or bursa

Other infections of the lower respiratory tract

Mediastinitis Meningitis or ventriculitis Oral Cavity Other male or female

reproductive Other infections of the

urinary tract Spinal abscess without

meningitis Sinusitis Upper respiratory tract,

pharyngitis Arterial or venous infection Vaginal cuff

PNEUMONIA

Criteria for defining nosocomial pneumonia – general comments applicable to all pneumonia specific site criteria

VAP: Ventilator-associated pneumonia (i.e., pneumonia in persons who had a device to assist or control respiration continuously through a tracheostomy or by endotracheal intubation within the 48-hour period before the onset of infection, inclusive of the weaning period) should be so designated when reporting date.

VAE: Ventilator-associated event new definition

BSI - BLOOD STREAM INFECTION

LCBI (Adult & Children) – Bloodstream Infection, Laboratory – Confirmed

CLABSI – LCBI occurring when a central line is in place, and no other source of infection noted (must meet criteria for other site)

OTHER HAIS BJ-Bone and Joint Infection

(Bone & Joint) CNS-Central Nervous

System Infection (Disc & Intracranial & Meningitis & Spinal Abscess)

CVS-Cardiovascular System Infection (VASC & ENDO & CARD & MED)

EENT-Eye, Ear, Nose, Throat or Mouth(Conj, Eye, Ear, Oral, Sinu, UR)

GI-Gastrointestinal System (GE, GIT, HEP)

IAB-Intra-abdominal (NEC) LRI-Lower Respiratory

Tract Infectin (Bron, Lung) REPR-Reproduction Tract

(EMET, EPIS, VCUF, OREP) SST-Skin and Soft Tissue

(Skin, DECU, Burn, BRST, UMB, PUST, CIRC)

SYS-Systemic Infection ( DI)