Cholera in South Africa 20002001

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Cholera in South Africa 2000/2001

• Catalina Anghel
• Andrea Borowski

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Overview

• What is cholera?
• Cholera in South Africa
• Data
• Models
• SIR model
• Modified SIR model according to Torres Codeco
• Conclusions

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1. What is cholera?

• Acute intestinal infection
• caused by the bacterium
• Vibrio cholerae
• Infection results in a diarrhoea that can lead to
  dehydration and death
• Infected people
• excrete bacteria between 7 and 14 days
• lt20 show typical symptoms of cholera
• Rarely person to person transmission

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2. Cholera in South Africa in 2000/2001

• Total number of infected 106 159
• Start in mid august 2000
• Affected region KwaZulu-Natal
• population 9.3 mi.
• most people use rivers and wells as their water
  supply
• Heavy rainfall starting in November 2000

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2.1. Data

• total infected cases and deaths from October 13,
  2000 to April 16, 2001

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• ratio of total deaths to total number of infected
  people decreased, then stabilized

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3. Models
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3.1 SIR model
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accumulative infectives c(t), fitted using SIR,
first trial
x 10
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raw data
fitted data
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7
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• Fitted a and ß numerically using a integration
  method embedded within a minimization routine
• a 0.0086 1/day
• ß 2.2 x 10-7 1/day

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number of infected
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3
2
1
0
0
20
40
60
80
100
120
140
160
180
200
days
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• Whole susceptible population becomes infected
• Number of infected increases and decreases over
  time

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• Fitted a, ß and S0 using the same method
• a - 0.025 1/day
• ß 1.5 x 10-7 1/day
• S0 82,500
• Un-physical results
• a lt 0
• S0lt total infected.

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3.2 Modified SIR model (Torres Codeco)
Infected (I)
r
Susceptible (S)
a
e
?(B)
Aquatic toxigenic V. cholerae (B)
m
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(No Transcript)
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• Fitted a, r and e
• a 1.332 (Codeco a 1)
• r 0.012 (Codeco r 0.2)
• Different definition for cholera cases
• e 0.0654
• (Codeco e 10)
• Hospitalizing

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• S and I plots similar to SIR model

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• Heavy rains and flooding have increased the risk
  of contaminating rivers and drinking wells.
• The risks are particularly high because many
  villages have no latrines, and human waste mixes
  with floodwaters.
• 10 million households were cut off from water in
  2001.

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• modified e over time to take rainy season into
  consideration

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• a 0.110, r 0.319
• e 1.566 (1sin(2p/365 -0.029))

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• Number of susceptibles decreases to 320,000 and
  stays constant
• Infected population decreases at the beginning
  (start of the epidemic in august!)

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Control mechanisms

• Hygienic disposal of human feces
• Adequate supply of safe drinking water
• Hygienic measures washing hands, cooking food

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How do control mechanisms influence the
parameters?

• Good sanitation reduces parameter e and water
  treatment reduces parameter a.
• The smaller these parameters are, the larger must
  be the susceptible pool in order to a cholera
  outbreak to develop.

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4. Conclusions

• Simple SIR model does not consider transmission
  through water supply.
• SIR model taking into account the aquatic
  reservoir corresponds to our data
• Through changing parameter e over time, we
  included the onset of the rainy season in the
  model.
• FUTURE
• Taking into account the onset of the epidemic
  (August-October)
• Seasonal changes also in parameter a
• Independent estimates for parameters to compare
  with fitted parameters
• Using the model to fit data from other cholera
  outbreaks

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References

• www.who.int
• www.textbookofbacteriology.net
• Endemic and epidemic dynamics of cholera the
  role of the aquatic reservoir, Claudia Torres
  Codeco, BMC Infectious Diseases, 2001