Public Health Lecture Notes PDF

Field of Pharmacy Sciences Bachelor of Pharmacy-PharmD (Clinical Pharmacy) Program Public Health (PMB506) Lecture 1: Background/Epidemiology 1 Prof. Dr. Mohammad Mabrouk Aboulwafa Date : Oct./1 /2024 Public Health Background Health: is a state of complete physical, mental and soc...

Field of Pharmacy Sciences Bachelor of Pharmacy-PharmD (Clinical Pharmacy) Program Public Health (PMB506) Lecture 1: Background/Epidemiology 1 Prof. Dr. Mohammad Mabrouk Aboulwafa Date : Oct./1 /2024 Public Health Background Health: is a state of complete physical, mental and social well-being. Public health can be defined as the combination of sciences, skills, and beliefs that are directed to the maintenance and improvement of the health of all the people. Public health actions are directed to the community. Public health actions are exerted through governmental agencies and are conducted through programs and activities which may include: 1-Providing clean air and water, this will be benefit for everyone. 2-Subjecting individuals to physician care, e.g.: a- large scale screening programs for diseases such as sexually transmitted diseases and screening for inappropriate conditions (e.g. hypertension, various cancers). b- evaluation of high-risk factors (e.g. smoking, drug abuse, obesity) that cause diseases. c- education of good health habits (nutrition and exercise). Preventive medicine It is concerned with preventing physical, mental, and emotional diseases and injury (i.e. keeping people well). Prevention is inseparable from treatment and cure, as in the case of communicable disease control and self-destructive behavior, such as addiction to tobacco and alcohol. The goals of medicine are: To preserve health, To restore health, and To relieve suffering. Prevention has three levels, these include: 1- Primary Prevention It means preventing of the occurrence of disease or injury, for example: immunization/chemoprophylaxis against infectious diseases using safety equipment to protect workers in hazardous occupations.  Primary prevention activities can be directed at: individuals (health education) the environment (environmental sanitation, safe drinking water, clean air, an environment free from toxic substances). 2- Secondary prevention It means early detection (through screening) and intervention (prompt treatment) preferably before the condition is clinically apparent and has the aim of: reversing, halting, or retarding the progress of a condition. For example early detection of neonatal phenylketonuria (PKU) and glaucoma testing. 3- Tertiary prevention It means minimizing the effects of disease and disability for preventing complications and premature deterioration. It includes: Rehabilitation for exploring a person’s remaining abilities and Attempts to restore the person to as normal as possible.  For example, rheumatoid arthritis: the use of splints and remedial exercises to prevent contractures and deformities. paraplegia: care of pressure points and bladder function Hands affected by RA Z-thumb Paraplegia: an impairment in motor and/or sensory function of the lower extremities. If the arms are also affected by paralysis, quadriplegia is the proper terminology. If only one limb is affected the correct term is monoplegia. Health education This term (education of good health habit) is applied to a wide range of approaches and topics relevant to health including for example: education of basic hygiene for children safety education for children and youth parent education for young adults chronic disease prevention and management in later adulthood. The various forms of health education occur through a variety of channels which may be interpersonal or some institutional e.g. schools. Health promotion It is the process of enhancing person, private and public support of positive health practices to become a societal norm (rules of behavior that are considered acceptable in a group or society), i.e. enhancing support for a healthful lifestyle. In this concern, legislation has proved to be an essential component which should constitute a governmental policy. Screening and Screening Tests It is the identification of persons who are sufficiently at risk from a specific disorder among apparently healthy individuals. Aim of screening: to direct people who are at risk to a subsequent diagnostic test or to make a prompt intervention and hence prevention. Parameters of a screening test. Screening tests are characterized by two measures which include: The detection rate (sensitivity) of a test: the proportion of affected individuals with positive test results. The false-positive rate of a test: the proportion of unaffected individuals with positive test results. This is sometimes given as the specificity, which is the false-positive rate expressed as a percentage subtracted from 100. so that, a false- positive rate of 3% is the same as a specificity of 97% Table: ( ): Definition of detection and false-positive rates Test result Affected unaffected Total Positive a b a+b Negative c d c+d Total a+c b+d Detection rate (sensitivity) = a/(a+c) False-positive rate (100 - specificity) = b/(b+d)  Sample size 100 affected unaffected 10 90 Screening test result Negative Positive Negative Positive Condition 1 1 9 90 0 Detection rate (sensitivity) = affected positive/total affected = (9/10)*100 = 90% (positive among affected) No false positive Specificity 100%  Sample size 100 affected unaffected 10 90 Screening test result Negative Positive Negative Positive Condition 2 0 10 89 