Hlth 345

• Epidemiology is the study of the distribution and determinants of health-related states or events in human
• populations, and the application of this study to prevent and control health problems.

• Study
• - Epidemiology involves sound methods of scientific investigation.
• Methods rely on careful observation and the use of valid comparison groups to determine whether the observed health events differ from what might be expected

- Study of frequency and pattern of health events in the population

- Frequency – number, and number in relation to the population

-Pattern– the health-related state or event by person, place, and time characteristics

Search for causes and other factors of health-related states or events.

Answering the who, what, when, and where questions is prerequisite to effective education, screening, prevention, and control programs.

Descriptive epidemiology involves characterization of the distribution of health-related states or events by

• - Person- who
• - Place- where
• - Time– when
• - Clinical criteria - what

- Analytic epidemiology involves identifying and quantifying associations, testing hypotheses, and identifying causes of health-related states or events

- Explains why and how health-related states or events occur

• Epidemiological findings contribute to preventing and controlling disease, injury, disability, and death
• - How?
• By providing information leading to informed public health policy and planning, as well as individual health decision making

• Epidemic
• – Health-related state or event in a defined population above the expected over a given period of time

• Endemic
• – Persistent, usual, expected health-related state or event in a defined population over a given period of time

• Pandemic
• – Epidemic affecting a large number of people, many countries, continents, or regions

• Common source
• - Point
• - Intermittent
• - Continuous

• Propagated
• - Spread from person-to-person

• Mixed epidemics
• - A mixture of common source and mixed

- Tend to result in more cases occurring more rapidly and sooner than host-to-host epidemics

- Identifying and removing exposure to the common source typically causes the epidemic to rapidly decrease

• Examples
• - Ananthrax, traced to milk or meat from infected animals
• - Botulism, traced to soil-contaminated food
• - Cholera traced to fecal contamination of food and water

• - Arise from infections being transmitted from one infected person to another
• - Transmission can be through direct or indirect routes
• - Host-to-host epidemics rise and fall more slowly than common source epidemics

• Examples
• - tuberculosis
• - whooping cough
• - Influenza
• - measles

Occurs when a common source epidemic is followed by person-to-person contact and the disease is spread as a propagated outbreak

• Example – Shigellosis occurred among a group
• of 3000 women attending a music festival. Over the next few weeks, subsequent generations of shigella cases spread by person-to-person transmission from festival attendees.

• Disease transmission usually occurs by
• - direct, person-to-person contact (e.g., STDs)
• - fomite-borne (e.g., Hepatitis A spread by a contaminated eating utensil)
• - vehicle-borne (e.g., HIV/AIDS spread through needle sharing drug users)
• - vector-borne transmission (e.g., Malaria spread through mosquitoes)

A case is a person who has been diagnosed as having a disease, disorder, injury, or condition

• Primary case, index case
• - The first disease case in the population is the primary case.
• - The first disease case brought to the attention of the epidemiologist is the index case.
• - The index case is not always the primary case.

Those persons who become infected and ill after a disease has been introduced into a population and who become infected from contact with the primary case

The interrelatedness of four epidemiological factors often contributed to an outbreak of a disease: (1) the role of the host, (2) an agent or disease-causing organism, (3) the environmental circumstances needed for a disease to thrive, survive, and spread, and (4) time-related issues.

• Shows the interaction and interdependence of agent, host, environment, and time as used in the investigation of diseases and epidemics.
• - Agent is the cause of the disease
• - Host is an organism, usually a human or an animal, that harbors a disease
• - Environment includes those surroundings and
• conditions external to the human or animal that cause or allow disease transmission
• - Time accounts for incubation periods, life
• expectancy of the host or the pathogen, and duration of the course of the illness or condition.

The habitat (living or nonliving) on which an infectious agent lives, grows, and multiplies and is dependent on for its survival in nature

Humans often serve as both reservoir and host

When an animal transmits a disease to a human

• Examples
• – Rabies, Rocky Mountain spotted fever, shigellosis

• A carrier contains, spreads, or harbors an infectious
• organism

• Example
• – Typhoid Mary

• - Direct transmission – direct physical contact such as touching with contaminated hands, skin-to-skin
• contact, kissing, or sexual intercourse

• - Indirect transmission – occurs when pathogens or agents are transferred or carried by some intermediate
• item, organism, means, or process to a susceptible host, resulting in disease

• There is a close association between the triangle of epidemiology and the chain of
• infection

• Goes beyond infectious disease to include behavior, lifestyle factors, environmental causes, ecological elements, physical factors, and chronic diseases must be
• taken into account.

