NEW HAVEN, Conn. — Bedbugs are causing a stir in New Haven, where the blood-sucking parasites have been making unwelcome appearances in places including Yale University.

In recent weeks, students at a city high school refused to enter a classroom where the bugs had been spotted and Yale's School of Medicine had to find new accommodations for visiting accepted students after bugs were seen in a dorm.

The city of New Haven only recently began keeping a tally, but anecdotal reports of bedbugs have been on the rise in recent years, according to Paul Kowalski, a director with the New Haven Health Department. Protocol calls for steam-cleaning and vacuuming of affected classrooms, counseling for the child and inspection of the source, which Kowalski said is typically the home.

"Schools are not the source," he said.

It's not just New Haven. After a decadeslong lull, scientists say bedbugs have spread across the continent over the last 15 years, a side effect of more international travel and trade.

While bedbugs are not known to transmit disease, they do cause itchy bites and no small amount of distress for people living in infested homes.

At Yale, some 30 admitted students who were supposed to stay in a medical school dorm for a visit in early April had to stay at a hotel because of the latest in a series of problems with bed bugs, the Yale Daily News reported.

Yale said in a statement that it was inspecting rooms.

Several sightings have been reported at New Haven's James Hillhouse High School. One parent, Nijija-Ife Waters, said more than 50 students refused to enter a classroom where a bug was seen on a keyboard. She said some parents were alarmed that the sighting occurred on the third floor, two floors up from earlier sightings.

"How did they reach the third floor? How did that happen? It's like 'Wow,'" she said.

The school system said the case was being addressed and there was no risk to the student population.

A rash of reports may suggest a heightened level of anxiety about the insects, and not an actual increase in their numbers, said Gale Ridge, an entomologist with the Connecticut Agricultural Experiment Station.

"Because of social stigma and lack of education toward this insect it goes mostly unreported," Ridge said.