1 False-positive rate = positive unaffected/(total unaffected) = (1/90)*100  1.1 Specificity = unaffected negative/total unaffected = (89/90)*100  98.9 (negative among unaffected) Sensitivity 100% if all affected individuals gave positive results Specificity 100% if all unaffected individuals gave negative results  Epidemiology It is the science that forms the basis for public health action and unites the public health professions. This term is derived from the Greek roots (epi meaning upon, demos meaning people, and logia meaning study). This term was originally applied to the study of outbreaks of acute infectious diseases and was defined as the science of epidemics. Now this term is refers to the study of the distribution and determinants of diseases or conditions (health-related states or events) in a defined population and the application of this study to the control of health problems.  In a detailed/descriptive manner, epidemiology is Included definition Character the Study of scientific, systematic, data-driven the distribution frequency, pattern and determinants causes, risk factors of health-related states and events not just diseases in specified populations patient is community, individuals viewed collectively and the application of this study to the since epidemiology is a discipline within control of health problems public health  Epidemiologic event: how can you characterize it?: Epidemiologists have to use 5 W’s to characterize an epidemiologic event (like outbreak of certain virus among a defined population), these include: What: diagnosis or health event Who: person Where: place When: time Why/how: causes, risk factors, and modes of transmission. This characterization method is similar to that taught for students of journalism to cover a good news story  Principles of epidemiology 1- Study Epidemiology is a scientific discipline, data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. In fact epidemiology is: often described as the basic science of public health is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science.  2- Distribution Epidemiology is concerned with the frequency and pattern of health events in a population: Frequency refers not only to the number of health events but also to the relationship of that number to the size of the population. The resulting rate allows epidemiologists to compare disease occurrence across different populations. Pattern refers to the occurrence of health-related events by time, place, and person. Time patterns may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence. Place patterns include geographic variation, urban/rural differences, and location of work sites or schools.  Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures. Characterizing health events by time, place, and person are activities of descriptive epidemiology. 5 W’s: one W what (event): three W’s are related to descriptive studies: time {when}, place {where}, and person {who} and one W is related to analytical studies {reason or cause/mode of transmission “Why” and “How”}.  3- Determinants Determinant: any factor that brings about a change in a health condition or other defined characteristic. Determinants include causes and other factors that influence the occurrence of disease and other health-related events. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. 4- Health-related states or events Epidemiology was originally focused exclusively on epidemics of communicable diseases but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. By the middle of the 20th Century, additional epidemiologic methods had been developed and applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health.  Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. Now, with the recent explosion in molecular methods, epidemiologists can make important strides (a long, decisive steps) in examining genetic markers of disease risk (molecular epidemiology). Indeed, the term health-related states or events may be seen as anything that affects the well-being of a population. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied.  5- Specified populations Although epidemiologists and direct health-care providers (clinicians) are both concerned with occurrence and control of disease, they differ greatly in how they view “the patient.” The clinician is concerned about the health of an individual; the epidemiologist is concerned about the collective health of the people in a community or population. In other words, the clinician’s “patient” is the individual; the epidemiologist’s “patient” is the community. 6- Application Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community- based practice.  View, responsibility and focusing of clinician and epidemiologist towards a health event Health Responsibility /focusing event Clinician Epidemiologist example A patient both are interested in establishing the correct diagnosis with focuses on focuses on: diarrheal treating and disease identifying the exposure or source that caused caring for the the illness individual the number of other persons who may have been similarly exposed the potential for further spread in the community interventions to prevent additional cases or recurrences  Differences between clinician and epidemiologist in application and practice Issue Clinician Epidemiologist Application and science and an art (skills). practice needs Health problem Diagnosis and Diagnosis the health of a prescription of community and proposing appropriate appropriate, practical, and treatment for a