[EPI] 1.01 - Overview of Epidemiology & Descriptive Epidemiology - Dr. Butacan

Overview of Epidemiology & Descriptive Epidemiology 4 NOVEMBER 2015 Dr. Remigio Jay-Ar Z. Butacan IV OUTLINE I. Overview of Epidemiology A. Definition B. Important concepts C. Famous Epidemiologists II. Descriptive Epidemiology A. Significance B. Important concepts III. Descriptive Epidemiology of HIV-AIDS in the Philippines IV. Mini-quiz

To explain the importance and application of epidemiology in the practice of medicine To analyze various illnesses in terms of descriptive characteristics of time, place and person.

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systematic and unbiased approach in the collection, analysis, and interpretation of data Not merely observation and data generation

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DISTRIBUTION

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Frequency - refers not only to the number of health events, but also to the relationship of that number to the size of the population. o Measure used to compare diseases across populations Pattern - refers to the occurrence of health-related events by time, place and person. (DESCRIPTIVE EPIDEMIOLOGY)  Answers ‘when’, ‘where’ and ‘who’

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OBJECTIVES 

 Epidemiology is data-driven and relies on a very

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DETERMINANTS

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Any factor, whether event, characteristic, or other definable entity, that brings about a change in a health condition or other defined characteristic (ANALYTIC EPIDEMIOLOGY)  Looks at the causes of a certain disease, answers ‘how’ and ‘why’ Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual.

Reference: Dr. Butacan’s Powerpoint slides and lecture Legend: Remember (Exams)

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I. Overview of Epidemiology A. Definition     

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EPI: meaning on or upon DEMOS: meaning people LOGOS: meaning the study of Basically, “the study of what befalls a population” Merriam Webster Definition o A branch of medical science that deals with the incidence, distribution, and control of disease in a population o Sum of the factors controlling the presence or absence of a disease or pathogen Dictionary of Epidemiology (Working definition; by Last) o The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

B. Important Concepts (based on the working definition) 1.

STUDY

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A quantitative discipline that relies on probability, statistics and sound research methods. A method of causal reasoning based on developing and testing hypotheses.

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HEALTH-RELATED STATES/EVENTS

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May be seen as anything that affects the well-being of a population Anything medically related to the population Originally focused on epidemics of communicable diseases but subsequently expanded to include noncommunicable diseases, chronic diseases, injuries, maternal-child health, occupational health and environmental health.

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SPECIFIED POPULATIONS

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Focuses on the collective health of the people in a community or population. o Identifying the exposure or source that caused the illness o The number of other persons who may have been similarly exposed o The potential for further spread in the community o Interventions to prevent additional cases or recurrences

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APPLICATION

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Applying the knowledge gained by the studies to community-based practice. Uses descriptive and analytic epidemiology as well as experience, epidemiologic judgment, and understanding of local conditions in “diagnosing” the health of a community

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3.

JOHN SNOW (1813-1858) and the Pathogenic Power Pump

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Considered one of the fathers of modern epidemiology Inspired fundamental changes in the water and waste systems and a significant improvement in general public health around the world Used a dot map to illustrate the cluster of cholera cases around the pump Used statistics to illustrate the connection between the quality of water source and cholera cases Hallmark event of the science of epidemiology

 C. Famous Epidemiologists  1.

JOHN GRAUNT (1620-1674) and the Population of London

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Developed early human statistical and census methods Credited with producing the first life table  life table - gives the probability of survival of each age Considered as one of the first experts in epidemiology Wrote the book “Natural and Political Observations Made upon the Bills of Mortality” o Used analysis of the mortality rolls in early modern London to try to create a system to warn of the spread of bubonic plague in the city  Famous book which was concerned mostly with public health statistics  He tabulated all causes of deaths in London. He failed in creating the system; however, he was successful in calculating the first estimation of the population of London through statistics. Because of that, he was elected into the Royal Society in 1662.

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2.

