Cost-effectiveness comparison of response strategies to a large-scale anthrax attack on the chicago metropolitan area: impact of timing and surge capacity

Abstract

Rapid public health response to a large-scale anthrax attack would reduce overall morbidity and mortality. However, there is uncertainty about the optimal cost-effective response strategy based on timing of intervention, public health resources, and critical care facilities. We conducted a decision analytic study to compare response strategies to a theoretical large-scale anthrax attack on the Chicago metropolitan area beginning either Day 2 or Day 5 after the attack. These strategies correspond to the policy options set forth by the Anthrax Modeling Working Group for population-wide responses to a large-scale anthrax attack: (1) postattack antibiotic prophylaxis, (2) postattack antibiotic prophylaxis and vaccination, (3) preattack vaccination with postattack antibiotic prophylaxis, and (4) preattack vaccination with postattack antibiotic prophylaxis and vaccination. Outcomes were measured in costs, lives saved, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs). We estimated that postattack antibiotic prophylaxis of all 1,390,000 anthrax-exposed people beginning on Day 2 after attack would result in 205,835 infected victims, 35,049 fulminant victims, and 28,612 deaths. Only 6,437 (18.5%) of the fulminant victims could be saved with the existing critical care facilities in the Chicago metropolitan area. Mortality would increase to 69,136 if the response strategy began on Day 5. Including postattack vaccination with antibiotic prophylaxis of all exposed people reduces mortality and is cost-effective for both Day 2 (ICER=$182/QALY) and Day 5 (ICER=$1,088/QALY) response strategies. Increasing ICU bed availability significantly reduces mortality for all response strategies. We conclude that postattack antibiotic prophylaxis and vaccination of all exposed people is the optimal cost-effective response strategy for a large-scale anthrax attack. Our findings support the US government's plan to provide antibiotic prophylaxis and vaccination for all exposed people within 48 hours of the recognition of a large-scale anthrax attack. Future policies should consider expanding critical care capacity to allow for the rescue of more victims.

Figure 1.

Inhalational Anthrax Disease Transition State Model, with both progression and resolution states from base-case estimates from a large-scale attack on the Chicago metropolitan area. Estimates consider a public health response of postattack antibiotic prophylaxis only that begins on Day 2 after an attack and is completed within 48 hours with 50% of the 2,655 ICU beds available to provide critical care. Estimates of victims in the disease transition states vary depending on timing of response, type of strategy, and available ICU beds.

Figure 2.

Cost-Effectiveness Acceptability Curves for including preattack vaccination with postattack antibiotic prophylaxis and vaccination strategies based on day of response and probability of attack. For the base-case 1% yearly probability of attack, including preattack vaccination with postattack antibiotic prophylaxis and vaccination has a low probability of being cost-effective that slowly improves for both the Day 2 and Day 5 response strategies as the willingness-to-pay thresholds increase from $0 to $300,000 per QALY gained. At a 0.1% yearly probability of attack, preattack vaccination is not likely to be cost-effective at all willingness-to-pay thresholds for both Day 2 and Day 5 response strategies. However, at 10% yearly probability of attack, including preattack vaccination is likely to be cost-effective for nearly all willingness-to-pay thresholds for both Day 2 and Day 5 response strategies.

Figure 3.

Effects of Increasing the Number of Intensive Care Unit (ICU) Beds Available to provide critical care therapy for fulminant victims on the overall number of deaths from inhalational anthrax. Estimates are based on the different postattack public health intervention strategies (ie, antibiotic prophylaxis compared with antibiotic prophylaxis and vaccination) and timing of the response strategy (ie, Day 2 compared to Day 5) to a large-scale attack on the Chicago metropolitan area.

Figure 4.

Effects of Varying the Number of Intensive Care Unit (ICU) Bed Availability over a wide range (ie, 0 to 500,000) of initially infected cases of inhalational anthrax on the total number of deaths from inhalational anthrax. These analyses were conducted for both the Day 2 and Day 5 response strategies using postattack antibiotic prophylaxis and vaccination with 1,000, 5,000, or 10,000 potentially available ICU beds in the Chicago metropolitan area.