1. Dvora Joseph Davey, PhD Candidate Epidemiology, UCLA
Introduction to Epidemiology, Reproductive Rate, and Basic HIV AAHU Fellows
Dvora Joseph Davey, PhD Candidate Epidemiology, UCLA

2. Outline of todays lecture
Definition and applications of epidemiology
Epidemiology and Prevention
Reproductive Rate
Prevalence vs. Incidence
Introduction to HIV Epidemiology

3. What is epidemiology?
Why does a disease develop in some people and not others?
Illness and ill health are not randomly distributed in human populations
Certain characteristics predispose us to, or protect us against, a variety of different diseases
Let’s start from the beginning here. What is epidemiology?
Why does a disease develop in some people and not others?
Illness and ill health are not randomly distributed in human populations
This is a key aspect of why epidemiology exists.
If disease were random then I wouldn’t have a job.
There are factors associated with illness.
Take smoking as an example (we’re going to use this example over and over because it’s such a strong risk factor for disease), smokers are more likely to get many types of disease than non-smokers – heart disease, lung cancer etc. This is not random.
Certain characteristics predispose us to, or protect us against, a variety of different diseases
What are some examples of characteristics that will predispose us to disease? –obesity, malnutrition, sex, age
Young people are less likely to get most types of cancer.

4. Definition of epidemiology
“The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems.” – L. Gordis
Next let’s decide on a common definition of epidemiology. There are many definitions that one can use for epidemiology. This is the definition that we will continue to use throughout this class.
“The study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control of health problems.”
So what does this mean? The study of the spread of disease and how we can use this information for control of disease.
What is a “health problem”? This could be infectious or chronic disease, an accidental or violent injury, a syndrome or symptom.
Why do we include injury in this? Injuries are the third leading cause of death nationally, and they are the leading cause of death for Americans between the ages of one and 44
millions of injuries could be prevented each year if more states adopted additional research-based injury prevention policies, and if programs were fully implemented and enforced.

5. Objectives of epidemiology
Identify etiology of disease and relevant risk factors
Determine the extent of disease found in the community
Study the natural history and progression of disease
Evaluate both existing and newly developed preventive and therapeutic measures and modes of health care delivery
Provide the foundation for developing public policy relating to environmental problems, genetic issues and other considerations regarding disease prevention and health promotion
Identify etiology of disease and relevant risk factors
We want to know how the disease is transmitted from one person to another or from a nonhuman reservoir to humans. And we want to identify causative factors that could lead to certain conditions. Why is this important? Our ultimate aim is to intervene to reduce morbidity and mortality from the disease. We need a rational basis for interventions (prevention). If we can identify the etiologic (or causative) factors, we can reduce exposure to these factors.
Determine the extent of disease found in the community
What is the burden of disease in the community? This is critical for health planning and training
Study the natural history and progression of disease
Certain diseases or conditions are have worse outcomes than others. For example some may be fatal, We want to understand this natural history (progression) of disease so that we can implement control measures.
Evaluate both existing and newly developed preventive and therapeutic measures and modes of health care delivery
Evaluate if a program/intervention is operating successfully
Provide the foundation for developing public policy relating to environmental problems, genetic issues and other considerations regarding diseases prevention and health promotion
Provide the foundation for developing efficient
public health campaigns and policies relating to
disease prevention

6. These are the 10 leading causes of death in the world from 2012.
*go through list*

7. Can someone give me an example of a non-communicable disease? -Cancer

8. shows the 15 leading causes of death in the United States in 2009.
If you want to reduce the largest number of deaths – what would you target?
The three leading causes—heart disease, cancer, and cerebrovascular disease—account for almost 55% of all deaths, an observation that suggests specific targets for prevention if a significant reduction in mortality is to be achieved

9. Observational studies of disease (1): Cohort study
A cohort is a group of people who share a common characteristic or experience within a defined period
The comparison group may be the general population from which the cohort is drawn
A cohort study is a form of longitudinal study that follows a group of people who do not have the disease, and uses correlations to determine the risk of contracting the disease.
Relative Risk is the probability of an event occurring (for example, developing a disease, being injured) in an exposed group to the probability of the event occurring in a comparison, non-exposed group

10. Observational studies of disease (2): Case-control study
A type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.
Case-control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the "cases") with patients who do not have the condition/disease but are otherwise similar (the "controls").
They require fewer resources but provide less evidence for causal inference
Odds Ratio (OR) describes the association between the presence/absence of "A" (HIV) and the presence/absence of "B" (unprotected anal intercourse) for individuals in the population.

