For the thousands of people traveled through Harvey’s flood waters to Houston’s George R. Brown Convention Center, safety was not yet at hand. Although delivered from the worst of the storm, the packed masses were one of the loci of another brewing problem, one that officials expect might last a year or more after landfall.

Every flood disaster is also a public-health disaster, and even as Harvey dissipates over the Gulf Coast, the beginnings of that secondary calamity were on display in the Houston area. During the worst of the flooding, hospitals faced critical shortages of food and medicine, people with serious chronic diseases had to make difficult decisions between evacuation and sheltering in place, and hundreds of victims faced prescription shortages and mental-health issues. And based on the health problems people in New Orleans and elsewhere in the region faced after Hurricane Katrina, experts expect major public-health emergencies, environmental illnesses, and outbreaks will only intensify in the aftermath of Harvey.

Those challenges are already taxing the city’s health infrastructure. According to Bill Gentry, a professor at the University of North Carolina School of Public Health and a former emergency management official, one key public-health issue that attends the early stages of any disaster is the set of risks facing people who are disabled or elderly and face special health needs. “With our push towards home health-care and taking care of more Americans in the home,” Gentry said, “it quickly turns into 'can we get their home health-care needs taken care of,’ with everything from oxygen to prescription meds to getting them clinical access, especially for dialysis. Those types of clinical worries compound as many days as the water stays up.”

Dialysis is a special concern, and for residents in Houston, already approaching crisis. As NPR reports, it’s important for patients with kidney failure to receive dialysis services every two to three days. But local dialysis centers are struggling with the demand, and with shortages of qualified staff, since several nurses who’d normally work in the centers are themselves displaced by the flood. And while companies like the DaVita Med Center and its locations around the Houston area are working around the clock to meet the area’s dialysis needs, as patients go longer without regular services and appointment reminders, the only solution to keeping them alive may be taking them to one of the area’s hospitals.

And the hospitals are running up against their limits, too. When I spoke to Mary Brandt, a pediatric surgeon at Texas Children's Hospital, she was driving home through receding floodwaters after five straight days of work. She and her colleagues had just completed the first shift of what she described as a “military kind of operation,” and fittingly had just been relieved by a team of reinforcements. “Texas Children's Hospital has leadership that has just gotten this down to an art,” Brandt told me. “Everything was covered.”

That military-like response among Houston-area hospitals was largely effective in dealing with some of the most immediate effects of the storm. Brandt’s team saw mostly children who’d faced non-life-threatening injuries and illnesses. Meanwhile, kids with ailments requiring management, like asthma, or those with fevers and other serious conditions were airlifted to the Texas Children’s Hospital building in The Woodlands, a suburb north of Houston. The triage and logistics systems in place for Houston’s hospitals helped ensure that patients with the most sensitive conditions received treatment and resources on time.

Still, there’s reason to suspect that effective disaster-management system will be stressed in the days to come. As Brandt notes, the bulk of patients with conditions directly related to the floods haven’t yet made it to hospitals. “Since the water's just subsiding,” Brandt said, “we're expecting there's going to be a huge number of patients that are going to come in today and tomorrow with problems that they needed to have taken care of in the last few days, but just couldn't get to us.” That “huge number” might be more than hospitals can handle, as Texas Children’s is already near its bed capacity, and local general hospitals like Ben Taub Memorial have already faced food and drug shortages.

There are a myriad of other health problems to come, and they often affect the most vulnerable citizens. Daring water rescues of Houston residents from nursing homes made headlines, but the most dangerous period during disasters for seniors is actually post-evacuation. According to Gentry: “What we learned through surveys was that even if we had 100 percent of the people evacuated successfully from nursing facilities, within eight weeks they usually saw a 10 percent fatality rate. That 10 percent was due just from the stress that results from the evacuation and the moving.”

To Gentry, perhaps the most overlooked health problems in the middle of disasters, both among seniors and the general population, are mental-health crises. But time and again, studies have shown that mental-health issues are actually the most predictable and durable of health problems that follow floods. Their extraordinary prevalence makes sense: Not only can the stress and losses of flooding trigger post-traumatic stress disorder and worsen other mental health conditions; even for people with well-managed illnesses, floods often mean a disruption in therapy and prescriptions. Also, for the sizable population of people who resettled in Houston after evacuating Louisiana during Katrina, the event could simply compound an existing trauma.

Ground zero for the budding mental-health disaster in Houston is the convention center, where in addition to queuing for basic needs like food and water, hundreds or even thousands of people are lining up to receive needed mental-health services from a makeshift team of professionals from around Harris County. Some patients have extremely sensitive conditions and are facing psychotic breaks on the convention floor. Some saw life-saving drugs simply dissolved by rising floodwaters, and fear losing their place in the shelter if they travel to find any open pharmacies. Some have no mental-health histories whatsoever, and many children facing extraordinary stress weren’t in line at all, but still were in need of care.

Psychiatrists Sophia Banu and Aya Aoshima-Kilroy are working to hold the line in the convention center, helping lead a team of doctors and nurses operating with a limited cache of supplies, an improvised organizational structure, and an impromptu team of volunteers serving as health extenders. Both had been on the clock for hours when we spoke on Wednesday.

