Lecture 11 (Epi Investigation) Flashcards
Reqs of ID
- Causative agent
- Host susceptibility
- Transmission
- Portal of entry
- Modes of transportation
- Environment conducive to transmission
Reservoir
-Natural habitat of infectious agent (where it lives/multiples)
Vector
- Insect that carries agent btwn hosts
- Most important: mosquito
Intermediate host
-Host in which asexual forms develop
Clinical infection
-Shows signs/symptoms
Non-clinical infection
- AKA inapparent, sub-clinical, silent
- No signs/symptoms –> ample opportunity to spread
Carrier
- Person w/nonclinical infection who can transmit
- Can be chronic
- Importance: not restricted therefore can transmit widely
Herd Immunity
- 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)
Incubation period (def, depends on what)
- Interval f/exposure to onset of clinical disease
- Depends on dose of agent, portal of entry, immune response of host
Endemic infection
-Always present in a pop
Epidemic
-Occurrence of an excess of disease over that expected in a pop
Outbreak
-Epidemic characterized by sharp rise and fall in inc w/in short period
Cessation of epidemics
- Source eliminated
- # exposed or susceptible is decreased
- Mode of transmission interrupted
Propagated source epidemic
-Infectious agent transmitted f/person to person (ex: flu)
Common source epidemic
- Transmission f/single, common source of infection
- Subtypes: point source, extended common source
Mixed source epidemic
- Common and propagated source epidemic (ex: Hep A through food, then fecal oral route)
- Single large peak then successive smaller peaks
Point-source epidemic
- 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
Extended common source epidemic
- Exposure to same source of infection continuously or at multiple points in time (ex: contaminated water, anthrax letters)
- Curve: spread out, possible irregular peaks
Attack rate
-Cumulative incidence of disease observed during an epidemic
x100 (%)
Different subtyping methods for ID
- Phenotypic typing systems: eval of characteristics expressed by isolate during in vitro cultivation
- Genotypic (molecular) typing systems: examination of DNA of isolate using PFGE
