Epidemiology

1. Epidemiology Kathy Huschle Northland Community and Technical College

2. Epidemiology The science of epidemiology is the study of the transmission, incidence, and frequency of disease. Handwashing, food preparation and other such concepts demonstrate our current understanding of epidemiology. Image illustrating bacteria found on hands

3. Terminology of Epidemiology • rate of disease • % of population infected • endemic • a disease that is constant in particular area • number of cases and severity are insufficient • common cold is an endemic disease Endemic goiters in Bolivia

4. Terminology of Epidemiology • epidemic • high incidence in population • death rate or potential harm is high • can be caused by endemic diseases or disease not normally found in the population SARS epidemic

5. Terminology of Epidemiology • pandemic • epidemic spreads worldwide • AIDS is pandemic on the planet • morbidity • the incidence of a disease • mortality • % of the population that dies due to disease 1918 Flu Pandemic

6. Terminology of Epidemiology • communicable or contagious diseases • pathogen is transmitted from one host to another • noncommunicable diseases • pathogen is acquired from the environment or the normal flora of an individual

7. Communicable Diseases • certain events must occur for a disease to spread • habitat or reservoir suitable for the pathogen has to be available • portal of exit for the pathogen to leave the reservoir • portal of entrance for the pathogen to enter the next host

8. Communicable Diseases: Reservoirs • for a disease to perpetuate itself, there must be a continual source of the disease pathogen • this continual source is called a reservoir, the natural habitat that the organism is found in; this may include • human • animal (domestic and wild) • water • soil

9. Human Reservoirs • humans are the principle living reservoir of human disease, sometimes the only reservoir • symptomatic “reservoirs” • obvious source of the infectious agent • asymptomatic “reservoirs” • a person with no obvious symptoms of the disease • many of the STD’s are transmitted by asymptomatic carriers

10. Animal Reservoirs • diseases that occur in domestic and wild animals and can be transmitted to humans are called zoonoses • nearly 150 of these disease exist: including • rabies • lymes disease • plaque • cat-scratch disease Flea carrying plague Tick carrying Lymes Rabid dog

11. Animal Reservoirs Cat scratch disease Rabies Lymes Disease

12. Animal Reservoirs • transmission routes of zoonoses can occur through • direct contact such as a bite • contamination with infected pet waste • air contaminated from hides, fur, feathers • insect vectors • consuming infected animal products Dog bite

13. Animal Reservoirs Click icon below to play the malaria games. Click on either “mosquito” or “parasite”.

14. Environmental Reservoirs • both soil and water can harbor pathogens • Clostridium and Bacillus genus are found in the soil • Vibrio and Giardia are found in water Bacillus anthrax Vibrio cholera Giardia Clostridium alderichii

15. Communicable Diseases: Portal of Exit • portal of exit • the mechanism that allows the pathogen to leave the reservoir • in the case of animals or humans this may involve a body orifice or the surface of the body along with the secretions, discharges and excretions

16. Portals of Exit • common portals of exit include • respiratory tract via coughing and sneezing • gastrointestinal tract via saliva and feces • genitourinary tract via secretions from the vagina or penis • insects and syringes provide a portal of exit for pathogens into the blood

17. Communicable Diseases:Portals of Entrance • portals of entrance • the mechanism which allows for the entry of a pathogen into the host: these may include • respiratory tract • pathogens are inhaled with droplets of moisture and on dust particles • most common portal of entry

18. Portals of Entry • genitourinary tract • once in the genitourinary tract, pathogens gain entry into the body through mucous membranes • gastrointestinal tract • pathogens enter via food, water and contaminated fingers

19. Portals of Entry • intact skin • impenetrable to microorganisms, but they can cross that barrier through hair follicles and sweat ducts • parenteral route • pathogens that gain access to tissues by inoculation through bites, injections, surgery, cracking skin, and other wounds • S. aureus is the most common pathogen due to it’s constant presence on the skin

20. Communicable Diseases:Routes of Transmission “portal of exit of the infected reservoir to the portal of entry of a new host” transmission routes include: contact food and water vectors

21. Route of Transmission: Contact • direct contact • also known as person-to-person transmission • involves physical contact with another person • includes • touching • kissing • sexual intercourse • many diseases spread with this mechanism include AIDS, mononucleosis

22. Route of Transmission: Contact • indirect contact • disease agent is transferred from it’s reservoir to the host via a non-living object called a fomite • common fomites include • tissue • cups • towels • toys • money

23. Route of Transmission: Contact • droplet transmission • pathogens are spread in droplet nuclei (mucus droplets) • only able to travel a short distance, generally less than 1 meter • droplets are discharged into the air by coughing, sneezing, laughing, talking • one sneeze may produce up to 20,000 droplets • important source of transmission in schools

24. Route of Transmission: Vehicle • vehicle transmission include transmission of pathogens by water, food, or air • water • usually spread by water contaminated with untreated or poorly treated sewage • sewage treatment plants ultimately dump their “treated” sewage back into the same waterways that provide drinking water for the community

25. Route of Transmission: Vehicle • food • microorganisms may be transmitted in foods that are inadequately cooked • or may be added during preparation under unsanitary conditions

26. Route of Transmission: Vehicle • air • involves droplets that are small enough to remain airborne longer than 1 m • viruses are common airborne organisms

27. Route of Transmission: Vectors • a vector is any animal that can carry a disease causing organism • most common vectors are insects • prevention of vector borne disease relies heavily on eradication of the vector

