The number of children enrolled in Medicaid and the Children’s Health Insurance Program, or CHIP — two government health plans for the poor — fell by nearly 600,000 in the first 11 months of 2018, a precipitous drop that has puzzled and alarmed many health policy analysts, while several states say it reflects the good news of an improving economy.

Enrollment in the two programs decreased by 599,000 children in the 48 states from which the U.S. Centers for Medicare and Medicaid Services, or CMS, has data from December 2017 to November 2018, the last month for which numbers are available. At the beginning of that period, Medicaid and CHIP enrolled nearly 36 million children in those states.

Missouri (8.1 percent), Idaho (6.7 percent) and Utah (6 percent) experienced the biggest percentage drops in children enrolled.

“I’m sure Idaho’s strong economy is playing a role,” enabling families to leave public health programs, said Niki Forbing-Orr, spokeswoman for the Idaho Department of Health and Welfare. She also cited other factors, such as the department not being able to reach beneficiaries to alert them it was time to re-enroll. Some, she said, may have simply moved out of state.

In total numbers, Texas rolls tumbled the most — by more than 134,000 children — followed by California with almost 130,000. Both states ascribed declining enrollment to strong economic growth. Texas also said that enrollment numbers the previous year, in 2017, had been particularly high because of extra steps the state took in the wake of Hurricane Harvey to ensure Medicaid and CHIP beneficiaries were re-enrolled. The larger numbers that year contributed to the big drop in 2018, Texas officials said.

That kind of large drop in child enrollment is unusual in the history of Medicaid and CHIP.

While experts seem uncertain about the cause, they too cite the possibility of the improving economy that might enable parents to leave government health plans. They say there are other likely causes, though, including actions by the Trump administration to undermine the Affordable Care Act, changes in data systems and immigrants’ fears of enrolling their children in public services.

Uncertainty about the status of the programs also may have played a role, analysts say. Congressional Republicans have sought cuts in Medicaid since President Donald Trump assumed office. And in 2017, Congress missed the deadline for reauthorizing CHIP funding by about four months, which prompted Minnesota to start dipping into its own funds to continue the program. Other states, including Colorado and Virginia, sent letters to parents warning of the possible cessation of services.

Medicaid and CHIP had been steadily gaining coverage since the late 1990s, and more than a third of the nation’s children rely on one or the other for health coverage. Health policy analysts and advocates for low-income children say the decrease might be a sign that more children are going without the health care they need.

“All kinds of warning lights are going off in my head,” said Tricia Brooks, a senior fellow at Georgetown University’s Health Policy Institute, who has blogged about the sudden drop in enrollment.

Not all analysts agree there is cause for concern. Edmund Haislmaier, a health policy expert at the conservative Heritage Foundation, for example, pointed out that the decrease is relatively small in programs that together enrolled nearly 35.4 million children as of November 2018.

“You’re talking about less than a 1.5 percent difference,” he said. “I would find it hard to make even a molehill out of that.”

A CMS spokesman said questions about the decline in child enrollment should be directed to the states.