ONE feature of the tragic case of Thomas Eric Duncan, the first traveler known to have carried the Ebola virus into the United States, rankles me as a physician: Even if every system in place to identify suspected carriers had been working perfectly, he may have still set off a mini-epidemic in Dallas.

Mr. Duncan, recall, was screened before his flight and found to have a normal temperature. Asked specifically about exposures, he denied any contact with the ill. On Sept. 25, when he first presented to the emergency room with a fever, he was discharged. He returned three days later with fulminant infection. But the fact remains that even if Mr. Duncan had been identified and isolated on the first visit, it may have been too late. He had probably been exuding the virus for days. The news that a nurse who helped treat Mr. Duncan has now tested positive for the disease, evidently because of a breach of safety protocols, adds to the picture of disorder.

In the wake of the Duncan case, three strategies to contain the entry and spread of Ebola in the United States have been proposed. The first suggests drastic restrictions on travel from Ebola-affected nations. The second involves screening travelers from Ebola-affected areas with a thermometer, which the federal government is beginning to do at selected airports. The third proposes the isolation of all suspected symptomatic patients and monitoring or quarantining everyone who came into contact with them.

Yet all these strategies have crucial flaws. In the absence of any established anti-viral treatment, we may need to rethink the concept of quarantine itself.