acceptable public health patient interventions to control and prevent disease in the community Application and combines medical uses the scientific methods of practice (scientific) descriptive and analytic approach knowledge with epidemiology as well as experience, experience, epidemiologic judgment, and clinical judgment, understanding of local conditions and understanding of the patient. Epidemiologist has a diverse backgrounds, including human and animal medicine, microbiology, statistics, computer programming, toxicology and entomology (science of study of insects) The goals of epidemiologist is: (a) identifying factors that cause disease or disease transmission, (b) prevent the spread of communicable and noncommunicable diseases and conditions. Uses of epidemiology Study of the distribution and determinants of diseases in a defined population helps to: identify factors that cause disease identify factors or conditions that can be used or modified to prevent the occurrence or spread of disease explain how and why diseases and epidemics occur evaluate the effectiveness of vaccines and different forms of drug therapy establish a clinical diagnosis of disease identify the health need of the community evaluate the effectiveness of health programs predict the future health needs of a population. Epidemiological study methods These studies include: I- Descriptive studies. Studies of the variation in the incidence of a disease according to: Time (how does the disease vary over time) Place (how does the disease vary from place to place) Person (how does the disease vary according to person characteristics such as age, sex or occupational group). Descriptive studies depend on the incidence and prevalence of the disease. The duration of a disease will be shortened if it either kills the patient or remits completely Thus, a condition with a high incidence and low prevalence could be either a common disease with a high fatality rate (e.g. lung cancer) or high remission rate (e.g. measles).  A disease with a low incidence and a high prevalence will be a chronic disease with a low fatality rate and low remission rate (e.g. rheumatoid arthritis). Uses of descriptive studies They are useful for: 1. suggestion of causes of disease. 2. assessment of the burden of different diseases in different communities. For example: the Japanese have a high incidence of stomach cancer but this declines substantially in Japanese migrants moving to the US, the incidence rates approximating to those of the native Americans within one to two generations. So, there must be an agent that causes stomach cancer to which the Japanese are more heavily exposed than the Americans. II- Analytical studies As noted earlier, epidemiologists can use descriptive studies/epidemiology to generate hypotheses (suggestion about the cause/risk factor), but only rarely to test those hypotheses. For that, epidemiologists must turn to analytic studies/epidemiology. Thus, analytic epidemiology is concerned with the search for causes and effects, or the why and the how. Epidemiologists use analytic epidemiology to quantify the association between exposures and outcomes and to test hypotheses about causal relationships. Epidemiology by itself can never prove that a particular exposure caused a particular outcome. Often, however, epidemiology provides sufficient evidence to take appropriate control and prevention measures. Analytical studies can be applied as observational studies.  Once the descriptive study have pointed to a possible association between exposure and a disease, the hypothesis can be explored further through analytical studies. The two most common types of analytical observational studies are cohort studies and case-control studies. Cohort studies (also called longitudinal or prospective study) In this study, a group of individuals is taken and categorized according to whether or not they are, or have been, exposed to a certain factor. Then, the group is followed over a period of time (often many years) The number of individuals who do and do not develop the disease of interest is recorded. This can be done using 2x2 table as follows:  Table ( ): Simple 2x2 table used in epidemiological studies to show the exposed and unexposed individuals who do and do not develop disease. Disease No disease Exposed a b a+b Not exposed c d c+d a+c b+d Disease rate in exposed subjects = a/(a+b) Disease rate in unexposed subjects = c/(c+d) Relative risk (r) = [a/(a+b)]/[c/(c+d)] The absolute excess risk (e) = a/(a+b) – c/(c+d) For example: lung cancer and smoking Group I: 1000 smokers, Group II: 1000 non smokers Disease No disease Total Exposed (smokers) 100 900 1000 Not exposed (non smokers) 5 995 1000 Total 105 1895 Relative risk (r) = (100/1000)/(5/1000)- 100/5 = 20 The absolute excess risk (e) = (100/1000)-(5/1000) = 0.095 Exposed individuals are then r times more likely than unexposed individuals to develop disease. A value of r that is statistically significantly greater than, or less than, 1 is evidence of an association. Advantages of cohort studies 1. The knowledge that the exposure preceded the occurrence of the disease 2. The ability to obtain a direct estimate of the incidence of the disease in the exposed and the unexposed groups (allowing both the relative risk and absolute excess risk to be estimated directly) 3. The ability to detect unsuspected association. Disadvantages of cohort studies 1. In case of chronic disorders such as cardiovascular disease and cancer, their long duration (many years), their large size (thousands of individuals) constitute a financial cost. 2. For a rare disease, few cases may develop only in a large study of this type. Case-control studies (also called retrospective study) In this type of study, a sample of individuals who have the disease (cases) and another sample who don’t (controls) were taken. The prevalence of exposure in those with and without the disease is determined retrospectively by the administration of a questionnaire. Example Prostate cancer and hormone administration Diseased individuals (Cases): 1000, Non diseased individuals (control): 1000 Hormone Cases (Prostate Control (No Total administration cancer) Prostate cancer) Hormone users 900 (a) 5 (b) 905 (a+b) Non hormone users 100 (c) 995 (d) 1095 (c+d) Total 1000 (a+c) 1000 (b+d) Disease rate in users = a/(a+b) Disease rate in unusers = c/(c+d) Relative risk (r) = [a/(a+b)]/[c/(c+d)] Relative risk = (900/905)/(100/1095) = (0.994475)/0.091324 = 10.89 ▪ If the disease being studied is rare, an approximation can be done as follows: ▪ Referring to the before 2x2 table, for a prospective study, Disease No disease Exposed a b a+b Not exposed c d c+d a+c b+d The relative risk (r) = [a/(a+b)]/[c/(c+d)] Now, since the disease is rare, a and c are much smaller than b and d, so that: a+b ≈ b, and a/(a+b) ≈ a/b c + d ≈ d, and c/(c+d) ≈ c/d Therefore, The relative risk (r) ≈ (a/b)/(c/d) = ad/bc, i.e. the cross products ratio of the 2x2 table. Advantages of case-control studies: 1. They are quick 2. Require relatively small numbers and hence they are reasonably economical. Disadvantages of case-control studies 1. The difficulty in certain studies of determining whether the exposure preceded the inception of the disease, 2. The difficulty in avoiding recall bias, e.g. sick people may recall a past exposure than healthy controls. 3. The difficulty in avoiding selection bias, so that recruitment of cases and controls is not influenced by weather or not exposed 4. The inability to obtain a direct estimate of incidence in exposed and unexposed groups and hence excess risk.  Table: Differences between cohort and case-control observational studies Parameter Cohort studies Case-control studies Study time Long duration (many years), They are quick (especially in case of chronic disorders such as cardiovascular disease and cancer) Study population Need large size (thousands of individuals) Require relatively small numbers. especially for a rare disease, since few cases may develop only in a large study of this type. Study cost Constitute a financial cost (due to study time They are reasonably economic and population size) Assurance of that There is assurance Absence of assurance exposure preceded disease inception Direct estimation of Can be determined in both the exposed and Inability to be determined disease incidence the unexposed groups Direct estimation of Can be determined Unable to get the direct estimation exposure excess risk in incidence Recall bias Can be avoided The difficulty in avoiding recall bias, e.g. sick people may recall a past exposure than healthy controls Selection bias Can be avoided The difficulty in avoiding selection bias, so that recruitment of cases and controls is not influenced by weather or not exposed 3- Intervention (experimental) studies. In an experimental study, the investigator determines through a controlled process the exposure for each individual (clinical trial) or community (community trial), and then tracks the individuals or communities over time to detect the effects of the exposure. For example, in a clinical trial of a new vaccine, the investigator may randomly assign some of the participants to receive the new vaccine, while others receive a placebo shot. The investigator then tracks all participants, observes who gets the disease that the new vaccine is intended to prevent, and compares the two groups (new vaccine versus placebo) to see whether the vaccine group has a lower rate of disease. Similarly, in a trial to prevent onset of diabetes among high-risk individuals, investigators randomly assigned enrollees to one of three groups - placebo, an anti-diabetes drug, or lifestyle intervention. At the end of the follow-up period, investigators found the lowest incidence of diabetes in the lifestyle intervention group, the next lowest in the anti-diabetic drug group, and the highest in the placebo group.  Intervention studies are experiments on humans in which a regimen is administered to an experimental group and the observed outcome compared with a control group which is not given the regimen. If a difference in outcome between the two groups is demonstrated then the effect can be inferred. These studies: resemble prospective studies in that subjects are followed up to determine their outcome. they differ in that some action or intervention is performed rather than only observing what takes place naturally. These studies are used to test the effectiveness of new drugs, vaccines or treatment regimen after providing to be safe on biological, pharmacological and toxicological laboratory studies. Two groups are taken: Study group to be given the new drug, vaccine or line of treatment Comparable control group not given anything (or placebo). Three types of control groups can be employed: Historical controls: affected patients seen before the new intervention. Geographical controls: affected patients seen at another unit which does not have the new intervention. Randomized controls: intervention is randomly assigned to concurrent patients in the same population.