Insights from Economic-Epidemiology
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Insights from economicepidemiology Ramanan Laxminarayan Resources for the Future, Washington DC Economic Epidemiology Mathematical conceptualization of the interplay between economics, human behavior and disease ecology to improve our understanding of – the emergence, persistence and spread of infectious agents – optimal strategies and policies to control their spread Economics Measuring health outcomes Provides a single metric to compare costs and benefits both contemporaneously and over time. Incorporating behavior Can alter conclusions reached by purely epidemiological models by incorporating behavior. Comparing public policies Increases relevance for application in the real world. Overview Individual response and disease Incentives of institutions (to invest in hospital infection control) Optimal allocation of resources between two regions (or hospitals) Individual response and disease Vaccinations – Insufficient incentives to vaccinate prevent attainment of herd immunity thresholds Drug resistance – Insufficient incentives to make appropriate use leads to ineffective drugs and increasing prevalence Testing – Private testing behavior adds to public information on disease prevalence Rational epidemics Prevalence response elasticity – Hazard rate into infection of susceptibles is a decreasing function of prevalence (opposite of epidemiological model predictions) – Application to HIV – Application to Measles Geoffard and Philipson, Int. Econ. Rev., 1996 Blower et al, Science, 2000 Blower et al, Science, 2000 When should governments intervene? Disease prevalence increases adoption of public programs Impact of public program may be zero if prevalence has already reached an individual’s threshold prevalence Paradoxically, the role of government subsidies is lowest when prevalence is highest since individuals will protect themselves regardless Philipson, NBER, 1999 Public price subsidies Can price subsidies or mandatory programs achieve eradication? – Increase in demand by folks covered by the program lowers the incentives to vaccinate for those outside the program Do monopolistic vaccine manufacturers have an incentive to eradicate disease? – Market for their product would disappear with eradication Geoffard and Philipson, Int Econ Rev, 1997 Disease Complementarities Incentive to invest in prevention against one cause of death depends positively on probability of dying from other causes Intervening to prevent mortality not only prevents a death but also increases incentives for the family to fight other diseases Dow et al, Am Econ Rev, 1999 Does the theory fit the facts? Do individuals actually observe prevalence? Why don’t we see prevalence responsiveness at work everywhere? Importance of observational learning (herd behavior)? Stoneburner and Low-Beer, Science, 2004 Stoneburner and Low-Beer, Science, 2004 Stoneburner and Low-Beer, Science, 2004 NNIS Data, 2004 Optimal infection control Infection dynamics are given by X c X 1 X X Equilibrium prevalence is given by X c S c 1 S c 1 2 4 S c 2S c Smith, Levin, Laxminarayan (PNAS, 2005) Objective Minimize costs of infection control and infections c DX c Local minima, if they exist, are solutions to 1 DX ĉ0 Smith, Levin, Laxminarayan (PNAS, 2005) Smith, Levin, Laxminarayan (PNAS, 2005) Strategic interactions with other hospitals X c X 1 XX X Z Y c Y 1 YY Y Z Ż r X/n n 1 Y/n ZZ The focal institution decides how much to invest in HIC by minimizing the net present value of discounted costs of HIC and hospitalization: 0 c DX t, c;n, c e t dt Smith, Levin, Laxminarayan (PNAS, 2005) Implications for policy Dutch experience: frequency of MRSA infections is < 0.5% after an intensive ‘‘search-and-destroy’’ campaign, compared with 50% in some areas In Siouxland (Iowa, Nebraska, S. Dakota), an epidemic of VRE was reversed Regionally coordinated response to epidemic Does this explain higher prevalence of ARB in areas with high concentration of health care institutions? Rowthorn, Laxminarayan, Gilligan Submitted Rowthorn, Laxminarayan, Gilligan Submitted Rowthorn, Laxminarayan, Gilligan Submitted Rowthorn, Laxminarayan, Gilligan Submitted Allocating resources Expenditure on drugs is subject to the budget constraint cF1 F2 M Finance is not transferable through time. Problem is to choose F₁and F₂ so as to minimise the following integral rt e I1 0 V Rowthorn, Laxminarayan, Gilligan Submitted I 2 dt Optimal allocation At low levels of infection in both populations – Preferentially treat population with higher transmission coefficient because of greater economic value associated with greater potential to prevent secondary infections At high levels of infection – Preferentially treat population with lower levels of infection since the higher probability of re-infection in high infection populations reduces the economic value of treatment Rowthorn, Laxminarayan, Gilligan Submitted 0.5 0.0 0 0.10 35 70 Time Region 1 Region 2 0.00 0 10 20 0.15 0.0 0 0.10 40 50 60 0 10 20 0.5 0 35 70 Time 0.05 50 40 50 60 0.2 0.5 0 35 0 35 70 Time 0.2 0.0 10 20 30 40 50 60 10 20 30 40 Time Proportion infected 0.50 0.25 0.00 0.00 70 i Worst path 0.8 50 60 70 0.25 0.50 0.75 Region 1 Proportion infected 0.75 0.6 1.0 0.4 0.2 0.5 0.0 0 35 0.50 0.25 70 Time 0.0 0 0.18 70 Time Treated 0.0 Proportion infected Treated 0.5 0.12 0.0 0 h 1.0 0.4 0.75 Time 0.8 0.6 f 1.0 0.4 0.06 Region 1 0.6 70 Best path 1.0 0.10 0.00 0.00 70 Region 2 30 60 Worst path 0.8 Time Proportion infected 40 0.0 0.00 g 30 Treated e 1.0 0.10 20 0.15 Time 0.0 10 Proportion infected 0.05 0.05 70 Proportion infected Treated Proportion infected 0.15 0 70 0.00 30 Best path 0.20 35 Time Time d 0.5 Region 2 0.05 0.20 1.0 Region 2 Proportion infected 0.15 c Worst path 0.20 1.0 Treated Proportion infected b Best path 0.20 Treated a 0 10 20 30 40 Time Rowthorn, Laxminarayan, Gilligan Submitted 50 60 70 0.00 0.00 0.25 0.50 Region 1 0.75 Closing thoughts Epidemiological models take little or no account of economic constraints or incentives faced by individuals or institutions Economic models mostly ignore the spatial and temporal dynamics of disease.
