Epidemiology Measurements and Calculations Handout 3 PDF

EPIDEMIOLOGY LECTURER: MRS. C. BECKFORD HARVEY MPH, PHD CANDIDATE  OBJECTIVES DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES. CONSTRUCT TABLES AND FIGURES USED TO REPRESENT EPIDEMIOLOGY DATA CALCULATE MEASURES OF DISEASE FREQUENCY AND INFECTION RAT...

EPIDEMIOLOGY LECTURER: MRS. C. BECKFORD HARVEY MPH, PHD CANDIDATE  OBJECTIVES DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES. CONSTRUCT TABLES AND FIGURES USED TO REPRESENT EPIDEMIOLOGY DATA CALCULATE MEASURES OF DISEASE FREQUENCY AND INFECTION RATES INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA ANALYZE EPIDEMIOLOGICAL DATA. PREPARATION OF TABLES AND GRAPHS – GRAPHS, HISTOGRAMS, POPULATION PYRAMIDS, BAR CHARTS, PIE CHARTS, SCATTER DIAGRAMS, MAPS (2 HOURS)  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES. EPIDEMIC - AN UNUSUAL AND UNEXPECTED OCCURRENCE OF A DISEASE. ENDEMIC - ENDEMIC REFERS TO THE CONSTANT PRESENCE AND/OR USUAL FREQUENCY OF A DISEASE OR INFECTIOUS AGENT WITHIN A SPECIFIC GEOGRAPHIC AREA OR POPULATION. IT INDICATES THAT THE DISEASE REGULARLY OCCURS AT A PREDICTABLE RATE IN THAT AREA. EXAMPLE- MALARIA IN CERTAIN PARTS OF SUB-SAHARAN AFRICA. IT IS CONSISTENTLY PRESENT IN THESE REGIONS, WITH PREDICTABLE RATES OF INFECTION YEAR AFTER YEAR.  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES PANDEMIC- IS AN OUTBREAK OF A DISEASE THAT OCCURS ON A GLOBAL SCALE, AFFECTING MULTIPLE COUNTRIES AND CONTINENTS, OFTEN CAUSING WIDESPREAD ILLNESS. EXAMPLE: THE COVID-19 PANDEMIC IS A RECENT EXAMPLE, WHERE THE NOVEL CORONAVIRUS SPREAD RAPIDLY ACROSS THE GLOBE STARTING IN LATE 2019, LEADING TO SIGNIFICANT HEALTH, SOCIAL, AND ECONOMIC IMPACTS WORLDWIDE.  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES IMMUNITY IS THE BODY'S ABILITY TO RESIST OR DEFEND AGAINST INFECTION, DISEASE, OR OTHER BIOLOGICAL INVADERS. IT CAN BE EITHER: INNATE (NATURAL) IMMUNITY: THE BODY'S FIRST LINE OF DEFENSE, PRESENT FROM BIRTH, PROVIDING NON-SPECIFIC PROTECTION. ACQUIRED (ADAPTIVE) IMMUNITY: DEVELOPED AFTER EXPOSURE TO A SPECIFIC PATHOGEN, THROUGH INFECTION OR VACCINATION, PROVIDING TARGETED, LONG-LASTING DEFENSE. EXAMPLE: AFTER RECEIVING A MEASLES VACCINE, A PERSON DEVELOPS ACQUIRED IMMUNITY, WHICH PROTECTS THEM FROM FUTURE MEASLES INFECTIONS. DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES IMMUNE RESPONSE: THE BODY'S DEFENSE MECHANISM ACTIVATED UPON RECOGNIZING FOREIGN SUBSTANCES (ANTIGENS) LIKE PATHOGENS. HERD IMMUNITY: WHEN A SIGNIFICANT PORTION OF A POPULATION BECOMES IMMUNE TO A DISEASE, REDUCING ITS SPREAD AND PROTECTING NON-IMMUNE INDIVIDUALS. IMMUNOGLOBULIN: ANTIBODIES PRODUCED BY THE IMMUNE SYSTEM TO NEUTRALIZE PATHOGENS LIKE BACTERIA AND VIRUSES. DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES HOST RESPONSE: THE WAY A PERSON'S BODY REACTS TO AN INVADING PATHOGEN, EITHER BY IMMUNE DEFENSES OR INFLAMMATORY PROCESSES. HYPERSENSITIVITY: AN EXAGGERATED OR INAPPROPRIATE IMMUNE RESPONSE TO A HARMLESS SUBSTANCE, SUCH AS IN ALLERGIES.  