Clinical Approach vs. Public Health Approach to Health Care

Transcription

1 DISEASE DETECTIVES PART ONE BACKGROUND & SURVEILLANCE Clinical Apprach vs. Public Health Apprach t Health Care Clinical Apprach primary rle is diagnsis and treatment f illness in individuals, preventive medicine (e.g., immunizatins, smking cessatin, besity cunselling and ther behaviral/lifestyle cncerns) has nly been addressed recently fcus remains n the individuals. Public Health Apprach primary rle is in cntrl and preventin f disease in ppulatins r grups f individuals, sme activities (e.g., diagnsing cases assciated with utbreaks and treating persns with cmmunicable diseases such as tuberculsis r syphilis) may verlap with thse in clinical medicine. There are ntable differences between the tw disciplines f clinical medicine and public health. Public Health Clinical Medicine Primary Fcus Ppulatins Individuals Emphasis Preventin Diagnsis Paradigm Organizatinal Lines f Specializatin Health Prmtin Whle Cmmunity Interventins aimed at Envirnment, Human Behavir and Lifestyle, and Medical Care Analytical (Epidemilgy); Setting and Ppulatin (Occupatinal Health); Substantive Health Prblem (Nutritin); Skills in Assessment, Plicy Develpment, and Assurance Treatment Whle Patient Medical Care Organ (Cardilgy); Patient Grup (Pediatrics); Etilgy, Pathphysilgy (Onclgy, Infectius Disease) Technical Skill (Radilgy) [Adapted frm: Fineberg, Harvey, MD, PhD, Dean, Harvard University Schl f Public Health, Traditinal Distinctins Between Public Health and Medicine. Table 5-1, Wh Will Keep the Public Healthy? Educating Public Health Prfessinals fr the 21st Century. Institute f Medicine,

2 Selected Histry f Epidemilgy and Ppulatin Health Circa 400 B.C. - Epidemilgy's rts are nearly 2500 years ld. Hippcrates attempted t explain disease ccurrence frm a ratinal rather than a supernatural viewpint Jhn Graunt, a Lndn haberdasher and cuncilman published a landmark analysis f mrtality data in s James Lind designed first experiment t use a cncurrently treated cntrl grup while studying scurvy determined limes culd prevent scurvy British sailrs became knwn as limeys 1790 s-edward Jenner develped the small px vaccine using clinical trials using cwpx William Farr built upn Graunt's wrk by systematically cllecting and analyzing Britain's mrtality statistics. Farr, cnsidered the father f mdern vital statistics and surveillance, develped many f the basic practices used tday in vital statistics and disease classificatin Jhn Snw the father f field epidemilgy. frmed and tested hypthesis n the rigin f chlera as waterbrne transmissin in Lndn - ne f the first studies in analytic epidemilgy 1880 s- Luis Pasteur recgnized the bacterial cause and develped a vaccine fr anthrax Rbert Kch frmalized standards (pstulates) t identify rganisms with infectius diseases 1910's - Flu pandemic Jseph Gldberger published a descriptive field study shwing the dietary rigin f pellagra 1940's - Fluride supplements added t public water supplies in randmized cmmunity trials Initiatin f the Framingham study f risk factrs fr cardivascular disease Epidemilgical studies link cigarette smking and lung cancer, demnstrating the pwer f casecntrl study design Field trial f the Salk pli vaccine - the largest frmal human experiment Mantel and Haenszel develp a statistical prcedure fr stratified analysis f case-cntrl studies MacMahn published first epidemilgic text with a systematic fcus n study design US Surgen General's Reprt n Smking and Health establish criteria fr evaluatin f causality 1970's - Large cmmunity based trials implemented, such as Nrth Karelia and Stanfrd Three Cmmunities; wrldwide eradicatin f smallpx 1980's - Chrnic disease, injury and ccupatinal epidemilgy; HIV epidemic 1990's Edward Sydenstricker (early 1900 s) became a pineer public health statistician Behaviral risk factr epidemilgy; preventin f adverse health utcmes thrugh plices and regulatins; natinal prgrams in breast and cervical cancer preventin; tbacc epidemilgy; emerging infectius diseases; criticism f epidemilgy fr being incnsequential ('small' risk ratis); standardizatin f surveillance methds; Mad cw disease (BSE) in England and Eurpe; variant Creutzfeld-Jacb disease; aging f USA; disaster epidemilgy 2000's - Genetic and mlecular epidemilgy; health disparities; racialism; HIPAA in the USA; West Nile Virus / biterrrism; anthrax and smallpx threat and vaccinatins SARS, quarantines and public health law; and wrld-wide epidemilgy; BSE in Canada SARS recurrence; BSE in USA; flu epidemic H1N1 pandemic 2