JAMES LIND (1716-1794) and the Scurvy of the Seas

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Scottish pioneer of naval hygiene in the Royal Navy Conducted the first ever clinical trial and developed the theory that citrus fruits cured scurvy o Clinical trial – research studies that test how well a certain medical approach (treatment) to a disease work in people  Scurvy is the chronic deficiency of Vitamin C, which is essential for the synthesis of collagen. Initially thought that scurvy is caused by the putrefaction of the body which can be cured by providing acids He gathered twelve scorbutic sailors and grouped them into six groups of two and gave them the following: o Group 1 : quart of cider o Group 2 : twenty-five drops of elixir of vitriol (sulfuric acid) o Group 3 : six spoonful of vinegar o Group 4 : half a pint of seawater o Group 5 : two oranges and one lemon o Group 6 : a spicy paste plus a drink of barley water  This clinical trial only lasted for 6 days. The sailors in group 1 and 5 recovered from scurvy. Thus, the theory that citrus fruits would cure scurvy was developed. (It’s the ascorbic acid specifically that cures this.)

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II. Descriptive Epidemiology A. Significance 

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Data familiarity  Thus, see the limitations, deficiencies, eccentricities, and outliers in the data Reveals the extent and pattern of the public health problem being investigated Creates description that can be easily communicated with tables, graphs, and maps  This is very important when trying to convey information to the general public. Information provides important clues to the causes of the disease, which can be turned into testable hypotheses  Descriptive Epidemiology is the foundation or the starting point of Analytic Epidemiology.

B. Important concepts

 For almost all diseases / illnesses, three basic epidemiologic questions may be asked: 1. When does the disease occur? (TIME) 2. Where does the disease occur? (PLACE) 3. Who develops the disease? (PERSON) 1. TIME  The occurrence of disease changes over time. Some of these changes occur regularly, while others are sporadic.  Health officials will be able to anticipate diseases occurring regularly and set preventive measures  For sporadic diseases, targeted actions may be applied.

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 Three major kinds of change with time (temporal

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variations) may be identified: a. Secular trends: long-term variations (changes that vary through long periods of time)

Epidemic changes: short-term trends, opposite of secular (span of days/weeks)

Figure 3. Reported cases for Salmonella Enteritidis in Chicago in a span of 8 days. Figure 1. Reported cases of Salmonellosis from 1972 to 2002.

 A relatively higher number of cases were reported at the days immediately prior to the onset of the party, primarily due to the presence of contaminated food at the event. As days passed, the number of cases decreased.

 Reported cases of Salmonellosis showed an increasing trend starting from mid-70’s, peaking in the latter 80’s, then started to go down. When you look at these long term variations (span of years), these are secular trends. b.

Cyclic variations: periodic fluctuations on an annual basis (seasonal variations); recurrent alterations in the frequency of disease

 Endemic rate - the usual rate of occurrence for a disease in a population

 Epidemic rate - a rapid and dramatic increase over the endemic rate

 Pandemic - a rapidly emerging outbreak of disease that affects a wide range of geographically distributed populations 2. 

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Figure 2. Positive cases for Influenza from 1994 to 2000, subdivided into months.

 Influenza has seasonal patterns, it will start to actually increase around October-November and actually start decreasing around February-March. Always expect a spike of cases of Influenza during winter. So having that data, you can actually prepare and inform the public.

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PLACE Describing the occurrence of disease by place provides insight into the geographic extent of the problem and its geographic variation. Characterization by place refers not only to place of residence but to any geographic location relevant to disease occurrence.  Displaying the pattern of disease will give you the idea of how diseases try to spread. With that you will have an idea of how to stop the spread or reccurrence of the disease. Frequency of disease can be related to place of occurrence in terms of areas set off either by natural barriers (e.g. mountain ranges, rivers, desserts; tropical versus temperate regions) or by political barriers (e.g. rural-urban differences; migration of people).  Example: Malaria – its vector, anopheles, tends to thrive in free-flowing bodies of water (natural barrier); difference between the management of HIV-Aids in the Philippines vs management of HIV-Aids in the US due to differences in health care policies (political barrier).

