Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems. • Various methods can be used to carry out epidemiological investigations: surveillance and descriptive studies can be used to study distribution; analytical studies are used to study determinants
Morbidity vs. Mortality • Morbidity- the incidence of disease in a population • Mortality- the incidence of death in a population
Incidence = # of New Cases Occurring in a Given Population in a Specified Time Period_ Population at Risk in That Time Period
Prevalence = # of Cases Existing in a Given Population at a Single Point in Time__ Population at That Time
Uses of Epidemiology • Community diagnosis; i.e., what are the major health problems occurring in a community • Establishing the history of a disease in a population; e.g., identifying the periodicity of an infectious disease
Describing the natural history of disease in the individual; e.g., natural history of HIV infection in the individual (infection-acute syndrome-asymptomatic phase-clinical disease-death) • Describing the clinical picture of disease; i.e., who gets the disease, who dies from the disease, and what the outcome of the disease is
Estimating risk; e.g., what factors increase the risk of heart disease, automobile accidents, and violence • Identifying syndromes and precursors; e.g., the relationship of high blood pressure to stroke, kidney disease, and heart disease • Evaluating prevention/intervention programs; e.g., vaccine and clinical trials • Investigating epidemics/diseases of unknown etiology
Methods of Surveillance • Local departments of health • Hospital/medical reports • Local pharmacies • Media
Disease Terms • Agent- source of infection • Virus, fungus, bacteria, protozoa, carcinogen, etc. • Host- person harboring the agent • Sick individual
Incubation period- the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent • Examples: • Common cold and influenza 1-3 days • Measles 9-12 days • SARS 7-10 days • Ebola 2-21 days
Pathways of Disease • Air • Water • Person to person contact • Intimate contact • Sharing of bodily fluids • Sex • Needles • Transfusion
Human Health Two indicators of human health Life expectancy - how long people are expected to live Infant mortality - how many children die before age of 1 year per 1000 live births Vary greatly between countries Developed countries Developing countries World average- 42
Health in Highly Developed Countries Health is generally good in these countries Average life expectancy Men = 75 years Women = 80 years Leading causes of death in US Cardiovascular disease, Cancer, Lung Disease We rank 33rd in infant mortality (6.6) Premature deaths caused by lifestyle Poor diet, Lack of exercise, Smoking, Obesity
Some U.S. facts: • In 1900 life expectancy was 51 for women and 48 for men • The leading causes of death were pneumonia, influenza, tuberculosis, diarrhea (gastritis and colitis)
Leading Causes of Death • Low income countries (Sub-saharan Africa, South America, etc.)
Emerging and Reemerging Diseases Emerging Disease - not previously observed in humans Usually jumps from animal host Ex: AIDS, lime disease, West Nile Virus, Creutzfeldt-Jakob Reemerging Disease - existed in the past and are recently increasing in incidence Ex: tuberculosis, yellow fever, malaria
Reasons for Emergence/Reemergence Evolution of disease so it transitions to human host Evolution of antibiotic resistance in disease Urbanization and overcrowding Increased pop. of elderly - susceptible to disease Pollution and environmental degradation Growth in international travel and commerce Poverty and social inequality
Diseases • Polio- a viral disease that can damage the nervous system and cause paralysis. • The polio virus enters the body through the mouth, usually from hands contaminated with the stool of an infected person. • Polio is preventable by immunization. • Since polio immunization has become widespread in the United States, cases of polio are rare. However, polio remains a problem in many parts of the world • Greatest risk is in the Indian subcontinent and, to a lesser extent, in West and Central Africa.