3 Main Cmpnents f Public Health Apprach Prblem t Respnse Public health prblems are diverse and can include: infectius diseases chrnic diseases emergencies injuries envirnmental health prblems ther health threats (frm CDC-Public Health 101 Series) Surveillance- What is the prblem r Is there a prblem? Risk Factr Identificatin- What is the cause? Interventin Evaluatin- What wrks? Implementatin-Hw d yu d it? Key Terms in Public Health clinical care: preventin, treatment, and management f illness and the preservatin f mental and physical well being thrugh the services ffered by medical and allied health prfessins; als knwn as health care. determinant: factr that cntributes t the generatin f a trait. epidemic r utbreak: ccurrence in a cmmunity r regin f cases f an illness, specific healthrelated behavir, r ther health-related event clearly in excess f nrmal expectancy. Bth terms are used interchangeably; hwever, epidemic usually refers t a larger gegraphic distributin f illness r health-related events. health utcme: result f a medical cnditin that directly affects the length r quality f a persn s life. 3

4 Health Determinants Genes and bilgy Health behavirs Scial and scietal characteristics Access t and use f health services and medical care (frm CDC-Public Health 101 Series) This chart is an estimate f hw these fur majr determinants influence health at the ppulatin level. Trillins f dllars are spent n health care, yet it nly determines abut 25% f ur health. The remaining 75% f what determines ur health as a ppulatin is ur ttal envirnment r eclgy, including the scial envirnment in which we live, plus ur health behavirs and t a lesser extent, ur genes and bilgy. An example f the rle these determinants play in ur daily lives is thrugh nutritin and physical activity. Bth are essential elements in prducing ptimal health and shuld be viewed in the cntext f such envirnmental factrs as scial and cultural nrms that influence fd chices and physical activity, envirnmental characteristics, such as availability (lack f healthy fd, pen space fr exercise, r safety in urban neighbrhds), and sectr influences, such as the marketing f prcessed fd. All f these factrs influence ur individual chices, which in turn, influence ur verall health. 4

5 (frm CDC-Public Health 101 Series) Majr Types f Public Health Issues in the US The CDC s Preventin Status Reprt lists the 10 mst imprtant public health prblems and cncerns are (listed alphabetically): Alchl-related harms Fd safety Healthcare-assciated infectins Heart disease and strke HIV Mtr vehicle injury Nutritin, physical activity and besity Prescriptin drug verdse Teen pregnancy Tbacc use Health Impact Pyramid Frieden TR. Framewrk fr public health actin: the health impact pyramid. Am J Public Health 2010;100:

6 Epidemilgy and Its Rle in Public Health Epidemilgy the disease detectives wh wrk t slve public health issues Definitin-the study f the distributin and determinants f health-related states r events in specified ppulatins, and the applicatin f this study t the cntrl f health prblem Purpses f Epidemilgy in Public Health Practice Determine the agent, hst, and envirnmental factrs that affect health Determine the relative imprtance f causes f illness, disability, and death Identify thse segments f the ppulatin that have the greatest risk frm specific causes f ill health Evaluate the effectiveness f health prgrams and services in imprving ppulatin health Types f disease agents bilgic, physical, and chemical Steps in Slving Health Prblems Step 1-Cllect Data Surveillance, determine Time/Place/Persn triad Step 2- Assessment- Inference Step 3- Hypthesis testing Determine hw and why Step 4- Actin-Interventin Descriptive Epidemilgy invlves identifying t the time, place, and the persn invlved in the nset f the healthrelated event. Analytical Epidemilgy is mainly cncerned with finding the causes f the health-related event and t identify the interventins f the health prblem. Descriptive vs Analytical Epidemilgy CDC - Public Health 101 Series Descriptive Epidemilgy refers t the studies that generate hyptheses and answer the questins wh, what, when and where f the disease r infectin. Analytic Epidemilgy refers t the studies that are cnducted t test fr hyptheses and t generate cnclusins n the particular disease. Hypthesis Descriptive epidemilgy is able t generate a hypthesis. Analytic epidemilgy is able t cnduct a test fr the hypthesis. Interventins Interventin studies are nt perfrmed in descriptive epidemilgy. Interventins are analyzed in analytic epidemilgy. 6

