Here's What Scientists Do When They Find Someone With Ebola

Every Ebola outbreak in history has been contained using a procedure that is both simple and crucial.

That process, known in epidemiology as contact tracing, refers to the science of tracking down all potential cases of a disease. “In public health we do contact tracing all the time, every day around the year, whether it’s for tuberculosis or sexually transmitted disease or meningitis or measles or other things,” said Centres for Disease Control and Prevention director Tom Frieden on a call with reporters. “It’s a core activity for us in public health.”

And it will be critical in stopping the spread of Ebola in the US.

Here’s a CDC graphic that shows it’s done:


1. Locate everyone who has touched or been in contact with the blood, vomit, mucus, or other bodily fluids of an infected person.

Brushing up against these liquids won’t necessarily give someone the virus, but someone who touches one or more of them and then touches her eyes or mouth could get sick. This is why public health authorities cast the net wide — they are looking for anyone who might get Ebola from the infected person they have already identified. That includes people who are at relatively low risk of becoming ill.

In Nigeria, where the outbreak appears to be contained, authorities followed up with 894 contacts.

2. Watch them closely.

Once the scientists find everyone who’s been in close proximity to the virus, the CDC, in coordination with other public health agencies, monitors anyone at risk for signs of illness. For Ebola, this can be a long and arduous process, since the virus can stew silently in the body of an infected person for up to three weeks before there are any symptoms.

Fortunately, no one is contagious until she begins showing physical signs of the disease, and people are most contagious when symptoms are at their worst or soon after death. In Dallas, high-risk contacts of the first patient diagnosed with Ebola in the US are being tested for fever twice a day.

3. Isolate and treat the sick.

If one of the contacts being monitored starts showing signs of illness — a fever, for example — that person is immediately isolated and tested for Ebola. If 21 days pass without symptoms, someone can be cleared as definitively “negative” for Ebola.

4. Repeat steps 1-3.

Once the sick person is diagnosed with or without the virus, she’s provided whatever care she needs, and the cycle starts again: The scientists track all of her contacts and monitor them for another 21 days. The process continues until everyone who could become sick is traced and either treated or cleared, until the outbreak has no potential of spreading further.

“Even one missed contact can keep the outbreak going,” the CDC writes on its website.

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