Small Pox • Smallpox is a serious, contagious, and sometimes fatal infectious disease • There is no specific treatment for smallpox disease, and the only prevention is vaccination • Smallpox outbreaks have occurred for thousands of years • Disease is now eradicated after a successful worldwide vaccination program • Last case of smallpox in the US-1949 • Last naturally occurring case in the world was in Somalia in 1977
After the disease was eliminated from the world, routine vaccination against smallpox among the general public was stopped because it was no longer necessary for prevention • Generally, direct and fairly prolonged face-to-face contact is required to spread smallpox from one person to another • Smallpox also can be spread through direct contact with infected bodily fluids or contaminated objects such as bedding or clothing • Rarely, smallpox has been spread by virus carried in the air in enclosed settings such as buildings, buses, and trains. Humans are the only natural hosts of variola (virus that causes is)
Tuberculosis • Disease caused by germs that are spread from person to person through the air • TB usually affects the lungs, but it can also affect other parts of the body, such as the brain, the kidneys, or the spine • A person with TB can die if they do not get treatment • Spread through the air • Estimated 1.7 million people died from TB in 2009 • The highest number of deaths was in the Africa Region
Influenza • Respiratory Viral infection (flu) • Spread through droplets in the air or on surfaces • Has been around for centuries • New strains appear yearly and travel quickly • Between 5%-2-% of the US population contracts the flu each year • Flu season is generally from September to May • About 36,000 people die each year in the US
Most susceptible are the very young and very old • Spanish Flu of 1918 killed 850,000 in the US • Particularly virulent strain that killed people equally of all ages • If a similar strain pops up it could kill 3 million people in the US alone • H1N1 (Swine flu strain) was the latest worry • Mix of human, bird and pig genetic material • Relatively new strain so many people had no immunity
Avian Flu- Spread from birds • Highly pathogenic Avian Influenza A (H5N1) • Difficult to catch but highly dangerous • Avian Influenza A (H7N9) Virus • Human infections with a new avian influenza A (H7N9) virus continue to be reported in China. The virus has been detected in poultry in China as well. While mild illness in human cases has been seen, most patients have had severe respiratory illness and some people have died. No cases of H7N9 outside of China have been reported. The new H7N9 virus has not been detected in people or birds in the United States.
West Nile Virus • Potentially fatal virus • Summer seasonal epidemic in North America • Spread through mosquitoes • Mosquitoes can also spread it to birds • 80% of the infected will have no symptoms • 1 in 150 will develop severe symptoms
Malaria • A parasitic disease that involves high fevers, shaking chills, flu-like symptoms, and anemia • Caused by a parasite that is passed from one human to another by the bite of infected Anophelesmosquitoes • After infection, the parasites (called sporozoites) travel through the bloodstream to the liver, where they mature and release another form, the merozoites • The parasites enter the bloodstream and infect red blood cells
The parasites multiply inside the red blood cells, which then break open within 48 to 72 hours, infecting more red blood cells • Also may be transmitted from a mother to her unborn baby (congenitally) and by blood transfusions • 300-500 million cases of malaria each year, and more than 1 million people die from it • Malaria, especially Falciparum malaria, is a medical emergency that requires a hospital stay • Without treatment death is almost certain
AIDS- Acquired Immune Deficiency Syndrome • Caused by HIV virus • Spread through fluid contact • Transfusion • Needle sharing • Sexual Contact • Breast Milk • Currently 33 million cases worldwide • 2.5 million children • 2.6 million new cases in 2009 • Sub-Saharan Africa is hit the hardest • 22 million cases
Adults and children estimated to be living with HIV 2009 Eastern Europe & Central Asia 1.4 million [1.3 million – 1.6 million] Western & Central Europe 820 000 [720 000 – 910 000] North America 1.5 million [1.2 million – 2.0 million] East Asia 770 000 [560 000 – 1.0 million] Middle East&North Africa 460 000 [400 000 – 530 000] Caribbean 240 000 [220 000 – 270 000] South & South-East Asia 4.1 million [3.7 million – 4.6 million] Sub-Saharan Africa 22.5 million [20.9 million – 24.2 million] Central & South America 1.4 million [1.2 million – 1.6 million] Oceania 57 000 [50 000 – 64 000] Total: 33.3 million[31.4 million – 35.3 million]
SARS- Severe Acute Respiratory Syndrome • SARS is a viral disease that causes respiratory (lung) symptoms and is spread by close person-to-person contact • First reported in the Guangdong Province of China in November 2002 • Spread through air and casual contact • Most people who have gotten SARS have recovered, but as many as 10-15% of SARS patients have died. The disease is more severe among older persons and those with other medical problems • No reported cases in recent years
FAQ Q: How many people die every year? During 2008, an estimated 57 million people died. Q: What is the number one cause of death throughout the world? Cardiovascular diseases kill more people each year than any others. In 2008, 7.3 million people died of ischaemic heart disease, 6.2 million from stroke or another form of cerebrovascular disease. Q: Isn't smoking a top cause of death? Tobacco use is a major cause of many of the world’s top killer diseases – including cardiovascular disease, chronic obstructive lung disease and lung cancer. In total, tobacco use is responsible for the death of almost one in 10 adults worldwide. Smoking is often the hidden cause of the disease recorded as responsible for death.
