Paralytic shellfish poisoning--Massachusetts and Alaska, 1990 [published erratum appears in MMWR Morb Mortal Wkly Rep 1991 Apr 12;40(14):242] Paralytic shellfish poisoning (PSP) is a foodborne illness caused by consumption of shellfish or broth from cooked shellfish that contain either concentrated saxitoxin, an alkaloid neurotoxin, or related compounds. This report summarizes outbreaks of PSP that occurred in Massachusetts and Alaska in June 1990. 