Stevenson intro epidemiology 100706

Veterinary Biometrics and Epidemiology: 

Veterinary Biometrics and Epidemiology Mark Stevenson Institute of Veterinary, Animal, and Biomedical Science M.Stevenson@massey.ac.nz Alisdair Noble Institute of Information Sciences and Technology A.D.Noble@massey.ac.nz

Housekeeping: 

Housekeeping Biometrics ‘the measurement of life’ Epidemiology the study of disease in populations

Housekeeping: 

Housekeeping 38 lectures 31 biometrics (Alasdair N) 7 epidemiology (Mark S) Mondays (0900 – 1000) Vet 1 Tuesdays (1400 – 1500) Vet 1 Fridays (1000 – 1100) AH 2

Housekeeping: 

Housekeeping Assessment Assignment 1 due 24 July Assignment 2 due 11 August Assignment 3 due 6 October Quiz 15 September Final exam

Housekeeping: 

Housekeeping Resources Petrie and Watson (2005) Statistics for Veterinary and Animal Science. London: Blackwell Science course notes sample exercises and problems (see EpiCentre web page) material on web sites listed in course notes questions: Alasdair or myself email to arrange a suitable time to visit

Housekeeping: 

Housekeeping How to do well in this paper attend lectures look at past exam papers think of examples that illustrate concepts that we’re talking about (not just the examples we give you …) evidence of additional reading Lectures we probably won’t cover all material intended you’ll need to read your notes

Introduction to Epidemiology: 

Introduction to Epidemiology Mark Stevenson EpiCentre, IVABS, Massey University, Palmerston North M.Stevenson@massey.ac.nz

Roadmap: 

Roadmap What is epidemiology? Disease in individuals and populations individuals: host, agent, environment populations: individual, place and time Temporal patterns of disease

What is epidemiology?: 

What is epidemiology? Epidemiology  the study of disease in populations What epidemiologists do describe the amount of disease in populations identify subgroups of the population with a high risk of disease and subgroups with low risk identify characteristics and activities associated with a high (or low) risk of disease modifying exposure to these characteristics and/or activities provides a rational basis for controlling disease

What is epidemiology?: 

What is epidemiology? Well-known examples smoking  lung cancer high fat diet, sedentary livestyle  heart disease thalidomide  birth defects

What is epidemiology?: 

What is epidemiology? What is the relevance of this to the veterinarian? services provided by veterinarians should be regarded as an investment, not a cost preventing disease  investment application of epidemiological principles to clinical practice  a preventive approach established paradigm in food animal medicine, but also important in companion animal practice cancer eye in a herd of hereford cattle recurrent FUS in a family pet

What is epidemiology?: 

What is epidemiology? This approach works well for diseases where the aetiology is known, but also for diseases where the aetiology is not known …

What is epidemiology?: 

What is epidemiology? For example November 1986: BSE first diagnosed in Great Britain to date there have been ~170,000 confirmed cases after the first 200 cases, epidemiological investigations identified that meat and bone meal was the vehicle of transmission the [relatively] prompt ban on feeding meat and bone meal in July 1988 prevented an epidemic much larger than the one observed

What is epidemiology?: 

What is epidemiology? So, if we can manage risk, we can manage disease even if we don’t know the exact cause

Roadmap: 

Roadmap What is epidemiology? Disease in individuals and populations individuals: host, agent, environment populations: individual, place and time Temporal patterns of disease

Disease in individuals and populations: 

Disease in individuals and populations Whether or not disease occurs in an individual depends on an interplay of three factors: the host the agent the environment Useful concept when explaining to clients why some animals become sick and others do not

Disease in individuals and populations: 

Disease in individuals and populations The level of disease in a population depends on an interplay of three factors: characteristics individuals within the population age structure, breed, sex spatial factors where is the disease especially common or rare, and what is different about those places? temporal factors calendar time subject-referent

Disease in individuals and populations: 

Disease in individuals and populations Individual factors that influence patterns of disease: age structure of population distribution of genotypes immunity of population population dynamics and migration

Disease in individuals and populations: 

Disease in individuals and populations ‘Place’ (spatial) factors that influence patterns of disease: proximity to pollutants proximity to infectious agents proximity to disease risks

Disease in individuals and populations: 

Disease in individuals and populations ‘Time’ factors that influence patterns of disease: calendar time examples: influenza in humans, bovine ephemeral fever in cattle subject-referent time examples: milk fever in dairy cattle, gestational diabetes in humans epidemic curves are a useful way to visualise temporal patterns of disease …

Slide21: 

Counts of BSE submissions by 6-month period, November 1986 to June 1997.

Roadmap: 

Roadmap What is epidemiology? Disease in individuals and populations individuals: host, agent, environment populations: individual, place and time Temporal patterns of disease

Temporal patterns of disease: 

Temporal patterns of disease Terms used to describe the temporal pattern of disease in a population: endemic disease occurs at expected frequency epidemic disease occurs at greater than expected frequency pandemic huge epidemic (international) sporadic single case or cluster of cases

Temporal patterns of disease: 

Temporal patterns of disease Endemic disease occurs at expected frequency disease present in population or region at all times level of disease usually low and predictable examples: lameness in dairy cattle long bone fractures in < 10 year olds

Temporal patterns of disease: 

Temporal patterns of disease Temporal patterns of onset can provide insight into nature of epidemic common source propagated

Temporal patterns of disease: 

Temporal patterns of disease Common source epidemics disease arises from a single source of exposure to a causal agent epidemic curve shows a steep initial rise in case numbers and then a rapid falling off in the tail examples: batch of contaminated feed causing an outbreak of salmonellosis in feedlot cattle milk vacuum problem causing an outbreak of clinical mastitis in a herd of dairy cows foodborne disease outbreaks

Temporal patterns of disease: 

Temporal patterns of disease Propagated epidemics occur when the agent is transmitted through the population from host to host (typically infectious conditions) nature of epidemic depends on characteristics of agent (virulence) and host (susceptibility) contact rate population density examples: influenza in humans contagious mastitis in dairy cattle

Slide28: 

Epidemic curve typical of a common source epidemic.

Slide29: 

Epidemic curve typical of a propagated epidemic.

Temporal patterns of disease: 

Temporal patterns of disease Other uses for temporal displays of disease data: identify seasonal trends identify long-term trends

Slide31: 

Monthly reports of human leptospirosis cases in the USA, 1980 - 1995

Roadmap: 

Roadmap What is epidemiology? Disease in individuals and populations individuals: host, agent, environment populations: individual, place and time Temporal patterns of disease