• - Immunization
• - Sanitation
• - Education
• - Media campaigns
• - Warning labels
• Active primary prevention
• - Requires behavior change on part of subject
• - Wearing protective devises
• - Health promotion
• - Lifestyle changes
• - Community health education
• - Ensuring healthy conditions at home, school and workplace
• Passive primary prevention
• Does not require behavior change
• - Vitamin fortified foods
• - Fluoridation of public water supplies

Occurs to reduce the progress of disease

The disease already exists in the person

Cancer screening – cancer already present. The goal is to detect the cancer before clinical symptoms arise in order to improve prognosis and prevent conditions from progressing and from spreading

• To reduce the limitation of disability from disease
• - The disease has already occurred
• - Physical therapy for stoke victims
• - Halfway houses for recovering alcoholics
• - Shelter homes for the developmentally disabled
• - Fitness programs for heart attack patients

He observed that different diseases occurred in different locations

He noted that malaria and yellow fever most commonly occurred in swampy areas

He also introduced terms like epidemic and endemic

• Believed that observation should drive the study of the
• course of disease
• Described and distinguished different diseases including
• some psychological maladies
• Advanced useful treatments and remedies including exercise, fresh air, and a healthy diet, which other physicians rejected at the time

• Applied experimental methods to identify that eating citrus fruits were effective remedies for scurvy among sailors at sea (H.M.S. Salisbury, 1747)
• Also made clinical observations, used experimental design, asked classical epidemiological questions, observed the population changes and its effect on disease, and considered sources of causation, including place, time, and season

• - A farmer/dairyman in the mid-1700s, noticed his milkmaids never got smallpox, but did get cowpox
• - Exposed his wife and children to cowpox
• - Variolation – Chinese had observed for centuries that getting a weaker strain of smallpox was protective against a stronger strain of the disease

• - Jenner attempted to give a dairymaid, exposed to a mild case of cowpox in her youth, a case of cowpox by cutting her arm and rubbing some of the infectious “grease” into the wound. She did not get ill.
• - He subsequently invented a vaccination for smallpox

• - In 1846 Semmelweis observed high level of deaths in mothers with childbed fever
• - Unclean hands with putrefied cadaver material on student doctors’ hands were used to conduct the routine daily pelvic exams, and the practice was never questioned
• - Identified the importance of washing hands to prevent the spread of disease

- Provides an example of both a descriptive and analytic epidemiologic study

• - studied an epidemic of cholera that developed
• in 1848 in the Golden Square of London

• - Steps of descriptive study
• Determined area persons with cholera lived and worked
• Mapped distribution of cases on a spot map
• Looked for clustering of cases around water pumps
• Identified water supply (pump) for those with cholera

• Identified the causes of rabies
• Investigated how sheep and humans contracted the bacteria called anthrax
• Showed that bacteria could cause disease
• Discovered a vaccine for anthrax

• With Pasteur, established the germ theory of disease
• - Used photography to take the first pictures of microbes in order to show the world that microorganisms do in fact exist and that they are what cause diseases
• - Koch showed that anthrax was transmissible
• and reproducible in experimental animals (mice)
• - Identified the spore stage of the growth cycle of microorganisms
• - Demonstrated that the anthrax bacillus was the only organism that caused anthrax in a susceptible animal

- Using the “Bills of Mortality” in London, he systematically recorded age, sex, who died, of what, where they died, and when

- Recorded how many persons per year died of what kind of event or disease

- Developed and calculated life tables and life expectancy

• - Divided deaths into two types of causes
• Acute (struck suddenly – e.g., cholera)
• Chronic (lasted over a long period of time – e.g., emphysema)

- Extended the use of vital statistics and organized and developed a modern vital statistics system, much of which is still in use today

Promoted the idea that some diseases, especially chronic diseases, may have a multifactorial etiology

Observed that disease among workers arose from two causes:

• - Harmful character of the materials that workers handled as the materials often emitted noxious vapors and very fine particles which could be inhaled
• - Certain violent and irregular motions and unnatural postures imposed upon the body while doing work

- Nurse

- Helped create changes in hygiene and overall treatment of patients

• Chronic carrier of typhoid fever, causing over 250 cases
• Personally had no symptoms of the disease
• 1907 to 1910, confined by health officials until released through legal action taken by her
• Taught public health officials and epidemiologists the importance of keeping track of carriers

• In 1887 eradicated beriberi from the Japanese Navy by adding vegetables, meat, and fish to their diet, which was mostly rice
• Kwashiorkor Disease

• - In 1850, published the first report on sanitation and public health problems
• - Shattuck’s report set forth the importance of
• establishing state and local boards of health and
• recommended an organized effort to collect and analyze vital statistics
• - Recommended the exchange of health information, sanitary inspections, research on tuberculosis, and the teaching of sanitation and prevention in medical schools

Suggested that morbidity statistics be classified into five general groups in order to be of value

• 1. Reports of communicable diseases
• 2. Hospital and clinical records
• 3. Insurance and industrial establishment of school illness records
• 4. Illness surveys
• 5. Records of the incidence of illness in a population continuously or frequently observed

• Case-control studies assessing the association between smoking and lung cancer
• Wynder and Graham in the US (1950)
• Doll and Hill in Great Britian (1950)
• Cohort study
• Doll and Hill (1951)