L6 Outbreak Investigations

Outbreak Investigation

A methodological appraoch to identify the origin, transmissionmode, and drivers of a disease outbreak through data collection, analysis and hypothesis testin, followed then by control measuresd and recommendations

EXAMPLE:

E.coli-0157 outbreak in South Wales, 2005

Outbreak investigation – key steps
1) Preparation (pre-outbreak)
2) Establishing the presence of an outbreak
3) Verify the diagnosis
4) Case definition
5) Case identification and contact tracing
6) Descriptive epidemiology: describing and orienting data
7) Evidence about origin and transmission routes
8) Control measures
9) Communicate the situation
10) Report writing, recommendations, ongoing surveillance

Cohort Studies

An observational study design following a group of people (cohort) over time to assess how exposure to a risk factor affects the development of disease.

Example:
Following farmers exposed to livestock to see if they develop Q fever compared to farmers with no livestock contact.

Cross-sectional Data

Data collected at a single point in time to describe disease prevelance, individual characteristics (e.g. sex, age), and spatial/temporal patterns, forming the basis for hypotheis generation in outbreak analysis

Attack Rate

The proportion of people who become ill in a defined population during an outbreak, often expressed as a percentage.

Formula:
Attack Rate = (Number of new cases during outbreak / Population at risk) × 100

Example:
During a leptospirosis outbreak among rice farmers, if 30 out of 150 exposed workers get sick, the attack rate is (30/150) × 100 = 20%.

Risk analysis

Evaluating the strength of association between exposure and disease using metrics like relative risk (RR), where RR > 1 indicates higer risk in exposed groups (e.g. univariates analysis in Cryptosporidium outbreaks)

Contact Tracing

Identifying and monitoring individuals exposed to an infected person to prevent further transmission, using interviews, event records, or even apps

Pathogen Origin

The source of a pathogen causing an outbreak, identfied through epidemiological, microbiological, and environmental evidence

Epidemic Curve

A graph showing the number of cases over time, indicating outbreak type: point source (sharp peak), continous (sustained), propogated (multiple peaks), or intermittent (irregulat peaks)

Hotspot and Risk mapping

Spatial analysis to identify areas with high disease incidence (hotspots) and predict risk based on environmental or exposure factors