In a 2007 decision by the Ninth US Circuit Court of Appeal, intentionally spitting on someone is “an offensive touching that rises to the level of simple assault,” that can be punished by up to six months in prison.

…at least nine HIV-positive individuals in the US have previously been sentenced to much longer prison terms for spitting. A 2003 analysis from the Yale University Center for Interdisciplinary Research on AIDS “found 24 instances of prosecutions for spitting…[and] convictions for HIV exposure in eight cases, in which there were two convictions for attempted murder, two for criminal exposure to HIV, one for assault with a deadly weapon, two for assault, and one for battery by body waste. The sentences imposed ranged from 90 days in jail to 25 years incarceration to life imprisonment.”