“The most concerning are those that have lost their medications,” said Aoshima-Kilroy due to theft or leaving them behind putting some patients in danger. In order to help fulfill demand for prescriptions, Aoshima-Kilroy said that employees of the Walgreens pharmacy who were also sheltered at the convention center tried to arrange deliveries from the pharmacy directly to the convention center.

Beyond the pharmacological needs of their patients, the mental-health team at the convention center is also working to combat the sheer trauma of the catastrophic flood event. “Some people are anxious and just need somebody to talk to, and so what I'm doing is just asking volunteers to go out into different areas in the stadium and looking for people who are looking distressed, dazed, or crying,” said Banu. “Not everybody comes and tells you 'I'm feeling this or feeling that.'” Banu’s team and its attachment of volunteers are also working to teach people basic stress-relief tactics and breathing exercises.

The health-care system in and around Houston is full of people like Brandt, Banu, and Aoshima-Kilroy, as well as the legions of nurses, emergency medical responders, and volunteers who work tirelessly against the odds to prevent major health-care crises. But the long-term odds are still in favor of such crises developing. According to Peter Hotez, the dean of the National School of Tropical Medicine at the Baylor College of Medicine, the blueprint created by Hurricane Katrina dictates exactly what to expect in the months to come around Houston.

“Both New Orleans and Houston are Gulf Coast cities. Both are associated with a lot of flooding. So what we saw with Katrina is likely relevant to what we're going to see with Harvey,” Hotez told me. Antibiotic resistant staph infections, a flesh-eating bacteria in the Gulf known as vibrio vulnificus, diarrheal disease from norovirus and other diseases and respiratory infections were just a few of the potential problems Hotez named.

Two long-term health problems that Hotez thinks might be especially damaging are mold and the prevalence of mosquitoes. Mold is a common threat after even minor floods, and proved a significant respiratory threat during the aftermath of Katrina. And although Hotez said mosquitoes will initially be washed away during the floods, standing water in ditches and in containers after the flood will spark new breeding patterns, and booms in the populations of mosquitoes that spread West Nile virus, dengue, chikungunya, and even zika, although there isn’t an existing corollary for the latter, which is new in the United States and hasn’t yet spread to Houston. According to Hotez, the spike in West Nile cases following Katrina in the New Orleans area “continued for a whole year after the flood.”

Harvey isn’t Katrina. For one, at least in part because of the debacles of public-health responses during Katrina—and previously, during 2001’s Tropical Storm Allison, when patients in Houston hospitals had to break windows to escape rising flood waters—the region is better prepared. FEMA is in better shape.

Additionally, Dr. Dan Sosin, deputy director and chief medical officer of Centers for Disease Control and Prevention’s Office of Public Health Preparedness and Response, confirms that his office has provided major grants to the region for preparedness. “Since 2002, the PHEP cooperative agreement has provided more than $11 billion to public health departments across the nation,” Sosin said in an email. “In fiscal year 2017, Texas received $37.8 million.” At least some of that $37.8 million went to a program called Enable Fort Bend, which was created after the last round of catastrophic floods in Fort Bend County, Texas, to help identify high-risk priority evacuees.   

When it became clear Harvey would be a major event in the area, officials across several domains of public health in the Texan Gulf Coast initiated battle-tested plans for evacuation, triage, and management that have already averted some of the initial problems that victims during Katrina saw. But as the stages of public-health disaster unfold, the sheer immensity of the region affected and of the amounts of people involved will prove daunting to officials.

“The difference is the scope of this is so much larger,” Hotez said. “New Orleans is a city of 400,000 people. Harris County is the second-largest county in the country with 6 million people. It's a whole order of magnitude greater in size and scope.”

The people of the hardest-hit communities in Texas and Louisiana will have outside help. Although an official with the United States Public Health Service confirmed to me that they anticipate needing to take a long-term role in public-health efforts in the region, a spokesperson with the Department of Health and Human services confirmed that “last week, the Secretary of the Department of Health and Human Services, Dr. Thomas E. Price, authorized the deployment of the U.S. Public Health Service Commissioned Corps in support of the U.S. Government’s public health and medical response efforts related to Hurricane Harvey.” As part of that support, the uniformed services corps will staff independent Federal Medical Stations and help facilitate the delivery of supplies and resources to health-care entities on the ground.

Still, even with a region prepared for the worst, and with some federal resources mobilized in assistance, the wide swathe of country affected by Hurricane Harvey and its record-breaking floods faces a long road ahead. The public-health safety net will be tested. Physicians and nurses will work many more hours than they should. The threats of outbreaks and major environmental hazards still loom large. And especially in Houston, which hosted a very large population of low-income people already pushed to the edge of the health-care system even before the storm, the challenges will be amplified by the health problems that already plagued local communities.

But, to a person, the first responders and physicians on the scene expressed their optimism, both in the planning and in the resolve of the people on the ground. “I'm really glad to be here, and to see so many people helping,” Banu told me. Aoshima-Kilroy said that even though she felt punch-drunk by the scale of the calamity, she was also “grateful to be in a profession that can be used or utilized in this time of need.”

Brandt expressed her hope that her colleagues could get Houston back up and running quickly. “I'm very proud of our response and the people,” she said. “This city is incredible.”