As Ruth Berggren slept in a darkened hospital room, the hot, muggy air settled damply on her skin. Nothing stirred; the air-conditioning and lights had shut down days before, when Hurricane Katrina knocked out Charity Hospital's main power. Berggren and her husband Tyler Curiel, leading scientists in New Orleans' academic community, had been waiting for rescue for days. They were hoping to save the patients of Charity's Ward 9 West.

Suddenly, Berggren heard someone shouting. She leapt from her bed and ran into the pitch-black hallway. She saw a sweaty young Marine, twitching nervously as he held his gun. “What are you doing here?” he barked, shining a flashlight in her face. “I was told this floor had been evacuated!”

Hearing the commotion, Curiel bounded into the hallway. The soldier, startled, raised his gun. “I'm the physician in charge of this ward, and we have not been evacuated!” a terrified Berggren shouted. The Marine lowered his gun and continued on his rounds.

Flight to safety: researchers Ruth Berggren and Tyler Curiel endured days in the flooded medical complexes of New Orleans (above). Credit: J. CHAMBERS

Later, Berggren recalled the episode as another frustrating reminder of her patients' situation. In the midst of a lawless, desperate city, poor people with AIDS had been abandoned yet again.

Berggren and Curiel, both faculty members at Tulane University, landed at the epicentre of the Katrina disaster more or less by accident. Berggren, an infectious disease specialist, teaches at Charity Hospital one month a year. She happened to be on call on Sunday 28 August, the day Katrina's winds began to pound the US Gulf Coast. Curiel, a cancer immunologist and oncologist, stayed behind with her.

The first days were relatively calm. The storm blew in on Sunday morning and out by Monday evening. At Tulane's medical centre, across the street from Charity, Curiel cared for patients and worried about what might happen if the power failed. He and a graduatestudent rushed through his lab, transferring valuable cell lines from electric freezers into tanks cooled by liquid nitrogen.

By Tuesday morning, New Orleans was drowning, swamped by waters that poured through a levee breach. Administrators at Tulane, a private hospital, hired helicopters and evacuated their patients. Then Curiel borrowed a canoe and paddled across the street to his wife.

A man in a white shirt was firing bullets at the rescue workers from a parking deck.

The situation at Charity was disintegrating. The hospital had no money to call in a private evacuation for its 250 patients. Bottled water was plentiful, but food was rationed to a few cups of ravioli and a handful of canned green beans each day. When the hospital ran out of diesel to power its generators, the staff helped patients on respirators breathe with hand pumps.

Despite the worsening conditions, the Ward 9 West shift manager, Mitch Handrich, vowed that no staff members would leave until every patient was evacuated. The staff tried to bolster patients' spirits; on Wednesday, they staged a talent show for the ward. That night, the National Guard finally arrived and evacuated five of Berggren's patients. But on Thursday morning, gunshots erupted as Curiel was helping load patients into trucks on the emergency room ramp. Curiel says he saw a man in a white shirt firing bullets at the rescue workers from a parking deck. “Sniper!” the guardsmen shouted.

Toxic smoke

Staff members scrambled to get the patients to safety. But the damage was done; the National Guard called off the operation and abandoned the building. Only 50 patients had been evacuated, leaving 200 stranded — including 13 in Berggren's ward. That night, Berggren and Curiel had their encounter with the Marine. When they woke up Friday morning, a chemical plant had exploded nearby, spreading a pall of tom, xic smoke for miles around. For the first time, they began to think they might not make it out of Charity alive.

But television coverage of the shootings alerted the nation to the hospital's plight. On Friday, the National Guard relaunched its evacuation effort. All of Berggren's patients were out of the hospital by Friday afternoon. The next day, Curiel, Berggren and her ward's staff evacuated to Texas.

One week later, Curiel returned, escorted by armed guards, to learn the fate of his research materials. He thought his life's work had been lost. But when he opened the first nitrogen tank, a tell-tale puff of cool vapour wafted up into his face. He knew then that his samples were safe.