As the aftershocks of the January 12 magnitude 7.0 earthquake outside of Port-au-Prince, Haiti, taper off and the dust settles, new needs are coming to light. The health of many of the three million residents said to have been shaken by the quake will be determined in the coming weeks as aid workers and others rush to treat the wounded, provide food and water, and try to prevent disease outbreaks.

Concern already has run high about the spread of cholera and typhus in a country whose everyday "water supply and basic sanitation services are still very deficient," according to the Pan American Health Organization. Many diseases, including malaria, HIV and typhoid, were already widespread issues in Haiti before the earthquake struck, and the intensely weakened health care system (established hospitals and clinics having collapsed or been damaged) and other infrastructure is expected to exacerbate these problems.

"In the weeks to come, we may have huge issues with public health," Pino Annunziata, who is helping to coordinate responses for the World Health Organization (WHO), told TIME. "This will be a major concern." And the tens of thousands who are reportedly seeking medical help at the few remaining hospitals and overwhelmed clinics speak to the urgent need for physical care. Doctors Without Borders (Medecins Sans Frontieres) reported already having treated more than 2,000 patients in Port-au-Prince as of January 14.

But not all of the human harm from this disaster will be of the physical variety. For example, many experts have noted that the multitude of dead bodies—some 50,000 possibly having died in the disaster already, the Red Cross estimates—don't pose an infectious disease risk so much as a psychological threat to the survivors.

Sandro Galea, chair of the Department of Epidemiology at Columbia University's Mailman School of Public Health in New York City, explains how and why so many Haitians will likely be hurting for months after food and water have been restored and the corporeal wounds have healed.

[An edited transcript of the interview follows.]

What are the biggest health and disease concerns for Haiti in the wake of the earthquake?
There is relatively little evidence of water-borne diseases appearing in the short term. It's actually relatively rare after these events. Cardiovascular disease and heart attacks could go up, and all of the dust could cause asthma. Unfortunately, these events happen and daily life continues. And when daily life continues, other injuries and other illnesses happen. This event introduces a layer of illness that is extra.

The largest burden of disease after these events is probably mental health issues.

What sorts of mental health issues will likely appear?
In the short-term you end up seeing, in the first few days, that people are dealing with wounds and trying to stay alive and stay well. You start seeing mental health issues within the weeks following the event. There is acute stress, which is considered to be a transient condition.

Post-traumatic stress can only be labeled a month after an event. You will start seeing high rates of post-traumatic stress and depression. You will probably end up seeing them three or four times higher than baseline.

What can be done to minimize these effects?
We know that stressors and challenges of daily life after these events can compound the impact of these events. The best thing we can do is to provide psychological first aid. In the long-term, behavioral therapy or medication might be beneficial based on the individual.

The key here is restoring lives—that will provide support to people.

Will initial counseling be important in administering this "psychological first aid"?
There is actually no good evidence that early counseling after an event actually makes things better, and there is some evidence that it actually makes things worse. Psychological first aid is giving people what they need to rebuild their lives. It will mean restoring people to their jobs, restoring people to their schools, restoring families.

Is it difficult to call attention to the issue of mental health in a situation like this?
Unfortunately with an event of this magnitude and loss of life, we tend to forget the long-term consequences. If people are not able to return to normal mental functioning, it results in the delay in return to well-being and building society.

It's critical to keep mental health in mind. It's understandable we tend to forget it, given the images of devastation. When the event is over, we tend to forget about these populations, and that is when these populations need the most support.

Have other recent disasters, like the 2008 magnitude 7.9 earthquake in China, helped us learn about the consequences of these events?
There's been a lot of interest in this area in the past decade, especially since the September 11th attacks. We have learned from the Madrid bombings, from the London subway and bus bombings, from the earthquakes in China, and the tsunami. We understand what the likelihood of mental illness is going to be.

So what is the rate of mental illness likely to be after an event like this?
In the first month after the event I would not be surprised to see 16 percent of the population with post-traumatic stress and a similar number—about 20 percent—with depression. That's a huge part of the population: about one in five.

You will find about half of the cases resolve about six months after the event.

Do you think there will be adequate ways to deal with this in Haiti?
This is part of the challenge with events that happen in poorer countries that don't have the infrastructure to deal with people trying to go back to normal life. I worry that there is not going to be the resources to deal with the overwhelming need that there's going to be.