Fewer people with developmental disabilities in Connecticut need the highest level of care, but rising costs are growing the gap between high-cost treatment in state-run facilities and lower-cost private alternatives.

According to 2013 data provided by the Department of Developmental Services, the number of people in federally-designated intermediate care facilities for individuals with intellectual disabilities fell below 1,000 last year. The federal government reimburses half the cost of care at these facilities.

The cost of care is growing rapidly at state-run facilities. At the highest-cost regional centers, run by DDS, the average cost per person rose 10.5 percent in a year, from just over $400,000 to a little more than $442,000.

Costs at Southbury Training School, slightly lower-cost but still state-run, increased by more than 8 percent and now exceed $350,000 per person.

Private-run ICF-IIDs saw costs rise by a more modest 3 percent, nearing $165,000 or less than half cost of the state-run programs.

With more than 600 people seeking residential services from DDS as of December, private facilities offer the possibility of helping more people without increasing costs.

A DDS spokeswoman attributed the rising costs to “the drop in consumer counts.”

Recently, DDS has come under scrutiny for the death of a Southbury Training School resident and falling behind on its abuse registry.