Epidemiology I.

Epidemiology I

Definition - Epidemiology
Epidemiology is the study of the distribution and determinants of disease or health outcomes in specified populations, and the application of this study to the control of health problems.

Hippocrates Some people consider Hippocrates to be the first epidemiologist. Hippocrates was a Greek physician. He wrote a book called, On Airs, Waters, Places, where he described epidemics. Hippocrates thought about environmental and behavioral issues that might be associated with disease. He focused on rational explanations for disease rather than supernatural explanations, which were the norm during his time. For example, malaria was even known about in ancient times.

Hippocrates Hippocrates described the malarial parasite periodicity and the malarial paroxysm. Which is a period of intense chills, followed by a period of intense fever, followed by a period of profuse sweating, followed by exacerbation or flare-up. Hippocrates was in favor of swamp drainage to prevent miasma or bad night air. As he observed it's link with yellow fever and malaria in people living near these swamps. Introduced term, ”ENDEMIC” and “EPIDEMIC”

Girolamo Fracastoro Italian physician Girolamo Fracastoro was another contributor to the field of epidemiology. Fracastoro showed several ways that transmission of infections can occur. By direct contact, by air, and via contaminated clothing. In 1546, Fracastoro presented his writing on contagion and contagious diseases, and proposed that diseases were each caused by a rapidly multiplying seed. He proposed that the seeds were transmitted by direct contact, air, or contaminated garments.

John Graunt John Graunt contributed to epidemiology as one of the first demographers. Demography is the statistical study of human populations. Graunt calculated survivorship on a chart, and he presented population and mortality statistics in London during the time of the plague. The statistical and census methods that he developed and used became the basis for modern demography.

John Graunt John Graunt did an analysis of the vital statistics of people living in London. He published his analyses in Natural and Political Observations Made Upon the Bills of Mortality in This publication was the first estimation of the London population that was statistically-based.

James Lind Lind was interested in the cause and
treatment of scurvy. Sailors in the 16 and 1700s often suffered from scurvy. Lind theorized that citrus fruits could cure scurvy. Scurvy is now known to be caused by a vitamin C deficiency. But back in the time of Lin, vitamins were unknown. It is now known that vitamin C is necessary to maintain healthy connective tissue. In the 1700s, during the circumnavigation of the world by ship, many sailors died, and many of those who died supposedly had scurvy. Lind had the idea that something was lacking in the diet of the ill sailors. Lind chose 12 men from a ship, all with scurvy, and sorted them into six pairs. He gave each pair a different supplement to their diet.

James Lind All of the sailors received the same basic diet, but one group received a quart of cider daily. Group two received 25 drops of elixir of vitriol, or sulfuric acid. Group three received six spoonfuls of vinegar. Group four received half a pint of seawater. Group five received two oranges and one lemon. And the last group received a spicy paste. Group five could no longer be treated after six days when they no longer had any fruit. However, one sailor in this group was already able to work. While the other sailor had almost progressed to the point that he too could soon return to his post. Lind's work was a benefit to the field of preventative medicine, led to improved nutrition and was a beginning step leading to modern day clinical trials.

Percivall Pott Percivall Pott was an English surgeon in the 1700s. Pott is considered to be the first person to show that an environmental carcinogen may cause cancer. Pott noticed that London men working as chimney sweeps had more scrotal skin sores than would be expected. He noticed coal soot in the sores of the men he examined and concluded that there was an association between men routinely exposed to soot and scrotal cancer.

Percivall Pott Pott's observations were the first time an environmental factor was noted as a cancer causing agent. Pott's work was the beginning of modern non-infectious disease epidemiology.

William Farr William Farr was a 19th century London epidemiologist who's considered one of the founders of modern epidemiology. Farr took statistical data and tested social hypotheses. He also classified causes of death in a way that accounted for broader factors that determine health. Farr demonstrated a relationship between population density and mortality rates.

William Farr He also mapped deaths, monitored
outbreaks, and developed a new categorization system for causes of death. The mortality data system that Farr developed was an antecedent to the International Classification of Diseases System that is used today. In 1849, there was a major outbreak of cholera in London, in which 15,000 people died. This image is an extract from Farr's report on mortality from cholera in the 1849 outbreak. It was published in the Annual Report of the Registrar General for Farr's report shows the relationship between water sources and cholera. And he even further classified cholera death by sub-districts of different elevations.

