Medical diagnostic Microbiology epidemiology 2024 progress.pdf

1. Unit
epidemiology of
diseases
2024

2. Learning Objectives
Define pathology, etiology,
infection, and disease
Explain the difference
between normal, transient,
and opportunistic microbes
Compare commensalism,
mutualism, and parasitism,
and give an example of
each.
List and explain Koch’s
postulates.
Differentiate a
communicable from a
noncommunicable disease.
Categorize diseases
according to frequency of
occurrence.
Define herd immunity.
Review the common
disease pattern: incubation
period, prodromal period,
periods of illness, decline,
and convalescence
Define reservoir of
infection and distinguish
between human, animal,
and nonliving reservoirs.
Give an example of each.
Explain three methods of
disease transmission.
Define nosocomial
infections and explain their
importance and prevention.
List probable reasons for
emerging infectious
diseases and name an
example for each.
Define epidemiology and
describe three types of
epidemiologic investigation.
Explain the function of the
CDC.
Define the following terms:
morbidity, mortality, and
notifiable disease.

3. DISEASE-
CAUSING
BACTERIA
• Pathology: Study of disease
• Pathogenesis: Development of disease
• Pathogen: organism causing disease
• Pathogenic agents have special properties that allow
them to attach, colonize invade the human body or
produce toxins.
• Etiology: Causes of disease In terms of infectious disease,
the etiologic agent is the microorganism causing that
disease.
An infection is when a microorganism has established itself
in a host - has colonized that host - whether not it causing
harm or imparting damage
• A disease on the other hand, is where there is impairment
to host function
• i.e.: infectious agent overcomes body’s defenses

4. Epidemiology
• science that evaluates occurrence, determinants,
distribution, and control of health and disease in a defined
human population
• health
• condition in which organism (and all its parts) performs its vital
functions normally
• disease
• impairment of the normal state of an organism or any of its
components that hinders the performance of vital functions
• epidemiologist
• one who practices epidemiology

5. Epidemiology
• The study of where and when diseases occur
(disease transmission, incidence, and
frequency)
• Centers for Disease Control and Prevention
(CDC)
• Collects and analyzes epidemiological
information in the United States
• Publishes Morbidity and Mortality Weekly
Report (MMWR)
• www.cdc.gov
• Worldwide disease surveillance: WHO

7. The Beginning of Epidemiology
John Snow 1848–1849 Mapped the occurrence of
cholera in London
Ignaz Semmelweis 1846–1848 Showed that handwashing
decreased the incidence of
puerperal fever
Florence
Nightingale
1858 Showed that improved
sanitation decreased the
incidence of epidemic
typhus

8. Occurrence of a Disease
Incidence: Fraction of
a population that
contracts a disease
during a specific time
Prevalence: Fraction
of a population having
a specific disease at a
given time
Sporadic disease:
Disease that occurs
occasionally in a
population
Endemic disease:
Disease constantly
present in a
population
Epidemic disease:
Disease acquired by
many hosts in a given
area in a short time
Pandemic disease:
Worldwide epidemic

9. Table 14.7 (1 of 2)
CDC
Case reporting: Health care workers report specified disease to local,
state, and national offices
Nationally notifiable diseases: Physicians are required to report
occurrence.
Morbidity: Incidence of a specific notifiable disease.
Mortality: Deaths from notifiable diseases.
Morbidity rate: Number of people affected in relation to total
population in a given time period.
Mortality rate: Number of deaths from a disease in relation to total
population in a given time period.

10. Classifying
Infectious
Diseases
Symptom: A
change in body
function that is felt
by a patient as a
result of disease
Sign: A change in a
body that can be
measured or
observed as a
result of disease.
•Signs (objective) -
Symptoms (subjective)
Syndrome: A
specific group of
signs and
symptoms that
accompany a
disease
Communicable vs.
Non-
communicable
vs. Contagious

11. Classifying Infectious Diseases cont.
Communicable disease: A disease that is
spread from one host to another
Contagious disease: A disease that is easily
spread from one host to another
Noncommunicable disease: A disease that
is not transmitted from one host to another

12. Severity or
Duration of
a Disease

13. In epidemiology, the Chain of Infection is fundamental to
infection prevention and control. All components of the chain of
infection must be present for an infection to occur. If one of the
‘links’ in the chain is missing or is deliberately broken, the spread
of disease to another is effectively controlled.

