Disease Detectives B/C

What is Disease Detectives? Epidemiology: Study of health/sickness of populations Includes Public Health Surveillance –Data collection for prevention and control of illness Uses scientific study methods –Heavy emphasis on data analysis

The event B/C events similar in content C has more math, vocab, evaluation of research design Nonprogrammable calculators (absolutely essential) One sheet of notes This year’s focus: population growth

Event format 2-3 data sets on public health problems Mostly short answer/fill in questions Multi-point math problems –Show work for partial credit! Matching/multiple choice for vocab Essays, long reading passages? –“ten steps to investigating an outbreak”

Population growth ????? Diseases of dense populations –Cholera, dysentery, influenza, typhoid, polio Encroachment into disease reservoirs –Sleeping sickness, Marburg virus –Ebola! Some general knowledge may be expected, especially of ebola

Background info Virus, bacteria, parasite – life cycles modes of transmission Immunity: active, passive, herd Epidemic, pandemic, endemic Case definition: person, place, time Epidemiological triad: agent, host, environment John Snow’s cholera study

Statistics Prevalence: #of existing cases at a given time (or period) Incidence: # of new cases in a period of time Both usually expressed as rates (e.g., per 1,000 pop.) –For incidence, person/time may be used (e.g., person/year) Attack rate: cases/exposed pop. Case fatality rate: CSD/cases

2x2 tables Disease +Disease - Exposure +# of people = a# of people = bRow sum = a+b Exposure -# of people = c# of people = dRow sum = c+d Column sum = a+c Column sum = b+d Total = a+b+c+d = n

Statistics: Relative Risk Technically, Relative Risk includes Risk Ratio, Rate Ratio and Odds Ratio Usually, Relative Risk = Risk Ratio Risk = # of cases/population Risk Ratio = risk in pop. of interest / control group risk preferably RR = exposed/unexposed, but may use baseline risk (whole pop.)

Odds Ratio Odds of outcome in pop. 1 odds of outcome in pop.2 = postives in pop. 1 negatives in pop. 1 divided bypositives in pop. 2 negatives in pop. 2 Or, by invert and multiply pos. in pop.1 X neg. in pop. 2 neg. in pop. 1 X pos. in pop.2

Research methods Case/control study: compare cases to some group of unaffected persons –Cannot use RR b/c no true baseline Cohort study: tracks population over time, compares to some baseline –Can use RR –May be prospective or retrospective Experimental methods –Basically limited to randomized clinical trials of treatments, supplements etc.

Example: Nurses’ health study Cohort study (prospective), so RR is applicable RR = 411/39242 / 596/74068 RR = 1.30 Breast Cancer + No Breast Cancer Totals Ever smoked Never Smoked Totals ,310

Example 2: Hip fractures case/control study, so must use OR OR = 60/20 / 579/213 or 60*213 / 20*579 = 1.1 # of months on hormone replacement therapy Hip fracture patients (Cases) Sample of other patients (controls)Totals > < Totals

Evaluating design: C 1.Random error - Avoidable with larger sample 2. Systematic error a.Selection (sample) bias - Controls may not represent population b.Recall bias \ c.Response bias | information bias d.Interviewer bias /

Stratified Analysis (C) Simpson Paradox: Sometimes a relationship that is true for a large group is not true for any subset of that group Stratified analysis looks at subgroups (strata) Most common: age adjustment Direct method: weight events /(e.g. deaths) by standard pop. Indirect method: apply standard rate to obtain expected events

Mantel-Haenstzel

Epi curves: point source Single peak, <1 incubation period Single environmental source; no PTP Example: transient environmental agents, most food contamination

Continuous common source One peak or declining peaks, >1 IP Ongoing environmental exposure; no PTP Example: persistent environmental agents, waterborne pathogens (cholera)

Progressive source (aka Propagated) Multiple, often successively higher peaks >1 IP Person-to person transmission Example: communicable diseases (MRSA, flu)

Line Listing Signs/SymptomsLabDemographics Case #Report Date Onset Date Physician Diagnosis NVJHAIgMSexAge 110/12/0210/5/02Hepatitis A1111M37 210/12/0210/4/02Hepatitis A1011M62 310/13/0210/4/02Hepatitis A1011M38 410/13/0210/9/02NA000 F44 510/15/02 10/13/02Hepatitis A1101M17 610/16/0210/6/02Hepatitis A0011F43

SIR Graph susceptible, infected, recovered (removed)

Links Free online introductory textbook from the CDC: pidemiologyInPublicHealthPractice.pdf pidemiologyInPublicHealthPractice.pdf Another, from Canada: CDC’s DD site: Weekly reports from CDC: Excellent series from UNC: Nice explanation of odds ratio & relative risk: mercy.org/stats/journal/oddsratio.asphttp:// mercy.org/stats/journal/oddsratio.asp Adjusted rates: ocw.jhsph.edu/courses/fundepi/PDFs/Lecture7.pdf Mantel-Haenszel: haenszel-method.aspxhttps://wiki.ecdc.europa.eu/fem/w/fem/the-mantel- haenszel-method.aspx Glossaries: glossary.xml glossary.xml