A 36-year-old woman has pleaded not guilty to multiple sexual assault charges involving a bedridden 16-year-old exchange student in Honolulu.

Rika Shimizu appeared at her arraignment Thursday before Judge Colette Gari­baldi in Circuit Court on five counts of second-degree sexual assault and four counts of fourth-degree sexual assault. Shimizu’s attorney, Gary Singh, pleaded not guilty to all charges on her behalf.

Garibaldi confirmed her bail at $600,000 and set her trial for May.

In February the victim reported to police that his dormitory supervisor, later identified as Shimizu, allegedly sexually assaulted him at least 10 times from October to February while he resided in a boardinghouse that she operated.

According to court documents, Shimizu is the sole proprietor of ESL Hawaii, a boarding home for exchange students from Japan who are attending school in Honolulu.

The first assault occurred in October when the boy was bedridden for several weeks due to a head injury. At the time, he was unable to go to the bathroom alone, prepare meals or change clothes.

As his guardian, Shimizu had the boy under her care while he lived in the boardinghouse.

During one late October night, police said, Shimizu entered his room and sexually assaulted him. He repeatedly told her to stop and that he was going to report her. Court documents said Shimizu told him she would accuse him of rape if he told anyone.

She also allegedly threatened to have him thrown out of the exchange program and expelled from school, alluding that his family would lose thousands of dollars that they invested in the exchange program.

The last assault occurred in February when Shimizu allegedly used her own key to unlock his room and sexually assault him, court documents said.

A family friend took the victim out of the house once he told his mother of the assaults.

Police arrested Shimizu on March 6 at a Kanewai Street residence near the University of Hawaii at Manoa campus. Two days later an Oahu grand jury returned an indictment against her, charging her with multiple counts of sexual assault.