MEDICINE AND PHARMACY FACULTY UNIVERSITY OF ORADEA EPIDEMIOLOGY By CONSTANTA TURDA, M.D.

History of Epidemiology

Hippocrates ( B.C.) On Airs, Waters, and Places Idea that disease might be associated with physical environment

Thomas Sydenham ( ) Recognized as a founder of clinical medicine and epidemiology Emphasized detailed observations of patients & accurate recordkeeping

James Lind (1700’s) Designed first experiments to use a concurrently treated control group

Edward Jenner ( ) Pioneered clinical trials for vaccination to control spread of smallpox Jenner's work influenced many others, including Louis Pasteur who developed vaccines against rabies and other infectious diseases

Ignas Semmelweis (1840’s) Pioneered handwashing to help prevent the spread of septic infections in mothers following birth

John Snow ( ) Father of epidemiology Careful mapping of cholera cases in East London during cholera epidemic of 1854 Traced source to a single well on Broad Street that had been contaminated by sewage

History of Epidemiology (Cont’d) Vital Statistics John Graunt ( ) William Farr ( ) Occupational medicine & Industrial Hygiene Bernardino Ramazzini ( ) Role of carriers in transmission Typhoid Mary & George Soper

Mary Mallon, a cook responsible for most famous outbreaks of carrier-borne disease in medical history Recognized as carrier during 1904 N.Y. typhoid fever epidemic When source of disease was traced, Mary had disappeared only to resurface in 1907 when more cases occurred Again Mary fled, but authorities led by George Soper, caught her and had her quarantined on an island In 1910 the health department released her on condition that she never accept employment involving the handling of food Four years later, Soper began looking for Mary again when two new epidemics broke out; Mary had worked as a cook at both places She was found and returned to North Brother Island, where she remained the rest of her life until a paralytic stroke in 1932 led to her slow death, six years later

Typhoid Mary

U.S. History of Epidemiology Lemuel Shattuck (1850) Proposed creation of a permanent statewide public health infrastructure Recommended establishing state & local health offices to gather statistical information on public health conditions Quarantine Commissions (1857) 1st Public Health Book (1879) U.S. Public Health Service founded (1902) Pure Food and Drug Act (1906) Pasteurization of milk (1913) 1st School of Public Health (1913)

Historic Aspects of the Development of Morbidity Statistics in the U.S. Edgar Sydenstricker (Early 1900’s) Pioneer public health statistician Three notable studies: Tuskegee syphilis study ( ) Framingham heart study (1948-present) Epidemiology of cigarette smoking (1950’s - present)

Modern History of Epidemiology in the U.S. Mortality stats in first half of century Unstable because of outbreaks of infection Stats reversed by 1950’s because of childhood immunizations, medical interventions and public health measures Economic growth reduced squalor Introduction of antibiotics in 50’s

Wake-up Calls Over-optimism in 60’s and 70’s AIDS recognized Cholera in the southern hemisphere Legionnaire’s disease New forms of hepatitis Chlamydia and heart disease Hospital acquired infections Antibiotic resistance

U.S.Mortality Index (annual deaths/100,000) Mid-century

Future Challenges Instant global transmission of pathogens Population overcrowding Ease of travel Importation of foods

DEFINITIONS What is epidemiology? What is an epidemiologist?

EPIDEMIOLOGY is the study of the nature, cause, control and determinants of the frequency and distribution of disease, disability, and death in human populations. Epidemiology: the study of factors influencing the occurence, transmission, distribution, prevention and control of disease in a defined population

An EPIDEMIOLOGIST is a public health scientist, who is responsible for carrying out all useful and effective activities needed for successful epidemiology practice

Methods of Epidemiology Public Health Surveillance Disease Investigation Analytic Studies Program Evaluation

Terminology Endemic Hyperendemic Holoendemic Epidemic Pandemic Epizootic Incidence Prevalence Terms used for reference to various forms of outbreaks

Endemic: a disease or pathogen present or usually prevalent in a given population or geographic region at all timesprevalent Hyperendemic: equally endemic in all age groups of a populationendemic Holoendemic: endemic in most of the children in a population, with the adults in the same population being less often affectedendemic Epidemic: a disease occuring suddenly in numbers far exceeding those attributable to endemic disease; occuring suddenly in numbers clearly in access of normal expectancyendemic Pandemic: a widespread epidemic distributed or occuring widely throughout a region, country, continent, or globally Epizootic: of, or related to a rapidly spreading and widely diffused disease affecting large numbers of animals in a given region

Incidence: rate of occurrence of an event; number of new cases of disease occuring over a specified period of time; may be expressed per a known population size Prevalence: number of cases of disease occurring within a population at any one given point in timedisease

Terms Associated with Disease Causation, etc. Host Agent Environment Fomites Vector Carrier – active Incubatory Convalescent Healthy Intermittent Your Assignment: Define these terms

Changing Patterns of Community Health Health patterns in constant state of flux Infectious versus chronic diseases Population and age-related

Chain of Infection Etiological agent Source/Reservoir Portal of exit Mode of transmission Portal of entry Susceptible host

Viruses RNA–DNA RNA viruses genetically unstable Lipid enveloped–nonenveloped Solvent-detergent treatments virucidal only for enveloped viruses Bacteria Gram-positive–gram-negativeAntibiotic sensitivity differs Diagnostic and therapeutic uses of gram-negative capsule Fungi Disseminated vs. superficial Mold vs. biphasic Parasites Complete cycle Larval migrans Prions Pathogenesis unclear Resistant to disinfection Classification of Microorganisms

