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Managing an Outbreak 


Who does what?

Primarily, an outbreak is declared by Public Health England. The relevant PHE health protection team then complete an investigation and/or risk assessment of the situation. Where the outbreak involves a vaccine preventable disease - e.g. Hepatitis A, measles, Meningococcal disease - NHS England regional public health commissioning teams may be alerted.  In London we have a specific IMMS01 response whereby there is always a public health commissioner on call who would then proceed to co-ordinate the btainment of vaccine and the subsequent vaccination of affected parties by immunisers. For other outbreaks, such as gastroenteritis where bowel specimens may be required or food samples taken, local authority environmental health teams would be involved. All outbreak incidents require all involved public health personnel to log actions taken and timings and it is good practice to undertake reflective learning at the end of the incident.


Basic Principles

Whatever cluster or outbreak investigation you would be involved in, there are four things that are required from you in public health:

  1. Limit number of primary cases
  2. Limit number of secondary cases
  3. Prevent re-occurrence
  4. Minimise the harm

Another useful tip (which I got from an experienced Consultant in Communicable Disease Control):

  • Take note of the Transmission Pathway
  • Take time to know the pathway rather than jumping in.
  • Know the source - route of transmission - susceptible people
  • Know natural history, know the face of your enemy


Useful Definitions

An outbreak of a disease is usually defined as two or more cases of a disease related in time and/or place in excess of normal expectancy

Endemic - habitual presence of a disease in a given geographical area (usual occurrence).

Epidemic - occurrence in a community or area of a group of illnesses of similar nature clearly in excess of normal expectancy derived from common or propagated source - i.e. an increase in incidence about that which may be continuously present in a population (endemic).

Food poisoning refers to any disease of an infection or toxic nature caused by or thought to be caused by consumption of food or water.


Types of Outbreaks

  • Food or waterborne (outbreak team would include environmental health officers)
  • Water (outbreak team would include the relevant water company)
  • Healthcare associated infections (outbreak team would include the infection control nurse/doctor)
  • Zoonotic disease (outbreak team would include state veterinary service/DEFRA)
  • Occupational lookbacks (outbreak team would include occupational health service)


Investigating Outbreaks

Epidemiological investigations are crucial. You need a close knowledge of the suspected disease. For example, incubation period of smallpox is 12 days so one would then concentrate on all contacts with index case 12 days before.

  1. Establish if an outbreak is occurring or has occurred
  2. Define what constitutes a case and decide if the provisional diagnoses fit with this definition
  3. Act with some speed in case the outbreak is genuine
  4. Treat and isolate the suspected cases
  5. Start contact tracing
  6. Initiate microbiological testing, if available

In plain English, you define the event, identify the cases and collect the data. Then you look at how the disease is being controlled (i.e. identification and treatment of patients). After that, get cracking at preventing the transmission to other people and finish up by writing up the experience including lessons learnt so that you can prevent future occurrences and contribute to the epidemiology of outbreaks.


Method for outbreak investigation

1. Define an outbreak

2. Define the objectives of outbreak investigation.

a. Identify source and mode of spread

b. Interrupt further transmission

c. Prevent secondary spread

d. Educate public, healthcare workers and others involved

e. Introduce future preventative measures

f. Prosecute: but need epidemiological and microbiological evidence

3. State the steps taken in an outbreak investigation:

a. Preliminary assessment - is it an outbreak? confirm numbers, evidence review, form an Outbreak Control Team, initiate immediate control measures

b. Prepare a case definition and fine cases: time/place/person/clinical symptoms/laboratory results

c. Undertake a descriptive study: collect data and analyse to generate an epidemic curve and then generate a hypothesis

d. Undertake an analytical study: cohort or case control and use to test the hypothesis - e.g. Cohort study for food outbreaks where the population is known e.g. wedding reception (attack rate and relative risk ratio) or Case-control study to sample large exposed population – odds ratio.

e. Verify hypothesis using microbiological or environmental tests

4. Initiate control measures:

a. Remove source: isolate/treat case, destroy food, close shop

b. Protect those at risk: hygiene, hand washing, water boiling and prophylaxis, e.g. hepatitis B injections, stop symptomatic food handlers form working, clean/disinfect premises, recall product

c. Prevent recurrence: recommendations, guidelines

5. Communication with media, reports, guidelines - bear in mind the severity of disease, unpleasantness of treatment and danger of panicking the community


Factors to Consider for Gastro Outbreaks

Gastro Outbreaks can be food borne or can spread person to person. The type can be identified by the clinical features and lab tests. Food borne tends to be a cluster with a point source (person to person is not a cluster and tends to come in waves). 

Consider how the food was prepared (raw, cooked inadequately?) and stored afterwards, check the food production and hygiene practices and did the food handlers have symptoms of gastro infection?


Investigating a Chemical Incident

  1. Check information - What is the chemical? Find out the risk to health
  2. Who is there? - HAZMAT officer? COMAH site?
  3. How many people were exposed?
  4. How big is the release?
  5. Check CHEMET - which way is wind blowing?
  6. Organize meeting - depending on the event - bronze, silver, gold level (PCT, acute trust, police, ambulance, environmental agency and communications officer)
  7. Control - public health decision is usually shelter or evacuate - risk assessment of pathway, may need to advise decontamination/PPE (targets); Local Council are responsible for the clean up
  8. Report - consider cohort/case control (environmental monitoring/biomonitoring)


Investigating Clusters

A cluster is an unusual aggregation, real or perceived of health events that are group together in time and space and that are reported to a health agency

Steps:

  1. Initial contact, if further evaluation is needed...
  2. Assessment, if excess has occurred...
  3. Preliminary evaluation, look at reference and excess then...
  4. Case evaluation, once diagnosis verified, if there are excess...
  5. Occurrence evaluation, use lit review and advise committee - excess and biologic and epidemiology plausibility?
  6. Do major feasibility study (case control study and exposure measurement; examines relationship between case cluster and exposure)