Sir Edwin Chadwick Sir Edwin Chadwick studied sanitation issues in the United Kingdom. Chadwick supported the idea that disease was directly related to people's living conditions and that there was a strong need for both public health and social reform. Chadwick proposed improvements such as fresh, clean water, water closets, which was a room with a flushing toilet in each home, and a sewage carrying system. Chadwick promoted use a special, water type pipes for sewage to reduce drinking water contamination. He thought that improvements in the health of the poor would be good for the nation overall. Chadwick published his ideas in The Sanitary Condition of the Laboring Population in 1842.

John Snow London physician John Snow, is known as The Father of Modern Epidemiology. Snow conducted the first outbreak investigation in London in Snow showed an increase in patients with cholera symptoms who lived or worked in one district. Snow counted and mapped cases of cholera according to where people lived and worked. He noted that many people who lived on or near Broad Street had died. All had been ill with cholera symptoms.

John Snow Snow is likely the first person who geographically counted and mapped cases of a disease. He compared Cholera in different parts of London and came to the conclusion that people who used the Broad Street water pump had much higher rates of illness when compared to people from other areas of London. Snow's research showed that contaminated water had spread cholera.

John Snow Snow's work is often considered the beginning of epidemiology, the study of health outcomes in populations. This figure shows a map of cholera in London prepared by John Snow. By the end of the outbreak, more than 600 people had died from cholera. And all were exposed to water from the Broad Street pump. This image shows the Broad Street pump. Removing the pump handle as a control measure that further confirmed John Snow's hypotheses, as a number of new cholera cases dropped. John Snow's memory continues to live on today through the John Snow Society.

John Snow The John Snow Society aims to promote the life and works of Doctor John Snow, the pioneer of the epidemiologic method. The John Snow Society encourages members to celebrate the memory of John Snow by visiting the John Snow Pub, which is located on the site of the original pump. This concludes our lecture on the history of epidemiology. In the next lecture, you'll learn about the definitions of epidemiology, and how epidemiology fits into public health.

Natural History and Spectrum of Disease
Natural history of disease refers to the progress of a disease process in an individual over time, in the absence of intervention. The process begins with exposure to or accumulation of factors capable of causing disease. Without medical intervention, the process ends with recovery ,disability, or death Introduction to epidemiology

Introduction to epidemiology

Infectivity refers to the proportion of exposed persons who become infected. Pathogenicity refers to the proportion of infected persons who develop clinical disease. Virulence refers to the proportion of persons with clinical disease who become severely ill or die Introduction to epidemiology

Hepatitis A virus in children has low Pathogenicity and low virulence, since many infected children remain asymptomatic and few develop severe illness. In persons with good nutrition and health, measles virus has high Pathogenicity but low virulence, since almost all infected persons develop the characteristic rash illness but few develop the life-threatening presentations of measles, pneumonia, or encephalitis. In persons with poorer nutrition and health, measles is a more virulent disease, with mortality as high as 5-10%. Finally, rabies virus is both highly pathogenic and virulent, since virtually 100% of all infected persons (who do not receive treatment) progress to clinical disease and death. Introduction to epidemiology

The natural history and spectrum of disease presents challenges to the clinician and to the public health worker. Because of the clinical spectrum, cases of illness diagnosed by clinicians in the community often represent only the “tip of the iceberg.” Many additional cases may be too early to diagnose or may remain asymptomatic. Introduction to epidemiology

For the public health worker, the challenge is that persons with inapparent or undiagnosed infections may nonetheless be able to transmit them to others. Such persons who are infectious but have subclinical disease are called carriers. Introduction to epidemiology

Frequently, carriers are persons with incubating disease or inapparent infection. Persons with measles, hepatitis A, and several other diseases become infectious a few days before the onset of symptoms. On the other hand, carriers may also be persons who appear to have recovered from their clinical illness, such as chronic carriers of hepatitis B virus Introduction to epidemiology

