After a magnitude 7.0 earthquake rocked Haiti in January, many experts worried that devastating outbreaks of infectious diseases would soon invade the region. In a nation where a large part of the population already lived without access to reliable sanitation and clean water, a disaster that further disrupted infrastructure seemed likely to lead to widespread infections, such as cholera, which spreads through feces-contaminated water. Although more than a million people are still living in tent encampments following the disaster, it was not until late last week that news of a potential cholera outbreak first emerged.

Some 259 people have died from the bacterial infection so far and another 3,342 have been sickened, according to Haiti's Ministry of Health, the BBC reports. Officials fear that the outbreak, which seems to have started around the Artibonite and Plateau Central regions, north of the capital, Port-au-Prince, could become endemic to the city, where about 89 percent of residents live in slums or slum-like conditions. Five people there have been diagnosed with the disease, according to the World Health Organization (WHO), but they likely contracted the illness before arriving in the capital.

"There are limited ways you can wash your hands and keep your hands washed with water in slums like we have here," Michel Thieren, an official from the Pan-American Health Organization, told the Associated Press.

The cause of the disease is the bacterium Vibrio cholerae, which releases a toxin that triggers severe diarrhea and rapid dehydration; both effects can quickly prove deadly. Cholera might sound like an ailment that was dispatched in 19th century, but it still infects some three million to five million people worldwide and kills at least 120,000 each year, mainly in India and sub-Saharan Africa.

Although the number of people who have died from the disease in Haiti is lower so far today than it had been over the weekend, the country is still bracing for further spread. "We are preparing ourselves for the worst case scenario, which is a cholera outbreak in the whole country," Michel van Herp, of Doctors Without Borders, told BBC News.

But why is the outbreak just now emerging in Haiti, and how is cholera still a global concern? Scientific American spoke with David Sack, a professor in Global Disease Epidemiology and Control at Johns Hopkins Bloomberg School of Public Health, to learn more about the disease and what is being done to control it.

[An edited version of the transcript follows.]

Why do you think this outbreak is happening now, more than nine months after earthquake?

I wish I knew more about the events that led to this outbreak. From what I can gather, the outbreak did not start in the area of the earthquake, so it's not clear that it is directly related to the earthquake. We don't know whether it was introduced or if the bacteria was indigenous to the area and had never been spread before.

Is the current outbreak likely linked to long-term use of these tent-based refugee camps?
The refugee situation makes it much more dangerous, but I'm not sure that's what started the outbreak. You need to have the organism there circulating first. And of course we haven't seen cholera in Haiti for many, many years. Even in the 1990s outbreak in Latin America, it did not jump across to the Caribbean islands.

So how is cholera usually spread?
It is fecal-oral. So the feces get into the food or water supplies, though mainly the water. There is also an environmental reservoir, so it usually starts in the environment.

Cholera can kill within a matter of hours. Who is most at risk for getting—and dying from—cholera?
Anybody can be at risk—it's one that can kill healthy people quickly. We usually think a lot of these diseases will preferentially hit the malnourished or otherwise vulnerable. But cholera is something that can affect anybody.

The main risk factors are people whose stomachs, for whatever reason, are not making the normal amounts of gastric acid—if someone has recently had stomach surgery or is taking drugs that inhibit the production of gastric acid. The other risk factors are genetic, which unfortunately there isn't much you can do about. If your blood type is O, you're at higher risk. When cholera struck Peru, the indigenous people there virtually all have blood type O, and they were at higher risk.

In terms of risk for death, it is people who don't have treatment available. If they don't get treatment in a very short amount of time, they have a very high risk of dying.

Are rehydration therapy and antibiotics the best treatments out there?
Yes. But what I have not seen is what the sensitivity pattern is for the antibiotics. We've seen in previous outbreaks that people don't know what the patterns are and they ship the wrong antibiotics.

So different antibiotics are needed to treat different strains of cholera?
Yes. That's why it's important to know the sensitivity of this strain. And you have to keep monitoring it because it could change in the future.

What are the best ways to keep the disease from spreading to more people? Is it mostly an issue of clean water?
There are different ways of making your water clean. One thing I haven't seen out there so far is consideration of the vaccine, which is available now. It has only been since March this year that the World Health Organization has recommended the use of the cholera vaccine on a wide scale. I think this is a situation where it might be considered.

From the numbers that have come out so far, it seems that there's been a mortality rate of roughly eight percent. Is that a pretty standard number of expected deaths?
Standard mortality should be zero. I've worked in Bangladesh for many years, and in our hospital, we treated thousands of patients, and nobody died of cholera. So no deaths are inevitable if you provide the right treatment.

Nobody's had much experience with it in Haiti, so case mortality rates become very high at first, but as facilities become more experienced and people learn where to get treatment, the case mortality rates should come down very quickly.

Cholera seems like a disease of the past—will it ever be eradicated?
No, because of its environmental reservoir. I don't see any way we could eradicate it like eradicating polio or smallpox. As long as you have an environment, you will have cholera.

How does Haiti's outbreak compare with others in recent years?
In Bangladesh, we have thousands of cases every year, but it doesn't make it into the newspapers because we have it every year.

Theoretically, governments and health ministries are supposed to report cases to WHO, but in general many of them don't do it at all. Cholera is a very sensitive subject. Many countries just don't want to report it for fear of its impact on trade and travel—and that used to be a reasonable fear, but I'm afraid now that they haven't been reporting it because it's become a tradition.

In the past we used to assume that cholera outbreaks would arise quickly then go away quickly—and by "quickly" I mean one to two months. But the outbreak in Zimbabwe a year ago has taught us that cholera outbreaks can persist for a year. I think it's becoming harder to predict how long we can expect this outbreak to persist.

Is that because we have a better understanding now about the outbreaks, or has there been a change in the disease spread itself?
It seems to be a difference in how it's transmitted, not so much our understanding. It's behaving differently now than it did in the past. Clearly it keeps changing its genetics. So, for example, recently the toxin that the organism produces has changed genetically, and it appears that the change has resulted in a more severe illness. But this organism is in the environment, and its genes are exchanged frequently with the environmental strains, so there's a lot of re-sorting that's going on. And when people get infected, the people themselves act as the amplifier and selector of the most virulent strain.