CHICAGO (Reuters) - After his first day working at St Joseph Mercy Ann Arbor hospital's newly created Fungal Outbreak Clinic, Dr David Vandenberg struggled to describe to his boss the enormity of what lay ahead. He settled on a line from the movie Jaws.

Rebecca Cook / REUTERS

Bonita Robbins, a patient suffering with arachnoiditis due to a contaminated steroid injection, sits on her hospital bed as she and her husband Ed listen to Infectious diseases Dr. Anurag Malani at St. Joseph Mercy Ann Arbor hospital in Ypsilanti, Mich.

"We're going to need a bigger boat," Vandenberg told Dr Lakshmi Halasyamani, chief medical officer of the Michigan hospital, echoing the film's local police chief after he first eyes a 25-foot (7.5-metre) killer shark.

The St Joseph Mercy clinic has been at the front line of the fight against one of the biggest ever U.S. outbreaks of fungal meningitis, a killer infection that has been traced to tainted steroid shots from a Massachusetts pharmacy.

So far, 620 Americans have developed serious infections related to the outbreak, including 367 cases of deadly meningitis, and 39 people have died. Of the 19 U.S. states affected, Michigan has been worst hit, handling more than one third of the total cases in the outbreak.

St Joseph Mercy - a 537-bed Catholic hospital located in Ypsilanti, on the doorstep of the University of Michigan - has treated 169 of the state's 223 cases of infections that can cause meningitis, including 7 people who died.

At one point it was so overrun that 87 of its 537 beds, which are usually occupied by patients with cancer or heart ailments and the like, were occupied by patients with fungal meningitis and related infections.

Dr Tom Chiller, the fungal disease expert at the U.S. Centers for Disease Control and Prevention, who has been overseeing the outbreak, praised the work of the hospital in helping to limit deaths from the outbreak.

"They have been incredibly creative in dealing with these complicated patients," he said.

In all, almost 14,000 people seeking relief from back and joint pain received injections from moldy steroid shots made at the now-bankrupt New England Compounding Center in Massachusetts before they were recalled in late September.

CDC experts initially feared death rates in the 40 to 50 percent range; instead, only about 6 percent of those infected have died, and the CDC credits the creative and dogged efforts of state and local health officials for keeping the death rates so low.

The first wave of the outbreak involved the most severe cases of meningitis - an inflammation of the membranes that cover the brain and spinal cord. But starting in mid-October, patients who had been recovering from meningitis were developing potentially fatal localized infections near the site where contaminated drug was injected to treat back or neck pain.

As they started seeing more cases of these local, secondary infections, the staff at St Joseph's devised a bold plan to screen all patients in their database looking for potential new infections that might have been missed in the first wave.

On December 20, the CDC issued an alert to doctors incorporating some of lessons learned by the efforts of doctors at St Joseph's and other hospitals, calling for increased screening of patients who may be harboring localized infections.

A bewildering fungi

Among the patients who developed secondary infections was Bonita Robbins, a 72-year-old retired nurse from Pinckney, Michigan, who received doses of the tainted drug at the Michigan Pain Specialists clinic in the nearby town of Brighton while seeking relief for lower-back pain.

The first shot brought some relief, the second did little to ease her aches, and the third was contaminated. In October, Robbins went to St Joseph's with a severe headache, back pain and pain in her thighs.

She spent 37 days in the hospital taking two kinds of antifungal drugs.

Dr Anurag Malani, an infectious disease specialist treating Robbins, said the challenge with the outbreak was that there was no medical literature to fall back on.

"No one has ever seen anything of this magnitude related to fungal infections, ever," he said.

Chiller said U.S. doctors had never treated meningitis caused by Exserohilum rostratum, the environmental mold causing most of the infections.

"It's just a rare, rare cause of infection." Seeing that mold in the meninges - membranes covering the brain and spinal cord - is "completely new."

Initially, St Joseph's Fungal Outbreak Clinic was started in order to coordinate the care of patients after their discharge, which included overseeing the administration of a complex regime of anti-fungal drugs.

It morphed into something bigger when some of its 53 patients with meningitis started returning with infections near the site in their back or neck where the contaminated drug was injected.

Then came a wave of patients like Robbins, who had been ruled out for meningitis with a spinal tap, but were still complaining of pain near their injection site.

Getting the "bigger boat"

"When it became obvious that the number of patients would be a much higher percentage than anticipated by the CDC, we expanded our clinic and started enlisting the help of several other hospitals," Vandenberg said.

Many of the patients had spinal abscesses, an infection in the space between the outside covering of the spinal cord and the bones of the spine. Others developed arachnoiditis, an infection of nerves within the spinal canal.

The decision to screen all patients in the hospital database who might have received tainted injections was not taken at the recommendation of the CDC.

"That was our own decision," said Vandenberg, a specialist in internal medicine overseeing the screening effort.

He admitted that the strategy was aggressive, but said that, especially early on, doctors feared the local infections might be precursors to meningitis, making catching them early a potentially life-saving move.

Excluding patients who had already been screened and those who had injections in areas other than the spine, the hospital targeted about 500 patients for MRI scans.

Most so far have had private insurance that covers the screening. For the uninsured, the hospital's Patient Financial Services department has been helping them to apply for financial support.

"We did over 400 MRIs in about a 4-week period," Vandenberg said. The hospital screened so many patients, in fact, that the state of Michigan sent in an emergency mobile MRI unit to help.

Vandenberg got the task of reading stacks of MRI reports, sometimes as many as 30 a day.

So far, about 20 percent of the MRIs have shown up as abnormal, meaning that patients have to come back for surgery and treatment.

Vandenberg makes all of those calls personally. Not all of them go smoothly. He likens the gravity of the conversation - learning you have a potentially deadly new disease that requires months of treatment with risky drugs - to telling someone they have cancer.

After one especially tough call, in which a heart patient feared he would not survive the surgery he would need to clear his infection, Vandenberg cracked.

"I started crying. I probably haven't cried for 15 years."

Signs outbreak is easing

But at last, after months of onslaught, there are signs the outbreak is easing.

Attendance at the hospital's daily support group has begun to taper off. And since the beginning of December, more than 50 patients with fungal infections have been discharged, while only 20 have been admitted, bringing the total number of fungus-related inpatient to 30.

Vandenberg nevertheless cautions that the outbreak is still far from over.

"Every single day of this screening program, we're finding one or two cases that are abnormal and need to be admitted," he said.

Vandenberg gave the CDC access to the clinic's database so the agency could see how the effort turned out, and this month, the CDC issued the alert to doctors incorporating some of the results of the MRI screening program.

The alert warned that some patients who got tainted injections but did not develop meningitis may still be at risk of localized infections.

And it urged doctors to consider ordering an MRI for all patients who still have pain, even if the pain is similar to what sent them in for treatment in the first place.

Chiller said the United States had not yet reached the end of the outbreak.

"Unfortunately, with fungi, the incubation periods are so long and they can remain indolent. I'm definitely concerned that we're going to continue to see more cases."

(Reporting by Julie Steenhuysen; Editing by Jilian Mincer, Mary Milliken and David Brunnstrom)