Infectious Disease

Question 1

Modes Of transmission

Answer 1

• Any mechanism by which a disease agent is spread to the host
• Agent to host
• Via direct contact, indirect inanimate vehicle, indirect animate vector, fomite
• Fomite: almost anything an infected individual (or reservoir) can touch, upon which can be left a residue of contagious pathogen

Question 2

Reservoirs

Answer 2

The normal habitat in which the agent lives, multiplies, and grows.
1.Human reservoirs
•Symptomatic
•Carriers- asymptomatic, no sign of symptoms
•Incubating cases
2.Animal/Insect reservoirs
3.Environmental reservoirs
•Inanimate objects: water, food, soil, air, fomites

Question 3

Patterns of disease

Answer 3

1.Sporadic - single case or cluster of cases: Infrequent disease occurrence AND Irregular and unpredictable
2.Endemic - disease occurs at expected frequency
3.Epidemic - disease occurs at greater than expected frequency
Point epidemic: Single common exposure; Does not spread; ex. Foodborne disease outbreaks
4.Pandemic – international/global epidemic

Question 4

Immunity and Susceptibility

Answer 4

• immune: had the disease previously or because they have been immunized
• susceptible: not at risk

Question 5

Herd Immunity

Answer 5

subgroup of population/community that are immune (naturally) and/or immune (vaccination)
• Susceptibles protected by immunity of others!

Question 6

Incubation periods

Answer 6

• interval from receipt of infection to the time of onset of clinical illness.
• Basis of quarantine periods to prevent spread of disease

Question 7

Critical variables to investigate an outbreak

Answer 7

• (1) When did the exposure take place?
  
  • (2) When did the disease begin?
  • (3) What was the incubation period for the disease?

Question 8

Cross-Tabulation

Answer 8

• Method used in which many etiologic factors are suspected, be able to see which factor(s) have higher association with outcome

Question 9

What makes infectious disease epidemiology ‘special?

Answer 9

• A case may also be a risk factor
  * People may be immune
  * A case may be a case without being recognized as a case
  * There is sometimes a need for urgency
  * Preventive measures (usually) have a good scientific basis

Question 10

The infectious disease process

Answer 10

1.Agents – microbe causing the illness
2.Reservoirs - where the agents live
3.Portals of entry and exit
•Transmission – how agents get in and out
4.Host immunity - factors that affect disease severity and progression

Question 11

Why are Outbreak Investigations Conducted?

Answer 11

1. Identify the cause of illness or other health problem
2. Characterize the extent of the problem and the affected population
3. Limit the scope and severity of a threat to public health
4. Identify the source of infection and mode(s) of transmission
5. Obtain information that can be used to prevent future outbreaks
6. Monitor success of disease control interventions
7. Identify new pathogens and obtain new information about known pathogens

Question 12

Steps of an Outbreak Investigation

Answer 12

1. Prepare for field work
2. Establish the existence of an outbreak
3. Verify the diagnosis
4. Define and identify cases
   a. establish a case definition
   b. identify and count cases
5. Perform descriptive epidemiology
6. Develop hypotheses
7. Evaluate hypotheses
8. As necessary, reconsider/refine hypotheses and execute additional studies
   a. additional epidemiologic studies
   b. other types of studies – laboratory, environmental
9. Implement control and prevention measures
10. Communicate findings

Question 13

Case Definition

Answer 13

Simple, objective and standard criteria using clinical and/or laboratory findings

1. Specifies person, place and time
2. Does NOT include the risk factor (i.e. exposure) under study
3. Broad vs. narrow definition…
4. Possible, probable, confirmed