12. Sensitivity, specificity, predictive value
Term
Definition
Sensitivity
Measures the proportion of positives that are correctly identified as such (e.g., the % of sick people who are correctly identified as having the condition).
Specificity
Measures the proportion of negatives that are correctly identified as such (e.g., the % of healthy people who are correctly identified as not having the condition).
Positive predictive value (PPV)
Proportion of positive results that are true positive
PPV= # of true positives/ number of true positives + number of false positives
Negative predictive value (NPV)
Proportion of negative results that are true negative
NPV= # of true negatives/ number of true negatives + number of false negatives
NPD generally established by a control group

13. Epidemiology and Prevention

14. Epidemiology and Prevention
Why identify those at high risk of disease?
To direct prevention efforts to those who are at highest risk
Identify factors that are associated with risk and modify these factors
A major use of epidemiologic evidence is to identify subgroups in the population who are at high risk for disease. Why should we identify such high-risk groups?
we can direct preventive efforts, such as screening programs for early disease detection, to populations who are most likely to benefit from any interventions that are developed for the disease.
we may be able to identify the specific factors or characteristics that put them at high risk and then try to modify those factors – some factors are not modifiable. What are some examples?

15. Prevention
Primary prevention denotes an action taken to prevent the development of a disease in a person who is well and does not (yet) have the disease in question. Primary prevention is Preventing the initial development of a disease
Secondary prevention involves identifying people in whom a disease process has already begun but who have not yet developed clinical signs and symptoms of the illness. This period in the natural history of a disease is called the preclinical phase of the illness. Our objective with secondary prevention is to detect the disease earlier than it would have been detected with usual care. By detecting the disease at an early stage in its natural history, often through screening, it is hoped that treatment will be easier and/or more effective Early detection of existing disease to reduce severity and complications
Tertiary prevention denotes preventing com­plications in those who have already developed signs and symptoms of an illness and have been diagnosed—that is, people who are in the clinical phase of their illness. This is generally achieved through prompt and appropriate treatment of the illness combined with ancillary approaches such as physical therapy that are designed to prevent complications such as joint contractures.Reducing the impact of the disease

16. approaches to prevention
Population-based
Applied to the entire population
Must be relatively inexpensive and noninvasive
High-risk approach
Targets those at highest risk
dietary advice for preventing coronary disease or advice against smoking may be provided to an entire population
An alternate approach is to target a high-risk group with the preventive measure. Thus, screening for cholesterol in children might be restricted to children from high-risk families.
Population-based approaches can be considered public health approaches, whereas high-risk approaches more often require a clinical action to identify the high-risk group to be targeted. In most situations, a combination of both approaches is ideal.
This will come up again later when we talk about public policy toward the end of the semester

17. Reproductive rate
In epidemiology, the basic reproductive rate (or R0 = R naught) of an infection can be thought of as the number of cases (ill people) one case generates on average over the course of its infectious period, in an otherwise uninfected population.
It helps determine whether or not an infectious disease can spread through a population.
When R0 < 1
the infection will die out in the long run. But if
R0 > 1
the infection will be able to spread in a population.
Generally, the larger the value of R0, the harder it is to control the epidemic.

18. Reproductive rate, cont.
The basic reproductive rate is affected by several factors including:
1. The duration of infectivity of affected patients
2. The infectiousness of the organism, and
3. The number of susceptible people in the population that the affected patients are in contact with.
In populations that are not homogeneous, the definition of R0 is more subtle.
An appropriate definition for R0 is "the expected number of secondary cases produced by a typical infected individual early in an epidemic".

