1.   Accidental transmission has also occurred through surgery, through either failure to sterilize instruments or the inadvertent use of infected donor tissue.

2.   But other experts say the cases point to serious holes in the system to monitor the trade in donor tissue.

3.   But three years ago he had a patient who developed a serious clostridial infection in his knee after receiving donor tissue.

4.   But, increasingly, donor tissue is being collected, processed and sold by subsidiaries of for-profit companies, in a rapidly growing industry that is largely unregulated.

5.   Donor tissue unquestionably saves lives and helps thousands of people each year with a growing list of life-enhancing products like knee ligaments and bone cement.

6.   First, donor tissues such as bones and tendons cannot be completely sterilized without losing the integrity that makes them desirable spare parts.

7.   Hundreds of thousands more need donor tissue, including corneas to restore sight, skin to treat burns, and bones and valves to reconstruct worn-out ones.

8.   The investigation has not demonstrated exactly when or where the donor tissues were infected, he said.

9.   These factors, and the growing use of donor tissue, are leading doctors like Malinin to question the system in place for providing them.

10.   This is the first report that donor tissue for knee surgery can cause illness or death, said Dr. Daniel Jernigan, a medical epidemiologist at the disease centers.