new york nearly third u.s. counties likely serve one insurer participate affordable care act aca marketplace 2017 accord analysis publish sunday kaiser family foundation 31 percent u.s. counties single option insurers within aca exchange would represent increase percent year nonpartisan group find despite share namesake kaiser family foundation associate healthcare provider kaiser permanente unitedhealth group inc unh.n aetna inc aet.n decide largely exit government-run online marketplaces 2017 sell subsidize plan create president barack obama national healthcare reform law cite low enrollment high service cost bulk decrease counties choice insurers due unitedhealth pullback announce april data underscore degree industry retrenchment curtail individual options within marketplaces insurer departures may lead high cost within market analysts say one county pinal county arizona risk insurer options within marketplace analysis find study author say another plan offer elsewhere state could expand serve county foundation say could take months data full impact change 2017 become clear number step remain full picture year marketplace competition know aca greatly expand insurance options available consumers individual marketplace say marjorie connolly spokeswoman u.s. department health human service statement u.s. counties see obamacare marketplace monopoly analysis