19. Morbidity Measures

20. Incidence
Incidence measures the number of NEW cases of a disease that occur during a specified period of time in a population AT RISK of developing the disease
Measure of disease in people who did not already have the disease at the beginning of the study
Represents a measure of risk

21. Incidence Rate
When we have information on exactly how long an individual was at risk, we can calculate incidence RATE
We must have information on:
Those who developed the disease of interest during the follow up period
# of people at risk who did not develop the disease of interest
# of people who were lost to follow up
When different individuals are observed for different lengths of time, we calculate an incidence rate (also called an incidence density), in which the denominator consists of the sum of the units of time that each individual was at risk and was observed. This is called person-time and is often expressed in terms of person-months or person-years of observation.

22. Incidence RATE
Denominator is TIME (= length of time people are followed, e.g. person-time or person-years)
If followed for 1 year = 1 person-years
Different people contribute different amounts of time to the denominator depending on how long they were followed
Especially useful when you have a small number of subjects
Let us consider person-years (py): One person at risk who is observed for one year = one person-year. One person at risk observed for 5 years = 5 person-years (py). But 5 people at risk, each of whom is observed for only 1 year, also = 5 person-years.

23. Incidence rate
𝑁𝑜. 𝑜𝑓 𝒏𝒆𝒘 𝒄𝒂𝒔𝒆𝒔 𝑜𝑓 𝑎 𝑑𝑖𝑠𝑒𝑎𝑠𝑒 𝑜𝑐𝑐𝑢𝑟𝑖𝑛𝑔 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑑𝑢𝑟𝑖𝑛𝑔 𝑎 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑒𝑑 𝑝𝑒𝑟𝑖𝑜𝑑 𝑜𝑓 𝑡𝑖𝑚𝑒 𝑇ℎ𝑒 𝒂𝒎𝒐𝒖𝒏𝒕 𝒐𝒇 𝑻𝑰𝑴𝑬 𝑐𝑜𝑛𝑡𝑟𝑖𝑏𝑢𝑡𝑒𝑑 𝑏𝑦 𝑝𝑒𝑟𝑠𝑜𝑛𝑠 𝑤ℎ𝑜 𝑎𝑟𝑒 𝑎𝑡 𝑟𝑖𝑠𝑘 𝑜𝑓 𝑑𝑒𝑣𝑒𝑙𝑜𝑝𝑖𝑛𝑔 𝑡ℎ𝑒 𝑑𝑖𝑠𝑒𝑎𝑠𝑒 𝑑𝑢𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑑𝑒𝑓𝑖𝑛𝑒𝑑 𝑝𝑒𝑟𝑖𝑜𝑑 𝑜𝑓 𝑡𝑖𝑚𝑒
The choice of 1,000 is completely arbitrary—we could have used 10,000, 1 million, or any other figure.

24. Uses for Incidence Measures
Assessing risk of disease
Determining how quickly disease is spreading
Looking at time trends in new cases of disease
Evaluating whether interventions are successful
Comparing new cases to new potential sources of exposure when investigating risk factors

25. Identifying newly detected cases of disease

26. Identifying newly detected cases of disease

27. Prevalence
The number of affected persons present in the population at a specific time divided by the number of persons in the population at that time
Measures the proportion of the population that is affected by the disease at that time
Includes both new and existing cases

28. Prevalence
𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒄𝒂𝒔𝒆𝒔 𝑜𝑓 𝑎 𝑑𝑖𝑠𝑒𝑎𝑠𝑒 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑎𝑡 𝑎 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑒𝑑 𝑡𝑖𝑚𝑒 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑟𝑠𝑜𝑛𝑠 𝑖𝑛 𝑡ℎ𝑎𝑡 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑎𝑡 𝑡ℎ𝑎𝑡 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑒𝑑 𝑡𝑖𝑚𝑒
For example, if we are interested in knowing the prevalence of arthritis in a certain community on a certain date, we might visit every household in that community and, using interviews or physical examinations, determine how many people have arthritis on that day. This number becomes the numerator for prevalence. The denominator is the population in the community on that date.

29. Calculating Prevalence
15 children were tested for asthma on February 13, 2015 at UCLA Elementary School
On February 13, 2015 there were 500 total children at UCLA Elementary School
What is the prevalence of asthma in UCLA Elementary School?

