Fortunately, we haven’t had very many Ebola patients in the US so far. But there have been quite a few interesting things to note about the group of patients we have had.

The first is that all of them except Thomas Eric Duncan seem to have contracted Ebola while caring for other Ebola patients. And if “carrying a woman to a cab to go to the hospital” is defined as “caring for,” that would include Duncan as well.

Note that I wrote “seem to have contracted Ebola while caring for other Ebola patients.” That’s because Dr. Rick Sacra, who contracted Ebola in Liberia, was not caring for known Ebola patients at all; he was treating pregnant women.

So we must conclude that both Dr. Sacra and the staff at the hospital where he worked in Liberia, although they are medical professionals in a country currently experiencing an epidemic of the disease, have encountered patients who are ill enough to transmit Ebola to others.  Yet, their symptoms are either not serious enough, or are atypical enough, that their Ebola status has gone unrecognized by the medical people treating them.

Dr. Sacra’s case is a sort of mirror image of Thomas Eric Duncan’s case.  Duncan also helped a pregnant woman who was not known or recognized to have Ebola at the time but who turned out to have been highly contagious. This fact sequence points out something that health professionals here have mostly been mum about: although Ebola is an extremely serious and often-lethal disease, it is not always recognizable as such, even by highly-trained (including Western) doctors and nurses.

There are many reasons for this (one is that what we think of as “typical” symptoms are not present in a significant number of cases), but for our purposes right now it’s enough to state that it is a troubling fact.

Another pattern that leaps out is that so far the death rate in the US has been much lower than in other places. This even includes the US citizens who got their initial treatment in Africa and were only flown here after they had become quite ill.

The good results might just be a coincidence, because the number of patients treated here has been very, very small. But if we assume there’s something to it, it could be some combination of early treatment (for about half the patients here, anyway), the high quality of our medical care in general (effective rehydration, etc.), and therapies which seem to include antiviral drugs and survivor transfusions.

The only Ebola death in the US so far has been Thomas Eric Duncan. He missed having the advantage of an early diagnosis because his case went unrecognized by the Dallas hospital ER he first visited.

He also had the misfortune of not matching the blood type of the available survivor donors, so he didn’t receive a transfusion from any of them. It’s also possible there was something different about his physiology; perhaps other illnesses had weakened his immune system, or there could even have been genetic factors that made him more susceptible to the illness.

It may be that we risk becoming a little too cocky, though, about our ability to treat Ebola. Our success so far appears to depend in part on the tiny number of cases. It wouldn’t take much to completely overwhelm our ability to give patients the sort of care these first victims have gotten, and then things could change dramatically.

What’s more, the fact that almost all the cases here have been among health care professionals caring for already-diagnosed Ebola patients is in a strange way a tremendous advantage, because it has enabled us to monitor them from the start and to treat them almost the moment they display symptoms—symptoms that in a person not known to have had prior contact with Ebola would cause no alarm. That, in turn, has two advantages: early treatment almost certainly makes it more likely that they will survive, and early isolation makes it less likely that they will spread the virus into the general public (or to other health care professionals, who will be wearing protection almost from the start while treating them).

A nightmare scenario would be if Ebola were to get out into a population that was unaware they had been exposed to it, and who therefore could easily interpret early symptoms as commonplace flu and therefore would be far more likely to infect others in the public before being diagnosed.

That’s the way Ebola could get out of control in this country. And that is why so many people (including me) are in favor of quarantining returning health care workers, and placing a moratorium on the issuing of visas to citizens of the Ebola-affected countries of West Africa, except in compelling circumstances.

This is not because we are unaware of the fact that Ebola is alleged to be contagious only in symptomatic individuals. It is because we realize that symptoms are not always heeded right away, the contagion is a continuum rather than an “off/on” phenomenon, and that there is a small percentage of African Ebola cases where there has been no previous known contact with a symptomatic ebola victim.

Being extra-careful makes sense, because the stakes—and the risks if things get out of control—are tremendously high.

[Neo-neocon is a writer with degrees in law and family therapy, who blogs at neo-neocon.]