Introduction to epidemiology
CHAIN OF INFECTION Introduction to epidemiology

CHAIN OF INFECTION The traditional model (epi triad) illustrates that infectious diseases result from the interaction of agent, host, and environment. More specifically, transmission occurs when the agent leaves its reservoir or host through a portal of exit, and is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host. This is sometimes called the chain of infection and is illustrated in Introduction to epidemiology

CHAIN OF INFECTION Introduction to epidemiology

CHAIN OF INFECTION Reservoir: is the habitat in which an infectious agent normally lives, grows, and multiplies. Reservoirs include humans, animals, and the environment. The reservoir may or may not be the source from which an agent is transferred to a host. For example, the reservoir of Clostridium botulinum is soil, but the source of most botulism infections is improperly canned food containing C. botulinum spores. Introduction to epidemiology

CHAIN OF INFECTION Human reservoirs. Many of the common infectious diseases have human reservoirs. Diseases which are transmitted from person to person without intermediaries include the sexually transmitted diseases, measles, mumps, streptococcal infection, most respiratory pathogens, and many others. Smallpox was eradicated after the last human case was identified and isolated because humans were the only reservoir for the smallpox virus. Two types of human reservoir exist: persons with symptomatic illness carriers Introduction to epidemiology

CHAIN OF INFECTION A carrier is a person without apparent disease who is nonetheless capable of transmitting the agent to others. Carriers may be asymptomatic carriers, who never show symptoms during the time they are infected, or may be incubatory or convalescent carriers, who are capable of transmission before or after they are clinically ill. A chronic carrier is one who continues to harbor an agent (such as hepatitis B virus or Salmonella typhi—the agent of typhoid fever) for a extended time (months or years) following the initial infection. Introduction to epidemiology

CHAIN OF INFECTION Carriers commonly transmit disease because they do not recognize they are infected and consequently take no special precautions to prevent transmission. Symptomatic persons, on the other hand, are usually less likely to transmit infection widely because their symptoms increase their likelihood of being diagnosed and treated, thereby reducing their opportunity for contact with others. Introduction to epidemiology

CHAIN OF INFECTION Animal reservoirs. Infectious diseases that are transmissible under normal conditions from animals to humans are called zoonoses .In general, these diseases are transmitted from animal to animal, with humans as incidental hosts. Such diseases include brucellosis (cows and pigs), anthrax (sheep), plague (rodents), trichinosis (swine), and rabies (bats, raccoons, dogs, and other mammals). Introduction to epidemiology

CHAIN OF INFECTION Another group of diseases with animal reservoirs are those caused by viruses transmitted by insects and caused by parasites that have complex life cycles, with different reservoirs at different stages of development. Such diseases include St. Louis encephalitis and malaria (both requiring mosquitos) and schistosomiasis (requiring fresh water snails). Lyme disease is azoonotic disease of deer incidentally transmitted to humans by the deer tick. Introduction to epidemiology

CHAIN OF INFECTION Environmental reservoirs. Plants, soil, and water in the environment are also reservoirs for some infectious agents. Many fungal agents, such as those causing histoplasmosis, live and multiply in the soil. The primary reservoir of Legionnaires’ bacillus appears to be pools of water, including those produced by cooling towers and evaporative condensers. Introduction to epidemiology

CHAIN OF INFECTION Portal of exit is the path by which an agent leaves the source host. The portal of exit usually corresponds to the site at which the agent is localized. Thus, tubercle bacilli and influenza viruses exit the respiratory tract, schistosomes through urine, cholera vibrios in feces, Sarcoptes scabiei in scabies skin lesions, and enterovirus 70, an agent of hemorrhagic conjunctivitis, in conjunctival secretions. Some blood borne agents can exit by crossing the placenta (rubella, syphilis, toxoplasmosis), while others exit by way of the skin (percutaneously) through cuts or needles (hepatitis B) or blood-sucking arthropods (malaria). Introduction to epidemiology

CHAIN OF INFECTION Modes of transmission: After an agent exits its natural reservoir, it may be transmitted to a susceptible host in numerous ways. These modes of transmission are classified as: Direct Direct contact Droplet spread Indirect Airborne Vehicleborne Vectorborne Mechanical Biologic Introduction to epidemiology

CHAIN OF INFECTION In direct transmission, there is essentially immediate transfer of the agent from a reservoir to a susceptible host by direct contact or droplet spread. Direct contact occurs through kissing, skin-to-skin contact, and sexual intercourse. Direct contact refers also to contact with soil or vegetation harboring infectious organisms. Introduction to epidemiology