17. Aetiology/ causative agent/infectious agents
• An infectious agent is a microorganism with the ability to cause an
infectious disease.
factors helping the organism to be infectious ➔
• Ability to attach
• Ability to grow and multiply
• ability to enter tissue (invasiveness)
• Ability to evade the host’s immunity
• Ability to overcome the host immune system
NB: To link a particular disease with an organism, KOCH”s POSTULATES must
apply

18. Koch’s
Postulates: Proof
of Etiology of
Infectious
Diseases
The same pathogen must be present in every case
of the disease
The pathogen must be isolated from the diseased
host and grown in pure culture
The pathogen from the pure culture must cause
the disease when it is inoculated into a healthy,
susceptible lab animal
The pathogen must be isolated from the
inoculated animal and must be shown to be the
original microbe

19. Anthrax & Koch’s
Postulates:
Compare to Fig 14.3 (Foundation Figure)

20. Exceptions to
Koch’s
Postulates
Modification of Koch’s postulates were necessary
1. to establish disease etiology for viruses and
bacteria, which cannot be grown on artificial
media
2. Some diseases, e.g.: pneumonia and
nephritis, may be caused by a variety of
microbes.
3. Some pathogens, such as S. pyogenes, cause
several different diseases.
4. Certain pathogens, such as HIV, cause disease
in humans only.

21. Correlation with a Single Causative Agent
• after recognition of infectious disease in a population, outbreak
correlated with specific pathogen
• clinical microbiologists help in isolation and identification of pathogen

22. Figure 33.4

23. The
Reservoir
Reservoirs ➔are a place within which
microorganisms can thrive and reproduce.
Natural habitat or source
For example, microorganisms thrive in
human beings, animals, and inanimate
objects such as water.

24. Human Sources/Reservoirs
• carrier
• infected hosts who are potential sources of infection for
others
• types of carriers
• active carrier has overt clinical case of disease
• convalescent carrier has recovered but continues to harbor large
numbers of pathogen
• healthy carrier harbors the pathogen but is not ill
• incubatory carrier is incubating the pathogen in large numbers
but is not yet ill

25. More Types of Carriers…
• casual, acute, or transient carriers
• convalescent, healthy, and incubatory carriers that harbor pathogen for brief
time
• chronic carriers
• convalescent, healthy, and incubatory carriers that harbor pathogen for long
time

26. Portal of Exit
• This is how a microorganism to leave the reservoir.
• For example, the microorganism may leave the reservoir through the
nose or mouth when someone sneezes or coughs, or can be carried
away from the body by faeces from an infected bowel.

27. Disease Transmissions
Contact Transmission:
• Direct: Close association between infected and
susceptible host.
• Indirect: Spread by fomites.
• Droplet: Transmission via airborne droplets from saliva
or mucus (coughing or sneezing)
Airborne Transmission: Pathogens carried on water
droplets or dust for a distance greater than 1 meter
Vehicle Transmission: Water, food, air
Vector Transmission: Arthropods carry pathogens from
one host to another (mechanical vector vs. biological
vector)

28. Portal of Entry
• The portal of entry is the means by which the infectious
microorganisms gains access into the new host.
• This can occur, for example, through ingestion, breathing, or skin
puncture.

29. Virulence and the Mode of Transmission
Evidence suggests correlation between mode of transmission and
degree of virulence
• direct contact → less virulent
• vector-borne → highly virulent in human host; relatively benign in vector
• greater ability to survive outside host → more virulent
• e.g., Mycobacterium tuberculosis and Corynebacterium
diphtheriae can survive weeks to months outside human hosts

30. Susceptible Host
• A susceptible host is a person who is susceptible to the disease,
lacking immunity or physical resistance, to overcome invasion by the
microorganism.

31. Patterns of
Disease:
Predisposing
Factors

32. Disease Development
and Stages
Incubation period: Time interval
between initial infection and
first appearance of signs and
symptoms.
Prodromal period: Characterized by appearance of first
mild signs and symptoms.
Period of illness: Disease at its height: all disease signs and
symptoms apparent.
Period of decline: Signs and symptoms subside.
Period of convalescence: Body returns to prediseased
state, health is restored.
Fig 14.5

33. Period of
illness
The Course of Disease, as Typified by Measles

34. Extent of Host
Involvement
Toxemia: Toxins in the blood
Viremia: Viruses in the blood
Primary infection: Acute infection that causes the
initial illness
Secondary infection: Opportunistic infection after
a primary (predisposing) infection
Subclinical disease: No noticeable signs or
symptoms (inapparent infection)

35. Extent of Host Involvement: An Infection can be
• Local: limited to small area of body
• Systemic: spread throughout body via _______
• Focal: spread from local infection to specific areas o
• Primary: acute infection causing initial illness
• Secondary: occurs after host is weakened from primary
infection
• Subclinical (inapparent): no noticeable signs and
symptoms
Sepsis: Toxic inflammatory condition arising from
spread of microbes or their toxins, from a focus
Bacteremia: Bacteria in the blood.
Septicemia: Growth of bacteria in the blood.

36. Nosocomial (Hospital-
Acquired) Infections
• Acquired as a result of a hospital stay.
• 5-15% of hospital patients acquire
nosocomial infections.
• Aseptic techniques can prevent
nosocomial infections.
• Hospital infection control staff
members are responsible for
overseeing the proper cleaning,
storage, and handling of equipment
and supplies.