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES INFECTION: THE INVASION AND MULTIPLICATION OF MICROORGANISMS LIKE BACTERIA, VIRUSES, OR PARASITES WITHIN THE BODY, CAUSING DISEASE. INFECTIVITY: THE ABILITY OF A PATHOGEN TO ENTER, SURVIVE, AND MULTIPLY IN A HOST. PATHOGENICITY: THE ABILITY OF A MICROORGANISM TO CAUSE DISEASE IN A HOST.  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES A CARRIER OF A DISEASE IS AN INDIVIDUAL WHO HARBORS A PATHOGEN (A DISEASE-CAUSING ORGANISM, SUCH AS A BACTERIUM, VIRUS, OR PARASITE) BUT DOES NOT EXHIBIT SYMPTOMS OF THE DISEASE. HOWEVER, THIS INDIVIDUAL CAN STILL SPREAD THE PATHOGEN TO OTHERS, POTENTIALLY CAUSING AN OUTBREAK OR CONTINUED TRANSMISSION OF THE DISEASE. EXAMPLE - ASYMPTOMATIC CARRIER OF SALMONELLA TYPHI, THE BACTERIUM THAT CAUSES TYPHOID FEVER A PERSON CAN BE A CARRIER TEMPORARILY OR FOR AN EXTENDED PERIOD  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES VIRULENCE: THE DEGREE OF DAMAGE A PATHOGEN CAN CAUSE TO THE HOST. IMMUNOGENICITY: THE ABILITY OF A SUBSTANCE, SUCH AS A PATHOGEN OR VACCINE, TO PROVOKE AN IMMUNE RESPONSE. SPORADIC: REFERS TO DISEASES THAT OCCUR INFREQUENTLY AND IRREGULARLY WITHIN A POPULATION.  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES ELEMENTS OF THE DISEASE PROCESS – CHAIN OF INFECTION: 1. INFECTIOUS AGENT: THE PATHOGEN (E.G., BACTERIA, VIRUS). 2. RESERVOIR: WHERE THE PATHOGEN LIVES (E.G., HUMANS, ANIMALS). 3. PORTAL OF EXIT: HOW THE PATHOGEN LEAVES THE RESERVOIR (E.G., RESPIRATORY DROPLETS). 4. MODE OF TRANSMISSION: HOW THE PATHOGEN SPREADS (E.G., AIRBORNE, DIRECT CONTACT).  DEFINE SELECTED TERMS RELATED TO INFECTIOUS DISEASES 5. PORTAL OF ENTRY: HOW THE PATHOGEN ENTERS A NEW HOST (E.G., THROUGH BROKEN SKIN). 6. SUSCEPTIBLE HOST: AN INDIVIDUAL WHO CAN CONTRACT THE DISEASE DUE TO WEAK OR ABSENT IMMUNITY.  MEASUREMENTS AND THEIR CALCULATIONS RATIOS, PROPORTIONS, INCIDENCE RATES, PREVALENCE RATES, DEMOGRAPHIC RATES. RELATIONSHIPS BETWEEN PREDICTIVE VALUE AND DISEASE PREVALENCE  FREQUENCY THE FUNDAMENTAL EPIDEMIOLOGICAL MEASURE IS THE FREQUENCY WITH WHICH AN EVENT OF INTEREST ( DISEASE, INJURY, DEATH) OCCURS IN THE POPULATION TO BE STUDIED. USUALLY EXPRESSED AS COUNT (#), TABLES, BAR CHARTS, LINE GRAPHS INCIDENCE