7 CDC - Public Health 101 Series In an Experimental Study, the investigatrs can cntrl certain factrs within the study frm the beginning. An example f this type is a vaccine efficacy trial that might be cnducted by the Natinal Institutes f Health. In such a trial, the investigatrs randmly cntrl wh receives the test vaccine and wh des nt amng a limited grup f participants; they then bserve the utcme t determine if it shuld t be used mre widely. In an Observatinal Study, the epidemilgist des nt cntrl the circumstances. These studies can be further subdivided int descriptive and analytic. In a Descriptive Study, the epidemilgist cllects infrmatin that characterizes and summarizes the health event r prblem. In the Analytic Study, the epidemilgist relies n cmparisns between different grups t determine the rle f different causative cnditins r risk factrs. 7

8 Basic Epidemilgy Terms Disease Frequency Endemic disease r cnditin present amng a ppulatin at all times Outbreak (lcalized epidemic) mre cases f a particular disease than expected in a given area r amng a specialized grup f peple ver a particular perid f time. Epidemic large numbers f peple ver a wide gegraphic area affected. Pandemic -An epidemic ccurring ver a very wide area (several cuntries r cntinents) and usually affecting a large prprtin f the ppulatin. Cluster an aggregatin f cases ver a particular perid esp. cancer & birth defects clsely gruped in time and space regardless f whether the number is mre than the expected number. (ften the expected number f cases is nt knwn.) Spradic a disease that ccurs infrequently and irregularly risk - The prbability that an individual will be affected by, r die frm, an illness r injury within a stated time r age span. rate number f cases ccurring during a specific perid; always dependent n the size f the ppulatin during that perid. rati value btained by dividing ne quantity by anther a rati ften cmpares tw rates. prprtin the cmparisn f a part t the whle as the number f cases divided by the ttal ppulatin des nt have a time dimensin, It can be expressed as a decimal, a fractin, r a percentage. Symbitic Relatinships between rganisms: Nrmal flra Many micrbes have a psitive symbitic relatinship with ther rganisms. Mutualism bth rganisms benefit. Cmmensalism ne rganisms and the ther is nt harmed r helped. Parasitism is the cnditin (ne rganism is helped and the ther is harmed) which takes place when humans are invaded by infectius micrbes. A parasite-hst relatinship is created. The parasite is ften called the infectius agent. 8

9 (CDC Self-Study Curse SS1978 Lessn 1) Natural Histry and Spectrum f Disease Natural histry f disease refers t the prgressin f a disease prcess in an individual ver time, in the absence f treatment. Many, if nt mst, diseases have a characteristic natural histry, althugh the time frame and specific manifestatins f disease may vary frm individual t individual and are influenced by preventive and therapeutic measures. Natural Histry f Disease Timeline Timeline shws state f susceptibility, expsure, subclinical disease in which pathlgic changes takes place, nset f symptms, fllwed by usual time f diagnsis, clinical disease, fllwed by recvery, disability, r death. The prcess begins with the apprpriate expsure t r accumulatin f factrs sufficient fr the disease prcess t begin in a susceptible hst. Fr an infectius disease, the expsure is a micrrganism. Fr cancer, the expsure may be a factr that initiates the prcess, such as asbests fibers r cmpnents in tbacc smke (fr lung cancer), r ne that prmtes the prcess, such as estrgen (fr endmetrial cancer). After the disease prcess has been triggered, pathlgical changes then ccur withut the individual being aware f them. This stage f subclinical disease, extending frm the time f expsure t nset f disease symptms, is usually called the incubatin perid fr infectius diseases, and the latency perid fr chrnic diseases. During this stage, disease is said t be asymptmatic (n symptms) r inapparent. This perid may be as brief as secnds fr hypersensitivity and txic reactins t as lng as decades fr certain chrnic diseases. Even fr a single disease, the characteristic incubatin perid has a range. Fr example, the typical incubatin perid fr hepatitis A is as lng as 7 weeks. The latency perid fr leukemia t becme evident amng survivrs f the atmic bmb blast in Hirshima ranged frm 2 t 12 years, peaking at 6 7 years. 9