30. Uses for Prevalence
Provides us with a snapshot of disease in a community at a given time
Helps with planning for health care system in a community
Used to guide resource allocation and distribution of services

31. Issues with Prevalence
We do not know when disease developed or how far along an individual is in the course of their disease
Does not measure risk of disease
Cannot be used to establish causal relationships
Problems identifying disease

32. Relationship between incidence and prevalence
Watch the video here:

33. Hiv epidemiology

34. HIV Prevalence and incidence in the us
Although persisting at far too high a level (approximately 50,000 infections per year), HIV incidence has been reduced by more than two-thirds since the height of the U.S. HIV epidemic, and HIV prevention efforts are estimated to have averted more than 350,000 HIV infections in the United States to date. Additionally, despite continued increases in the number of people living with HIV over the past decade (about 1.1 million people living with HIV today), new HIV infections have not increased, indicating that HIV testing, prevention, and treatment programs are effectively reducing the rate of transmission overall.

35. HIV Epidemiology in the united states
First case of HIV diagnosed in 1981
Over 1.2 million people aged 13 years and older in the United States are living with HIV infection, and almost 1 in 8 (12.8%) are unaware of their infection (CDC, 2015).
Gay, bisexual, and other men who have sex with men (MSM), particularly young African American MSM, are most seriously affected by HIV.
By race, blacks/African Americans face the most severe burden of HIV

36. HIV Incidence (new infections):
The estimated incidence of HIV has remained stable overall in recent years, at about 50,000 new HIV infections per year.
Within the overall estimates, however, some groups are affected more than others. MSM continue to bear the greatest burden of HIV infection, and among races/ethnicities, African Americans continue to be disproportionately affected.
Source: CDC, Estimated HIV incidence among adults and adolescents in the United States,

37. Hiv prevalence
HIV Diagnoses (new diagnoses, regardless of when infection occurred or stage of disease at diagnosis):
In 2013, an estimated 47,352 people were diagnosed with HIV infection in the United States.
In that same year, an estimated 26,688 people were diagnosed with AIDS.
Overall, an estimated 1,194,039 people in the United States have been diagnosed with AIDS.

38. Hiv related mortality
An estimated 13,712 people with an AIDS diagnosis died in 2012
Approximately 658,507 people in the United States with an AIDS diagnosis have died overall.
The deaths of persons with an AIDS diagnosis can be due to any cause—that is, the death may or may not be related to AIDS.

39. HIV morbidity and mortality
HIV is generally a silent disease when first acquired, and this period of latency varies.
The progression from HIV infection to AIDS varies from 5–12 years.
In the past, most individuals succumbed to the disease in 1–2 years after being diagnosed with AIDS.
However, since the introduction of potent anti retroviral drug therapy and better prophylaxis against opportunistic infections, mortality rates have declined dramatically.

40. In conclusion Epidemiology is:
an invaluable tool for providing a rational basis on which effective prevention programs can be planned and implemented
invaluable for conducting clinical investigations to evaluate both new therapies and those that have been in use for some time, as well as newly developed interventions for disease prevention
The ultimate goal is to improve the control of disease through both prevention and treatment that will prevent deaths from the disease and will enhance the quality of life of those who have developed serious illness

41. QUIZ! 1: Epidemiologists are interested in learning about :
A: the causes of diseases and how to cure or control them
B: the frequency and geographic distribution of diseases
C: the causal relationships between diseases
D: all of the above
2: TRUE OR FALSE: Incidence measures the number of existing cases of a disease that occur during a specified period of time in a population AT RISK of developing the disease
3. TRUE OR FALSE: Prevalence measures the number of affected persons present in the population at a specific time divided by the number of persons in the population at that time
4. How is a rate different from a proportion?
5. HIV incidence in the US is highest among which risk group?
A. Drug users
B. Heterosexual men
C. Men who have sex with men
D. Hispanic/Latino men & women
Hint: Pathogenesis more simply means: the development of disease
Put your full name – first and last on the top right of the paper. This will not be for a grade. Please give this your best shot as I will be looking at your answers.

42. Questions?
Contact info:
Dvora Joseph Davey