Spain’s Ebola patient zero is a nurse’s assistant.

No one can say she kept mum about the fact that she’d been near an Ebola patient recently. Authorities were well aware of her exposure, because she was on the team that cared for a Spanish missionary and a Spanish priest, both of whom were shipped back to Spain after they contracted Ebola in Africa. Both of them have died.

But although health workers in Dallas did not originally know that America’s patient zero, Thomas Duncan, had been recently exposed to Ebola, there is a similarity between the unnamed nurse’s disease trajectory and that of Duncan. As with him, there also was a delay in her hospitalization and diagnosis. She is said to have reported her first symptom, a fever, on September 30, and yet she was only hospitalized this week. Since authorities knew in advance that she’d been exposed, why the delay, which put many more people at risk? Should they not have erred on the side of caution?

There are various possibilities. Perhaps the authorities had such faith in their isolation and protection techniques that they thought it impossible that a health worker could contract Ebola while working under state-of-the-art conditions in a Western hospital, as opposed to in Africa. Or perhaps (as I’m beginning to suspect) the diagnostic criteria for Ebola aren’t rigorous enough.

One of the first symptoms of Ebola is a fever, defined as above 101.5. But see this [emphasis mine]:

Health authorities said on Monday night that the nurse was in stable condition. She had alerted them to a slight fever on 30 September, said Antonio Alemany from the regional government of Madrid, and checked into a hospital in Alcorcón with a high fever on Sunday. Ebola protocol was immediately activated at the hospital and initial and secondary tests were both positive for the virus.

A “slight fever”—in other words, not high enough to be textbook Ebola. But the textbook may be wrong. Her fever didn’t become high enough to fit the criterion until five days later. The same mild fever was the case with Duncan, whose temperature was 100.1 on his first visit to the ER, when they sent him home with antibiotics (unlike the nurse, however, he already had other symptoms of Ebola). According to the woman who two days later called 9/11 for an ambulance for Duncan when he became extremely ill, his temperature even at that later stage was only 100.4 when she took it.

If both the US patient zero and Spain’s patient zero presented with mild fevers, it becomes harder to think of it as a freak occurrence. It just may be that mild fevers are more common in Ebola than previously thought, especially in the early stages. In fact, could they not be fairly common, and this fact previously missed because in Africa people don’t typically tend to get medical help until the later stages of the illness?

This is speculation on my part, of course; I’m not a doctor. But logic suggests it as a possibility, and it seems to be a potentially important issue to look into. If fever is being used as a marker for Ebola, it makes sense to make sure that fever is defined in a way that conforms to the disease’s early presentation, not just its late manifestation.

One other important question the Spanish nurse’s illness raises is how she managed to contract Ebola in the first place. There are only two possibilities, as I see it. The first is that an error (either hers or someone else’s at the hospital) was made in following the procedures for the isolation of Ebola patients. The other is that the procedures were followed but are sometimes inadequate, and more must be done to protect the people who care for Ebola patients.

This particular epidemic, as opposed to previous ones, has been marked by more medical staff contracting the disease. Is it because they have been careless? Is it because the epidemic is larger? Or is it because something has changed and made Ebola easier to contract?

These three possibilities are not mutually exclusive, either; the answer could be “all of the above.” But the most frightening one is that third one.

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