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Example of an Epidemiologic Data presented in the context of Person: MALE LUNG CANCER DEATHS

Figure 4. Representation of the spot map utilized by John Snow to visualize the cholera outbreak in London.

 Bigger blot = higher reported mortality. Blue dots = different locations of the pump. Green dot = pump of interest. From here, it can be seen that mortalities particularly surround a pump (pump of interest). Upon investigation of said pump, it was found that the pump was dug just 3 meters away from a cess pit (septic tank). The septic tank leaked fecal matter to the water source, which was the true reason for the cholera outbreak. Upon terminating the use of the water pump, the further spread of cholera was stopped. 3. 

PERSON Person variation in reporting epidemiologic data deals with the organization and analysis which presents data through: a. Inherent characteristics o Age, sex, race b. Biologic characteristics o Immune status c. Acquired characteristics o Marital status, educational attainment d. Activities o Occupation, leisure activities, use of medications/tobacco/drugs e. Living conditions o Socioeconomic status, access to medical care

Figure 5. Trend of Lung Cancer deaths in the US.

 This data shows that male lung cancer deaths significantly outnumber female lung cancer deaths.

 It presented two variations: Gender and the trend in the 1930s to the last year of the previous millennium. III.

Descriptive Epidemiology of HIV/AIDS in the Philippines

The Global trend of HIV-AIDS is decreasing across all continents. However the Philippines is part of the 7 unique countries in the world which shows more than 25% increase in HIV cases over the past 13 years together with: 1. Armenia 2. Bangladesh 3. Georgia 4. Kazhakstan 5. Kyrgystan 6. Tajikistan 7. Philippines Descriptive epidemiology allows efficient information dissemination to the public by effectively presenting data through graphs and figures.

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IV.

Mini Quiz

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Questions answered by DESCRIPTIVE EPIDEMIOLOGY include the following EXCEPT: A. What specific age groups are affected by the disease? B. Is there a specific region in the country where the disease predominantly occurs? C. How was the disease transmitted? D. Has there been an increase in the prevalence of the illness in the last five years?

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Which pattern of disease distribution according to TIME would be most appropriate to monitor for chronic NONCOMMUNICABLE DISEASES like malignant neoplasms? A. Short-term fluctuation B. Secular trend C. Seasonal pattern D. All of the above

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Which pattern of disease distribution according to TIME would be most appropriate to monitor for COMMUNICABLE diseases like leptospirosis? A. Short-term fluctuation B. Secular trend C. Seasonal pattern D. Epidemic curve

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A rapidly emerging disease outbreak that affects a wide range of geographically distributed populations is referred to as a/an: A. Endemic disease B. Epidemic disease C. Pandemic disease D. None of the above

Figure 6: Cases of HIV in the Philippines

 Pink – asymptomatic cases  Black – full blown AIDS From 1984-2014, o 20,424 cumulative cases of HIV in the Philippines --18,567 of which are asymptomatic cases and 1,857 are full blown AIDS cases. o Asymptomatic carriers may transmit the disease by unprotected sexual contact o Gender and age variation affects HIV cases.

Figure 7. Reported HIV cases for males and females (1984-2014)

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Age group with the most number of cases with HIV: 25-29 years old Males have a significantly higher incidence rate than females

Figure 8. Proportion of HIV-AIDS cases represented by a cluster using sexuality as a variable.

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Cream – heterosexual individuals Maroon – bisexual individuals Lavender – homosexual individuals The number of heterosexuals diagnosed with HIV-AIDS had steadily decreased in the last 5 years  The number of bisexuals and homosexuals diagnosed with HIV-AIDS had a significant increase in the last 5 years At present, homosexual transmission is the predominating mode of HIV-AIDS transmission, followed by the bisexual type.

Answers: 1. C (Descriptive epidemiology is mainly concerned with the time, place and person) 2. B 3. C (Short-term fluctuation is synonymous to epidemic changes) 4. C

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