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Chapter x

MEDICAL SOCIOLOGY, 13TH EDITION
William C. Cockerham

Chapter 2

Epidemiology

Introduction

Epidemiology is a multi-disciplinary field that studies the origin and distribution of health problems, whether infectious diseases, chronic ailments, or problems resulting from unhealthy behaviors

Epidemiological Measures

Case: An episode of a disorder, illness, or injury involving a person
Prevalence: The total number of cases of a health disorder that exist at any given time
Point prevalence (the number of cases at a certain point in time, usually a particular day or week)

Epidemiological Measures

Period prevalence (the total number of cases during a specified period of time, usually a month or year)
Lifetime prevalence (the number of people who have had the health problem at least once during their lifetime)
Incidence: Refers to the number of new cases of a specific health disorder occurring within a given population during a stated period of time

Epidemiological Measures

Distinguished from prevalence as the rate at which cases first appear, while prevalence is the rate at which all cases exist
Crude rate: The number of persons (cases) who have the characteristics being measured during a specific unit of time
Examples: Birth rates and mortality rates

The Development of Epidemiology

Epidemics only began to affect human populations as trade between regions increased and as humans began moving in greater proportions into cities
Bubonic plague
Affected Europe between 1340 and 1750
Killed approximately one-third of the European population

The Development of Epidemiology

Transmission of the disease was not understood initially but social patterning in the distribution of the disease was observed
John Snow’s investigations into cholera outbreaks in London
He systematically mapped out cases of infection, interviewed victims, and traced their daily activities to a common source: contaminated well-pumps

The Development of Epidemiology

Provided the foundation of modern epidemiological methods
Causal agents recognized today:
Biological agents - bacteria, viruses, or insects
Nutritional agents - fats and carbohydrates
Chemical agents - gases and toxic chemicals that pollute the air, water, and land
Physical agents - climate or vegetation

The Development of Epidemiology

Social agents - occupation, social class, location of residence, or lifestyle
Social environment refers to actual living conditions, such as poverty or crowding, and also the norms, values, and attitudes that reflect a particular social and cultural context of living

The Development of Epidemiology

i.e., what a person does, who a person is, and where a person lives influences what health hazards are most likely to exist in that individual’s life
Stages in the field of epidemiology:
Sanitary era (early 19th century) - focus was largely on sewage and drainage systems, and the major preventive measure was the introduction of sanitation programs

The Development of Epidemiology

Infectious disease era (late 19th to mid-20th century) - principal preventive approach was to break the chain of transmission between the agent and the host
Chronic disease era (mid- to late 20th century) - focus was on controlling risk factors by modifying lifestyles, agents, or the environment

The Development of Epidemiology

Eco-epidemiology (21st century) - preventive measures are multidisciplinary as scientists from many fields use their techniques to deal with a variety of health problems at the molecular, social behavioral, population, and global levels

Disease and Modernization

The health profiles of industrialized societies are different from that of developing countries
Modernizing countries experience:
Reduced mortality from infectious diseases and parasitic disorders
Declines in other diseases of the digestive and respiratory systems with a communicable component

Disease and Modernization

Increases in life expectancy
Declines in infant mortality
Increases in mortality from heart disease, cancer, and other physical ailments associated with modern living

The Complexity of Modern Ills: Heart Disease

Heart disease represents an example of the complexity of modern health problems
Multiple factors contribute to the risk of developing heart disease by pathways not yet fully understood
Significant risk factors include:
Sex (specifically male) – Advancing age
High blood pressure – Cigarette smoking
Diabetes – Obesity

The Complexity of Modern Ills: Obesity

In 2013, the American Medical Association (AMA) officially recognized obesity as a disease
People determined to be obese by the BMI may be otherwise healthy
And others measured as not obese may have a dangerous level of lower abdomen body fat and metabolic problems linked to excessive weight

Pandemics: HIV/AIDS and Influenza

Infectious diseases are either returning or are newly emerging through the effects of globalization, urbanization, and global warming
Pandemics are epidemics that affect people in many different countries and are the deadliest infectious threat to health in a globalizing world

Pandemics: HIV/AIDS – U.S.

Primary mode of transmission (CDC 2007):
Among adult and adolescent males:
64 percent of all cases reported were homosexual and bisexual men
13 percent were IV drug users
7 percent were homosexuals and IV drug users
11 percent resulted from heterosexual contacts
2 percent from other causes like blood transfusions

Pandemics: HIV/AIDS – U.S.

Among adult and adolescent females:
72 percent are from heterosexual contact with infected males
25 percent are infected from IV drug use
3 percent from other sources

Pandemics: HIV/AIDS – Worldwide

Africa (33.3 million cases)
South of the Sahara the hardest hit
Primary mode of transmission: heterosexual contact
Migrant labor system plays a vital role in transmission, spreading disease from urban to rural areas
Women account for 60 percent of cases

Pandemics: HIV/AIDS – Worldwide

Western Europe (850,000 cases) and Eastern Europe (1.4 million cases)
Primary mode of transmission: Homosexual activity and IV drug use
Asia (South/Southeast Asia, 3.8 million cases; East Asia and China, 770,000 cases)
Primary mode of transmission: Heterosexual activity (especially through migrant labor systems and prostitution)

Pandemics: HIV/AIDS – Worldwide

Latin America (2.0 million cases) and Caribbean (230,000 cases)
Originally spread through homosexual activity and IV drug use
Now spreading to women through bisexual activity by men

Pandemics: Influenza

Past outbreaks, such as 1918 “Spanish flu,” have killed millions worldwide
Recent outbreaks of H1N1 (“Swine flu”) and H5N1 (“Avian flu”) have the potential to become especially serious pandemics
Predicting outbreaks of influenza and controlling the spread of infection remains challenging for epidemiologists