An HIV-positive former track coach has plead guilty to sexually abusing dozens of boys. Carlos Deangelo Bell, 30, is accused of abusing 42 boys while employed at two Charles County schools in Maryland.

Bell entered a plea deal admitting guilt on 27 counts, including sexual abuse of a minor, second-degree sex offence by force, third-degree sex offence, attempted transmission of HIV virus, second-degree assault, filming child pornography, solicitation of a minor and displaying obscene matter, state attorney Anthony Covington said.

The offences began in May 2015, with the victims ranging in age from 11 to 17 years old, Covington said.

The ex-school aide was arrested in July 2016 at his home after a six-month investigation. According to ABC 13, Bell was removed as an instructional assistant at Benjamin Stoddert Middle School in Waldorf and as an indoor track coach at La Plata High School when the investigation began.

Investigators began the inquiry in December 2016 after receiving a tip about "possibly inappropriate behaviour with a student while he was coaching track," a statement by the Charles County Sheriff's Office said.

Charles County Sheriff Troy Berry said a student's parent noticed suspicious text messages that were sexual in nature on their child's phone.

Bell's electronic devices from work and from home were sent to the Maryland State Police crime lab. Authorities found sexually explicit images involving the victims.

"Some of the evidence...included graphic images of Bell sexually assaulting victims. Some of the crimes appeared to have been committed on school property, and others at his home in Waldorf," the sheriff said.

The sheriff's office said Bell told investigators that he is HIV positive and investigators were able to corroborate the diagnosis. Some of the victims were tested for HIV last year, authorities said. However, police are unaware of any tests that came back positive.

Bell is set to be sentenced on 28 March. According to KTLA, prosecutors plan to recommend a sentence of up to 190 years in prison.