Volume 21, Number 7—July 2015
Estimating Ebola Treatment Needs, United States
|Arriving persons||Input 1: infections/mo*||Input 2: at-risk population||Input 3: US arrival rate/mo†||Output 1: importations/mo‡||Output 4: additional secondary cases§||Output 2: total cases/mo‡|
*Infections in travelers who are not HCWs were based on the monthly incidence identified in World Health Organization situation reports during June–October 2014 (online Technical Appendix 1 Table 1) (5). The high value was the highest monthly incidence [September] rounded to the nearest whole number; the low value was set at 30% of the high value. Infections in HCWs were based on estimates of the number of HCWs in West Africa with and without Ebola virus infection at different times in the epidemic [online Technical Appendix 1 and Appendix 1 Tables 2–4]. HCW, health care worker; NA, not applicable.
†The low estimate of US arrival rates for travelers who are not HCWs and both the low and high rates for HCWs were based on the count of screened airline passengers originating in Liberia, Sierra Leone, and Guinea in the month from mid-October through mid-November 2014 (Centers for Disease Control and Prevention [CDC], unpub. data). For the high US arrival rate for travelers who are not HCWs, we assumed a 50% increase over the low value [3,000 = 2,000 × 1.5] to approximate the arrival rate in 2013, before the epidemic (3). Rates of HCW arrivals were based on travelers who identified themselves as having worked in a health care facility during the previous 21 d during screenings at their airport of entry to the United States during November 5–December 1, 2014, and the exposure risk category assigned to them according to CDC’s Interim US Guidance for Monitoring and Movement of Persons with Potential Ebola Virus Exposure (4,6). The low estimate value of arrivals of HCWs (30 arriving HCWs) was approximately the lowest rate of high-risk and some-risk HCWs entering the United States. The high estimate value (60 arriving HCWs) was approximately the highest rate of high-, some-, and low-risk HCWs entering the United States (CDC, unpub. data).
‡Output 1 = (Input 1 / Input 2) × Input 3; Output 2 = Output 1 + (Output 1 × Input 4). See online Technical Appendix 1 for further details.
§Assumed number of additional secondary transmissions occurring in the United States per primary case based on the range of experience from the outbreak: 1 imported case to the United States resulted in 2 secondary infections, and several case-patients have been treated without any secondary infections (7).
¶Number of medical evacuations was obtained from unpublished Medical Evacuation Missions Reports (US Department of Health and Human Services, unpub. data).
1These first authors contributed equally to this article.
2These senior authors contributed equally to this article.