An antibody treatment of a bacterial infection can save many people stricken with a form of blood poisoning that kills at least 30,000 Americans each year, a study concludes.

The treatment employs monoclonal antibodies, copies of natural chemicals that fight microbes and other invaders. In this case, the antibodies target a bacterial poison called endotoxin.While the experimental new treatment improves survival rates, the illness still is frequently fatal, and experts caution that other approaches will be needed to bring the infection under control.

A study of the treatment was published Thursday in the New England Journal of Medicine. Dr. Elizabeth J. Ziegler of the University of California, San Diego, directed the study, which was sponsored by the treatment's maker, Centocor Inc. of Malvern, Penn.

The therapy is intended to control a form of blood poisoning called gram-negative bacteremia.

The poisoning occurs when ordinarily harmless bacteria invade the bloodstream, often when people are already weak from other health problems, and causes life-threatening complications, including low blood pressure, fever and kidney failure.

Doctors tested the antibody treatment - known as HA-1A or Centoxin - on 543 people at 24 hospitals who were suspected of having gram-negative bacteremia. The patients were randomly assigned to receive antibodies or dummy placebos, and 200 of them eventually turned out to actually have had gram-negative bacteremia.

Results showed that 30 percent of those getting antibodies died, compared with 49 percent of those in the comparison group.

"Our results indicate that HA-1A is safe and that it substantially reduces mortality in patients with sepsis (infection) and gram-negative bacteremia," the researchers wrote.

In an accompanying editorial, Dr. Seldon M. Wolff of New England Medical Center noted that between 30,000 and 100,000 people die in the United States annually from gram-negative bacteremia.