37. Relative Frequency of Nosocomial Infections
Table 14.5

38. Common Causes of Nosocomial Infections
Percentage of Total
Infections
Percentage Resistant
to Antibiotics
Coagulase-negative staphylococci 25% 89%
S. aureus 16% 80%
Enterococcus 10% 29%
Gram-negative rods 23% 5-32%
C. difficile 13% None

39. Source
Endogenous pathogen
• brought into hospital by patient or acquired when
patient is colonized after admission
Exogenous pathogen
• microbiota other than the patient’s
Autogenous infection
• caused by an agent derived from microbiota of patient
despite whether it became part of patient’s microbiota
following admission

40. Control, Prevention, and Surveillance
• proper training of personnel in basic infection control
measures
• e.g., handling of surgical wounds and hand washing
• monitoring of patient for signs and symptoms of
nosocomial infection
• The Hospital Epidemiologist
• individual responsible for developing and implementing
policies to monitor and control infections and
communicable diseases
• reports to infection control committee or similar group

41. Bioterrorism Preparedness
Bioterrorism
• “intentional or threatened use of viruses, bacteria, fungi, or toxins from living
organisms to produce death or disease in humans, animals, and plants”

42. Examples of Intentional Uses of Biological
Agents for Criminal or Terror Intent
• 1984 in The Dalles, OR
• Salmonella typhimurium in 10 restaurant salad bars
• 1996 in Texas
• intentional release of Shigella dysentariae in a hospital lab break
room
• 2001 in seven eastern U.S. states
• use of weaponized Bacillus anthracis spores delivered through U.S.
postal systems
• all of above caused hospitalizations, the anthrax episode
resulted in five deaths

43. Table 33.6

44. Choosing Biological Agents as
Weapons
• biocrime when chosen as a means for a localized
attack vs. bioterrorism when chosen for mass
casualties
• characteristics that favor their use
• invisible, odorless, and tasteless
• difficult to detect
• take hours or days before awareness that they have been
used
• fear and panic associated with the anticipation that they
were used

45. Control of Epidemics
Three types of control measures
• reduce or eliminate source or reservoir of infection
• break connection between source and susceptible individual
• reduce number of susceptible individuals

46. Reduce or Eliminate Source or Reservoir
• quarantine and isolation of cases and carriers
• destruction of animal reservoir
• treatment of sewage
• therapy that reduces or eliminates infectivity of cases

47. Break Connection between Source
and Susceptible Individuals
• chlorination of water supplies
• pasteurization of milk
• supervision and inspection of food and food handlers
• destruction of insect vectors with pesticides

48. Reduce Number of Susceptible Individuals
• raise level of herd immunity by
• passive immunity following exposure
• active immunity for protection

49. Vaccines and Immunization
Vaccine
• preparation of one or more microbial antigens used to induce protective
immunity
• may consist of killed, living, weakened (attenuated) microbes or inactivated
bacterial toxins (toxoids), purified cell material, recombinant vectors or DNA
Immunization
• result obtained when vaccine stimulates immunity
• vaccines attempt to induce antibodies and activated T cells to protect host from
future infection
• Vaccinomics is the application of genomics and bioinformatics to vaccine
development

50. Emerging Infectious Diseases(EIDs)
• Diseases that are
new, increasing in
incidence, or
showing a potential
to increase in the
near future
• CDC, NIH, and WHO
are responsible for
surveillance and
responses to
emerging diseases

51. Contributing
factors for
EIDs
• Genetic recombination (E. coli 0157; H5N1 avian
flu)
• Evolution of new strains (V. cholerae 0139)
• Inappropriate use of antibiotics and pesticides
(Antibiotic resistant strains)
• Changes in weather patterns (Hantavirus)
• Modern Transportation (West Nile virus)
• Ecological disaster, war, and expanding human
settlement (Coccidioidomycosis)
• Animal control measures (Lyme disease)
• Public Health failure (Diphtheria)
• Improved case reporting

52. Reasons for Increases in Emerging and
Reemerging Infectious Diseases
• crowding
• habitat disruption
• shift in distribution of nosocomial pathogens
• excessive or inappropriate use of antimicrobial therapy
• medical practices that lead to immunosuppression
• rapid global transportation systems

53. Crossing the Species Barrier
Clinical Focus, p. 371

54. Bibliography
• Lecture PowerPoints Prescott’s Principles of Microbiology-Mc
Graw Hill Co.
• Tille, P.M., 2017. Bailey & Scott’s diagnostic microbiology, Fourteenth
edition. ed. Elsevier, St. Louis, Missouri.
• Tortora, G.J., Funke, B.R., Case, C.L., 2019. Microbiology: an
introduction, Thirteenth edition. ed. Pearson, Boston.
• wikipaedia