Two Harvard affiliates were among the five Boston-area hospitals that received threatening letters Wednesday, a scare that prompted police and hazardous materials teams to rush to the scene.

Police responded to reports of suspicious mail at Brigham and Women’s Hospital and Beth Israel Deaconess Medical Center in the early afternoon.

All the envelopes delivered to the hospitals appeared to be from the same sender, but police found no trace of powder, according to media reports and the Boston Police Department’s online log.

The exact intent of the letters mailed to the hospitals remains unclear, but no biological threat was found.

Wednesday’s scare began after employees at New England Baptist Hospital noticed an envelope with excessive postage and suspicious-looking writing scrawled on the front around 10:47 a.m. The hospital notified police, which in turn warned hospitals in the area.

Throughout the late morning and early afternoon—as hospitals scoured mailrooms for suspicious letters—other hospitals reported finding similar letters, triggering a flurry of hazmat team deployments to four other hospitals in the Boston area.

The letters appear to be from by a patient advocate in Westborough, Massachusetts, said BPD spokesman David Estrada. According to the online log, the suspect is “a zealous advocate for patient’s rights and makes statements critical of the care provided by these hospitals.”

No arrests have been made in the case so far, according to Estrada, who declined to comment on the details of the investigation.

Although hazmat teams were deployed to Beth Israel to collect one of the suspicious letters, the hospital did not evacuate or suffer any disruptions in service, said Michael Keating, a spokesman for the hospital.

Keating declined to comment on whether the hospital had experienced similar threats in recent years, citing hospital policy against commenting on security issues.

Officials at Brigham and Women’s Hospital could not be reached for comment.

Wednesday’s incident is not Harvard’s first run-in with suspicious letters this year.

In late January, Law School professor Alan M. Dershowitz received a letter containing a suspicious white powder, a threat that turned out to be a hoax.

Since the anthrax scares of 2002, threatening mail has become a popular method for turning an innocuous letter into a alarming—if not always lethal—terrorism device.

—Staff writer Elias J. Groll can be reached at egroll@fas.harvard.edu.