10 MECHANISM OF DISEASE CHAIN OF INFECTION The diagram abve is a mdel used t understand the infectin prcess. Each link in the chain must be present and in the crrect sequential rder fr an infectin t ccur. 1. Agent - a micrbial rganism with the ability t cause disease 2. Reservir - a place where agents can thrive and reprduce 3. Prtal f exit - a place f exit prviding a way fr an agent t leave the reservir 4. Mde f transmissin - methd f transfer by which the rganism mves r is carried frm ne place t anther 5. Prtal f Entry - an pening allwing the micrrganism t enter the hst 6. Susceptible hst a persn wh cannt resist an micrrganism invading the bdy, multiplying and resulting in infectin 10

11 CHARACTERISTICS OF THE ELEMENTS vectr - an animate intermediary in the indirect transmissin f an agent that carries the agent frm a reservir t a susceptible hst. An rganism that transmits the infectin as a msquit transmits the malaria prtzans. fmite - a physical bject that serves t transmit an infectius agent frm persn t persn. A cmb infested with ne r mre head lice wuld be a fmite r the dust particles cntaining infectius cld virus that remain after drplets f infected saliva are cughed int the air. znsis - An infectius disease that is transmissible frm animals t humans. Micrbes which can be infectius agents include bacteria, viruses, fungi, prtza, algae, parasitic wrms, and ther pathgenic agents as prins. Persns mre vulnerable t becming susceptible hsts include the yung, the elderly, and peple with weakened immune systems. Envirnments which bring the agent and hst tgether might invlve such things as cntaminated fd that is ingested, an envirnment that allw a vectr t intrduce the agent int the hst as a msquit bite, air that allw an agent t be inhaled by a hst r agents spread by cntact between tw peple. Smetimes there are rganisms as insects, arthrpds, r even mammals as dgs r bats wh can act as vectrs (rganisms wh allw the infecting agent t thrive, reprduce, and then act as the mde f transmissin) Infectius dse - the amunt f pathgen (measured in number f micrrganisms) required t cause an infectin in the hst. Usually it varies accrding t the pathgenic agent and the cnsumer's age and verall health. Perid f cmmunicability - the perid when yu are infectius and can spread yur germs (whether bacteria, viruses, r parasites) t an uninfected persn CONDITIONS WITHIN THE HOST Cntaminatin when a ptentially infectius agent exists in the hst but has nt yet in invaded the tissues f the hst. The micrbe may be destryed by the bdy defenses r it may becme part f the nrmal flra. Infectin when the infectius agent begins its invasin f the hst tissue and its rapid multiplicatin. The infectin may be lcalized r it may spread t alternative sites as deeper rgans r tissues becming systemic Disease when the cumulative effects f the infectin cause damage in the tissues Three terms are used t describe an infectius disease accrding t the varius utcmes that may ccur after expsure t its causative agent. Infectivity refers t the prprtin f expsed persns wh becme infected. Pathgenicity refers t the prprtin f infected persns wh develp clinical disease. Virulence refers t the prprtin f persns with clinical disease wh becme severely ill r die. Terms used t describe the health issue. Incidence: rate f ccurrence f an event; number f new cases f disease ccurring ver a specified perid f time; may be expressed per a knwn ppulatin size Prevalence: number f cases f disease ccurring within a ppulatin at any ne given pint in time 11

12 Surveillance The nging, systematic cllectin, analysis, and interpretatin f health-related data essential t planning, implementatin, and evaluatin f public health practice, clsely integrated with the timely disseminatin f these data t thse respnsible fr preventin and cntrl Gal f Public Health Surveillance Prvide infrmatin that can be used fr health actin by public health persnnel, gvernment leaders, and the public t guide public health plicy and prgrams Purpses f Surveillance Assess public health status Define public health pririties Evaluate prgrams Stimulate research Cllabratin Partners 911 systems Agriculture Ambulance services Emergency management Federal agencies Health care prviders Hspitals Industry Law enfrcement agencies Medical examiners Nurse htlines Pharmaceutical agencies Pisn cntrl centers Schls State and lcal public health agencies Urgent care and emergency departments Veterinarians Uses f surveillance Identify patients and their cntacts fr treatment and interventin Detect epidemics and ther health prblems Estimate magnitude and scpe f a health prblem Measure trends and characterize diseases Detect changes in health practices Mnitr changes in infectius and envirnmental agents Assess effectiveness f prgrams and cntrl measures Develp hyptheses and stimulate research 12

