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 STDs 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
Clostridium alderichii
Vibrio cholera
Giardia
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 DiseasesPortals 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 its
  constant presence on the skin

20
Communicable DiseasesRoutes 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 its 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 dont 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
• its 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 its 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

51
Nosocomial Infections

• reservoirs of infectious agents in hospitals can
  include
• other patients
• hospital environment, such as toilets,
  respirators
• health care workers
• in their concern for their job, often workers
  will report to work with mild cases of flu or
  cold
• in a hospital setting, most of the patients have
  impaired health, which means an impaired immune
  system, making them susceptible to even the
  mildest cases of illness

52
Nosocomial Infections

• patients own flora
• much of our own flora is opportunistic, taking
  advantage of any opportunity to enter the body,
  such as a needle stick from an IV

Bacteroide fragilis is an anaerobic bacteria
found as normal flora of the digestive system.
It is one of the most common opportunistic
infections from surgery.
53
Nosocomial Infections

• transmission of infectious agents in a hospital
  setting can include
• medical devices
• urinary catheters can introduce E.coli into the
  bladder causing urinary tract infections
• respirators have the potential to deliver
  microorganisms directly into the lungs

Endoscope
54
Nosocomial Infections

• health care workers
• great care must be taken, particularly when
  moving from patient to patient
• airborne
• generally controlled with design of air flow and
  high-efficiency particulate (HEPA) filters

55
Nosocomial Infections

• prevention of nosocomial infections begins with
  recognition of their existence
• then policies are established to prevent their
  development, which includes
• sterilization of equipment
• hand washing
• gloves, gowns, masks
• using aseptic techniques

56
Nosocomial Infections

• 5-15 of patients admitted to health care
  facilities develop nosocomial infections
• 2 million/year
• 100,000 of these patients die
• nosocomial infections are the 4th leading cause
  of death in the United States
• S. aureus a normal resident of the skin accounts
  for approximately 34 of nosocomial infections

57
Nosocomial Infections
Rates of four major nosocomial infections
expressed as number of infections per 10,000
patient-days at National Taiwan University
Hospital from 1991 to 1999. BSI, bloodstream
infection UTI, urinary tract infection SSI,
surgical site infection RTI, respiratory tract
infection.