Let's talk about basic epidemiology. Let's first talk about some basic epidemiologic terms. Epidemiology, in the Greek terms, the study of what is upon the people. So Epi means upon, Demos, people, Logos, study. The study of what is upon the people. An epidemic, therefore, is visited upon a population. An epizootic is visited upon an animal population. An endemic means that it resides within a population, and an enzootic resides within an animal population. How do we measure disease frequency? Well, the important term is population at risk. The incidence of a disease is the number of new cases per population at risk during a specified time period. So the risk of becoming ill or causation studies would be looking at the incidence of the disease. Prevalence, on the other hand, is the number of existing cases per population at risk during a specified time period. So incidence is the number of new cases. Prevalence is the number of already existing cases. Prevalence then looks at the probability of a population being ill or the disease burden of a population. Prevalence, therefore, is equal to the incidence times the average disease duration. Let's look at the Lyme disease incidence in humans in the United States. This is in 2016, and as you can see by this map, Lyme disease is hyperendemic in the Northeast area, and it appears to be endemic in this part of the United States as well, with a few cases scattered around parts of the country. Now, if we compare that to the disease incidence or prevalence in dogs from 2011-2015, there's a lot more cases of Lyme disease in dogs. In fact, there are 50 times more dog cases of Lyme in the South and West than the CDC's reported human cases. Let's talk about disease prevalence in humans globally in 2015. You can see that the countries that are in purple or in deep blue have a very high prevalence rate of diabetes. So let's measure disease severity. The case fatality rate is the proportion of cases with the disease who die within a specified time period. For example, 1 death out of 3 cases is equal to 33 percent case fatality rate. Mortality rates is investigating diseases with a high case fatality rate or the death rates in a population. Morbidity rates, on the other hand, is investigating diseases with low case fatality rates, such as chickenpox, mumps, and upper respiratory tract diseases, diseases that are not likely to kill you. Let's look at the estimated tuberculosis mortality rates of 2013, but these exclude the tuberculosis deaths among HIV positive patients. Just looking at non-HIV positive patients, you still have a high mortality rate in parts of the world, particularly in Sub-Saharan Africa and South Asia. So when we monitor health and disease in a population, we look at that population's vital statistics. We look at birth rates, we look at death rates, we look at the crude mortality rate, which equals the number of deaths in a specified time period per number of persons at risk of dying during the same time period times 1,000. We look at age-specific death rates. We look at infant mortality rate, which is the death rate of children in the first year of life. This measure is particularly sensitive to socioeconomic changes and to health interventions. Therefore, it serves as a good indicator of the overall health of a community. If you look at the infant mortality rate across various countries, including the United States, you see that unfortunately, the United States has a very high infant mortality rate compared to other similar countries. Monitoring health and disease, we look at the maternal mortality rate, or the risk of mothers dying from complications of pregnancy or childbirth, and that can range from 3 to 1,500 per 100,000 births. We can look at the adult mortality rate and compare health gaps between countries. We can look at life expectancy, which is a summary measure of population health. For example, the life expectancy globally in 2015 varies dramatically across countries and regions. Some countries have a much higher life expectancy, such as Canada and Europe, and some countries have very low life expectancies, such as in Sub-Saharan Africa. Why is epidemiology so important? Well, It provides data for better development, implementation, and evaluation of health-related policies. It's important to monitor the health of the most vulnerable populations and that includes infants, pregnant women, and the elderly. According to the World Health Organization, epidemiology has not fulfilled its mandate to influence public policy. Policy decisions are not necessarily made by the best scientific evidence, but instead often by politics. Let's talk about cost-effectiveness versus cost-benefit. Cost-effectiveness is the ratio of money spent and the number of lives saved. So for example, oral rehydration therapy for diarrhea is cheap and saves many lives. The cost-benefit compares the cost of treating disease to the cost of preventing it. So is treating rabies cheaper than preventing rabies through extensive dog vaccination programs? It's harder to calculate because it's hard to figure out the money saved through prevention. But your risk of rabies exposure varies tremendously across country. This map is from 2013, and you can see some countries have very low risk of rabies exposure versus some areas where countries have very high risks of rabies exposure. Now, many animals can get rabies, but the greatest risk to humans is generally through dog transmitted rabies, and you can see the differences across various regions of the world where dog rabies is present. So follow the money. You can determine a society's values by how much money it spends in specific areas. You can do a comparative budget analysis between government entities, and that's useful to determine political priorities. So the questions for this session then are, how much does your government spend on public health? Go to your state or regional health department website, does it have a web page on statistics or data that you can analyze? If so, what data does it include? Does your state or region website have data for you to consider the following questions? What is the birth rate in your state? What is the infant mortality rate? What is the maternal mortality rate? Does it differ by race or ethnicity? What is the life expectancy? What are the leading causes of death? Have the birth and death rates increased or decreased over the past 10 years? How do the rates of another state or region compare with yours? With that, I'd like to thank you for your time and attention with this session.