CHAIN OF INFECTION Infectious mononucleosis (“kissing disease”) and gonorrhea are spread from person-to-person by direct contact. Hookworm is spread by direct contact with contaminated soil. Droplet spread refers to spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking. Droplet spread is classified as direct because transmission is by direct spray over a few feet, before the droplets fall to the ground. Introduction to epidemiology

CHAIN OF INFECTION In indirect transmission, an agent is carried from a reservoir to a susceptible host by suspended air particles or by animate (vector) or inanimate (vehicle) intermediaries. Most vectors are arthropods such as mosquitoes, fleas, and ticks. These may carry the agent through purely mechanical means. For example, flies carry Shigella on appendages; fleas carry Yersinia pestis (agent that causes plague) in the gut and deposit the agent on the skin of a new host Introduction to epidemiology

CHAIN OF INFECTION In mechanical transmission, the agent does not multiply or undergo physiologic changes in the vector. This is in contrast to instances in which an agent undergoes part of its life cycle inside a vector before being transmitted to a new host. When the agent undergoes changes within the vector, the vector is serving as both an intermediate host and a mode of transmission. This type of indirect transmission is a biologic transmission Introduction to epidemiology

CHAIN OF INFECTION Guinea worm disease and many other vectorborne diseases have complex life cycles which require an intermediate host. Since the agent undergoes part of its life cycle in the intermediate host, the agent cannot be transmitted by the intermediate host until the agent has completed that part of its life cycle. Therefore, this is an indirect, vectorborne, biologic transmission. Introduction to epidemiology

CHAIN OF INFECTION Vehicles that may indirectly transmit an agent include food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels). As with vectors, vehicles may passively carry an agent—as food or water may carry hepatitis A virus—or may provide an environment in which the agent grows, multiplies, or produces toxin—as improperly canned foods may provide an environment in which C. botulinum produces toxin. Introduction to epidemiology

CHAIN OF INFECTION Airborne transmission is by particles that are suspended in air. There are two types of these particles: dust and droplet nuclei. Airborne dust includes infectious particles blown from the soil by the wind as well as material that has settled on surfaces and become resuspended by air currents. Introduction to epidemiology

CHAIN OF INFECTION Droplet nuclei are the residue of dried droplets. The nuclei are less than 5 μ (microns) in size and may remain suspended in the air for long periods, may be blown over great distances, and are easily inhaled into the lungs and exhaled. This makes them an important means of transmission for some diseases. Tuberculosis, for example, is believed to be transmitted more often indirectly, through droplet nuclei, than directly, through droplet spread. Legionnaires’ disease and histoplasmosis are also spread through airborne transmission. Introduction to epidemiology

CHAIN OF INFECTION Portal of entry An agent enters a susceptible host through a portal of entry. The portal of entry must provide access to tissues in which the agent can multiply or a toxin can act. Often, organisms use the same portal to enter a new host that they use to exit the source host. For example, influenza virus must exit the respiratory tract of the source host and enter the respiratory tract of the new host. Introduction to epidemiology

CHAIN OF INFECTION The route of transmission of many enteric (intestinal) pathogenic agents is described as “fecaloral” because the organisms are shed in feces, carried on inadequately washed hands, and then transferred through a vehicle (such as food, water, or cooking utensil) to the mouth of a new host. Other portals of entry include the skin (hookworm), mucous membranes (syphilis, trachoma), and blood (hepatitis B). Introduction to epidemiology

CHAIN OF INFECTION The final link in the chain of infection is a susceptible host. Susceptibility of a host depends on genetic factors, specified acquired immunity, and other general factors which alter an individual’s ability to resist infection or to limit pathogenicity. An individual’s genetic makeup may either increase or decrease susceptibility. General factors which defend against infection include the skin, mucous membranes, gastric acidity, cilia in the respiratory tract, the cough reflex, and nonspecific immune response. Introduction to epidemiology

