Patricia Thomson was a little intimidated when she arrived on the watch floor at the Naval Network Warfare Command.

The bubbly teenager, fresh out of boot camp and information technology school, was daunted at first by the hushed and darkened maritime operations center, a sort of mission control at the heart of the Navy's information network.

Even low-ranking sailors like Thomson, a seaman, need a security clearance to work at the cyber warfare facility, which is staffed around the clock. Most enlisted sailors who worked there were older, more experienced and higher-ranking. It was heady stuff for Patty, the youngest of seven kids.

As she left Little Creek Naval Amphibious Base to drive home to Missouri for Christmas last year, Patty seemed to have found her niche. She had a car, a paycheck, a room in the barracks she shared with her best friend, and dreams of someday becoming a chief petty officer.

Shortly after returning to Norfolk in late December, Patty became ill. What seemed at first to be an ordinary case of the flu quickly developed into a series of more troubling problems that mystified her doctors and alarmed her parents. She lost vision in one eye. She had trouble breathing. At one point, doctors suspected she'd had a stroke.

At her mother's insistence, Patty started keeping a detailed record of her ailments and appointments. Within a month, she was too sick to continue.

During long hours at Patty's hospital bedside, her mother took over the job, compiling a hand-written spreadsheet in her search for clues and a cure.

Weeks later, Patty was dead.

Despite her grief, Cecilia Thomson often finds herself chuckling as she shares stories about her fourth and youngest daughter.

"There wasn't anything she wouldn't try," Cecilia Thomson said.

Her daughter played soccer and learned to pole vault. She had an independent streak - wearing black and pink Chuck Taylor high-top sneakers with her homecoming dress, for instance.

Patty was always on the go, always surrounded by friends. "You'd never see her, no matter how old, without a smile," Cecilia Thomson said.

She was also deeply religious.

Every summer during high school, she went to Mexico with a Catholic youth group to help build homes for needy families. A tattooed memorial to a friend covered much of her back. It depicted a heart, angel wings, a rosary, and the inscription "Matthew 5:8."

Patty enlisted in the Navy's delayed entry program at the beginning of her senior year at Fort Zumwalt South High School in St. Peters, Mo. Her parents were surprised but supportive.

Cecilia Thomson smiles mischievously when asked why Patty chose the Navy: "She said because she liked the uniforms!"

After boot camp, Patty went to Pensacola, Fla., where the Navy trains its information technology specialists. That's where she met Seaman Anitra Brown.

Brown said Patty's contagious laugh had a way of putting anxious classmates at ease before exams or after grades were posted.

Both were assigned to Little Creek's Naval Network Warfare Command, and they lived together on the second floor of Williams Hall, a five-story barracks for single enlisted sailors.

Patty loved driving her Mitsubishi Eclipse - the convertible was great for trips to the beach - and she taught Brown, who grew up in New York City, how to drive on back roads in Virginia Beach.

"I guess I was going too slow," Brown said, laughing at one memory. "She started yelling out the window, 'She doesn't know how to drive yet. Just go around!' "

Petty Officer 2nd Class Dawneen Walker took Patty under her wing at Little Creek.

"When I first met her, I thought she was a shy young girl from - for lack of a better term - the boondocks," Walker said. "She was very friendly, always wanting to help people."

After about three weeks, Walker said, Patty felt at home on duty. She was motivated to do well, and once you got to know her, she was "almost too bubbly."

Patty was such an extrovert that whenever she came home to visit, Cecilia Thomson felt like she had to book time to catch up with her daughter.

During her week of leave at Christmas, Patty doted on her 11 nieces and nephews and crammed in visits with high school friends.

"It was like a race against time to see as many people and hug as many people as possible," Thomson said.

Patty's medical records are a stack of paper more than 2 inches high. Cecilia Thomson's hand-drawn spreadsheet, color-coded with pastel highlighters, begins Dec. 28, a day after Patty found that a plumbing problem in the barracks had only gotten worse.

Patty and Brown, her roommate, had had problems with a clogged tub drain before Christmas.

A plumber had worked on the problem multiple times while they were away - at a cost of $1,129. But the bathroom still wasn't fixed.

Now, the toilet was backing up into the tub, which still wouldn't drain.

Human excrement - some wet, mostly dried - lined the tub. The stench of rotten eggs made the sailors nauseated.

When the roommates alerted barracks personnel, they quickly found themselves in a bind. The plumber wouldn't finish repairs until the tub was clean, they were told. And if they wanted to move into a suite with a functioning bathroom, they'd have to clean out the broken tub first.

