Lecture 14 - Diagnostic Microbiology and Epidemiology

Question 1

What is epidemiology?

Answer 1

Study of the Occurrence, Distribution and Determinants of Health and Disease

• Focuses on Public Health
• Health of the Human Population as a Whole

Question 2

How do we classify disease?

Answer 2

Endemic
-restricted areas and low incidence

Epidemic
-restricted areas and high incidence

Pandemic
-worldwide and high incidence

Question 3

What is incidence vs prevalence?

Answer 3

Incidence

• number of new cases
• record of disease spread

Prevalence

• Number of new and existing cases
• record of total disease burden

Faucet and bathtub example

Question 4

What is mortality and morbidity?

Answer 4

Mortality

• incidence of death
• fatal cases only

Morbidity

• Incidence of disease
• fatal and nonfatal cases

Question 5

What do we look at when we are trying to control and eradicate disease?

Answer 5

How do they live

Where do they live

How are they transmitted

Question 6

How do pathogens live?

Answer 6

Host-Dependent

• grow/reproduce only in host
• cause chronic infections

Host-Independent

• grow/reproduce outside of the host
• acute infections

Question 7

What are the stages of disease progression in acute infections?

Answer 7

Infection - pathogen invades, colonizes
Incubation Period - pathogen grows, no symptoms
Acute Period - appearance of symptoms
Decline Period - decline of symptoms
Convalescent Period - host recovery

Question 8

Where do pathogens live?

Answer 8

Disease reservoirs
-Where they can reproduce, grow, and spread

Types

• Animate = living like lymes disease and ticks
• Inanimate = nonliving like soil

Question 9

How is disease transmitted?

Answer 9

Direct Host-to-Host

• person to person = human to human
• zoonosis = non-human to human, human dead-end host

Indirect Host-to-Host

• Vectors = reservoir to human using living carrier
• vehicles = reservoir to human using nonliving carrier

Question 10

What are the different types of epidemics?

Answer 10

Common-Source Epidemics

• Inanimate Reservoirs like contaminated water
• quick increase/decrease in number of cases

Host-to-Host Epidemics

• Animate Reservoirs like influenza
• longer duration but lower number of cases

Question 11

What are the types of host-pathogen coevolution?

Answer 11

Selection pressures for mutual coexistence

• common for host-dependent pathogens
• decreased pathogen virulence and increased host resistance

No selection pressures for mutual coexistence

• common for host-independent pathogens
• pathogen virulence remains high but host resistance remains low

Question 12

What are nosocomial infections?

Answer 12

Infections acquired by patients in hospitals

Selects for highly virulent, antibiotic resistant pathogens - host independent

• Low host resistance
• Many pathogen reservoirs
• Breaching of skin barrier
• Drug usage = antibiotic resistance

Question 13

What is the Basic Reproductive Number R0?

Answer 13

Number of secondary cases from an infected individual

• how many ppl you transmit disease to
• R0<1, disease will die out
• R0=1 disease is maintained
• R0>1, disease outbreak, possible epidemic

Question 14

How do we calculate the basic reproductive number, R0?

Answer 14

R0 = rcd

r=transmissibility
c=avg rate of contact between ppl
d=duration of infectious stage

Question 15

What is herd immunity?

Answer 15

Prevent epidemics by limiting pathogen transmission

• the immune individuals protect pl w/o immunity
• increase pathogen virulence = more immune ppl needed to prevent epidemic

Question 16

What public health measures do we take to identify, track, contain and eradicate infectious disease?

Answer 16

Disease Management

1. Control against vehicles
2. Control against reservoirs
3. Immunization
4. Quarantine
5. Surveillance

Question 17

How do we control against vehicles?

Answer 17

Water Purification

Food purity/preparation
-pasteurization

Air Filtration
-HVAC and air masks

Question 18

How do we control against reservoirs?

Answer 18

Domestic Animals
-vaccination programs at vet

Wild Animals
-bait traps and oral vaccines

Insect vectors
-insecticides

Question 19

How do we use immunization in disease management?

Answer 19

Highly controlled Child Immunization

Booster shots for adult immunization

Question 20

How do we use quarantine in disease management?

Answer 20

Restricted movement of disease carriers
-prevent spread of highly contagious disease

Human and Animal Quarantine

• humans w/ active infections
• animals that are disease vectors

Question 21

How do we use surveillance in disease management?

Answer 21

Monitor disease incidence and prevalence

• apply disease tracking data
• implement control strategies

CDC in U.S.
WHO internationally

Question 22

What are emerging diseases and what are the types?

Answer 22

Sudden increase in disease prevalence

Types

• New Diseases
• Reemerging diseases

Question 23

What are the factors of disease emergence?

Answer 23

1. Human demographics and behavior
2. Economic Development and land use
3. International travel
4. Pathogen adaptation
5. Loss of health standards

Question 24

What is biological warfare?

Answer 24

Use of biological agents to kill/incapacitate

Characteristics
-easy to produce/deliver

Delivery

• aerosol
• drinking water
• food

Question 25

What is diagnostic microbiology? What are the techniques of diagnostic microbiology?

Answer 25

detection, identification, and characterization of infectious disease
-clinical microbiology

Techniques

1. Culturing
2. Immunoassays
3. Molecular, DNA/RNA

Question 26

What is the key to diagnostic microbiology?

Answer 26

Specificity

• ability to recognize single pathogen strain
• no false positives

Sensitivity

• Lowest amount of pathogen cells detected
• highest sensitivity=1 pathogen cell

Question 27

What are the culturing techniques used in diagnostic microbiology?

Answer 27

Selective Media
-only target microbe will grow

Differential Media
-more than one microbe grows but media allows you to tell the difference

Question 28

How do we determine susceptibility of pathogen using culturing techniques?

Answer 28

Antibiotic tests
-disc diffusion and minimum inhibitory concentration

Antibiograms

• periodic reports of pathogen resistance
• nosocomial pathogens

Question 29

What are immunoassays used for? What are the types?

Answer 29

detect specific pathogens/pathogen products

• no culture needed
• uses pathogen-specific antibodies

Types of Immunoassays

• Immunofluorescence
• ELISA

Question 30

What is the immunoassay type, immunofluorescence?

Answer 30

Label antibodies with fluorescent tag
Light emitted when antibodies bind
Early detection in vivo

Question 31

What is the immunoassay type, ELISA?

Answer 31

Enzyme-Linked Immunosorbent Assay

• high sensitivity and specificity
• enzyme attached to antibody

Types

• direct ELISA = detects antigen
• indirect ELISA = detects antibody

Question 32

What are the steps of direct ELISA?

Answer 32

1) Antibodies Bound to Wells
2) Add Patient Sample
3) Add Enzyme-­‐Antibody
4) Wash Wells
5) Add Enzyme Substrate

Question 33

What are the molecular methods used in diagnostic microbiology? What are the types?

Answer 33

It detects pathogen DNA/RNA

• Most pathogens can’t be cultured so helpful
• High specificity and sensitivity

Types

• Nucleic Acid Probes
• PCR testing

Question 34

What is the molecular method of diagnostic microbiology, nucleic acid probes?

Answer 34

Single stranded DNA specific to pathogen gene
-uses a reported like a fluorescent dye

Probe binds to target gene, dsDNA
Reporter gets activated and emits light

Question 35

What is the molecular method of diagnostic microbiology, PCR testing?

Answer 35

Detect and amplify target DNA
-using pathogen-specific primers

Additional PCR tests

• RT-PCR to detect RNA in viruses
• q-PCR for real time info on numbers during PCR