CHAIN OF INFECTION General factors that may increase susceptibility are malnutrition, alcoholism, and disease or therapy which impairs the nonspecific immune response. Specific acquired immunity refers to protective antibodies that are directed against a specific agent. Individuals gain protective antibodies in two ways: 1) They develop antibodies in response to infection, vaccine, or toxoid; immunity developed in these ways is called active immunity. 2) They acquire their mothers’ antibodies before birth through the placenta or they receive injections of antitoxins or immune globulin; immunity that is acquired in these ways is called passive immunity. Introduction to epidemiology

CHAIN OF INFECTION Note that the chain of infection may be interrupted when an agent does not find a susceptible host. This may occur if a high proportion of individuals in a population is resistant to an agent. These persons limit spread to the relatively few who are susceptible by reducing the probability of contact between infected and susceptible persons. This concept is called herd immunity. Introduction to epidemiology

CHAIN OF INFECTION The degree of herd immunity necessary to prevent or abort an outbreak varies by disease. In theory, herd immunity means that not everyone in a community needs to be resistant (immune) to prevent disease spread and occurrence of an outbreak. In practice, herd immunity has not prevented outbreaks of measles and rubella in populations with immunity levels as high as 85 to 90% Introduction to epidemiology

CHAIN OF INFECTION One problem is that, in highly immunized populations, the relatively few susceptible persons are often clustered in population subgroups, usually defined by socioeconomic or cultural factors. If the agent is introduced into one of these subgroups, an outbreak may occur. Introduction to epidemiology

CHAIN OF INFECTION Implications for public health By knowing how an agent exits and enters a host, and what its modes of transmission are, we can determine appropriate control measures. In general, we should direct control measures against the link in the infection chain that is most susceptible to interference, unless practical issues dictate otherwise. Introduction to epidemiology

CHAIN OF INFECTION For some diseases, the most appropriate intervention may be directed at controlling or eliminating the agent at its source. In the hospital setting, patients may be treated and/or isolated, with appropriate “enteric precautions,” “respiratory precautions,” “universal precautions,” and the like for different exit pathways. In the community, soil may be decontaminated or covered to prevent escape of the agent. Introduction to epidemiology

CHAIN OF INFECTION Sometimes, we direct interventions at the mode of transmission. For direct transmission, we may provide treatment to the source host or educate the source host to avoid the specific type of contact associated with transmission. In the hospital setting, since most infections are transmitted by direct contact, handwashing is the single most important way to prevent diseases from spreading. Introduction to epidemiology

CHAIN OF INFECTION For vehicle borne transmission, we may decontaminate or eliminate the vehicle. For fecal-oral transmission, we may also try to reduce the risk of contamination in the future by rearranging the environment and educating the persons involved in better personal hygiene. For airborne transmission, we may modify ventilation or air pressure, and filter or treat the air. For vector borne transmission, we usually attempt to control (i.e., reduce or eradicate) the vector population. Introduction to epidemiology

CHAIN OF INFECTION Finally, we may apply measures that protect portals of entry of a susceptible potential host or reduce the susceptibility of the potential host. For example, a dentist’s mask and gloves are intended to protect the dentist from a patient’s blood, secretions, and droplets, as well to protect the patient from the dentist. Prophylactic antibiotics and vaccination are strategies to improve a potential host’s defenses. Introduction to epidemiology

epidemiologic transitions.
An epidemiologic transition describes changing patterns of population age distributions, mortality, fertility, life expectancy, and causes of death. The human population has gone through four major disease transitions since the agricultural period began.

First Transition The first transition is related to the emergence of infectious diseases and diseases related to nutrition. And to the beginning of the practice of agriculture and food production. 10,000 years ago, people became less dependent on hunting and gathering once they were able to produce food and domesticate animals. This shift led to zoonotic disease, nutrient deficiencies, and increased contact with disease vectors during agricultural activities.

Second Transition The second transition was a time where human immune systems and disease-causing organisms both evolved, resulting in a change from major epidemics of disease to endemic disease. People developed physical and genetic changes that serve to minimize the effects of diseases.

Third Transition The third transition resulted when disease patterns changed from infectious to chronic and degenerative diseases, in developed parts of the world due to improvements in nutrition, public health, and clinical medicine. Cardiovascular diseases and cancer began to occur more during this transition. They are often associated with the longer lifespan and a sedentary lifestyle.

