By Liz Szabo

USA TODAY

The number of babies born addicted to the class of drugs that includes prescription painkillers has nearly tripled in the past decade, according to the first national study of its kind.

About 3.4 of every 1,000 infants born in a hospital in 2009 suffered from a type of drug withdrawal commonly seen in the babies of pregnant women who abuse narcotic pain medications, the study says. It's published today in The Journal of the American Medical Association.

That's about 13,539 infants a year, or one drug-addicted baby born every hour, says the study's lead author, Stephen Patrick, a fellow in neonatal-perinatal medicine at the University of Michigan.

Treating drug-addicted newborns, most of whom are covered by the publicly financed Medicaid program, cost $720 million in 2009, the study says.

The country has an obligation to help these newborns, who "have made no choices around drug abuse and addiction" and are "the most vulnerable and the most blameless" members of society, says Marie Hayes, psychology professor at the University of Maine, who was not involved in the study.

Unlike in the 1980s and 1990s, when hospitals saw a surge in babies born addicted to crack cocaine, many newborns today arrive hooked on powerful prescription painkillers, such as Vicodin and Oxycontin, Patrick says. The type of withdrawal Patrick studied, called neonatal abstinence syndrome, produces different symptoms from those caused by cocaine. The syndrome also can be caused by illegal opiates, such as heroin, Patrick says, but this surge in addicted babies probably is explained by the national "epidemic" of prescription drug abuse.

The number of pregnant women who used or abused narcotic painkillers increased fivefold from 2000 to 2009, his study found. These mothers now account for 5.6 out of 1,000 hospital births a year, the study found. The findings also were presented at the annual meeting of the Pediatric Academic Societies in Boston.

"The prevalence of drug use among pregnant women hasn't changed since the early 2000s," says Andreea Creanga, a researcher with the Centers for Disease Control and Prevention, noting about 4.5(PERCENT) of pregnant women use illegal drugs. "But the types of drugs that women are using is changing."

The CDC has flagged prescription painkiller abuse as a major health threat, noting that these drugs now cause more overdose deaths than heroin and cocaine combined. And the problem is getting worse. The death rate from overdoses in 2007 -- 12 deaths per 100,000 people -- was roughly three times higher than in 1991, a CDC report in November showed. Most of that increase came from prescription drugs.

Many of these mothers tell their doctors they didn't realize prescription painkillers could harm their babies, perhaps because the drugs are technically legal, says Mark Hudak, a spokesman for the American Academy of Pediatrics who wrote the group's 2012 clinical report on newborn withdrawal. Other mothers are addicted when they become pregnant and simply unable to quit, he says.

Babies born in withdrawal are often born small and are at a higher risk of death than other infants, Patrick says. Doctors try to relieve the pain of surviving babies by treating them with methadone, a narcotic painkiller commonly used to treat heroin addicts. Doctors reduce the dose slowly over weeks to avoid causing sudden withdrawal symptoms, Patrick says.

Doctors and nurses sometimes can tell which babies are going through withdrawal from the hallway, without even seeing them, simply by hearing their cries, Patrick says. These babies are irritable and hard to console, with stiff, rigid muscles that won't relax. They have tremors, seizures and breathing problems. They have trouble feeding and resist taking a bottle. They throw up frequently and produce watery diarrhea. "It's like a colicky baby times 10," Patrick says.

Sometimes, these babies are exposed to multiple drugs in the womb, from tobacco and alcohol to antidepressants and other psychiatric drugs, says Howard Heiman, associate chief of the neonatal intensive care unit at Cohen Children's Medical Center of New York. Researchers need to find better ways to treat drug-addicted mothers and to identify and treat addicted babies as early as possible.

Some states have been hit harder than others, Hayes says, particularly those with high rates of rural poverty, such as Maine and Kentucky. In Florida, the number of babies with withdrawal syndrome soared from 354 in 2006 to 1,374 in 2010, according to the Florida Agency for Health Care Administration. In response, Florida's attorney general has convened a task force to address the problem of drug-addicted newborns.