AND PREVALENCE ARE OF FUNDAMENTAL IMPORTANCE TO ALL OF EPIDEMIOLOGY. A RATE IS THE FREQUENCY ( NUMBER) OF EVENTS THAT OCCUR IN A DEFINED TIME PERIOD DIVIDED BY THE AVERAGE POPULATION AT RISK  MEASURES OF CENTRAL TENDENCY- MEAN MODE MEDIAN MEAN, MEDIAN, AND MODE ARE ALL MEASURES OF CENTRAL TENDENCY. IN EPIDEMIOLOGY, MEASURES OF CENTRAL TENDENCY SUMMARIZE A DATASET BY IDENTIFYING THE CENTRAL OR TYPICAL VALUE. THESE MEASURES HELP SUMMARIZE AND INTERPRET LARGE SETS OF DATA BY IDENTIFYING A CENTRAL POINT MEAN (AVERAGE) THE ARITHMETIC AVERAGE, REPRESENTING THE TYPICAL VALUE IF ALL DATA POINTS WERE SPREAD EVENLY THE MEAN IS THE SUM OF ALL VALUES IN A DATASET DIVIDED BY THE NUMBER OF VALUES. IT IS COMMONLY USED TO CALCULATE AVERAGE VALUES LIKE THE AVERAGE AGE AT DIAGNOSIS, AVERAGE NUMBER OF CASES, OR AVERAGE EXPOSURE LEVELS IN A POPULATION.  MEASURES OF CENTRAL TENDENCY- MEAN MODE MEDIAN MEDIAN (MIDDLE VALUE) THE MEDIAN IS THE MIDDLE VALUE IN A DATASET WHEN THE VALUES ARE ARRANGED IN ASCENDING OR DESCENDING ORDER. IF THERE IS AN EVEN NUMBER OF VALUES, THE MEDIAN IS THE AVERAGE OF THE TWO MIDDLE VALUES. IF THE AGES ARE 25, 30, 35, AND 90, THE MEDIAN IS (30 + 35) / 2 = 32.5.  MEASURES OF CENTRAL TENDENCY- MEAN MODE MEDIAN MODE (MOST FREQUENT VALUE) - THE MODE IS THE VALUE THAT OCCURS MOST FREQUENTLY IN A DATASET. EXAMPLE: IF A GROUP OF PATIENTS HAS AGES OF 25, 30, 30, AND 90, THE MODE IS 30 (SINCE IT APPEARS TWICE). INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA PREVALENCE IS THE PROPORTION OF A POPULATION THAT HAS A PARTICULAR DISEASE OR CONDITION AT A SPECIFIC POINT IN TIME OR OVER A SPECIFIED PERIOD. PROPORTIONS ARE FRACTIONS IN WHICH THE NUMERATOR IS INCLUDED IN THE DENOMINATOR FORMULA IS P= # OF CASES X 100 # OF PEOPLE IN THE POPULATION INVOLVES UNDERSTANDING VARIOUS ASPECTS OF THE DATA COLLECTED TO ASSESS HEALTH PATTERNS, RISKS, AND OUTCOMES.  INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA INCIDENCE RATE DEFINITION THE NUMBER OF NEW CASES OF A DISEASE OR CONDITION THAT DEVELOP IN A SPECIFIC PERIOD WITHIN A POPULATION AT RISK. UNLIKE PREVALENCE, FOR RATES THE NUMERATOR AND DENOMINATOR USE DIFFERENT UNITS OF MEASUREMENT EXPRESSED AS THE NUMBER OF NEW CASES PER UNIT OF TIME OF OBSERVATION ( # OF NEW CASES DIVIDED BY THE TOTAL PERSON-TIME AT RISK. FORMULA INCIDENCE RATE = # NEW OF CASES DISEASE- FREE PERSON- TIME AT RISK USUALLY EXPRESSED PER 1000 POPULATION OR PER 10,000 POPULATION OR PER 100,000 POPULATION INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA MORTALITY RATE DEFINITION: THE NUMBER OF DEATHS DUE TO A PARTICULAR CAUSE PER UNIT OF POPULATION, USUALLY EXPRESSED PER 