Public health officials say H.I.V. cases in southern Illinois are on the rise.  The Southern Illinois H.I.V. Care Connect office in Jackson County’s health department tracks the data in 19 counties.  They say the region has averaged 14 to 15 new H.I.V. cases a year.  But that number jumped to 21 in 2012 and to 23 last year.  Paula Clark of the county health department says more than half of the cases involve people who are 24 years old or younger.  As an infectious diseases specialist at Southern Illinois Healthcare, Dr. Erica Kaufman says she suspects “a lot of young people … don’t know about H.I.V.”  The region covers Mount Vernon to Cairo.