The women balked. They asked to speak to the senior chief petty officer in charge of the barracks. He didn't budge.

So they did what any low-ranking sailors in that situation would do: They followed orders and got to work.

A petty officer on duty gave the women a trash bag, sponges and disinfectant. They propped the bathroom door open for ventilation.

The cleanup took about 20 minutes.

A week later, after days of nausea and a loss of appetite, Patty collapsed at work from stomach pain. A friend took her to the emergency room at Portsmouth Naval Medical Center.

Anitra Brown also experienced abdominal pain and went to Portsmouth for care.

Brown said doctors told her the pain seemed linked to her gall bladder, but they didn't find anything specific wrong. They gave her pain medication, and after a week or two, she started feeling better.

Patty, though, was quickly incapacitated.

On Jan. 5, during a return trip to the ER, she lost much of the sight in her left eye. She became extremely fatigued and was put on antibiotics for kidney and urinary tract infections.

On Jan. 9, Bill and Cecilia Thomson drove to Virginia to help take care of their daughter.

"We just figured she was getting over the bad flu," Cecilia Thomson said.

Two days later, they took Patty to Bethesda Naval Medical Center in Maryland, where eye specialists concluded she had a rare condition caused by a virus. It might go away on its own, it might leave her blind. Only time would tell.

Patty was too exhausted to ride back to Norfolk, so the family spent the night in Maryland. They stopped in Washington, D.C., the next day to see some sights. Patty managed to walk four blocks before calling it quits.

That weekend, she told her mother about the sewage she and Brown had cleaned up two weeks earlier.

Cecilia Thomson immediately started wondering whether there was a link. Unable to sleep that night, she sat in their room at Little Creek's Navy Lodge and began piecing together a timeline of Patty's illness.

The next eight days were a blur. Patty's symptoms were getting worse - and changing.

Her stomach pain was unrelenting; she slept fitfully most of the day and night. More troublesome to Cecilia Thomson was her daughter's loss of balance. She needed help getting dressed and undressed, showering and walking to the bathroom.

On follow-up visits to Little Creek's Boone Clinic and the hospital, Cecilia Thomson informed doctors of the sewage exposure.

She pushed to meet with someone about conditions in the barracks. The civilian employee she talked to said he would have Patty's old room sanitized before anyone else moved in. She suggested it be tested for possible bio hazards; he told her he didn't have that authority.

As Cecilia Thomson prepared to return to Missouri on Jan. 20, she met with a senior chief petty officer in Patty's chain of command to share her concerns about her daughter's condition.

She worried that once she and her husband left, no one would closely monitor Patty. She didn't want her daughter sent back to the barracks, where the problem might have originated. And she didn't think Patty could handle five flights of stairs to her new room at Williams Hall.

Before the Thomsons departed, the senior chief took them back to Boone Clinic, where staff agreed that one doctor should examine Patty, study her growing medical file, consider the sewage exposure and look at the case as a whole.

With Patty assuring them she'd be OK, the couple left for home.

"I think she was feeling guilty about keeping us there," Cecilia Thomson said.

She told herself everything would be fine and ignored the parental instinct nagging her to stay.

"I was sick all the way home just thinking about it," she said.

The next day, Patty had trouble breathing. Her friends took her to the hospital.

Soon after, a clinic doctor theorized Patty had suffered hydrogen sulfide poisoning while cleaning up the bathroom mess. The poisoning occurs when lungs absorb hydrogen sulfide, also known as "sewer gas," released during the organic breakdown of sewage.

He ordered hyperbaric oxygen treatments at a local civilian hospital - but they couldn't be scheduled for another week. In the meantime, Patty's condition continued to deteriorate.

Cecilia Thomson flew to Norfolk on Jan. 23.

At a follow-up eye appointment in Portsmouth, Patty was in so much abdominal pain, the ophthalmologist sent her to the emergency room.

Cecilia Thomson said they waited for eight hours, only to be told to go home and call back in the morning.

There seemed to be no end to Patty's misery.

She was horribly itchy, though her skin showed no rash. Her breathing was labored, her exhaustion extreme. She was plagued with debilitating headaches.

On Jan. 31, after finishing the second of what was supposed to be 10 hyperbaric oxygen treatments, Patty noticed more vision loss in her left eye.

That night, she was admitted to Portsmouth Naval Medical Center.

Patty's hospital records, filled with handwritten notes from at least a dozen physicians, depict a search for clues to a medical mystery.

