Long, warm summer nights mean beach picnics and seafood dinners -- but the BC Centre for Disease Control warns that heat and undercooked shellfish are a dangerous combination.

The centre is reporting an unprecedented number of shellfish-related illnesses so far this summer.

Thirty-five cases of the intestinal ailment Vibrio parahaemolyticus have been recorded in June and July with most sufferers enduring three to seven days of diarrhea, nausea, vomiting, fever, headache and bloody stools.

B.C.'s hot summer is blamed because warm water increases the concentration of naturally-occurring bacteria within shellfish and unless oysters, clams, mussels, scallops and cockles are fully cooked, the bacteria is easily passed to humans -- with unpleasant results.