Fourth Transition The fourth transition started at the end of the 20th century. This is the period when both new diseases and the reemergence of infectious ones occurred as well as the rapid spread of disease due to globalization. So let's compare the four epidemiologic transitions.

Transition summary The first transition started when hunter gatherers began to practice agriculture and began to live in one place. There was a transition from few epidemics to major epidemics. The second transition happened because populations developed immunologic resistance and disease-causing organisms changed. There was a transition from major epidemics of disease to endemic diseases. The third transition came from improved public health and sanitation. There was a transition from infectious diseases to non-infectious chronic and degenerative diseases. The fourth transition was due to increased globalization. There was a resurgence and rapid spread of infectious diseases.

Epidemic Disease Occurrence
Level of disease The amount of a particular disease that is usually present in a community is the baseline level of the disease. This level is not necessarily the preferred level, which should in fact be zero; rather it is the observed level. Theoretically, if no intervention occurred and if the level is low enough not to deplete the pool of susceptible persons, the disease occurrence should continue at the baseline level indefinitely. Introduction to epidemiology

Thus, the baseline level is often considered the expected level of the disease. For example, over the past 4 years the number of reported cases of poliomyelitis has ranged from 5 to 9. Therefore, assuming there is no change in population, we would expect to see approximately 7 reported cases next year. Introduction to epidemiology

Different diseases, in different communities, show different patterns of expected occurrence: a persistent level of occurrence with a low to moderate disease level is referred to as an endemic level a persistently high level of occurrence is called a hyperendemic level an irregular pattern of occurrence, with occasional cases occurring at irregular intervals is called sporadic. Introduction to epidemiology

Occasionally, the level of disease rises above the expected level. When the occurrence of adisease within an area is clearly in excess of the expected level for a given time period, it is called an epidemic. Public health officials often use the term outbreak, which means the same thing, because it is less provocative to the public. When an epidemic spreads over several countries or continents, affecting a large number of people, it is called a pandemic. Introduction to epidemiology

Epidemics occur when an agent and susceptible hosts are present in adequate numbers, and the agent can effectively be conveyed from a source to the susceptible hosts. More specifically, an epidemic may result from the following: A recent increase in amount or virulence of the agent The recent introduction of the agent into a setting where it has not been before An enhanced mode of transmission so that more susceptibles are exposed Some change in the susceptibility of the host response to the agent Factors that increase host exposure or involve introduction through new portals of entry Introduction to epidemiology

Epidemiology and public health.
Epidemiology has been used to evaluate the success of immunization programs, such as the one being implemented here in Mogadishu. Public health is a multidisciplinary field whose goal is to promote the health of the population through organized community efforts. Public health protects against threats to health, empowers people to lead healthy lives, improves the quality of health services. And prepares leaders to advance health.

Epidemiology in PH Two aspects of public health where epidemiology is used. Are Prevention, such as raising public awareness about the need for child car seats, and Interventions such as promoting healthy eating by lowering the cost of health foods.

Levels of prevention Epidemiology is used, to develop, target, and evaluate prevention strategies. There are three levels of public health prevention. These are : Primary Secondary Tertiary

Primary prevention Primary prevention occurs before a person gets a health outcome and tries to prevent the health outcome from occurring. Primary prevention may reduce the prevalence, risk and, or rate of a health outcome. An example of primary health prevention is vaccination. Vaccines prevent diseases from being contracted.

Secondary prevention Secondary prevention occurs after a disease has occurred, but before the person notices symptoms. Secondary prevention aims to find and treat disease early, which may lead to the disease being cured. An example of a secondary health prevention is the doctor checking for suspicious skin growths, in order to detect and treat skin cancer early.

Tertiary prevention Tertiary prevention refers to a person who already has symptoms of the disease. The goal of tertiary prevention is to prevent damage and pain from disease. Slow down disease progression, prevent complications, provide better care and help people recover. An example of a tertiary prevention would be offering dietary advice to help manage the symptoms of diabetes.

Epidemiology and intervention
Epidemiology is also used to evaluate interventions in the population. Public health interventions can occur at two levels, Individual or Structural.

