A deadly form of fungal meningitis has spread to nine states, killing eight people, sickening 105, and potentially infecting thousands upon thousands more. Investigators say the outbreak is due to a contaminated steroid drug distributed from a "compound pharmacy" in Massachusetts. Such pharmacies often mix batches of drugs on their own to undercut prices set by major manufacturers, and now critics say it's time for the Food and Drug Administration to crack down. Here, a guide to the outbreak, who's at risk, and what it means for you:

First off: What exactly is meningitis?
It's "an inflammation of the protective membranes covering the brain and spinal cord," says JoNel Allecia at NBC News. The disease can cause "headache, fever, nausea, and stiffness of the neck," along with "confusion, dizziness, and discomfort from bright lights." Because it affects the central nervous system, the disease can also be deadly.

And it was caused by a contaminated steroid drug?
In this case, yes: Specifically, a lumbar epidural steroid injection, which is used to treat back pain. The use of such drugs skyrocketed in the 1990s, says The New York Times, and while it's since tapered off, the numbers remain robust. In 2011, for example, 2.5 million Medicare recipients had the injection, as did an equal number of younger people. By soothing irritated or inflamed nerves, the injections help patients hold off on expensive surgery. In this case, more than 17,600 contaminated vials of a spinal injection drug were distributed to pain clinics in 23 states. 

How did the vials get infected?
Officials haven't quite figured that out yet. But the injections came from the New England Compounding Center in Massachusetts, which has gotten into trouble with health authorities before. Over the past decade, several complaints have been submitted against the center. In 2006, for example, the state Health Department inspected the center after it was accused of illegally producing an anesthetic topical cream.

What happens next?
The Centers for Disease Control and Prevention says that as many as 13,000 patients may have been exposed to the fungal infection, and local health officials in Ohio are calling for police to check on patients who may have received injections, many of whom are elderly. "If that means knocking on doors, then that's what they will do," Beth Bickford, executive director at the Association of Ohio Health Commissioners, said in a statement Monday.

Do we need tighter regulations?
Sen. Richard Blumenthal (D-Conn.) is among the lawmakers calling for stronger government oversight of compounding pharmacies. "The Food and Drug Administration has more regulatory authority over a drug factory in China," Kevin Outterson, an associate professor of law at Boston University, tells The New York Times. With some 7,500 compounding pharmacies in the U.S. taking in $3 billion in sales annually, something needs to be done to ensure proper safe-handling procedures are followed. "They have not been regulated the way major pharmaceutical companies are," Dr. William Schaffner, chairman of Preventive Medicine at Vanderbilt University Medical Center, tells CBS News. "They have fallen into a regulatory gap. That's something that really needs to be addressed by the Congress." 

Sources: The Associated Press (2), CBS News, NBC NewsNew York Times, Reuters