Can Difficult-to-Reuse Syringes Reduce the Spread of HIV Among Injection Drug Users? -Caulkins, Kaplan, Lurie, O

1
Can Difficult-to-Reuse Syringes Reduce the Spread
of HIV Among Injection Drug Users?-Caulkins,
Kaplan, Lurie, OConnor Ahn

• Presented by
• Arifa Sultana
• Zoila Guerra
• Vikram Sriram

2
Outline

• Introduction
• Models
• Model I - One type of syringe
• Model II - Multiple type of syringe
• Future work

3
Introduction

• Principal cause of HIV
• Prevention/controlling methods
• Using syringes that is impossible to reuse. (may
  not be feasible)
• Distributing Difficult-to-reuse (DTR) syringes

4
Design approaches for DTR

1. Syringes containing hydrophilic gel
2. Plungers disabled when reload
3. Needles disabled after the first use
4. Valves that prevent second loading

5
Benefits of DTR

• Reduce the frequency of reused syringes
• Reduce the syringes sharing with other

6
Objectives of the paper

• Proportion of injections that are potentially
  infectious and transmit HIV (i.e. proportion
  infectious injection)
• Which effect would be greater?
• Regular
• DTR Regular

7
Assumptions

• Total number of syringes and the frequency of
  injection remain constant.
• Consider only intentional injections.
• Here the syringe is treated as infinitely lived.

8
Model I One type of Syringe

• To find out the impact of DTR in spread of HIV
• How often an injection drug users (IDUs) injects
  with an infectious syringe.
• Kaplan 1989 introduced one type syringe model
  considering syringes perspective.

9
How this model differ from Kaplans 1989 model?

• Kaplan1989 changes in the proportion of number
  of IDU's who are infected and changes in
  proportion of number of syringes which are
  infected.
• This paper on the proportion of injections
  that are made with infectious syringes.
• Kaplan1989 one type of syringe
• This paper one and multiple types of syringes
• Kaplan 1989 followed individual syringes
• This paper Sequence of syringes in succession
• Kaplan 1989 Used differential equations
• This paper Discrete-time Markov model

10
Model I (Cont.)

• Discrete-time Markov model Find the probability
  that the syringe is infectious
• The epochs are the instants of time just before a
  session in which a syringe is used to inject
  drugs.
• At each epoch a syringe can be in two states
• Uninfectious (U)
• Infectious (I)
• Probability from uninfectious to infectious PUI
• Probability from infectious to uninfectious PIU

11
Model I (Cont.)

• How a Un-infectious Infectious?
• Used by infected user
• the probability of use by an infected user
• Become infectious through that use
• the probability become infectious
  through that use
• Remain infectious until just before subsequent
  use
• probability of remain infectious until
  just before subsequent use.
• probability that a syringe which is
  infectious immediately after use, ceases to be
  infectious before its next use.

12
Model I (Cont.)

• Probability of uninfectious syringe become
  infectious
• PUI f f (1- ?)

13
Model I (Cont.)

• How a infectious un infectious
• Both used by an uninfected user
• probability of both used by an
  uninfected user.
• Have that use render the syringe un-infectious
• probability that the use renders the
  syringe un-infectious
• 2. Cease to be infectious between uses (by
  killing virus or replacing syringe)
• probability of cease to be infectious between
  uses

14
Model I (Cont.)

• Probability of infectious syringe become
  uninfectious
• pUI (1- f)?(1-(1-f)?)?)
• here ?
• Where
• probability of dry out/killing virus
• n mean of geometric random variable

15
Model II

• There is more than one type of syringe
• The overall fraction of potentially infectious is
  the weighted sum of the fractions for each type
  of syringe.
• Focus on two types of syringes.
• How the proportion of infectious injections would
  change if DTR syringes are introduced into the
  current environment

16
Model II (Cont.)

• The outcome depends on
• Number of both DTR and regular syringes consumed
  after the DTR syringes are introduced compares to
  the number of regular syringes consumed before
  DTR syringes are introduced.

17
Model II (Cont.)

• s rate of consumption of syringes introduced by
  intervention/rate of consumption of regular
  syringes before the intervention
• r change in rate of consumption of regular
  syringes caused by intervention/rate of
  consumption of regular syringes before
  intervention

18
Model II (Cont.)

• If the number of injections remains the same
  after the introduction of DTR syringes,
  nR(1r)nRsnD where
• average number of times a DTR syringe is
  used
• average number of times a regular syringe
  was used before DTR syringes were introduced
• average number of times regular
  syringes are used after DTR are introduced

19
Future work

• Finding proportion of infectious injections for
  both models
• Explaining properties of the model
• Estimating parameter values
• Numerical estimates

20
Thank You