Despite batteries of tests, extensive lab work and scans of Patty's body with cutting-edge equipment, definitive answers eluded them.

One doctor noted that Patty's varied symptoms could be explained by exposure to hydrogen sulfide gas and bacterial toxins from the sewage.

"Will continue to follow this complicated patient very closely," he wrote on Feb. 1.

An attending physician took a different view of the case. His working diagnosis that day: hysteria.

Cecilia Thomson was furious but said nothing.

A neurologist offered his opinion.

"It is clear that all her symptoms started after her exposure to sewage material.... Thinking about exposure to hydrogen sulfide is very good and more likely, perhaps with other unknown vapor agents."

An MRI indicated a possible recent stroke, but the neurologist didn't think that was likely.

Some physicians began to suspect sarcoidosis, an inflammatory disease that produces tiny lumps of cells, or granulomas, in various organs.

Imaging of her brain and lungs showed lesions in both. The nodules on her lungs were too numerous to count.

Sarcoidosis commonly attacks the lungs but can also affect the central nervous system, the eyes, the liver and the kidneys. It's a poorly understood disease, typically treated with steroids, that can be fatal but sometimes goes away on its own.

Before conducting a biopsy on Patty's lung on Feb. 4, the surgeon wrote in her chart: "Very unusual case as noted above. Bottom line the diagnosis has yet to be made and the case for steroids is not absolute."

Patty's lung tissue showed characteristics of sarcoidosis, but it wasn't "classic for sarcoid," according to her chart.

Doctors seemed to settle on that diagnosis and put Patty on high- dose steroids.

Three days after the biopsy, Patty suffered a seizure. She also experienced anxiety attacks and short-term memory lapses.

Occasionally, the old Patty would reappear - carefree and happy.

Still, Cecilia Thomson was bothered by her daughter's difficulties balancing and walking and the childlike mannerisms she began exhibiting.

Her gait was so unsteady that physical therapists insisted she use a walker to move up and down the halls. She had to take frequent breaks during therapy sessions, which consisted of tasks such as moving between a bed and a chair, standing in place and taking side steps.

Cecilia Thomson told herself that muscles deteriorate quickly if they're not used, and Patty had spent more than a month in bed.

Doctors decided Patty should recuperate at her parents' house. She was discharged from Portsmouth on Valentine's Day and given a month long convalescent leave.

Cecilia Thomson tried to be hopeful.

"She seemed to be walking better, so I assumed she was on the road to recovery and it would just take a while," she said.

She packed up copies of Patty's inpatient and outpatient medical records, as well as three CDs filled with images from numerous MRIs and scans. She also took home eight bottles of prescription pills and compression stockings to keep Patty's legs from swelling.

At home in Wentzville, Mo., Cecilia Thomson slept beside her daughter so she could hear her every need.

Within a few days, Cecilia concluded Patty wasn't improving.

She sometimes talked like a little girl. She forgot which friend's death had spurred her to get the massive tattoo across her back.

Dawneen Walker, who called to check on her friend, tried not to be alarmed when Patty would start a sentence, then drift off and begin mumbling. She seemed to have lost her short-term memory.

Cecilia Thomson also noticed basic coordination problems. Patty had trouble getting food onto her fork or spoon and difficulty getting the spoon to her mouth.

She could hardly walk, even with assistance.

On Feb. 21, a week after Patty's discharge from the naval hospital, Cecilia Thomson took Patty to the emergency room at Barnes- Jewish Hospital in St. Louis.

A spinal tap indicated she had meningitis. Several days later, doctors concluded the test had been a false positive.

There were more tests, more lab work, more questions.

As days passed, Patty grew calm. After weeks of pain and anxiety, she seemed serene.

On March 2, Patty slipped into a coma. She died the next day.

Two weeks later, Cecilia Thomson received an e-mail from one of Patty's doctors at Portsmouth Naval Medical Center.

"I spent more time on Patty's case than I have ever spent on any other patient; hours were consumed on most evenings researching her illness, which still remains a mystery," the physician wrote. "I have been overwhelmed with the amount of e-mails and phone calls from other clinicians involved in her care and who were also shocked and deeply saddened by her death.

"I think of Patty often and she inspires and motivates me to be the absolute best physician I can be; she never complained and was always optimistic and happy, despite the many challenges and discomfort she endured. Patty was an unequivocal sweet, kind and wonderful person. I wish that I had the opportunity to know her better."

Back at Little Creek, the Navy undertook an investigation into the plumbing mess and the order Patty and her roommate were given to clean it up.

