What is Epidemiology?
Epidemiology is the scientific method used to track population health and to find causes of disease (and health) in groups of people. It is often called the basic science of public health, but its principles extend to clinical research.
• chronic diseases (e.g., heart disease, cancer and diabetes)
• infectious diseases (e.g., flu and HIV)
• illnesses that result from environmental exposures to such agents as chemicals or pollutants
• illnesses that are related to genetic traits (e.g., cystic fibrosis, cancers)
• injuries (e.g., workplace injuries, injuries from violence and car accidents)
• mental illnesses (e.g., depression and schizophrenia)
• the risks and benefits of drugs
What Do Epidemiologists Do?
Epidemiologists improve the public’s health by studying causes of and solutions for health problems. On a typical day, an epidemiologist might spend time • designing a health study,
• collecting or analyzing data,
• writing reports,
• speaking to the public and colleagues about research findings • state or local health departments
• government agencies like the Centers for Disease Control and Prevention (CDC)
• academic institutions, including schools of public health and medicine
• private companies
• consulting firms
• international agencies like the World Health Organization. The responsibilities of an epidemiologist may range from finding factors that affect a community’s health to carrying out sophisticated, scientific research using the most advanced techniques of modern molecular biology and genetics. What Is an Epidemic? Epidemiologists define an epidemic as any unusual occurrence of disease, generally first noticed by an unexpected number of cases occurring over a particular amount of time or in a particular place. During the course of an epidemic, epidemiologists work to identify the disease and its causes. For example, the surprising number of cases of a deadly form of pneumonia in China led to the identification of SARS and the virus that causes SARS. We usually think about epidemics as acute events that take place rapidly and cause a dramatic increase in the numbers of deaths. Epidemics, however, can also be slow, or chronic—but equally deadly. Over the last 100 years, for example, there has been an ever-accelerating epidemic of lung cancer caused by cigarette smoking. Lung cancer had been rare at the start of last century, but at the century’s end, high rates of smoking had made the disease a common killer. Epidemiologists use the same methods to study both acute epidemics and chronic epidemics.
Is Air Pollution Bad for Health?
For centuries, we have known that air pollution threatens health. Inhaling harmful particles or gases can damage both the heart and lungs, and cause premature death. Particles are solid material, usually so small as to be invisible, that contaminate the air. hey come from vehicle emissions, power plants, nature, and other sources. There are also pollutants in the form of gases, such as carbon monoxide and ozone, now a problem in much of the United States. Even hundreds of years ago, air pollution was a problem in cities, where coal was burned to heat homes and later to generate electricity and power industry. Today, our cities are polluted by motor vehicles, power plants, and factories. Epidemiologists study air pollution and work in parallel with colleagues called toxicologists who carry out laboratory studies to learn about the risks of air pollution. What Job Opportunities Are Available in the Field? Epidemiologists can find career opportunities in research, academia, pharmaceutical industry, hospitals, laboratories, and at the state and federal levels as public health officers. Epidemiology covers many different areas of specialization, such as the study of infectious and chronic diseases, environmental and occupational determinants of diseases, cluster investigation, and genetics. How Serious Are Influenza Epidemics?
The worst epidemic occurred in 1918 and killed more than half a million Americans and between 50 million and 100 million people worldwide. Two later epidemics, in 1957 and 1968, killed 70,000 and 34,000 Americans, respectively. In the past 20 years in the United States, there have been 11 flu epidemics that have killed more than 20,000 people a year.
In most epidemics, 90 percent of the people who die are older than 65 years and the remaining deaths are largely among children under 5 years. People between the ages of 5 and 65 have a lower risk of death from most types of influenza. A flu epidemic occurs when the flu virus changes significantly from strains that circulated in recent years (a phenomenon called "shift"). Since this happens rapidly, the current vaccine is not effective against the new virus; the population does not have immunity from previous exposure and there is no time to create a new vaccine. The result is that many people get sick.
Because the US hasn’t experienced a major influenza epidemic for almost 40 years, it is difficult to predict the impact of an epidemic in today’s environment. The increased amount of travel in recent years and the speed at which people can travel from country to country would almost certainly help the virus to spread faster than in the past. As most new influenza viruses seem to originate in Asia, epidemiologists, physicians and public health practitioners from around the world keep careful watch of the types of flu circulating there, so that perhaps the next new flu virus can be stopped before it creates another epidemic.
