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Summer Course: Introduction to Epidemiology. August 26 , 0845-1015. Descriptive Epidemiology. Dr. N. Birkett, Department of Epidemiology & Community Medicine, University of Ottawa. Scenario (1).
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Summer Course:Introduction to Epidemiology August 26, 0845-1015 Descriptive Epidemiology Dr. N. Birkett, Department of Epidemiology & Community Medicine, University of Ottawa
Scenario (1) A 34 year old domestic worker who had recently emigrated from South-East Asia to Ottawa presents at the ED with a 6-week history of cough, fever, night sweats, weakness, fatigue & shortness of breath. She was previously in good health and has had 2 uncomplicated pregnancies (parity=2). Chest x-ray shows cavitary lesions & a sputum smear shows acid-fast bacilli. TB was diagnosed. Treatment included 8 weeks of directly observed four drug therapy. Then, 10 weeks of two drugs taken three times per week.
Scenario (2) The patient lived in an apartment with her husband and two children. TB skin tests were positive for husband and 3 year old daughter. Preventive treatment was given to all immediate family members. There was one positive skin test in 54 other apartment residents. No work contacts were positive.
Session Overview • Role of descriptive epidemiology • Main features • Person • Place • Time
Uses (1) • Assessing the Health Status of a Population • Generating Hypotheses about causal factors • Planning and Evaluating Public Health Programmes • Evaluating clinical outcomes and treatments
Key Elements • Person (age, sex, race, religion, SES) • Place (country, state/province, city) • Time (year, season, month, week, day, hour) • Identification of disease clusters in time & space (epidemics/outbreaks)
Person factors (1) • Age • Disease incidence generally increases with age • Aging process vs. accumulation of ‘experience’ • Sex • Breast cancer: 1:99 (Male:female) • Esophageal cancer: 10:1 (Male:female) • Hormones • Habits • Sexual practices • Occupational exposures • Societal roles/attitudes
Person factors (2) • Race/ethnicity • Controversial. How to define race? • Biological vs. social construct • Minority groups have more disease and worse outcomes. • SES • Health practices • Access to Health Care • Discrimination • Stress • Environmental/occupational exposures
Person factors (3) • SES (socio-economic status) • Lower worse health • Life expectancy 6.6 years lower in the poorest group. • Complex causal pathway • Nutrition • Race • Habits • Environmental/occupational • Access to/use of health/preventive services • Political isolation • Others
Person factors (4) • Religion • Genetic (in-breeding) • Tay-Sachs disease largely restricted to Jews of European descent. • Behavioral • Mormons have 24% lower cancer rate • Nuns, cervical cancer and breast cancer • Social support • Spiritual impact? • Occupation • Percival Pott and scrotal cancer in chimney sweeps (1775)
Person factors (5) • Marital status • Married people have better health in general (e.g. lower suicide rates) • Does marital support better health • Are people who are predisposed to better health more likely to marry or be more attractive? • Stress of failed marriage
# reported TB cases(USA 2002) 10 yrs 20 yrs
Place factors (1) • Strong overlap with medical geography. • Small area estimation • GIS Basis • Geopolitical units • Natural features
Place factors (2) Aspects include: • Physical Environment • Climate • Water • Soil • Air • Biological environment • Flora/fauna • Social environment • Cultural traditions
Place factors (3) Scale of Comparisons • Global • Cancer rates • Regional • CHD and birth defects are more common in Eastern Canada than Western Canada. • Neighborhood • Childhood lead poisoning was higher in one specific 28 block area of Boston than in other parts of the city. • Traced to use of lead paint in that area. Pica and soil contamination.
Time factors (1) • Frequently called ‘temporal’ or ‘secular’ trends. • Mainly relates to changes over calendar time. • Years (most common), months, weeks, days, diurnal, hours. • Seasonal effects
Time factors (2) Interpretation • Can be tricky. Need external information, other clues. • Changes in exposure levels or susceptibility • Progression in diagnostic abilities • Ultrasound and congenital heart defects • Completeness of reporting • Child sexual abuse • Denominator issues, changes in age distribution. • Changes in treatment.
Time factors (3) • Population pyramids can be animated to show population changes over time. Here are some examples from Statistics Canada. • CANADA: 1901-2001 • Ontario 1956-2006 • NFLD: 1949-2001 • Nunavut, 1991-2001 • Yukon: 1901-2001
Migrant studies (1) • When people move, does the incidence of disease: • Change to reflect their new country • Likely due to environmental causes • Stay the same as in the old country • Likely due to genetic factors • Perhaps due to early environmental exposures • Become somewhere in between. • Japanese migrants to Hawaii/California • Italian migrants to various countries • 26,000,000 migrants between 1876 & 1985 • ‘East block’ Europeans migrating to the West
Migrant studies (2) • Why does TB incidence persist at elevated level? • Latent infections prior to migration • Residence in migrant communities in new country; localized high transmission rates • Crowded housing • Inadequate access to preventive or therapeutic services • Noncompliance with therapy • Resistant organisms • Re-infection on return to country of origin
Summary • Descriptive Epidemiology plays a major role in identifying outbreaks and unknown risks. • Provides preliminary information about groups are particular risk. • Can provide hypotheses about potential risks or causes. • Very common activity with governments and health units.