Individual interventions
Individual interventions focus on changing individual risk factors or behavior. Individual intervention approaches rely on the assumption that people have the autonomy and capacity to make choices and then follow through on their choices. An example of an individual intervention, might be educating individuals on the health benefits of quitting smoking. Structural interventions focus on changing physical, social, and/or economic factors in the environment to improve public health. Provision of clean drinking water.

INDividual Improving road safety standards, changes in car designs or changes in urban design to increase physical activity are examples of structural interventions. In contrast to an individual intervention, a structural intervention to prevent smoking, might promote taxation of tobacco products to make them less affordable.

Structural interventions
Structural interventions rely on the assumption that public health problems have some social causation. Public health is preventing illness and disability and prolonging life. Promoting physical and mental health and efficiency. Community efforts for sanitation of the environment. Prevention of diseases and injuries. Education of the individual. Organization of services for the diagnosis and treatment of disease. And promoting a standard of living adequate for the maintenance of health.

WHAT DOES EPIDEMIOLOGY MEASURES
Epidemiology looks at the distribution of a disease in a given group Involves the use of numbers( Biostatistics) Investigates the number of actual cases with the number of potential cases to determine the rate RATE = ACTUAL CASES = Numerator POTENTIAL CASES Denominator Denominator. The group who is a risk for a particular event or disease RATE IS Always PER

Incidence rate The rate at which new events occur in a population usually over a one year period Incidence rate= num. of new events num. of individual who can be exposed to the event Attack Rate- a form of incidence rate in which the denominator is reduce further for some known exposure ( Acute conditions)

Prevalence Rate - all the person in a population who experience an event ( illness)
Prevalence rate = num. of person with illness total population at risk Point prevalence = the num. of individual who have an illness at a particular time. E.g. : the num. of individual with cancer at the end Oct. divided by the total population at that time

Period Prevalence = num
Period Prevalence = num. of individual who have an illness at a specific time period. e.g. the num. of cancer in 2007 divided the total population mid year in 2007

the relationship Prevalence and incidence
Prevalence = incidence rate multiplied by the average duration of the disease Applied when both incidence and duration are stable Prevalence is greater than incidence if the disease is long tem. Chronic condition e.g. diabetes and hypertension has a higher prevalence than incidence , acute conditions has a higher incidence.

Factor Incidence Prevalence Increasing survival rates for disease NO CHANGE INCREASE Rapid Recovery DECREASE Reduce risk factors Vaccine Death from condition Effective treatment initiated

Crude, Specific and Standardized Rates
Crude rate – measured rate of the whole population Specific Rate - measured rate for sub group of population e.g.. Age , sex, race, religion Standardized rate – adjust or remove any difference between two population based on the standardize variable Allows for uncontaminated comparison Adjusted to make group equal on the same form factor. Crude rate can be calculate by adding age specific rates i.e.: proportion of the population in the specified age group multiply by the age specific rate. Standardized rate is also called the adjusted rate.

Crude Mortality rate- num. of deaths
total population Cause specific mortality rate – death from cause Total population Case Fatality Rate – Death from Cause num. of person with the disease Proportionate Mortality Rate(PMR) –Death from cause All deaths

Screening TESTS Sensitivity – asses the individuals who actually have the disease under investigation. True Positives- individuals whom the test has correctly identified as being ill False Positives- individuals whom the test has incorrectly identified as being ill. Sensitivity , only measure the distribution of persons with the disease

Sensitivity = True Positives
(True Positives+ False Negatives)

Specificity Specificity/ true negative rate- asses how well a test identify truly well individuals True Negatives - individuals who are well whom the test has identified as truly being well False Positives - well individuals whom the test has incorrectly identified as being ill

Specificity = True Negatives
(True Negatives + False Positives)

Predictive Value Predictive Value - measure the percentage of test result that match the actual value. Positive Predictive value- the probability that someone with a positive test actually has the illness + predictive Value = True Positive (True Positive + False Positives)

Negative predictive value – the probability of no disease in a person who receives a negative test result The person with a negative test is a true negative True negatives (True negatives + False Negatives) Looks at the distribution of persons who receive a negative test result

Accuracy It is the total percentage correctly selected,
Identify the degree to which a measurement or an estimate is based on the measurement. (TP+TN)/(TP+TN+FP+FN) I.E Total screened patient

