Custom-mixed medicines like the steroid shots suspected in the current meningitis outbreak have long been a source of concern, and their use is far wider than many people realize.

These medicines are made in private and hospital pharmacies and are used to treat everything from cancer to menopause symptoms to vision loss.

Often these products are name-brand medicines split into smaller doses, or drug combinations mixed from ingredients sold in bulk. That can easily lead to contamination if sterile conditions aren't maintained. The germ suspected in the current outbreak can spread in the air.

A shortage of many drugs has forced doctors to stretch supplies and seek custom-made alternatives if the first-choice treatment was not available. The steroid suspected in the current outbreak has been in short supply.

"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," says David Miller, executive vice president of the International Academy of Compounding Pharmacists, a trade organization.

Drug shortages are one reason for the remarkable growth of these custom-made products. More than 7,500 compounding pharmacies operate in the U.S., up from 5,000 in 2009, Miller says. They account for a $3 billion segment of the drug market and 3 percent of all prescriptions filled, he says.

Some say this industry needs more regulation.

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

The outbreak of fungal meningitis has sickened at least 35 people in five states. Five of them have died. They all received the steroid shots, mostly for back pain.

The Food and Drug Administration has says the steroid came from the New England Compounding Center, based in Framingham, Mass. The company recalled three lots of the drug last week and has says 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.