Volume 23, Number 1—January 2017
Modeling Tool for Decision Support during Early Days of an Anthrax Event
|Parameter||Baseline value||Range†||User adjustable‡||Reference|
|Case counts for days 1, 2, 3§||20, 10, 70||1–4 days of data||Yes||(12)|
|Median inhaled spore count, no.¶||360||1–8,000||Yes||(13,14)|
|Median incubation, d ± SD||6.9 ± 1.8||10.3–5.0 ± 2.2–1.6||Yes||(13)|
|Population size of the impacted jurisdiction, no.
|PEP Impact model|
|Size of population to receive prophylaxis||500,000||Yes#||Assumed|
|PEP throughput at full capacity, daily||250,000||Yes||Assumed**|
|Delay to PEP campaign start, d††||2||1–2||Yes||(9)|
|Ramp-up period until PEP campaign throughput reaches full capacity, d||0||Yes||Assumed**|
|PEP campaign duration at full throughput capacity, d||2||1–4||Yes||Assumed**|
|PEP uptake, %‡‡||65||40–90||Yes||(11)|
|Antibiotic efficacy, %||90||Yes||(15–17)|
|Adherence to PEP regimen at event day 60, %||40||25–80||Yes||(18)|
|Time until antimicrobials are protective, d
|Healthcare Impact model|
|Public health messaging starts, d of event§§||2||Yes||Assumed|
|Proportion seeking care relative to public health message timing, by disease state||(2)|
|During prodromal stage, %||40 before; 80 after||Yes|
|During fulminant stage, %||95 before; 95 after||Yes|
|Daily transition fraction from prodromal to fulminant illness, by outcome||(19)|
|Eventually recover, %||20||No|
|Eventually die, %||50||No|
|Maximal length of prodromal illness, by outcome||(19)|
|Eventually recover, d||5||No|
|Eventually die, d||2||No|
|Length of fulminant illness among untreated, d||0||No||Assumed|
|Length of fulminant illness among treated who die, d¶¶||1||No||(19)|
|Median ± SD of normal distribution of length of treatment among those who recover, d¶¶||18 ± 3||No||(19)|
|Recover with treatment, by stage of illness when treatment initiated, %##||Assumed|
|Prodromal who recover after fulminant illness, %***||50||Yes||(2)|
*Amerithrax, anthrax attacks in the United States during 2001; CRI, Cities Readiness Initiative; PEP, postexposure prophylaxis.
†Values provided were used in our evaluation of the influence of the number of days of case data on Epi-Curve projections (case counts parameter), to create high and low final case count estimates (median inhaled spore count and median incubation parameters), and to evaluate various PEP scenarios (all PEP-Impact model parameters) (Table 3). Range values used in the univariate sensitivity analysis of PEP parameters differ (Table 4).
‡Anthrax Assist user can readily change the input value.
§Case counts from the first 3 days of the 1979 Sverdlovsk (USSR) anthrax event epidemic curve inflated by a factor of 10. When 4 days of case counts are used (Table 4), the fourth day of counts is 40.
¶360 spores is a dosage estimated to have occurred during the 1979 Sverdlovsk (USSR) anthrax event (13). One spore represents the minimum possible infectious dose, and 8,000 is a plausible high dose (14).
#Cannot exceed the value of the Epidemic-Curve model “Population size of the impacted jurisdiction” parameter. When less, proportionately fewer infected persons are eligible for PEP protection.
**Value chosen so that PEP dispensing is in accordance with US CRI guidelines and is completed within 2 days after the decision to initiate PEP (9).
††Determined by counting days from date of earliest illness onset (i.e., event day 1).
‡‡Percentage of population targeted to receive PEP who actually obtain and start PEP.
§§Public health messaging only influences treatment-seeking behavior in the absence of a PEP campaign or prior to campaign initiation.
¶¶Same length assumed for patients initiating treatment in the fulminant versus prodromal stage of illness.
##Assumes an improved treatment effectiveness compared with the 2001 US anthrax attacks as a result of clinical experience gained in treating inhalation anthrax cases in the United States since and the recent availability of intravenous antitoxin; in addition to the full complement of medical resources used during the 2001 attacks: an acute-care bed and the associated medical care staff (including respiratory therapists), pleural fluid drainage, mechanical respiratory ventilation, and intravenous antimicrobial drugs. In the United States in 2001, 6 (67%) of 9 persons who sought treatment during the prodromal stage of illness recovered (however, 2 who died did not receive antimicrobial drugs with activity against Bacillus anthracis until they exhibited fulminant illness), and both persons who sought care during fulminant illness died (2,20).
***On the basis of 6 survivors during the 2001 Amerithrax attacks who sought treatment during the prodromal illness stage: cases 2, 3, 4, 7, 8, 9 (2,20). Progression to fulminant illness was defined as severe symptomatic disease characterized by respiratory distress requiring pleural effusion drainage, or mechanical ventilation, marked cyanosis, shock, or meningoencephalitis.
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1These senior authors contributed equally to this article.