Baltimore mayoral candidate and state Sen. Catherine Pugh addresses a rally to mark the anniversary of the death of city resident Freddie Gray at the War Memorial Plaza across from the City Hall April 25, 2016 in Baltimore, Maryland.
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(CNN) —  

Democratic Baltimore Mayor Catherine Pugh will be taking an “indefinite leave of absence,” her office announced Monday, citing a battle with pneumonia. The announcement comes at the same time she’s facing a scandal over a major purchase of children’s books she authored by the University of Maryland Medical System and other groups.

“She has been advised by her physicians that she needs to take time to recover and focus on her health,” a statement from Pugh’s office read, adding that, “with the Mayor’s health deteriorating, she feels as though she is unable to fulfill her obligations as Mayor of Baltimore City.”

The announcement came the same day Maryland Republican Gov. Larry Hogan wrote to the Office of the State Prosecutor requesting an investigation into the sales of thousands of Pugh’s book, “Healthy Holly,” to the University of Maryland Medical System while she was a member of its board.

“All Marylanders have an expectation that their public officials as well as individuals involved with institutions that are funded by and closely related to the State, will follow the highest legal and ethical standards,” Hogan wrote in a letter obtained by CNN.

CNN has reached out to the Office of the State Prosecutor and Pugh’s office for comment.

UMMS spent $500,000 to fund the purchase of some 100,000 books from Pugh’s company Healthy Holly LLC, confirmed UMMS spokesman Michael Schwartzberg, who explained that the company never had possession of any Healthy Holly books, nor did it distribute books. Book distribution was managed by Healthy Holly LLC.

“I sincerely want to say I apologize that I have done something to upset the people, the people of Baltimore that I love and care for,” Pugh said in a news conference last week.

Pugh recently returned $100,000 to the medical system and canceled her book deal. She has also resigned from the hospital’s board, according to Schwartzberg..

Pugh also received about $114,000 from Kaiser Permanente for some 20,000 books from 2015 to 2018, according to the health care provider. Kaiser Permanente said it delivered the books to back-to-school fairs, elementary schools, communities of faith and early childhood education and care centers.

“We purchased Healthy Holly books because we believe residents would be inspired by a book about health and wellness authored by a member of the Baltimore community,” the company said in a statement obtained by CNN. “Kaiser Permanente has been available to Baltimore City government employees since 1986. Our purchase of the Healthy Holly books nearly 30 years after being selected as one of the health plan providers for the city employees has no connection with our commitment to continue offering our care to Baltimore City government employees.”

Kaiser said it is reviewing the process through which books are selected and procured.

The Baltimore Sun reported that in September 2017, the city’s spending board, controlled by Pugh, awarded Kaiser a $48 million contract to provide health insurance to city employees from 2018 to 2020, with options to renew.

Associated Black Charities, a public foundation that works to encourage healthier and more prosperous communities, said it spent approximately $80,000 between 2011 and 2016 to buy some 10,000 copies of Pugh’s books – a project the organization learned about while she was still a state senator.

“This idea resonated with ABC because it fit well with the organization’s mission at the time of addressing racial health disparities, including high rates of obesity among African-American children,” the organization said in a statement.

After the Pugh revelations in recent weeks, Associated Black Charities’ board re-examined the project and unanimously passed a resolution prohibiting the organization from entering into business arrangements with any elected officials or politically appointed persons, regardless of the person’s product and its relationship to the charity’s core mission and agenda.

City Council President Bernard C. “Jack” Young will take over as “ex officio Mayor of Baltimore City” during Pugh’s absence.

CNN’s Eli Watkins contributed to this report.