13 Public Health Surveillance Prcess 5 Step Prcess 1. Data Cllectin Reprted diseases r syndrmes Electrnic health recrds (e.g., hspital discharge data) Vital recrds (e.g., birth and death certificates) Registries (e.g., cancer, immunizatin) Surveys (e.g., Natinal Health and Nutritin Examinatin Survey [NHANES]) 2. Data Analysis Data analysis by place is the usual methd used t examine reprts either by where the case was reprted r, ideally, by where the illnesses ccurred. Data analysis by lcatin allws preventin resurces t be directed t where the expsure ccurred. 3. Data Interpretatin Data Interpretatin is clsely cupled with data analysis. By identifying the persn, place, and time, ne can mre easily determine hw and why the health event happened 4. Data Disseminatin Data disseminatin describes hw t distribute infrmatin t thse wh need t knw. Methds f distributin include health agency newsletters, bulletins, r alerts surveillance summaries and reprts medical and epidemilgic jurnal articles press releases and scial media Target audiences can include public health practitiners clinicians and ther health care prviders plicy and ther decisin makers cmmunity rganizatins the general public 5. Link t Actin - withut actin, the cllected data serve n real purpse. 13

14 Types f Surveillance Passive Surveillance - diseases are reprted t health care prviders - simple and inexpensive - limited by incmpleteness f reprting and variability f quality - example- a physician sees a patient, diagnses measles, and then initiates a case reprt by cntacting the lcal health department and prviding the details as required fr a case f measles. the lcal health department relies n the physician t reprt the case. Active Surveillance - health agencies cntact health prviders seeking reprts - ensures mre cmplete reprting f cnditins - used in cnjunctin with specific epidemilgic investigatin - are mst apprpriate fr epidemics r where a disease has been targeted fr eliminatin - Example-if a health department receives a case reprt fr measles, a serius vaccine-preventable disease, active surveillance will be triggered. Public health practitiners will actively search fr ther cases, using a standard case definitin: calling dctrs' ffices fr any cases, fllwing up t find additinal cases amng thse expsed, checking labratries. Sentinel - Reprting f health events by health prfessinals wh are selected t represent a gegraphic area r a specific reprting grup - Is used when high-quality data are needed abut a particular disease that cannt be btained thrugh a passive system - Can be active r passive - Mnitring trends r key health indicatrs - Invlves nly a limited netwrk f carefully selected reprting sites - Data cllected in a well-designed sentinel system can be used t signal trends, identify utbreaks and mnitr the burden f disease in a cmmunity, prviding a rapid, ecnmical alternative t ther surveillance methds. - Because sentinel surveillance is cnducted nly in selected lcatins, hwever, it may nt be as effective fr detecting rare diseases r diseases that ccur utside the catchment areas f the sentinel sites. - The sentinel may be a disease, an event. r a ppulatin - Example, a netwrk f large hspitals might be used t cllect high-quality data n varius diseases and their causative rganisms, such as invasive bacterial disease caused by Haemphilus influenzae type b, meningcccus r pneumcccus. 14

15 Syndrmic Surveillence - Fcuses n ne r mre symptms rather than a physician-diagnsed r labratry-cnfirmed disease - Is the analysis f medical data t detect r anticipate disease utbreaks - Has been histrically used t target the investigatin f ptential cases - Its use fr detecting utbreaks assciated with biterrrism is increasingly being explred by public health fficials - Example: Influenza utbreak Using a nrmal influenza utbreak as an example, nce the utbreak begins t affect the ppulatin, sme peple may call in sick fr wrk/schl, thers may visit their drug stre and purchase medicine ver the cunter, thers will visit their dctr's ffice and ther's may have symptms severe enugh that they call the emergency telephne number r g t an emergency department. Syndrmic surveillance systems mnitr data frm schl absenteeism lgs, emergency call systems, hspitals' ver-the-cunter drug sale recrds, Internet searches, and ther data surces t detect unusual patterns. When a spike in activity is seen in any f the mnitred systems disease epidemilgists and public health prfessinals are alerted that there may be an issue. 15