Do­ing the math on Ebola

The pres­i­dent must act to pre­vent a cat­a­strophic epi­demic

The Washington Times Weekly - - Commentary - By Robert Charles

Big facts and ba­sic math tell the whole story. We have only be­gun to see the po­ten­tial ef­fects of Ebola na­tion­wide. We still have a chance to get this right, but Pres­i­dent Obama needs to get ac­tive. Big Fact No. 1: A two-in-75 in­fec­tion rate for med­i­cal per­sonal ex­pe­ri­enc­ing Ebola ex­po­sure is a non-triv­ial rate. It is sig­nif­i­cant. Less than a month ago, a sin­gle Ebola case had been di­ag­nosed in the United States. That pa­tient com­plained of symp­toms on Sept. 26 and was dead by Oct. 8. In 12 days, he ex­posed 75 health care work­ers to the dis­ease, two of whom are now in­fected.

Iron­i­cally, un­like the gen­eral pub­lic, th­ese nurses had haz­mat suits and a Cen­ters for Dis­ease Con­trol (CDC) pro­to­col. One or the other did not work, since the CDC says the nurses were not at fault. Un­known are the num­bers of other (as yet un­cov­ered) cases ar­riv­ing in the United States daily, and those ex­posed but as yet still undis­cov­ered.

Big Fact No. 2: In­cu­ba­tion for Ebola, as deadly as the bubonic plague, is 21 days. This means that un­less some­one is quar­an­tined for that time fol­low­ing ex­po­sure, pub­lic risk re­mains high. The like­li­hood that any ex­po­sure leads to an in­fec­tion goes up after 10 days or symp­toms. Presently, no quar­an­tine ex­ists for those leav­ing in­fected West African coun­tries. No quar­an­tine ex­ists for those en­ter­ing U.S. air­ports. Pas­sen­gers are left un­mon­i­tored if they do not evince “a fever” or “look sick.” They are asked to “self-mon­i­tor.” Think about this. By the time a per­son rec­og­nizes Ebola symp­toms, if they do — and get to a hos­pi­tal, if they do — it is too late to pre­vent ex­po­sure. They may have been in­fec­tious for days.

Big Fact No. 3: Air­planes con­tinue to come to the United States di­rectly and in­di­rectly from in­fected coun­tries, even as Ebola deaths in­crease across West Africa. To­tal num­bers of planes com­ing to the U.S. from West Africa and to­tal pas­sen­gers ar­riv­ing via Europe — un­known. Only five U.S. air­ports tak­ing in­ter­na­tional flights have any screen­ing — and even then, they have no an­swer for the 21-day in­cu­ba­tion for those in­fected by not show­ing symp­toms. With no check­ing at other air­ports or land cross­ings, how many may en­ter? No one knows.

What does this add up to? A daunt­ing health prob­lem. Do the math. If two in­fec­tions re­sulted from 75 peo­ple be­ing ex­posed to just one pa­tient, and this group had pro­tec­tive gear, what are the chances that a larger pop­u­la­tion, with­out gear, will be in­fected — and how fast? Imag­ine that each of the 75 ex­posed bumped into another 75 per­sons. We do not know if peo­ple can be car­ri­ers with­out be­com­ing in­fected them­selves, or how many of those ex­posed are not yet show­ing signs of in­fec­tion. Al­ready, another 5,625 per­sons could have been ex­posed — or, on the other hand, may not. We do not know.

That is, alas, how ex­po­nen­tial num­bers work — quickly. Imag­ine the 75:2 ra­tio of ex­po­sures to in­fec­tions for the next 75. Imag­ine that no more ini­tial in­fec­tions are dis­cov­ered. Of the 5,625 po­ten­tially ex­posed per­sons, 150 per­sons could still end up in­fected over the next 21 days (that is, two in ev­ery 75). Maybe all 75 ex­posed to the first pa­tient were put in iso­la­tion be­fore be­com­ing in­fec­tious. We can hope so, but we do not know.

Hy­po­thet­i­cally, follow the num­bers. All this from one in­fected per­son treated in a “pre­pared” hos­pi­tal. If th­ese 5,625 newly ex­posed per­sons all were to be­come in­fected, and each then met 75 other per­sons within 21 days or be­fore di­ag­no­sis, most en­coun­ters would be with­out pro­tec­tive gear. At that point, we could see 421,875 ex­posed Americans — and a sharp rise in the ra­tio of ex­po­sure to in­fec­tion.

All this could hap­pen within 42 days from Oct. 15, the date on which the sec­ond of the two nurses was dis­cov­ered in­fected. It prob­a­bly will not, but once in­fec­tions mul­ti­ply, the num­bers be­gin to work against us. That is why we can­not let it hap­pen.

Epi­demics hap­pen fast. By third-level con­tact from a mere 75 peo­ple ex­posed to Ebola, the next leap could the­o­ret­i­cally be enor­mous. At 75 con­tacts per per­son, those 421,875 ex­posed Americans could, within 21 days, po­ten­tially in­fect 31,640,625 ad­di­tional Americans — one-tenth of the U.S. pop­u­la­tion. At that point, preven­tion is more or less aca­demic, and the coun­try would pivot to cri­sis ed­u­ca­tion, triag­ing cases, use of prim­i­tive treat­ments and a lot of prayer. Those would be our op­tions.

All this is un­likely, as long as known ex­po­sures to Ebola are con­tained, all con­tacts found and mon­i­tored, then iso­lated and treated as needed. As long as no one slips through the cracks, pro­tec­tive gear and pro­to­cols work and are ac­tu­ally used. As long as the pres­i­dent ef­fec­tively stops flights from West Africa to the United Stat­tes with po­ten­tially in­fected per­sons, ju­di­ciously lim­it­ing air traf­fic to United Na­tions, Red Cross and mil­i­tary planes, as we did in Afghanistan and Iraq. The cri­sis will not ex­pand if the pres­i­dent stops in­fected per­sons from get­ting to this coun­try through Europe; if he sets up an egress zone from West Africa, ef­fec­tively quar­an­tin­ing po­ten­tial pas­sen­gers for 21 days be­fore flights; if the pres­i­dent pro­vides in­surance by quar­an­tine on this side of the At­lantic Ocean for po­ten­tially ex­posed pas­sen­gers. The epi­demic will not take hold if mis­takes made are quickly ac­knowl­edged, and pro­to­cols here fixed.

Fi­nally, it will not hap­pen if Mr. Obama spends real time fo­cused on this is­sue, in­stead of seek­ing to con­vince Americans not to think about it. How­ever, crank­ing this dis­ease down de­pends on a lot of ifs. Given the un­for­giv­ing na­ture of this dis­ease — and of ba­sic ex­po­nen­tial math — the pres­i­dent owes all Americans his full at­ten­tion and con­sid­er­ably more trans­parency than he has given us. We have a chance to get this right, but the pres­i­dent needs to do the math — and quickly step up. Robert B. Charles is a for­mer as­sis­tant sec­re­tary of state in the George W. Bush ad­min­is­tra­tion.


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