Transcript Lecture 2 Introduction, Part II
MEDICINE AND PHARMACY FACULTY UNIVERSITY OF ORADEA
EPIDEMIOLOGY
By CONSTANTA TURDA, M.D.
History of Epidemiology
Hippocrates
(460-377 B.C.)
On Airs, Waters, and Places
Idea that disease might be associated with physical environment
Thomas Sydenham
(1624-1689)
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
(1749-1823)
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
(1813-1858)
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 (1620-1674)
William Farr (1807-1883) Occupational medicine & Industrial Hygiene
Bernardino Ramazzini (1633-1714) Role of carriers in transmission
Typhoid Mary & George Soper
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 her and had her quarantined on an island , caught 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 (1932-1970)
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)
• • • •
1900 - 500 1918-1919- 850 Mid-century-1982 - 30 1982-1994 - 60
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 times Hyperendemic: population equally endemic in all age groups of a Holoendemic: endemic in most of the children in a population, with the adults in the same population being less often affected Epidemic: a disease occuring suddenly in numbers far exceeding those attributable to endemic disease; occuring suddenly in numbers clearly in access of normal expectancy 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 time
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
• • • • • Classification of Microorganisms Viruses
•RNA–DNA • RNA viruses genetically unstable •Lipid enveloped–nonenveloped • Solvent-detergent treatments virucidal only for enveloped viruses
• • • Bacteria
•Gram-positive–gram-negative•Antibiotic sensitivity differs • Diagnostic and therapeutic uses of gram-negative capsule
• Fungi
•Disseminated vs. superficial •Mold vs. biphasic
• • • Parasites
•Complete cycle •Larval migrans
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
• •
•Indirect•Fomites • 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
Some Important Food- and Waterborne Infections
• • • • • • • •
Salmonellosis 2. Campylobacter 3. Shigellosis 4. Clostridium perfringens food poisoning 5. Staphylococcal enterotoxin food poisoning 6. Cholera 7. Giardiasis 8. Listeriosis
Some Important Airborne Infections • • •
1. Tuberculosis 2. Influenza 3. Childhood Infections
− Measles, mumps, rubella, pertussis
• • •
4. Parainfluenza 5. RSV 6. Legionella
• • Some Important Vectorborne Infections
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
Reservoirs of Infectious Diseases • • • •
1. Human 2. Animal (zoonoses) 3. Soil 4. Water
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
Some Infectious Diseases Spread by Contact • • • • • • •
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
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
Infectious Agents: 3 Important Epidemiologic Properties •
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
Definitions of Some Relevant Terms (cont.)
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.
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