A319 AIRBUS FLT CREW ENCOUNTERS TURB WHILE ENRTE; PAX INJURED; EMER DECLARED; ACFT DIVERTS.

Narrative

AFTER 1 1/2 HRS OF FLYING S OF SOME TSTMS; WITH THE SEATBELT SIGN ON; WE FINALLY FOUND A GOOD RIDE FOR 10 MINS NO TURB. WE FLEW INTO MODERATE TURB. THE WX RADAR WAS CLR OF ALL THE TSTMS AND RAIN. ALL OF THE WX WAS E OF THE VOR. FROM MY SEAT; I COULD SEE S OF THE ACFT STARS AND THE GND IN FRONT OF THE ACFT WAS CLR; NO RAIN OR LIGHTNING WAS OBSERVED. OUT OF NOWHERE WE FLEW INTO MODERATE TURB FOR 5-10 SECONDS WITH A VERY BRIEF PERIOD OF RAIN. THE AUTOPLT NEVER TURNED OFF BUT THE ACFT DSNDED AROUND 300 FT BEFORE ROUNDING OUT AND I THEN SLOWLY AND SMOOTHLY BROUGHT THE PLANE BACK TO OUR CRUISE ALT. IN THE CABIN; A PAX WAS WAITING TO USE THE AFT LAVATORY EVEN THOUGH THE SEATBELT SIGN WAS ON. UPON ENCOUNTERING THE TURB; THE PAX FELL TO THE FLOOR INJURING HIMSELF. THERE WAS AN EMER ROOM DOCTOR ON BOARD WHO THOUGHT THE PAX HAD BROKEN HIS HIP AND SAID WE SHOULD LAND AT THE NEAREST ARPT. AFTER GETTING THIS INFO; WE DECLARED A MEDICAL EMER AND DIVERTED. THE REST OF THE FLT WAS UNEVENTFUL. AFTER ARRIVING; I WAS THEN INFORMED THAT MY SECOND AND THIRD FLT ATTENDANT HAD INJURED THEIR ANKLES. ONCE AGAIN THE SEATBELT SIGN WAS ON FOR A GOOD WHILE. I HAD ALSO TOLD THE PAX BEFORE WE LEFT THAT THERE WOULD BE WX ALONG THE RTE THAT WE WOULD BE GOING AROUND AND THAT IF THE SEATBELT SIGN WAS ON THAT I EXPECTED THEM TO REMAIN SEATED.