1 Environmental Health and Safety (ENVR3504) Introduction to Epidemiology Miss D. Brooks

2 Epidemiology  Greek roots: epi = upon, among; demos = people, district; logos = study, word, discourse;  Epidemiology, "the study of what is upon the people“

3 Disease  Disease: is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs; has a known specific cause or causes (called its etiology).  A syndrome, is a collection of signs or symptoms that occur together.

4 Epidemiology  A Science: Study of factors determining and influencing the frequency and distribution of disease (determinants of disease), disability and death in human populations  A Scientific Method: An investigative method used to detect the sources and determinants of health problems

5 The Father of Epidemiology  Hippocrates (5 th century B.C.)- a Greek physician Examined the relationships between the occurrence of disease and environmental influences

6 Purpose of Epidemiology  Explains the etiology of health conditons To provide a basis for developing: Control measures Prevention measures Public measures and practices i.e. to control disease and its spread

7 Disease Management

8 Purpose of Epidemiology cont’d  Principles of Disease Control:  Prevention: Halting occurrence of disease before the onset.  Treatment: Remedial action started once disease is contracted.

9 Purpose of Epidemiology cont’d  Principles of Disease Control cont’d  Surveillance: Ongoing systematic collection, collation, analysis and interpretation of data on disease occurrence Dissemination of information so that action may be taken

10 Role of WHO in Disease Control  World Health Organization (WHO) Organized in 1948 Over 160 member states Facilitates international cooperation in all aspects of health.  emphasis on prevention Trains personnel, support the collection of vital statistics of populations:  Death and birth rates  Morbidity (illness whether fatal or not)  Mortality (deaths and causes of deaths)

11 Health vs. Disease

12 Factors Affecting Health and Disease

13 Basic Factors Influencing Disease  Disease Determinants among populations: Age Sex Occupation Environment Living conditions Geography Factors related to agents

14 Types of Diseases  Infectious disease An infectious disease, as opposed to a noninfectious disease, is a disease that involves pathogen infection; any disease caused by a pathogen is an infectious disease; any disease not caused by a pathogen is a non-infectious disease.  Communicable disease An infectious disease that may be passed from individual to individual (particularly when all individuals involved are of the same species)  Noncommunicable disease An infectious disease that is not spread from individual to individual but instead is acquired from an inanimate object or other species (zoonoses)  Contagious disease A communicable diseases that is easily passed from individual to individual is said to be contagious

15 Patterns of Spread of Infectious Disease  Endemic: Always present in small amounts in an area  Epidemic: Outbreak- spreads rapidly within a group or geographical area New cases exceed usual prevalence.  Pandemic: Disease is widespread across a country, continent, or worldwide.

16 Infectious Diseases  Basic natural history of infectious diseases: Exposure Microbial Invasion 1 st line (primary) defence

17 Basic Natural History of Infectious Diseases cont’d 2 nd line defence- Immune System Infection Transmission

18 Transmission Routes  Usually related to habitats of organism in the body. E.g., respiratory tract pathogens usually spread through air, GI tract pathogens spread by contaminated water.  Direct person-to-person contact with the skin or bodily fluids of a diseased person. Examples are dysentery, boils, and several airborne diseases  Fecal-oral transmission is the usual route of transmission of enteric diseases.Infectious agents present in stools of infected persons are transmitted to uninfected persons through contaminated food or water that is ingested by mouth. Examples are cholera, typhoid, dysentery, botulism, staphylococcal food poisoning, polio, hepatitis A and E, polio, and amebiasis.  Indirectly through the air - airbourne or droplet infection (sneezes, tobacco smoke, coughs, dust). –. Examples are colds, influenza, measles, mumps, chicken pox, and pneumonia. 

19 Transmission Routes  Mucus-to-mucus contact by kissing or sexual intercourse. Examples include sexually transmitted diseases (STDs), infectious mononucleosis, and hepatitis B.   Direct contact with the skin, flesh (raw or not thoroughly cooked), saliva, or other bodily fluids of domestic or wild animals. Examples are rabies, plague, anthrax, tularemia, and trichinosis.   Indirectly through inanimate fomites (objects). Examples are staphylococcal infection, streptococcal infection, colds, hospital-acquired wound infections through use of improperly sterilized items.  Blood contamination indirectly by arthropod vectors. Examples are malaria, typhus, plague, African sleeping sickness, encephalitis, yellow fever, and dengue fever.

20 Epidemiology Triangle  A model showing relationships among key factors involved in the spread of disease:

21 Epidemiology Triangle Epidemiology Triangle has three corners (called vertices):  Agent, the organism or substance that causes the disease (the “what” of the Triangle)  Host, or organism harbouring the disease (the “who” of the Triangle)  • Environment, or those external factors that cause or allow disease transmission (the “where” of the Triangle)

22 Agent  Time  In the center of the Triangle is time. Most infectious diseases have an incubation period— the time between when the host is infected and when disease symptoms occur.  Or, time may describe the duration of the illness or the amount of time a person can be sick before death or recovery occurs. Time also describes the period from an infection to the threshold of an epidemic for a population.

23 The Triangle of Epidemiology

24 Controlling Epidemics  Airborne diseases block spread with aerosols isolate patients with contagious diseases wear masks (common in Japan)  Arthropod-transmitted diseases control vector populations by insect control measures  Direct Contact diseases wash hands frequently minimize contact use condoms to prevent STD

25 Controlling Epidemics cont’d  Food and Waterborne diseases sanitation: sewage treatment and water disinfection (e.g. chlorine) careful food preservation  Wounds and Cuts antisepsis: cleaning with soap and water; topical antiseptics careful surgical procedures; use of antibiotics  Reducing or eliminating reservoirs If reservoir is domestic animals, this is attainable. E.g. bovine tuberculosis has been essentially eliminated.

26 Controlling Epidemics cont’d  Breaking the transmission route Public health measures are effective in controlling food- and waterborne diseases. Respiratory transmission difficult to control. In Japan, face masks are worn by many people with respiratory disease. Good, but need major changes in social behavior for this to be accepted and useful.  Reducing the number of susceptible individuals Vaccinations have been enormously successful for many diseases. Ex: measles, polio, diphtheria no longer significant diseases because of immunization programs. Only major source of continued disease is immigrants; still screen immigrants for contagious diseases (e.g. TB)

27 Controlling Epidemics cont’d  Quarantine  Seven diseases are so serious that infected individuals may be quarantined by international agreement until no longer no longer infectious:  smallpox  cholera  plague,  yellow fever  typhoid fever  relapsing fever  SARS (Severe Acute Respiratory Syndrome)