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,Outline,Introduction Models Model I - One type of syringe Model II - Multiple type of syringe Future work,Introduction,P
2、rincipal cause of HIV Prevention/controlling methods Using syringes that is impossible to reuse. (may not be feasible) Distributing Difficult-to-reuse (DTR) syringes,Design approaches for DTR,Syringes containing hydrophilic gel Plungers disabled when reload Needles disabled after the first use Valve
3、s 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
4、 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 (IDUs
5、) injects with an infectious syringe. Kaplan 1989 introduced one type syringe model considering syringes perspective.,How this model differ from Kaplans 1989 model?,Kaplan1989: changes in the proportion of number of IDUs who are infected and changes in proportion of number of syringes which are infe
6、cted.This paper: on the proportion of injections that are made with infectious syringes. Kaplan1989: one type of syringeThis paper: one and multiple types of syringes Kaplan 1989: followed individual syringesThis paper: Sequence of syringes in succession Kaplan 1989: Used differential equationsThis
7、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) Infe
8、ctious (I) Probability from uninfectious to infectious PUI Probability from infectious to uninfectious PIU,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 th
9、at 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.,Model I (Cont.),Probability of uninfectious syringe becom
10、e infectious PUI = f (1- ),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 use
11、s (by killing virus or replacing syringe)= probability of cease to be infectious between uses,Model I (Cont.),Probability of infectious syringe become uninfectiouspUI =(1- f)+(1-(1-f)here = Where = probability of “dry out”/killing virusn = mean of geometric random variable,Model II,There is more tha
12、n 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.),Th
13、e 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 r
14、egular syringes before the interventionr = 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)nR+snD where=
15、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,Future work,Finding proportion of infectious injections for both models Explaining properties of the model Estimating parameter values Numerical estimates,Thank You,
