(CNN) -- The Food and Drug Administration is urging anyone who has used any product by the New England Compounding Center to be vigilant for signs of meningitis, such as a headache or stiff neck.
At least 233 people have become ill after receiving steroid injections made by the compounding center for back, neck and joint pain. Fifteen of those sickened have died. On Monday, the FDA announced that two more patients were sickened after other products made at the compounding center were used in heart and eye surgery.
But there's one problem for patients trying to take a proactive role in their health: The New England Compounding Center was making more than 2,400 drugs and other products, and many patients would never know whether they received them.
The list of New England Compounding Center products (PDF) takes up more than 70 pages and includes many hospital staples, such as morphine and saline, which are often used in surgery when the patient would have been asleep.
"It would be very difficult for a patient to sort this out," said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center and a consultant to the Tennessee Department of Health.
Even doctors would have a hard time knowing whether they used a New England Compounding Center product on patients without doing an extensive search through patient records.
The FDA warning applies to products made at the compounding center after May 21. The FDA doesn't know how many people have received such products since that date, said FDA spokeswoman Sarah Clark-Lynn.
"We understand that this is scary," Clark-Lynn said.
The FDA has not released a list of hospitals and doctors who've received New England Compounding Center products. Without that information, Schaffner said, it's impossible for doctors to warn patients who might have been infected.
"It's puzzling the FDA hasn't done that," he said.
He said it would be especially important to have a distribution list for the second steroid and the heart surgery drug, since those might be linked to new infections.
"We want to get information out to patients and alert them," he said. "But without more specific information and lot numbers, this FDA announcement isn't operationable."
Clark-Lynn said the FDA is working on it.
"This is an ongoing investigation, and we're moving very quickly," she said. "We just don't have all the answers yet."
CNN's John Bonifield contributed to this report.