Poverty Medicine

Here are some MeSH that I found for Poverty Medicine:

• Poverty
• Poverty Areas
• Homeless Persons
• Medical Indigency

There are similar ones in CINAHL:

• Poverty
• Homelessness
• Homeless Persons
• Health Services for the Indigent
• Indigent Persons

Keywords of potential use:

• impoverish*
• disadvantaged
• vulnerable
• "at risk"
• marginali*
• "street involved"
• street

 The last one is because I came across some other variations such as "street entrenched" and "street youth", but of course you're also more likely to come across irrelevant results.