Epidemiology: Surveillance and Outbreak Investigations: THE JON SNOW STORY (L20) – Flashcards

Showed that public health interventions based on epi info can proceed and be effective even with imperfect knowledge of the etiological agent of a disease! • Removing the pump handle saved hundreds of lives, despite the fact that Snow did not know the cause of cholera Also: Voted best Doctor EVER (take that Hippocrates!) Invented anesthesia

• Each bar on map is a death, shows a clustering of cases near the broad street pump • Houses near the OTHER pump only had 10 deaths; of those, 5 victims always drank water from the Broad St. pump • Took sample from the pump, examined it under microscope, saw white, flocculents • Mapping allowed him to support his theory the pump was the source of cholera

an active disease accounting process intended to monitor the overall disease and health status of a population continuously and systemically - in vet med: based on PREVALENCE SURVEYS

o Way to define the normal limits for disease (expected frequency) o Detect outbreaks/epidemics in their early stages o Track longer term "secular changes" o Certify that disease is absent o Evaluate the efficacy of public health interventions

• When the incidence of disease in a given time period is above the normal range • Generally suspected when rates of occurrence (incidence) exceed limits defined by 95% confidence intervals around time averaged means

detection description and measurement of periodicities from temoporal disease occurrence data; example: moving average

• Secular trends: overall, long term increases or decreases in rate of occurrence (Height, obesity) • Seasonal fluctuations: regular changes in occurrence with periods shorter than a year (Flu season) • Cyclic changes: regular changes in occurrence with period longer than a year (Outbreak of dz every few years in mumps: due to children being born, getting it, herd immunity protects for a bit, then the cycle occurs again when herd immunity lost) • Irregular variation: random or unpredictable changes in occurrence over time

based on clinical signs, microbio and serologic features etc. Necessary to an outbreak investigation to accurately classify cases vs non- cases.

must also be defined for an outbreak investigation. Who is at risk? = Denominator

first case to be brought up to a public health official (not necessarily first case of outbreak)

A case that gets infected from exposure to the souce of the dz/agent (not first case either)

Case that gets dz from exposure to a primary case

Recall from Exam 1. Measures initial speed of outbreak "How BAD the situation is"

Recall from Exam 1. Measured *ongoing* speed of outbreak. = # individuals that become diseased in *subsequent* period/(initial PaR - primary cases)

compare attack rates from sick vs non sick animals to figure out if factor is associated with the dz.

Causal factors will have: - higher attack rates in exposed groups than unexposed - greatest difference between attack rates - relative risk >1 for exposed groups - Confidence Intervals that don't cross 1 - nonexposed level=endemic dz level.

used for single exposure outbreaks (one cause, like the potato salad!) - can be done by hand in the field, using exposure specific attack rates.

Quarante Giorno (40 days!) to prevent spread of black plague. *Quarantine period should be longer than incubation period.* • Quarantine individuals coming into the population to prevent reintroductions of the disease agent • Quarantine individuals leaving the population to prevent the spread of disease

• Limit access by people • Clean and disinfect equipment: beware fomites! Equipment includes vehicles • Call appropriate officials (state vet, especially for reportable dz) • Adopt a generous "down time" policy for health professionals serving multiple clients and herds (beware iatrogenic transmission)

*Prevention*: exclude a disease from an unaffected popln -->Requires continuous effort and vigilance for as long as the possibility remains that a disease may occur *Control*: reduce the frequency or cost of dz to some socially or economically acceptable level *Eradication*: the complete elimination of an infectious agent from a geographic region. Ex. Rinderpest (smallpox)

• Mass treatment: treat all (food/water) • Mass immunization • Slaughter • Environmental hygein: prevent contact with contam environ (disinfection) • Biological control ("applied ecology"): reduce the vector or reservoir • Education: essential but can be ineffective

Sporadic Point Source Propagating

graph of the times of onset of cases - Y axis = raw number of cases; X axis = different time points Contains info about: o Avg # secondary infections causes by a primary infection (early curve) o Time between exposure and onset of dz (incubation period) o Types of epidemic (sporadic, point source, propagating)

Probability of dying if you get the disease • # deaths due to disease/total # of cases of dz • CFR = "honest" measure of severity of an outbreak