LINDA WERTHEIMER, HOST:

Zika is on the rise in Colombia. According to new figures just released, more than 37,000 people have been sickened by the virus since an outbreak began there last fall. For most people, Zika symptoms are mild, but the uptick is worrying because the virus could be linked to complications like birth defects and a rare neurological condition that can cause temporary paralysis. It's called Guillain-Barre syndrome. NPR's Nurith Aizenman is in Colombia in a place that's seen a dramatic number of Zika infections. Good morning, Nurith.

NURITH AIZENMAN, BYLINE: Good morning.

WERTHEIMER: Let's talk first about Guillain-Barre.

AIZENMAN: Yeah. So as you just said, Linda, Guillain-Barre, it's a condition that affects your neurological system. Basically, your immune system attacks your nerves, and in a lot of cases, it can be really severe. People can be fully paralyzed for weeks. They have to be on breathing machines. It can take you months to recover, and some people never walk again. Normally, it's extremely rare, but people here are really worried because there's been this dramatic surge in cases since the Zika outbreak began. And this is happening in a lot of the countries where the Zika outbreak is happening. It's in Brazil, in El Salvador, Venezuela. I'm in the city called Cucuta, and I visited a couple of ICUs here, including one at the main hospital. I talked to a neurologist named Jairo Lizarazo. Here he is.

JAIRO LIZARAZO: (Foreign language spoken).

AIZENMAN: He's saying that around the end of January they suddenly started to get a lot of cases, and now they're seeing about a case every day - a new case every day. Across Colombia, they've seen almost a hundred cases since last fall, which is just way more than usual.

WERTHEIMER: Do we know for sure that Guillain-Barre is linked to Zika virus?

AIZENMAN: It's an open question. It's hard to tell if someone has had Zika unless you test them right away while they still an active infection, but the Guillain-Barre symptoms tend to develop a while afterwards. And even if someone has had Zika, you've got to prove it wasn't just a coincidence that they then developed Guillain-Barre. So people here, including Dr. Lizarazo who we just heard from, are launching studies to look into this, but there are no firm answers yet.

WERTHEIMER: OK. What about microcephaly, babies born with abnormally small heads? What is happening with that in Colombia?

AIZENMAN: It's definitely a concern. The latest numbers are that about 6,300 pregnant women in Colombia are suspected to have fallen sick with Zika. So far, there haven't been any of those babies born with microcephaly like we saw - we've seen in Brazil. But that said, if you think about the time wave of the Zika epidemic, it hit Brazil first. The numbers in Colombia didn't really start swelling until late last year.

And researchers suspect that Zika may cause these birth defects if the woman is infected in her first trimester. So based on that timing, officials we've spoken with say they would expect that if Zika is causing microcephaly it would be several more months before we'd see these cases in Colombia. So, for now, they're monitoring pregnant women who've had Zika. They're going to run a very large study in cooperation with the U.S. Centers for Disease Control, and Colombia is seen as a key to trying to prove a link between birth defects and Zika.

WERTHEIMER: We don't have too much time left, but let me ask you how the health care system in Colombia is holding up.

AIZENMAN: There are a lot of dedicated and excellent doctors here, but from what I've seen, the system is already feeling the strain. I've gone to several clinics where they're asking pregnant women to come in for more tests. And these Guillain-Barre cases are really expensive. One of the main treatments for the disease requires you to clean out the blood - antibodies from the blood. It's really costly and here is Dr. Lizarazo again, the neurologist from the hospital in Cucuta.

LIZARAZO: (Foreign language spoken).

AIZENMAN: He's saying there's already a deficit of ICU beds, and with more Guillain-Barre, it's going to be really tough.

WERTHEIMER: NPR's global health correspondent Nurith Aizenman, thank you very much. Transcript provided by NPR, Copyright NPR.