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What Is Bird Flu and Why Are We Worried About It? Bird flu (otherwise known as avian influenza) is a fatal form of the flu; it kills about 30 percent of its human victims. Birds, like people, become infected with the influenza virus. There are many different types of the flu virus. Humans are not usually infected by bird flu, but if a person is in close contact with birds and the bird flu changes so that it can infect a human, that person might get sick. Those at risk for bird flu are mostly poultry farmers or others who have direct contact with infected birds. Because flu viruses are able to change rapidly and mix with other flu viruses, scientists continue to watch bird flu viruses. Even if a poultry farmer catches a bird flu from his chickens, the virus is not usually able to pass from that infected farmer to another person. The problem begins when that farmer has the human flu virus at the same time as having the bird flu virus. If the two viruses mix and can spread from person to person, this could result in a brand new influenza virus that we have never seen or treated. If no one has been vaccinated for this new strain of flu and no one has had it before, it could make a lot of people sick.
The last two influenza pandemics, in 1957 and 1968, were caused by the mixing of a human virus with a bird virus; this mixing can happen in pigs as well as humans. If the virus recombines in a way that allows it to spread easily between humans, it has the potential to cause another influenza pandemic.
Recently, health professionals have been expressed concern about a bird flu (Type A/H5N1) that has infected several poultry farmers in Southeast Asia. Scientists continue to watch the bird flu viruses in Asia to prevent bird flu from causing the next flu pandemic.
How Well Do Flu Vaccines Work?
It depends on how closely the flu viruses used in the vaccine match the actual flu virus that hits a population and the immune system of the vaccinated person.
Since the flu virus changes each year, the flu vaccine changes as well. There are many strains of flu and it is difficult to tell which one will circulate in any given year. Moreover, because it can take up to nine months to manufacture a flu vaccine, vaccine producers have to predict early in the year which influenza virus will circulate in the following year.
To do this, vaccine makers collect flu viruses from all around the world every year to decide which viruses should be used. The three strains judged most likely to cause trouble are selected (two Type A strains and one Type B). How well the vaccine works in any given year depends on how closely the three vaccine strains match the actual flu viruses that eventually circulate.
Even when the vaccine is not an exact match to the flu virus, it still usually provides some protection. In 1997-98, for example, the vaccine was not a good match for that year’s flu virus, but the risk for unvaccinated people to contract the flu was still twice as great as the risk for those who were vaccinated. This could have been due to how the virus has changed from previous years, and how similar it is to one of the viruses used to make the vaccine.
There are two types of vaccines that protect against the flu. The "flu shot" is an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm. A different kind of vaccine, called the nasal-spray flu vaccine (sometimes referred to as LAIV, for Live Attenuated Influenza Vaccine), was approved in 2003. The nasal-spray flu vaccine contains attenuated (weakened) live viruses, and is administered by nasal sprayer.
The nasal-spray flu vaccine is approved for use only among healthy people between the ages of 5 and 49 years. The flu shot is approved for use among people over 6 months of age, including healthy people and those with chronic medical conditions.
Flu vaccines do not work as well for people over the age of 65 as they do for younger people; they are also less effective on people with compromised immune systems (such as those with HIV or who are receiving treatments for cancer). It is important for health care workers or people who live with or take care of older adults to be vaccinated themselves so that they do not get the flu and pass it along to those who don’t have protection. For more information on influenza, visit the CDC’s website on flu. Why Is the 1918 Flu So Famous? The 1918 flu killed millions of young, healthy people. In a normal flu epidemic, most deaths occur among young children and the frail elderly. The 1918 flu, however, was most fatal to perfectly healthy adults in their 20s and 30s. Scientists estimated at the time that 20 million people around the world died from the 1918 flu; but now, most think that estimate is far too low. They talk of 50 million, perhaps 100 million deaths, from the 1918 pandemic—more deaths in one year than in the 20 years of the AIDS epidemic. In the United States, the 1918 flu epidemic overwhelmed cities. Everyone was out sick. There were too few milkmen, too few firefighters, too few telephone operators and too few gravediggers. Cities didn’t have enough workers to process death certificates. As it was illegal to conduct burials without one, bodies and caskets stacked up inside—and outside—funeral homes. The epidemic killed—at a very, conservative estimate—550,000 Americans in ten months. For more information on the 1918 flu, see the article in the School's magazine. What Is a Pandemic? A pandemic is an epidemic occurring over a very wide area, crossing international boundaries and usually affecting a large number of people. It is the term for a global epidemic. Due to its impact around the world, HIV/AIDS is considered a pandemic. The 1918 influenza is another example of a pandemic. Pandemics do not have to be caused by infectious diseases. The spread of health behaviors can create pandemics as well. For example, the increase in cigarette smoking around the world has led to a pandemic of lung cancer. Epidemiologists are concerned about pandemics because the increased amount of travel in recent years and the speed at which people can travel from country to country would almost certainly help disease to spread faster than in the past. | 
