EPIDEMIC MODELLING OF AIDS INCIDENCE DATA FOR SUBSAHARAN AFRICA

1
EPIDEMIC MODELLING OF AIDS INCIDENCE DATA FOR
SUB-SAHARAN AFRICA

• ELVIS AMOAKWA NURO 2ND YEAR PhD
• SCHOOL OF GEOGRAPHY-UNIVERSITY OF MANCHESTER
• SUPERVISOR PROFESSOR RICHARD THOMAS

2
INTRODUCTION

• The magnitude and the directionality of the
  HIV/AIDS epidemic
• Limited data to base estimates
• Modelling approach can make a valuable
  contribution (Thomas, 1992).

3
AIM OF THE STUDY

• Investigate the magnitude and directionality of
  the HIV/AIDS
• Examine the implication for future AIDS
  incidence

4
OBJECTIVES OF THE STUDY

• Identify starting dates for initial HIV
  infections in each country
• Estimate the eventual size of the epidemic based
  on procedures that have been applied to countries
  of Western Europe(Thomas,2000)
• Estimate transmission probability
• Estimate the date of forecast endemic state
• Reconstruct national transmission pathways at the
  start of the epidemic and at the peak of the
  epidemic.

5
COMMUNITY SI MODEL FOR HIV/AIDS STATE DIAGRAM
susceptible incidence infective
removalsincubationAIDS x ??rxy/n
?y ?y/D ?w
?w/A npopulation at risk(epidemic size to be
estimated) r partnership acquisition rate10
per year ? probability a partnership result in
transmission (to be estimated about 0.1) D
period of communicability 2 years A period of
uninfectivity prior to the onset of AIDS 4
years DIFFERENTIAL EQUATIONS dx/dt -?rxy/n,
and dx/dt ?rxy/n-y/D, dw/dt y/D-w/A Some of
the epidemiological parameters in the model are
given estimates taken from published sources. The
duration of the period of communicability(D2
years) and antigen suppression(A4 years) are
drawn from research into viral abundance and
antigen concentration in patients after HIV
infection(Anderson and May, 1991). Similarly an
average value of r10 partners per year for those
at high risk is taken from survey of sexual
behaviour made at different times during the
course of the epidemic(Knox et al, 1993 Johnson
et al, 1994).
6
Table 1. Epidemic dates and statistics fitted by
the single country model
7
Table 2. Estimated peak year for HIV/Predicted
cases
8
(No Transcript)
9
(No Transcript)
10
Table 1. Epidemic dates and statistics fitted by
the single country mode
11
Table 1. Epidemic dates and statistics fitted by
the single country mode (cont)
12
CONCLUSION

• Estimated date for start of the epidemic 1974
• Epidemic started concurrently in West Africa and
  Central Africa Ghana and D.R.Congo respectively
• Transmission pathways at peak of epidemic Cote
  dIvoire infecting West African sub-region while
  D.R.Congo, Tanzania and South Africa infect
  central, east and southern Africa respectively.