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Can Difficult-to-Reuse Syringes
Reduce the Spread of HIV
Among Injection Drug Users?
-Caulkins, Kaplan, Lurie, O’Connor & Ahn
Presented by:
Arifa Sultana
Zoila Guerra
Vikram Sriram
Outline

Introduction

Models


Model I - One type of syringe

Model II - Multiple type of syringe
Future work
Introduction

Principal cause of HIV

Prevention/controlling methods
 Using
syringes that is impossible to
reuse. (may not be feasible)
 Distributing
syringes
Difficult-to-reuse (DTR)
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
Benefits of DTR

Reduce the frequency of reused
syringes

Reduce the syringes sharing with
other
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
Assumptions

Total number of syringes and the
frequency of injection remain constant.

Consider only intentional injections.

Here the syringe is treated as infinitely
lived.
Model I –
One type of Syringe

To find out the impact of DTR in spread of
HIV


How often an injection drug users (IDU’s)
injects with an infectious syringe.
Kaplan [1989] introduced one type
syringe model considering syringe’s
perspective.
How this model differ from
Kaplan’s [1989] model?

Kaplan[1989]: 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.

Kaplan[1989]: 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
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
Model I (Cont.)
How a Un-infectious

Used by infected user
f


Infectious?
= 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
1   

= 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.
Model I (Cont.)
Probability of uninfectious syringe become
infectious
PUI = f φ (1- ω)
Model I (Cont.)
How a infectious
1.
un infectious
Both used by an uninfected user
(1  f ) = 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
Model I (Cont.)
Probability of infectious syringe become uninfectious
pUI =(1- f)θ+(1-(1-f)θ)ω)
here
   
ω= 
n
Where
 = probability of “dry out”/killing virus
n = mean of geometric random variable
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
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.
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
Model II (Cont.)
If the number of injections remains the same after
the introduction of DTR syringes,
nR=(1+r)n’R+snD
where
nD = average number of times a DTR syringe is
used
nR = average number of times a regular syringe
was used before DTR syringes were
introduced
n = average number of times regular syringes
'
R
are used after DTR are introduced
Future work

Finding proportion of infectious
injections for both models

Explaining properties of the model

Estimating parameter values

Numerical estimates
Thank You