A previously unknown bacteria caused the outbreak of legionnaires' disease which killed 29 persons in Philadelphia last summer, federal health officials said yesterday.

Although the discovery is a "major breakthrough," researchers do not yet know how the disease originated, Dr. Alexander D. Longmuir '31, visiting professor of Epidemiology, said yesterday.

True Cases

"Now we can eliminate the true cases from those that had nothing to do with the epidemic, make a careful analysis, and look for a treatment," Longmuir, one of three Harvard professors on a seven member panel investigating the outbreak for the National Center for Disease Control (NCDC), added.

The NCDC recently proved that the same organism caused an epidemic in 1967 at St. Elizabeth's Hospital in Washington, killing about 20 people, he said.

The Philadelphia epidemic affected 151 other persons, primarily members of the American Legion, attending a convention at the Bellevue-Stratford Hotel in Philadelphia.

Know-Nothings

Researchers know little about the nature of the bacteria, Dr. Louis Weinstein, visiting professor of Medicine and a second member of the panel, said yesterday.

"There hasn't been a start towards a treatment. A lot of work towards identifying the bacteria must be done," he said.

The NCDC researchers first isolated the bacteria in two patients, and then inoculated guinea pigs with it, Langmuir said.

The guinea pigs' blood was then injected into fertilized egg yolks. Subsequent tests linked the bacteria to the earlier St. Elizabeth cases.

The bacteria is probably not contagious, an NCDC spokesman said yesterday, adding that there is no evidence of any new cases.

The NCDC staff will return to the Bellevue-Stratford in search of additional specimens, Associated Press reported yesterday. The hotel has been closed for several months, due to publicity about the disease.