Epidemiology
in Biostatistics
The study of disease in populations rather than individuals
Aimed at understanding determinants of disease to try and manipulate them
Population: those at risk of the disease
Determinants (sometime population specific i.e. does this apply to my population?)
Intrinsic aka genetic
Extrinsic aka environmental
Infectivity: is ability of agent to establish in host (ID50 = no of agents required to infect 50% of population)
Transmissibility:
Virulence: is ability to cause disease (LD50 = no of agents to kill 50% of population)
Pathogenicity:
Carrier is host infected with agent without disease (dysfunction)
For an agent to survive it need high infectivity and low virulence i.e. carrier is ideal
Also needs a shorter lifespan therefore evolves faster than host
Antigenic drift = host retains some immunity
Antigenic shift = immunity lost (agent can reinfect previously exposed host e.g. HFM, Trypanosomiasis)
Prepatent period: infection until detection
Incubation: infection to disease
Period of communicability:
Via
contact
Exhalation: droplets
Excretion: stool, urine, menses
Secretion: milk, semen, mucous from any orifice
Placenta/fluids
Horizontal v Vertical (mother to child: transplacental, intrapartum, breast milk)
Vehicle
Fomite: boil water and wash food or cook
Vector: transmits agent between infected and susceptible host
Mechanical vector: no development in vector
Biological vector: also acts as a host
Transovarial transmission: vector passes agent to its offspring
transtadial transmission: vector carries agent between developmental stages (if different food in different stage > interspecies transmission)
Definitive host: agent undergoes sexual development
Intermediate host: agent undergoes asexual development
The study of disease in populations rather than individuals
Aimed at understanding determinants of disease to try and manipulate them
Population: those at risk of the disease
Determinants (sometime population specific i.e. does this apply to my population?)
Intrinsic aka genetic
- agent (infection v non-living: H2O, nutrition, temp, toxins)
- host
Extrinsic aka environmental
- hand hygiene
- quarantine
- vaccine
- drugs..
Infectivity: is ability of agent to establish in host (ID50 = no of agents required to infect 50% of population)
Transmissibility:
Virulence: is ability to cause disease (LD50 = no of agents to kill 50% of population)
Pathogenicity:
Carrier is host infected with agent without disease (dysfunction)
- true carrier: never develops disease
- Incubatory carrier: transmits prior to disease
- Convalescent carrier: transmits after diease
For an agent to survive it need high infectivity and low virulence i.e. carrier is ideal
Also needs a shorter lifespan therefore evolves faster than host
Antigenic drift = host retains some immunity
Antigenic shift = immunity lost (agent can reinfect previously exposed host e.g. HFM, Trypanosomiasis)
Prepatent period: infection until detection
Incubation: infection to disease
Period of communicability:
Via
contact
Exhalation: droplets
Excretion: stool, urine, menses
Secretion: milk, semen, mucous from any orifice
Placenta/fluids
Horizontal v Vertical (mother to child: transplacental, intrapartum, breast milk)
Vehicle
Fomite: boil water and wash food or cook
Vector: transmits agent between infected and susceptible host
Mechanical vector: no development in vector
Biological vector: also acts as a host
Transovarial transmission: vector passes agent to its offspring
transtadial transmission: vector carries agent between developmental stages (if different food in different stage > interspecies transmission)
Definitive host: agent undergoes sexual development
Intermediate host: agent undergoes asexual development