100,000 PEOPLE PER YEAR. FORMULA CRUDE DEATH RATE MR = # OF DEATHS(DEFINED PLACE AND TIME PERIOD) X 1000 POPULATION MIDPOINT POPULATION ( SAME PLACE AND TIME PERIOD) PROVIDES INFORMATION ON THE IMPACT OF A DISEASE ON THE POPULATION’S HEALTH AND HELPS IN EVALUATING THE EFFECTIVENESS OF HEALTH INTERVENTIONS. FOR EXAMPLE, A HIGH MORTALITY RATE FOR CANCER MAY INDICATE A NEED FOR IMPROVED TREATMENT OR PREVENTION STRATEGIES.  EQUATIONS OF THE MOST COMMONLY USED RATES CRUDE BIRTH RATE INFANT MORTALITY RATE AGE –SPECIFIC DEATH RATE MATERNAL MORTALITY RATE NEONATAL MORTALITY RATE SEE HANDOUT  INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA MORBIDITY RATE IS THE FREQUENCY OR RATE OF OCCURRENCE OF DISEASE WITHIN A POPULATION. IT MEASURES THE BURDEN OF ILLNESS AND PROVIDES INSIGHT INTO THE HEALTH NEEDS OF A POPULATION. FOR INSTANCE, HIGH MORBIDITY RATES FOR A CHRONIC DISEASE LIKE DIABETES CAN HIGHLIGHT THE NEED FOR BETTER MANAGEMENT AND SUPPORT SERVICES. INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA RISK IS THE PROPORTION OF PERSONS WHO ARE UNAFFECTED AT BEGINNING OF A STUDY PERIOD BUT WHO UNDERGO THE RISK EVENT ( DEATH, DISEASE, INJURY DURING THE STUDY PERIOD. RELATIVE RISK (RR) (RISK RATIO) A MEASURE THAT COMPARES THE RISK OF A HEALTH EVENT AMONG THOSE EXPOSED TO A RISK FACTOR WITH THE RISK AMONG THOSE NOT EXPOSED. A RELATIVE RISK GREATER THAN 1 INDICATES AN INCREASED RISK DUE TO THE EXPOSURE, WHILE A RELATIVE RISK LESS THAN 1 INDICATES A DECREASED RISK. INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA ODDS RATIO ( OR) IS A MEASURE OF ASSOCIATION BETWEEN EXPOSURE AND AN OUTCOME, CALCULATED BY COMPARING THE ODDS OF THE OUTCOME OCCURRING IN THE EXPOSED GROUP TO THE ODDS IN THE UNEXPOSED GROUP. SIMILAR TO RELATIVE RISK, AN ODDS RATIO GREATER THAN 1 SUGGESTS AN ASSOCIATION BETWEEN EXPOSURE AND THE OUTCOME. EXAMPLE, AN ODDS RATIO OF 3 FOR DEVELOPING HEART DISEASE AMONG THOSE WITH HIGH CHOLESTEROL INDICATES THAT THOSE WITH HIGH CHOLESTEROL ARE THREE TIMES MORE LIKELY TO DEVELOP HEART DISEASE COMPARED TO THOSE WITH NORMAL CHOLESTEROL LEVELS. INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA WE USE RELATIVE RISK IN COHORT. RANDOMIZED CONTROLLED TRIALS, OR PROSPECTIVE STUDIES WHERE ACTUAL RISK CAN BE CALCULATED A COHORT STUDY IS A PROSPECTIVE OR RETROSPECTIVE OBSERVATIONAL STUDY THAT FOLLOWS A GROUP OF INDIVIDUALS (COHORT) OVER TIME TO SEE IF EXPOSURE TO A CERTAIN RISK FACTOR LEADS TO THE DEVELOPMENT OF A DISEASE OR OUTCOME.. INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA USE ODDS RATIO IN CASE-CONTROL STUDIES WHERE THE RISK CANNOT BE DIRECTLY MEASURED BUT ODDS ARE USED