"I was angry. I was very angry," said Brown, Patty's roommate. "Even as a seaman, she and I knew there was something wrong with the way they handled it."

Those who looked into the situation agreed.

The investigation found that barracks personnel had no standard operating procedures for responding to potentially hazardous waste, nor had they been trained to handle such situations.

Because of that, no individuals were disciplined, but commanders were sharply critical of the way the situation was handled.

Rear Adm. Mark S. Boensel, commander of the Navy's Mid-Atlantic Region, concluded that personnel at Williams Hall "clearly exercised poor judgment by instructing barracks residents to clean up potentially hazardous material. Had they engaged their senior leadership, this incident could have been handled more appropriately."

"Barracks staff personnel failed to use common sense," investigators wrote.

The women "should have been removed from their rooms immediately upon the discovery of the waste situation," and staff "should not have ordered them to clean up the waste in the bathroom without first consulting the safety office, preventative medicine and/or medical department."

As a result of the incident, the Navy's Mid-Atlantic Region has standardized a trouble-call process at all housing facilities for single sailors.

It issued a standard operating procedure for dealing with sewage spills and blood-borne pathogens and trained housing managers on it.

Beth Baker, a Navy spokeswoman, said all barracks residents in the region are now informed when they check in about whom to call when problems arise.

In late July - on what would have been Patty's 20th birthday - Cecilia Thomson finally received some answers about her daughter's illness.

A general autopsy did not find a specific cause of death, but neuropathologists who examined 18 sample sections taken from Patty's spinal cord and brain saw similar microscopic patterns of chronic inflammation.

The diagnosis: acute disseminated encephalomyelitis, or ADEM.

ADEM is a brief but intense attack of inflammation in the brain and spinal cord that damages the protective covering of nerve fibers.

The disease occurs when the body's defense mechanisms go awry in response to an infection or vaccination. Instead of fighting the infection, the immune system attacks the central nervous system.

Descriptions of the disease sound eerily familiar to Patty's family.

Symptoms come on quickly, beginning with fever, fatigue, headache, nausea and vomiting. Inflammation may damage brain tissue, leading to vision loss in one or both eyes, weakness to the point of paralysis and difficulty coordinating muscle movements.

Many different bacteria and viruses have been linked to ADEM, which typically begins a week or two after an infection.

Neuropathologists who examined Patty's brain tissue also found signs of a much deadlier condition, called acute hemorrhagic leukoencephalitis, or AHLE.

Dr. John Leake, a physician at Rady Children's Hospital in San Diego who has published papers about both illnesses, said ADEM is rarely fatal, but AHLE is often deadly.

Leake said there is no way to say with certainty whether an infectious agent from the sewage triggered Patty's illness. Infections spread in myriad ways.

Two other experts on the disease contacted by The Virginian-Pilot also said there is no way to know what caused Patty's illness.

Portsmouth Naval Medical Center has asked the Armed Forces Institute of Pathology to review the autopsy results.

Cecilia Thomson takes some solace in knowing that there was probably little doctors could do for her daughter.

"From everybody I've talked to, more than likely, once this ball got rolling, there was no stopping it," she said. "Even if they had diagnosed it earlier, the outcome would have been the same."

She is glad the Navy acknowledged failings at Williams Hall.

After reading through the investigation report, Cecilia Thomson said she accepts that there is no single person to blame.

"It was a series of events no one in particular was keeping track of," she said. "Nobody realized the extent of the situation."

She believes that Patty's exposure to sewage - possibly from breathing the fumes that had built up in the bathroom, or from cleaning up the mess - was related to her illness.

But she accepts that there is probably no way to know for sure.

"Patricia was a joy. She was a treasure.... She was a blessing that we were allowed to share in for 19 years."

Brown, Patty's roommate, moved out of the Little Creek barracks after getting married.

She tries not to think too much about her friend's final months. She's glad Patty is no longer suffering.

"I try to remember her smiling and laughing because that's one thing she did very well," Brown said.

To memorialize her friend, she's thinking about getting the same tattoo that covered Patty's back, with a heart, a rosary, an angel's halo and wings, and the inscription "Matthew 5:8."

The verse reads: Blessed are the pure in heart, for they shall see God.

When Cecilia Thomson needs to feel connected to Patty, she gets behind the wheel of her daughter's Mitsubishi Eclipse. Nobody else is allowed to drive the car, which stays in the family garage.

She ordered a special license plate for the convertible - PATTYO.

On the road, with the country music Patty loved blasting through the stereo, Cecilia Thomson feels her daughter next to her.