The first Dallas Ebola patient might not have been contagious when he was sent home after his first emergency-room visit with a 103 temperature, while the nurse who took the Cleveland flight with a 99.5 temperature could have been. Two victims with the same symptoms (as measured by temperature, which is hardly a definitive diagnostic) very well might not harbor the same contagion, and the extent to which they become contagious could well escalate at different rates with their temperatures. Of course, those who come in contact with Ebola victims will also vary in their susceptibility to infection, through direct or indirect contact. The New York City doctor was found to be a victim with a temperature of 100.3. Americans can be forgiven if they now see a fever symptom as far less definitive as official pronouncements have suggested.

Healthcare officials and media pundits have played “symptoms” as, again, tightly defined on-off switches: “When you have the identified symptom [at some ill-defined fever], you have Ebola and are contagious. When you don’t have the symptom, you can’t be contagious, even if you have been infected.” The New York Times reported the New York doctor checked his temperature twice a day, and when he showed a fever, he checked himself into the hospital where he was put in isolation. The doctor did what he should have, according to Doctors Without Borders in a comment to the New York Times: “Self-quarantine is neither warranted nor recommended when a person is not displaying Ebola-like symptoms.”
This suggests the doctor was only infectious when he identified his symptoms, at the time he took his temperature. Was it not possible for him to become infectious before he took his temperature, and was mingling with people on the streets of the city? Even if he had identified his symptom at the exact time he became infectious, could he have not been infectious a minute or an hour earlier?