INSTEAD A CASE-CONTROL STUDY IS A RETROSPECTIVE OBSERVATIONAL STUDY THAT COMPARES INDIVIDUALS WITH A SPECIFIC CONDITION OR DISEASE (CASES) TO THOSE WITHOUT THE DISEASE (CONTROLS), TO ASSESS WHETHER EXPOSURE TO A PARTICULAR RISK FACTOR IS ASSOCIATED WITH THE CONDITION 2X2 TABLE INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA RELATIVE RISK (RR) - THE RELATIVE RISK COMPARES THE RISK OF AN EVENT (E.G., DEVELOPING A DISEASE) IN THE EXPOSED GROUP TO THE RISK IN THE UNEXPOSED GROUP. RR=A/(A+B) DIVIDED BY C (C+D) WHERE: A/(A+B) IS THE RISK OF DISEASE IN THE EXPOSED GROUP. C/(C+D) IS THE RISK OF DISEASE IN THE UNEXPOSED GROUP. INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA  INTERPRETATION OF ODDS RATIO ( OR) RESULTS OR = 1: NO ASSOCIATION BETWEEN EXPOSURE AND DISEASE. OR > 1: POSITIVE ASSOCIATION (EXPOSURE MIGHT INCREASE THE LIKELIHOOD OF DISEASE). OR < 1: NEGATIVE ASSOCIATION (EXPOSURE MIGHT DECREASE THE LIKELIHOOD OF DISEASE). INTERPRETING KEY COMPONENTS OF EPIDEMIOLOGIC DATA ATTRIBUTABLE RISK DEFINITION: THE DIFFERENCE IN THE RATE OF A HEALTH OUTCOME BETWEEN AN EXPOSED GROUP AND AN UNEXPOSED GROUP, INDICATING THE PROPORTION OF THE RISK ATTRIBUTABLE TO THE EXPOSURE. HELPS IN QUANTIFYING THE IMPACT OF A RISK FACTOR ON THE OCCURRENCE OF A DISEASE. EXAMPLE, IF 30% OF LUNG CANCER CASES ARE ATTRIBUTED TO SMOKING, THIS INDICATES THE PROPORTION OF CASES THAT COULD BE PREVENTED IF SMOKING WERE ELIMINATED. AR=INCIDENCE IN EXPOSED MINUS THE INCIDENCE IN UNEXPOSED  SCENARIO IN A COHORT STUDY: AMONG 100 SMOKERS, 40 DEVELOPED LUNG CANCER. AMONG 100 NON-SMOKERS, 10 DEVELOPED LUNG CANCER. CALCULATE THE ____________________ INTERPRET THE RESULTS RESULTS  SCENARIO IN A CASE CONTROL STUDY: AMONG 100 SMOKERS, 40 DEVELOPED LUNG CANCER. AMONG 100 NON-SMOKERS, 10 DEVELOPED LUNG CANCER. CALCULATE THE ____________________  SCENARIO CALCULATE THE ATTRIBUTABLE RISK INTERPRET THE RESULTS RESULTS. INTERPRET THE RESULTS RESULTS THE END  REFERENCES GIESECKE, J. (2017). MODERN INFECTIOUS DISEASE EPIDEMIOLOGY (3RD ED.). CRC PRESS. NELSON, K. E., & WILLIAMS, C. M. (2020). INFECTIOUS DISEASE EPIDEMIOLOGY: THEORY AND PRACTICE (3RD ED.). JONES & BARTLETT LEARNING. LUCAN, S. C., KATZ, D. L., ELMORE, J. G., & WILD, D. (2013). JEKEL'S EPIDEMIOLOGY, BIOSTATISTICS, PREVENTIVE MEDICINE, AND PUBLIC HEALTH: WITH STUDENT CONSULT ONLINE ACCESS (4TH ED.). ELSEVIER SAUNDERS. CELENTANO, D. D., SZKLO, M., & FARAG, Y. (2024). GORDIS EPIDEMIOLOGY (7TH ED.). ELSEVIER. FRIEDMAN, G. D. (1980). PRIMER OF EPIDEMIOLOGY. MCGRAW-HILL FRIIS, R. H., & SELLERS, T. (2020). EPIDEMIOLOGY FOR PUBLIC HEALTH PRACTICE (6TH ED.). JONES & BARTLETT LEARNING.