A Clinician’s View Diseases classified according to signs and symptoms: 1. Diarrheal diseases 2. Respiratory diseases 3. Cutaneous/soft tissue infection 4. CNS diseases 5. Septicemic diseases 6. Fever of undetermined origin

Modes of Transmission Contact transmission Vehicle transmission Vector transmission

An Epidemiologist’s View Means of Spread of Infectious Diseases Contact Direct IndirectFomites Body secretions (blood, urine, saliva, etc.) Vector Airborne Small-particle aerosol

Some Infectious Diseases Spread by Contact Salmonellosis 2. Campylobacter 3. Shigellosis 4. Clostridium perfringens food poisoning 5. Staphylococcal enterotoxin food poisoning 6. Cholera 7. Giardiasis 8. Listeriosis

Salmonellosis 2. Campylobacter 3. Shigellosis 4. Clostridium perfringens food poisoning 5. Staphylococcal enterotoxin food poisoning 6. Cholera 7. Giardiasis 8. Listeriosis Some Important Food- and Waterborne Infections

Some Important Airborne Infections 1. Tuberculosis 2. Influenza 3. Childhood Infections − Measles, mumps, rubella, pertussis 4. Parainfluenza 5. RSV 6. Legionella

1. Malaria 2. Viral encephalitis − SLE, WEE, EE, VE, California virus 3. Schistosomiasis 4. Tularemia 5. Dengue 6. Yellow fever 7. Rocky Mountain spotted fever 8. Leishmaniasis 9. Trypanosomiasis Some Important Vectorborne Infections

1. Human 2. Animal (zoonoses) 3. Soil 4. Water Reservoirs of Infectious Diseases

Some Infectious Diseases with a Human Reservoir 1. AIDS (HIV infection) 2. Syphilis 3. Gonorrhea 4. Shigellosis 5. Typhoid fever 6. Hepatitis-B virus 7. Herpes simplex virus

Some Diseases with an Animal Reservoir (Zoonoses) 1. Nontyphoidal salmonellosis 2. Brucellosis 3. Anthrax 4. Listeriosis 5. Viral encephalitis (SLE,WEE, CEE) 6. Rabies 7. Plague

Some Important Diseases with a Soil Reservoir 1. Histoplasmosis 2. Coccidioidomycosis 3. Blastomycosis 4. Tetanus 5. Botulism

Some Infectious Diseases with a Water Reservoir 1. Pseudomonas infections − Sepsis, UTI, “hot tub” folliculitis 2. Legionnaires’ disease 3. Melioidosis

Sexually transmitted diseases − Syphilis, gonorrhea, chlamydia, AIDS 2. Staphylococcal infections 3. Streptococcal infections 4. Many nosocomial infections 5. Rhinovirus colds 6. Brucellosis (slaughter house contact) 7. Hepatitis B virus infection Some Infectious Diseases Spread by Contact

Classes of Epidemics Common source (vs. sporadic) Point source Intermittent Continuous Propagated Your Assignment: Define these terms & identify which apply to the following three graphs

1. Infectivity − The propensity for transmission − Measured by the secondary attack rate in a household, school, etc. 2. Pathogenicity − The propensity for an agent to cause disease or clinical symptoms − Measured by the apparent : inapparent infection ratio 3. Virulence − The propensity for an agent to cause severe disease − Measured by the case fatality ratio Infectious Agents: 3 Important Epidemiologic Properties

Incubation period = The period between exposure to the agent and onset of infection (with symptoms or signs of infection) Secondary attack rates = The rates of infection among exposed susceptibles after exposure to an index case, such as in a household or school

Inapparent(or subclinical infection)− An infection with no clinical symptoms, usually diagnosed by serological (antibody) response or culture Immunity− The capacity of a person when exposed to an infectious agent to remain free of infection or clinical illness Herd immunity− The immunity of a group or community. The resistance of a group to invasion and spread of an infectious agent, based upon the resistance to infection of a high proportion of individual members of the group. The resistance is a product of the number of susceptibles and the probability that those who are susceptible will come into contact with an infected person. Definitions of Some Relevant Terms (cont.)

Persistent infection− A chronic infection with continued low-grade survival and multiplication of the agent Latent infection− An infection with no active multiplication of the agent, as when viral nucleic acid is integrated into the nucleus of a cell as a provirus. In contrast to a persistent infection, only the genetic message is present in the host, not viable organisms. Definitions of Some Relevant Terms (cont.)

Disease Investigation Establish diagnosis Identify specific agent Describe according to person, place and time Identify source of agent Identify mode of transmission Identify susceptible populations

Epidemiology and Clinical Practice Clinical practice dependent on epidemiology Epidemiology defines natural history of disease Even descriptive information is useful

The Epidemiologic Approach Multistep process First - determine association Then prove causation Not all associations are causal Examine validity, false assumptions- e.g. - fluoride in water

Analytic Studies Type of study Design Analysis of data

Epidemiology and Prevention Identify high risk populations Modify risks Prevent exposures

Levels of Prevention Primary Secondary Tertiary

Levels of Prevention (cont’d) Primary Involves halting any occurrence of a disease or disorder before it happens

Levels of Prevention (cont’d) Secondary Health screening and detection activities

Levels of Prevention (cont’d) Tertiary Retard or block the progression of condition