A319
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; General Physical Injury / Incapacitation
Weather
We were cruising at FL360; in cirrus type clouds; experiencing continuous light chop.  Seat belt sign was on; and no returns were depicted on the weather radar display.  We had heard no PIREPs or advisories concerning turbulence or convective activity.  Suddenly; the turbulence increased to moderate; and we heard rain hitting the airplane.  This lasted 5-10 sec; then we experienced a rapid; almost instant 1;500 fpm climb to an altitude about 400 feet above the assigned altitude.  Immediately thereafter; we felt a drop as we exited the clouds.  The Captain was Pilot Flying and returned the airplane to the assigned altitude....By the time we coordinated with flight attendants as to passenger and/or crew injuries; made a plan as to how best to address the situation; and checked in with Center; we were very near our top of descent.  We were still getting information as to passenger injuries and we needed to prepare for our approach.  We requested a straight-in; expedited approach.  During the descent; we were still coordinating with the cabin crew; answering questions from Center; and setting up for the approach and landing.   I (pilot not flying) called ahead to Operations to advise them that we were in-range and needed medical personnel to meet the flight. I'm not sure how we could have avoided this event. The Captain did have the seat belt sign on; and made a predeparture PA telling the passengers to leave seat belts fastened while seated.  He also made a PA 'Flight attendants be seated immediately'; as the event began; which according to the number 1; allowed him to avoid injury.
A319 Flight Crew experienced turbulence in cirrus clouds at FL360 which caused abrupt altitude gain and resulted in passenger injury.