Research study Design Cohort Studies:
-group who are free from condition under investigation -exposure to risk factors linked to cause of illness -assessment of incidence rate between exposed and non exposed group Types: Historical Prospective Prospective – taking place in present time Historical- occur in the past Clinical treatment trial- members of the cohort with a specific illness are given on treatment and other members given another treatment or placebo

Case Control studies Subjects with specific disorder i.e. the case Subjects without disease i.e. control Exposure to risk factors are assessed

Cross Sectional Studies:
Information is collected from a group of individuals who provide a picture of the disease over time Provide info on the relationship between risk factors and health status of a group of individual at one specific point in time

Analyzing studies Relative risk – compares the incidence rate of a disorder among individuals exposed to a risk factor e.g. : incidence rate of colon cancer among smoker is 20/1000, the incidence rate of colon cancer is 2/1000 The chance of eithers is 20/1000 divided by 2/1000 = 10 Means that a smoker is 10 times at risk of getting colon ca than non smoker

Attributable Risk Used for determining what would happen in a study population if the risk factors were removed Illness incidence rate in non exposed individuals is subtracted from the incidence rate of the illness in those who have been exposed to risk factor

Bias in studies Bias used to construct a study so that one outcome is more likely to occur than another Types: Selection Bias Measurement Bias Lifetime Bias Experimenter Expectancy Recall Bias Late look Bias Confounding Bias Design Bias Sampling Bias

The selected sample is not representative of the population
Selection Bias The selected sample is not representative of the population Can occur if the subjects are permitted to chose whether which group to go into or The investigator purposely chooses which patient go into which group Types: Berkson Bias Non respondent Bias Solution: random, independent data Berkson Bias= use of hospital records to asses prevalence Non respondent Bias-= people include in a study are different from those who are not

Information is gathered in a manner that distort the information
Measurement Bias Information is gathered in a manner that distort the information Hawthrone Effect occurs when subject’s behavior is altered because they are being study Solution– A control Group E.g. when assessing patient satisfaction with their respective physician they are ask leading question like you don’t like your doctor do you

Experimenter expectancy
Experimenter’s expectation inadvertently communicated to the subjects who then produce the desired effect(Pygmalion Effect) Solution Double Blind Studies

Gives a false estimates of survival rates
Lead time Bias Gives a false estimates of survival rates Solution: life expectancy to asses benefits e.g. patient seems to live longer with the disease after it is uncovered , but in reality there is no increase in survival, but the disease was discovered sooner so patient appears to live longer

Participants inaccurately recall events in the past
Recall Bias Participants inaccurately recall events in the past Solution - Confirmation E.g. a mother of children with cleft palate over estimate how much medication they took during pregnancy, it makes it appears that certain medication are link to cleft palate

Late look Bias Individual with severe disease are less likely to be uncovered in a survey because they will die first Solution- class disease in terms of severity

Sampling Bias Subjects are not representative of the population being studied Solution- random, independent sample

Confounding Bias The factor that is being investigated is related to other factors or of less interest Can obscure a relationship or make it seems that there is one when there is none e.g. comparing the relationship b between exercise and heart disease in two population when one population is younger and the other is older. Are the difference due to exercise or age

common issue is no comparable groups
Design Bias-= parts of the study do not fit together to answer the question of interest common issue is no comparable groups Solution: Random assignment Design Biased = comparing the effects of an anti hypertensive drug in hypertensive and normotensive

Preventing Bias Involves the use of : Blind studies Placebos
Crossover Studies Randomized Studies

Blind Studies Single blind studies - only the subject does not know what treatment they are receiving Double Blind Studies- neither the subject nor the evaluator knows what treatment the subject is receiving or which group received the treatment or is the control.

Placebos In a blind study a patient is given a placebo(in active drug) rather than an active drug Control group receive the placebo while the experimental group receive the active drug Placebo Effect

Crossover Studies Two groups
One group receive the drug the other a placebo Later the placebo group is given the drug and the group who was initially given the drug is given the placebo Each subject act as their control

Regarded as the most scientifically rigorous study in epidemiology
Randomization Subjects are randomly allocated into the intervention group and control group Regarded as the most scientifically rigorous study in epidemiology

Epidemiology I.

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Epidemiology I.

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Presentation on theme: "Epidemiology I."— Presentation transcript:

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