Lecture 11 (Epi Investigation)

Question 1

Reqs of ID

Answer 1

• Causative agent
• Host susceptibility
• Transmission
• Portal of entry
• Modes of transportation
• Environment conducive to transmission

Question 2

Reservoir

Answer 2

-Natural habitat of infectious agent (where it lives/multiples)

Question 3

Vector

Answer 3

• Insect that carries agent btwn hosts

- Most important: mosquito

Question 4

Intermediate host

Answer 4

-Host in which asexual forms develop

Question 5

Clinical infection

Answer 5

-Shows signs/symptoms

Question 6

Non-clinical infection

Answer 6

• AKA inapparent, sub-clinical, silent

- No signs/symptoms –> ample opportunity to spread

Question 7

Carrier

Answer 7

• Person w/nonclinical infection who can transmit
• Can be chronic
• Importance: not restricted therefore can transmit widely

Question 8

Herd Immunity

Answer 8

• Resistance of pop to spread of an ID due to large proportion of members being immune
• If large prop is immune, unlikely that infected person will encounter a susceptible person
• Prop req’d varies (flu ~0.8)

Question 9

Incubation period (def, depends on what)

Answer 9

• Interval f/exposure to onset of clinical disease

- Depends on dose of agent, portal of entry, immune response of host

Question 10

Endemic infection

Answer 10

-Always present in a pop

Question 11

Epidemic

Answer 11

-Occurrence of an excess of disease over that expected in a pop

Question 12

Outbreak

Answer 12

-Epidemic characterized by sharp rise and fall in inc w/in short period

Question 13

Cessation of epidemics

Answer 13

• Source eliminated
• # exposed or susceptible is decreased
• Mode of transmission interrupted

Question 14

Propagated source epidemic

Answer 14

-Infectious agent transmitted f/person to person (ex: flu)

Question 15

Common source epidemic

Answer 15

• Transmission f/single, common source of infection

- Subtypes: point source, extended common source

Question 16

Mixed source epidemic

Answer 16

• Common and propagated source epidemic (ex: Hep A through food, then fecal oral route)
• Single large peak then successive smaller peaks

Question 17

Point-source epidemic

Answer 17

• Exposure of grp of ppl to same source of infection at single pt in time (ex: food poisoning at church picnic)
• Curve: single defined peak

Question 18

Extended common source epidemic

Answer 18

• Exposure to same source of infection continuously or at multiple points in time (ex: contaminated water, anthrax letters)
• Curve: spread out, possible irregular peaks

Question 19

Attack rate

Answer 19

-Cumulative incidence of disease observed during an epidemic

x100 (%)

Question 20

Different subtyping methods for ID

Answer 20

• Phenotypic typing systems: eval of characteristics expressed by isolate during in vitro cultivation
• Genotypic (molecular) typing systems: examination of DNA of isolate using PFGE