IPCC Report.pdf - Adam Curry

Chapter 9Case Studieswith increased health-related vulnerability. Waxing and waning immunityas a result of prior exposure has a significant impact on populationvulnerability to cholera over long periods (Koelle et al., 2005b).While physiologic susceptibility is important, social and economic driversof population susceptibility persistently seem to drive epidemic risk.Poverty is a strong predictor of risk on a population basis (Ackers et al.,1998; Talavera and Perez, 2009), and political factors, as illustrated bythe Zimbabwe epidemic, are often important drivers of epidemic severityand persistence once exposure occurs. Many recent severe epidemicsexhibit population susceptibility dynamics similar to Zimbabwe, includingin other poor communities (Hashizume et al., 2008), in the aftermathof political unrest (Shikanga et al., 2009), and following populationdisplacement (Bompangue et al., 2009).9.2.7.2.3. Adaptive capacityCholera outbreaks are familiar sequelae of complex emergencies. TheDRM community has much experience with prevention efforts to reducethe likelihood of cholera epidemics, containing them once they occur,and reducing the associated morbidity and mortality among the infected.Best practices include guidelines for water treatment and sanitation andfor population-based surveillance (Sphere Project, 2004).9.2.7.3. Description of EventZimbabwe has had cholera outbreaks every year since 1998, with the2008 epidemic the worst the world had seen in two decades, affectingapproximately 92,000 people and killing over 4,000 (Mason, 2009). Theoutbreak began on 20 August 2008, slightly lagging the onset ofseasonal rains, in Chitungwiza city, just south of the capital Harare(WHO, 2008a). In the initial stages, several districts were affected. InOctober, the epidemic exploded in Harare’s Budiriro suburb and soonspread to include much of the country, persisting well into June 2009and ultimately seeding outbreaks in several other countries. Weatherappears to have been crucial in the outbreak, as recurrent point-sourcecontamination of drinking water sources (WHO, 2008a) was almostcertainly amplified by the onset of the rainy season (Luque Fernandez etal., 2009). In addition to its size, this epidemic was distinguished by itsurban focus and relatively high case fatality rate (CFR; the proportion ofinfected people who die) ranging from 4 to 5% (Mason, 2009). Mostoutbreaks have CFRs below 1% (Alajo et al., 2006). Underlying structuralvulnerability with shortages of medicines, equipment, and staff athealth facilities throughout the country compounded the effects of thecholera epidemic (WHO, 2008b).9.2.7.4. InterventionThere are several risk management considerations for preventingcholera outbreaks and minimizing the likelihood that an outbreakbecomes a disastrous epidemic (Sack et al., 2006). Public health has awide range of interventions for preventing and containing outbreaks,and several other potentially effective interventions are in development(Bhattacharya et al., 2009). As is the case in managing all climatesensitiverisks, the role of institutional learning is becoming ever moreimportant in reducing the risk of cholera and other epidemic disease asthe climate shifts.9.2.7.4.1. Conventional public health strategiesThe conventional public health strategies for reducing cholera riskinclude a range of primary, secondary, and tertiary prevention strategies(Holmgren, 1981).Primary prevention, or prevention of contact between a hazardousexposure and susceptible host, includes promoting access to clean waterand reducing the likelihood of population displacement; secondaryprevention, or prevention of symptom development in an exposed host,includes vaccination; and tertiary prevention, or containment of symptomsand prevention of complications once disease is manifest, includesdehydration treatment with oral rehydration therapy.9.2.7.4.2. Newer developmentsEnhanced understanding of cholera ecology has enabled developmentof predictive models that perform relatively well (Matsuda et al., 2008)and fostered hope that early warning systems based on remotely sensedtrends in sea surface temperature, algal growth, and other ecologicaldrivers of cholera risk can help reduce risks of epidemic disease,particularly in coastal regions (Mendelsohn and Dawson, 2008).Strategies to reduce physiologic susceptibility through vaccination haveshown promise (Calain et al., 2004; Chaignat et al., 2008; Lopez et al.,2008; Sur et al., 2009) and mass vaccination campaigns have potentialto interrupt epidemics (WHO, 2006c), and may be cost effective inresource-poor regions or for displaced populations where provision ofsanitation and other services has proven difficult (Jeuland andWhittington, 2009). Current World Health Organization policy on choleravaccination holds that vaccination should be used in conjunction withother control strategies in endemic areas and be considered forpopulations at risk for epidemic disease, and that cholera immunizationis a temporizing measure while more permanent sanitation improvementscan be pursued (WHO, 2010). Ultimately, given the strong associationwith poverty, continued focus on development may ultimately have thelargest impact on reducing cholera risk.9.2.7.5. OutcomesManaging the risk of climate-sensitive disease, like risk management ofother climate-sensitive outcomes, will necessarily become more iterativeand adaptive as climate change shifts the hazard landscape and509