Q: What are the main differences between rich and poor countries with respect to causes of death? • In high-income countries more than two thirds of all people live beyond the age of 70 and predominantly die of chronic diseases: cardiovascular disease, chronic obstructive lung disease, cancers, diabetes or dementia. Lung infection remains the only leading infectious cause of death. • In middle-income countries, nearly half of all people live to the age of 70 and chronic diseases are the major killers, just as they are in high-income countries. Unlike in high-income countries, however, tuberculosis, HIV/AIDS and road traffic accidents also are leading causes of death. • In low-income countries less than one in five of all people reach the age of 70, and more than a third of all deaths are among children under 15. People predominantly die of infectious diseases: lung infections, diarrhoeal diseases, HIV/AIDS, tuberculosis, and malaria. Complications of pregnancy and childbirth together continue to be leading causes of death, claiming the lives of both infants and mothers.
Q: How many young children die each year? More than 8 million deaths in 2008 were among children under five years of age, and 99% of them were in low- and middle-income countries.
Why counting the dead matters Measuring how many people die each year and why they have died is one of the most important means – along with gauging how various diseases and injuries are affecting the living – for assessing the effectiveness of a country’s health system. Having those numbers helps health authorities determine whether they are focusing on the right kinds of public health actions. A country where deaths from heart disease and diabetes rapidly rise over a period of a few years, for example, has a strong interest in starting a vigorous program to encourage lifestyles that will help prevent these illnesses. Similarly, if a country recognizes that many children are dying of malaria, but only a small portion of the health budget is dedicated to providing effective treatment, an adjustment can be made. Industrialized countries have systems in place for assessing causes of death in the population. Many developing countries do not have such systems, and the numbers of deaths from specific causes have to be estimated from incomplete data. It is widely acknowledged that progress in this realm is crucial for improving health and reducing preventable deaths in the developing world.
Center for Disease Control (CDC) • Founded in 1946 • Headquartered in Atlanta, Georgia • More than 15,000 employees in nearly 170 occupations • Field staff assigned to all 50 states and more than 50 countries • CDC is our nation’s health protection agency, and our scientists and disease detectives work around the world to track diseases, research outbreaks, and respond to emergencies of all kinds.
CDC works with partners around the country and world to: • Prepare the US to respond to emergency health threats • Investigate deadly disease outbreaks around the world • Stop disease outbreaks before they spread • Detect harmful germs rapidly in the US food supply • Strengthen the quality, response and effectiveness of America’s laboratories • Provide critical data that saves lives and protects people • Put proven prevention strategies to work • Provide life-saving vaccines
CDC’s Mission • CDC works 24/7 keeping America safe from health, safety, and security threats, both foreign and domestic. • Whether diseases start at home or abroad, are chronic or acute, curable or preventable, human error or deliberate attack • CDC fights disease, and supports communities and citizens to do the same. • CDC is the nation’s health protection agency — saving lives, protecting people from health threats, and saving money through prevention.