28. Influencing Factors to Epidemiology of Disease • dose • # of cells to produce enough damage to cause disease symptoms • this number varies with the mechanism of contact, and the route of entry • the gastrointestinal tract generally requires a large infectious dose, due the acidic environment found in the stomach

29. Influencing Factors to Epidemiology of Disease • incubation period • a long incubation can allow for the extensive spread of the disease before a person becomes symptomatic • without symptoms, most people don’t realize that they have even been exposed to a disease

30. Influencing Factors to Epidemiology of Disease • population characteristics may pre-dispose people to certain disease-causing agents • immunity • previous exposure will lessen the spread of a disease • general health • overcrowding, malnutrition, and fatigue all lend themselves to enhancing the spread of disease Water pollution in India

31. Influencing Factors to Epidemiology of Disease • age • young and old are more susceptible to disease • the young have a developing immune system, the old have an immune system that is wearing out • gender • some diseases are more likely to develop in different genders

32. Influencing Factors to Epidemiology of Disease • religious and cultural practices • for example, the eating of raw fish can increase the chance of parasitic disease • genetic background • may make some populations less susceptible to diseases

33. Epidemiology • epidemiology uses several methods to investigate a disease outbreak, in order to determine the causative agent, reservoir, and route of transmission • descriptive study • analytical study • experimental study

34. Epidemiology: Descriptive Study • process of collecting all data that describes the occurrence of the disease under study • person • place • time • the above information is used to compile a list of potential risk factors

35. Epidemiology: Descriptive Study • person • variables that include sex, age, gender, occupation, economic class may yield clues regarding risk factors involved in developing the disease This graph demonstrates the significant increase in the incidence of tetanus in age groups over 25. This increase is most likely due to the fact that are receiving the immunizations needed to protect from the disease. For children the tetanus vaccination is required for school.

36. Epidemiology: Descriptive Study • place • location of disease acquisition if known, assists in the identification of reservoirs and vectors

37. Epidemiology: Descriptive Study • time • rapid rise in numbers of people that become ill indicates exposure to a single common source of infection • gradual rise in infected people indicates that the disease is probably contagious, being transmitted from one person to another This graph demonstrates the number of cases of gastrointestinal diseases. Note the rapid rise during the summer months and think about picnics and food poisoning.

38. Epidemiology: Analytical Study • once the descriptive clues are determined, they are then analyzed to determine which of them are relevant risk factors • retrospective studies are done following the disease outbreak • compares actions and events of the individuals that developed the disease and looks for common factors • prospective studies look ahead, using the information gathered in the retrospective study, to predict any tendencies in future development of the disease

39. Epidemiology: Experimental Study • these studies are used to examine the effect of the relationship between the risk factors and the preventative factors • experimental studies assist in the evaluation of the effectiveness of treatment on preventing a disease

40. Surveillance of Infectious Disease • the diligent surveillance of disease across the world plays an important role in the prevention of disease worldwide • many organizations work together to bring about the successful control of disease • National Centers for Disease Control and Prevention (CDC) • Public Health Departments • World Health Organization (WHO)

41. National Center for Disease Control and Prevention: CDC • lead federal agency for protecting the health and safety of people at home and abroad • 8500 employees in 47 states and 45 countries • provides support for state, local, and private health agencies • serves as a collection point for information regarding diseases of public concern • be sure to look at the table on page 496 in your textbook regarding notifiable infectious diseases • these are disease that must be reported to the CDC for tracking

42. Public Health Departments • the mission of the public health departments throughout the United States is to protect, maintain and improve the health of the people • in addition to infection surveillance and control, public health departments; • collect and examine specimens • test water for the public • ensure that lab standards throughout the states are maintained • work closely with the CDC when necessary

43. World Health Organization: WHO • WHO is the United Nations specialized agency for health established in 1948 • it’s mission is “the attainment by all peoples of the highest possible level of health” • in this case health is defined as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity • WHO is governed by it’s 192 Member States WHO

44. World Health Organization: WHO • 4 main functions of WHO • provide worldwide health guidance • set global standards for health • strengthen national health programs • share health technology information worldwide

45. Disease Trends • reduction in bacterial and viral disease are primarily due to • improved sanitation • reservoir and vector control • vaccination • antibiotics The eradication of smallpox from the world in 1977 was due to the availability of vaccination.

46. Disease Trends • complete eradication of many diseases is hindered by • political upheaval in countries • many times vaccinations and antibiotic needed to control a disease never reach the people who need it, due to war or political unrest • the cost of control • complacency • often parents become lax about following up or even starting vaccinations in young children • the disease for which the vaccination is given is not prevalent so the thought is,” why bother?”

47. Emerging Diseases • emerging diseases are ones that have significantly increased in the past 2 decades • emerging diseases can be new diseases or diseases that have existed for years • microorganisms that cause these diseases are ones that can be very adept at taking advantage of changing circumstances, oftentimes allowing them to thrive and multiply

48. Emerging Diseases • several factors that can contribute to the emergence and/or reemergence of diseases include • microbial evolution • complacency • changes in human behavior • advances in technology • population expansion • development • distribution of food • war and civil unrest • climate change

49. Emerging Diseases • please be sure to look at figure 20.10 on page 498 in your text for more information on emerging diseases These diseases have presented themselves in approximately the last 20 years.

50. Nosocomial Infections • hospital, nursing home, or other health care facility acquired infections • common infections include • pneumonia • urinary tract infections • many infections are caused by the patients own flora • about 1/3 of these infections are preventable