Story
Think broadly! Consider all the options!
Think how new data could help us narrow down the options!
District MO, hospital X has 18 deaths following illness: fever, vomiting, abdo pain, diarrhoea. One of them was a midwife in the hospital
Spreading across roads.
How might you prepare to investigate this outbreak
Team
- Epidemiologist
- Clinician
- Logistician/Financial
- Community Liasion/Translator
- Infection Control Specialist
- Pathologist/Microbiologist
- Local Government/Health Department
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You go to hospital to investigate. By this time 32 people are admitted.
Main features are:
- Pyrexia
- Headache
- Haematemesis
- Bloody Diarrhoea
- Retrosternal and Abdominal Pain
- Arthritis
- Prostration leading to death
11/17 staff members have died of illness.
2 weeks later, the district is quarantined.
What Main categories of disease should you think:
- Infectious
- Non-Infectious
Infectious
Viral
Haemorrhagic
- Marburg
- Lassa
- Ebola
- Crimean Congo Haemorrhagic Fever
- Dengue
- Yellow Fever
Bacterial
- GI: Shigella (relatively likely) / Salmonella / e.coli 0157
- Meningococcal disease
- Plague
Non Infectious
Poisonings
- Pesticides
- Aflatoxin (contamination of mould in grain)
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A virus is isolated from samples sent to the WHO reverence lab, similar to previously known viruses which cause haemorrhagic fever, a serological test is developed by the reference lap
What modes of transmission should we consider
Direct
- Respiratory Droplets (Direct Transmission) and droplets
- Faeco-oral
- Bodily Fluid (vomitus, etc)
- Sexual
- Skin-to-skin
- Transfusion
- Mother to child
Indirect
- Fomites (inanimate objects that can transmit - clothes, towels, door handles)
- Zoonotic
- Respiratory airborne
- Vectors (mosquitoes, flies, bats, rats)
- Food-borne
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A missionary nurse with the illness has been transported to the capital, a nurse who has cared for her has become ill and died.
Your team has been investigating contacts, these contacts have had a range of disease from minor illness with headache, fever, abdo pain, vomiting, and bleeding.
What is the next step in your investigation?
You need to identify what is a case and what isn’t a case
Proven: A symptomatic person, vius was isolated or demonstrated by electron microscopy, or positive serological test, within three weeks of onset symptoms
Probable: a person living in area who died after one or more days with two or more of the following: headache, fever, abdo pain, nausea, vomiting, bleeding
Possible: A person with headache and/or/fever for at least 24 hours with or without signs and sypmtoms, who had contact with a proven or probable case in the preceding three weeks
These mix of case definitions gives you a wide range of sensitivity vs specificity.
So now you need to do some case finding!
- Contact Tracing (Household)
- Hospital Records
- Primary Care Facilities
- Active Case Finding (Going round house to house)
When you’ve found your cases, what next?
- Demographics of population with disease (time, place, person)
Epidemic Curves
SEE NOTES DRAWN
You plot incidence over time, with a single box for each case. You colour in these cases if they die
Point Source - one single source of exposure, you’ll see some single skewed distribution
Extended Source - prolonged source of infection, you’ll see a stretched distribution curve
Propogated Source - Often seen in person to person source, you’ll see repeated peaks in incidence like waves on the sea
Summary Of Story so far
- Virus has caused large epidemic in central africa, haemorrhagic fever
- Cases began in sept, peaked in month, tapered off during october
- Case fatality rate decreased as epidemic progressed
- All ages and both sexes were affected. Infants and women age 15-29 were most susceptible
- Cases occured in wide number of villages
- Most cases in yambuku. further away along roads, the less case attack rate we’ve got
What hypotheses would you have for mode of transmission so far?
This will need a case control study. Compare our people with disease against the people without the disease, and try and determine modes of transmission.
2 Main Things:
- Transmission through hospital exposure
- Contact with an unwell patient?
Other questions you might ask
- Exposure to bodily fluids, sexual contact?
- Breastfeeding?
- Exposure to animal groups
- Sharing food or water supply?
Then with your cases, match against a well person from age and village.