The number of homeless Americans crept up in 2018, marking the second year in a row that homelessness in the U.S. has increased, according to a new government report.

A lack of affordable housing has contributed to the slight rise in homelessness, which had declined every year from 2010 to 2016, according to housing advocates and former Department of Housing and Urban Development officials.

“More and more communities are addressing the problems that cause homelessness, but we are losing the battle because of affordability,” said Mel Martinez, former HUD Secretary under President George W. Bush, who added that he was “very disappointed” in the report’s numbers.

The HUD figures are based on a national one-night count conducted every year, which found 550,000 homeless in January 2018.

Overall, homelessness is still down significantly compared to a decade ago. And given the small size of the overall increase in 2018 — 0.3 percent — the Trump administration described the level of homelessness as “largely unchanged” from the previous year.

“Our state and local partners are increasingly focused on finding lasting solutions to homelessness even as they struggle against the headwinds of rising rents,” HUD Secretary Ben Carson said in a statement, which pointed to falling numbers of homeless families with children as well as homeless veterans.

But a rise in individual people who are homeless helped drive the overall increase, particularly among the unsheltered homeless living on the street or in parks, abandoned buildings and other areas, according to the HUD report, which was released on Monday.

“The big problem really seems to be individual adults — that’s where we need to concentrate our efforts. The system to help them is just not as robust,” said Nan Roman, president and CEO of the National Alliance to End Homelessness, an advocacy group.

“Families and children are priorities, and there is a lot of political will around veterans. But for individuals, there is not as much public support.”

The problem is particularly acute in western states, said Chad Williams, head of the Southern Nevada Regional Housing Authority, who moved to Las Vegas this year from Washington. “I thought homelessness in D.C. was bad 'til I got here," Williams said.

In California, homelessness has increased by 10 percent since 2016, according to the new report, and the state has one of the highest rates of single adults who are homeless. The waitlist for shelters tops 1,000 per night in San Francisco. In Fresno, city officials point to a lack of housing infrastructure.

“Fresno has always focused on getting people into permanent housing, and because of the shortage of permanent housing beds, that’s ticked up the rate,” said Mark Standriff, a city spokesman.

Standriff said that new funds from the state government could help alleviate the problem, noting that the local efforts have helped reduce homelessness over the past decade, though it has risen recently. Federal lawmakers, including Rep. David Price, D-N.C., are calling for Congress to step up as well.

“Congress should provide more resources to address this problem while prioritizing state and local initiatives that demonstrate successful housing outcomes for vulnerable populations,” said Price, the top-ranking Democrat on housing issues for the House Appropriations Committee.

On the federal and local levels, there’s been a significant push to fund supportive housing programs, which combine long-term rental assistance and case management to combat chronic homelessness. But that’s left less money to support other kinds of initiatives that would provide more immediate outreach and shelter as well as long-term assistance, said Josh Leopold, who worked on the United States Interagency Council on Homelessness under Obama.

“At the federal level, this needs to be a priority again,” Leopold said. “It’s been a rare policy area where there’s widespread agreement about the most effective policy approach and bipartisan support — you don’t get those things often.”