The severe paralytic shellfish poisoning outbreak in two southern provinces, Thailand, July 2017

Abstract

Background: On June 2017, we were notified about two food poisoning outbreaks associated with shellfish consuming from Pattani and Narathiwat provinces. Then we conducted outbreak investigation which aim to identify the cause of the outbreaks and to provide the specific prevention measure for prevent the future outbreak.
Materials/methods: Descriptive study was conducted by medical records reviews, patient interviews and active case finding. A case defined as people who live in Maikan District and Saiburi District in Pattani Province and Bajoi District in Narathiwat Province and have numbness at lip or hands or feet and at least one following: weakness of limbs, imbalance, dizziness, unconsciousness, nausea, vomiting and feel floating during June–July 2017. The risk factor was carried out by unmatched case–control study. The environmental survey and laboratory testing were conducted for plankton density and saxitoxin concentration.
Results: Total 46 cases met definition without death. The total attack rate was 14.79%. They were 10 out–patients, 11 in-patients and 25 cases in community. The male:female ratio was 1:1.1. Median age was 41 years (IQR = 23). Most of cases was 26–60 years (78.2%). All cases were Muslim who fasting in Ramadon and collected and ate bivalve shellfish. Most of clinical presentations were weakness of limbs (78.3%) and followed by imbalance, dizziness, unconsciousness, nausea, vomiting and feel floating. The onset after cooked bivalve shellfish was 30 minutes to 15 hours. Odds ratio of bivalve shellfish consuming was 92.0 (95%CI 23.8, 355.3). The saxitoxin in bivalve shellfish meat was 31.8 times above normal level. Alexandrium spp. plankton in the affected canal was found 278,240 unit/L.
Conclusions: Normally bivalve shellfish is not poisoning. Since 2016, the water in the canal didn’t flow to a sea. Then Alexandrium spp. plankton in the affected canal has overgrown more than regular concentration. The bivalve shellfish has massive consumed Alexandrium spp. plankton. Health education to avoid consume bivalve shellfish in the affected pool and open drainage the obstructed canal to sea in May 2018 (2 million Euro budget). There is disease free since July 2018.