Over the past six months, 18 mothers and 19 newborns have become sick with a dangerous bacterial infection soon after being released from Beth Israel Deaconess Medical Center, triggering a state investigation that uncovered serious problems with the hospital’s infection control practices.

Ten of the infected patients became so ill that they required hospitalization. Two of those had serious complications.

The most recent of the staph bacterial infections, a type resistant to many common antibiotics, was identified earlier this week.State authorities have asked the US Centers for Disease Control and Prevention for help in determining what caused these infections, which are generally spread by skin-to-skin contact. Based on research from similar outbreaks in maternity wards in other cities, a CDC investigator said the cluster at Beth Israel Deaconess is probably related to someone – such as a healthcare worker, patient, or visitor – who brought the bacteria into the hospital, and the institution’s hygiene practices failed to stop it from spreading.

The Massachusetts Department of Public Health ordered the hospital to come up with “an immediate plan of correction” for its infection control systems by Monday. It is also forcing Beth Israel to undergo a hospitalwide inspection of many of its operations as a condition of its continued participation in the federal Medicare insurance program.

Paul Dreyer, director of the state’s Bureau of Health Care Safety and Quality, said he did not think the problem warranted more urgent steps, such as temporarily halting the hospital’s delivery of babies.

“This is a very small number of cases out of 5,000 deliveries” a year, he said. “And there were no deaths. In terms of actual harm to patients, we didn’t think it rose to that level of concern.”

State public health officials began investigating the outbreak in December after being notified of the problem by the hospital. They later found what they called “serious deficiencies” in infection control. The outbreak began in November.

Paul Levy, the chief executive officer of Beth Israel Deaconess who has made transparency of medical errors and problems a cornerstone of his tenure, declined a Globe request for an interview yesterday. He said through his spokesman that he would wait to comment until after the hospital completes its report to the state.

Levy, however, did issue a message on his blog to all hospital staff yesterday, notifying them of the latest cases associated with methicillin-resistant Staphylococcus aureus – the formal name for the type of staph known as MRSA. He included a memo written by members of his top staff that explained the recent problem and efforts to strengthen infection control practices, including “hand hygiene and sterilization.”

The memo said most problems were “superficial skin infections and breast infections” that have been “successfully treated, in most cases with antibiotic creams or pills.”

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