Dirty conditions at the pharmacy, faulty sterilizing equipment, tainted ingredients or careless lab technicians could have led to contamination of the steroid medication blamed for the outbreak.

Health authorities are still investigating, and the New England Compounding Center of Framingham, Mass., has not commented on what might have gone wrong, so outside experts can only speculate.

The outbreak has killed at least 15 people and sickened more than 200 others in 15 states. Nearly all had received steroid injections for back pain.

(Copyright 2012 The Associated Press. All rights reserved.)