Two people blinded in Washington, D.C., in 2005. Three dead in Virginia in 2006 and three more in Oregon the following year. Twenty-one dead polo horses in Florida in 2009. Earlier this year, 33 people in seven states with fungal eye infections.

And now, at least five people dead and 35 sickened with fungal meningitis that has been linked to steroid shots for back pain.

All these disasters involved medicines that had been custom-mixed at what are called "compounding pharmacies" — laboratories that supply hospitals, clinics and doctors to a much wider degree in the U.S. than many people realize.

These pharmacies mix solutions, creams and other medicines used to treat everything from menopause symptoms and back pain to vision loss and cancer. Unlike manufactured drugs, these products are not subject to approval by the Food and Drug Administration. And some have turned out to be dangerously contaminated.

Compounding pharmacies often obtain drugs from manufacturers and then split them into smaller doses, or mix ingredients sold in bulk. Any of those steps can easily lead to contamination if sterile conditions aren't maintained. For example, the fungus suspected in the current meningitis outbreak can spread in the air.

The risks from these products have long been known but are being amplified now by a national shortage of many drugs that has forced doctors to seek custom-made alternatives to the usual first-choice treatments.

"Because of the incredible number of drugs that are out of stock or back-ordered, compounding pharmacies are working with local hospitals, clinics and physicians to fill that gap," said David Miller, executive vice president of the International Academy of Compounding Pharmacists, a trade organization.

These products have had remarkable growth. More than 7,500 compounding pharmacies operate in the U.S., up from 5,000 in 2009, Miller said. They account for a $3 billion segment of the drug market and 3 percent of all prescriptions filled.

Some say this industry needs more regulation.

"There's not a lot of oversight of compounding pharmacies" compared with drug manufacturers, said Allen Vaida, executive vice president of the Institute for Safe Medication Practices, a suburban Philadelphia advocacy group that tracks medication errors.

Dr. William Schaffner, an infectious-disease specialist at Vanderbilt University, agreed.

"They fall into this gray area and no one supervises in a rigorous fashion their manufacturing processes. The state pharmacy boards don't have the resources or the knowledge or experience," and the FDA does not get involved unless a problem occurs, he said.

The FDA has said the steroid in the current meningitis outbreak came from the New England Compounding Center, based in Framingham, Mass. The company recalled three lots of the drug last week and has said it has voluntarily suspended operations and is working with regulators to identify the source of the infection. Investigators also are looking into the antiseptic and anesthetic used during the injections.

On Thursday, investigators urged doctors nationwide to avoid all products from the New England company. At least 23 states have received vials from the three recalled lots.

Compounding pharmacies are supposed to supply products to meet unique patient needs, and to prepare drug products that are not available commercially, based on an individual prescription. They may cross a line if they supply a product on a large scale to a clinic or hospital without individual prescriptions, Miller and other experts said.

"They, in effect, since they do this on a large scale, have become mini-pharmaceutical companies," Schaffner said.

That appears to be the basis for an FDA warning to the New England company and four other firms in December 2006. The FDA told them to stop compounding and distributing anesthetic creams "marketed for general distribution rather than responding to the unique medical needs of individual patients." Too much anesthetic in a rubbed-on cream can cause seizures and irregular heartbeats, and at least two deaths have resulted, the FDA said.

Miller, of the pharmacy trade group, said that in the current outbreak, it appears that the New England company was dispensing drugs widely to clinics and hospitals instead of filling individual prescriptions.

Some compounding pharmacies have had more than one troubling episode. And some products seem to have problems over and over again.

In May, officials reported 33 cases in seven states of a fungal eye infection stemming from products mixed in a Florida pharmacy that also prepared supplements that killed 21 elite polo horses in 2009.

The same steroid in the current outbreak was also tied to five cases of a different type of fungal infection in North Carolina in September 2002. Those patients also had shots from pain clinics, and one died.