Background information and demographics of case patients.
We investigated three different outbreaks in Narshingdi, Natore, and Dhaka Districts of the country reported during April and June 2008. These areas are inland and far from the coastal belt of the country (). The outbreaks in Narshingdi and Natore were in rural areas, whereas the Dhaka outbreak was in an urban setting. In total, we identified 95 people who had eaten puffer fish from the three outbreak areas. In Narshingdi, we identified 19 people, and 7 of them died. In Natore, 35 people developed symptoms, including 4 deaths. In Dhaka District, 9 of 11 people who consumed the fish developed symptoms, and 3 of them died. Their median age was 24 years (mean age = 24 years; standard deviation = 18 years), and 50 (53%) of them were male.
Map of Bangladesh showing Narshingdi, Natore, and Dhaka Districts and a coastal area (Cox's Bazaar).
Clinical profile of case patients.
Of the 95 identified people who had eaten the fish, 63 (66%) of them developed symptoms, and 14 (22%) of them subsequently died of intoxication. Among the 63 case patients, 32 (51%) of them were male, with a median age of 25 years. The duration between consumption of the fish and illness onset was 1–3 hours for 29 (46%) cases and less than 30 minutes for 14 (22%) cases; among those who died, nine (64%) died within 1 hour of consuming the fish (). Case patients frequently reported tingling sensation in the body (91%), perioral numbness (68%), dizziness (64%), weakness in the limbs (60%), and nausea/vomiting (46%) ().
Distribution of cases (N = 63) by duration between consumption of the fish and illness onset in Narshingdi, Natore, and Dhaka Districts.
Symptoms of the case patients after consumption of puffer fish from the three outbreaks in Narshingdi, Natore, and Dhaka Districts (N = 63)
Size, local availability, and source of puffer fish.
The outbreaks were caused by large marine puffer fish ranging from 0.2 to 1.5 kg (). The fish were sold at US $0.50–0.88/kg, whereas other types of fish of similar weight cost US $1.50–1.76/kg. During our investigation, the community residents and local health authority in the outbreak area in Narshingdi District reported that they had not seen puffer fish in their village in the last 20–30 years. On the day of the outbreak, this large-size marine puffer fish arrived from one of the coastal areas to be sold in local markets. In Natore, small-size fresh water puffer fish are widely available in the village rivers and beels (water bodies), but community residents were unfamiliar with the larger variety of the marine puffer fish that was sold in the fish depot of the local market on the day of the outbreak. Although 62% of the respondents (N = 65) from Natore were not sure from where these larger puffers came, some (19%) believed that the fish had come from the coastal region of the country. In Dhaka, the fish were not purchased from a market, but a community waste cleaner collected five puffer fish from a community waste bin and brought them home for his family to eat.
Picture of puffer fish from the stock that caused the outbreak in Natore District.
Knowledge and practice relating to puffer consumption.
In Narshingdi, none of our respondents (N = 19) had previous experience of eating the fish and were not aware of the potential intoxication from eating it. All of our respondents knew that the fish was puffer fish, because they were told this by the fish sellers. Similarly, in the Dhaka cluster, people who consumed the fish (N = 11) knew it was puffer fish, because the community cleaner who distributed the fish told them; however, they were unaware of its toxicity and had no previous experience with eating fresh-water or marine puffer fish. The respondents (94%; N = 65) from Natore mentioned that they regularly enjoyed consuming the small, locally available fresh-water puffer fish, which are about the size of a finger, without becoming ill. Most of them were not familiar with the large puffer fish, and only 21 (32%) said they could identify the large fish that they were buying as puffer fish because of its similar appearance to the small river puffer fish.
Qualitative investigation of puffer fish trade in the coastal area.
We conducted informal group discussions with one fish wholesaler, one dry-fish preparer, one deep-sea fishermen, and one community resident. We also conducted in-depth interviews with two fish wholesalers, three dry-fish preparers, two deep-sea fishermen, and five community members.
Deep-sea fishermen reported that they catch 4–5 species of puffer fish in the sea, each weighing between 0.2 and 3 kg (). They consider puffer fish to be less valuable than other fish; local people do not eat the fish, because they know it is toxic. Fishermen do not usually sell puffer fish, but if their catch yields up to 20–30 kg of puffers, they may sell it to fish vendors in the wholesale market at US $0.18–0.29/kg. The wholesalers, in turn, sell the fish to dry-fish preparers, who process the fish by removing the gall bladder, liver, intestines, and eggs, leaving only the skin and head with the flesh of the fish. Dried-fish vendors believe that the gall bladder and eggs of the fish contain the toxin and that discarding these parts makes the fish edible. The dried puffer fish is inexpensive and sold at US $0.3/kg, compared with other dry fishes that are sold at US $1.5–3/kg. Dried puffer fish is used as poultry feed and also consumed by ethnic people. Fish wholesalers reported that occasionally, when there is an abundant catch of puffer fish, some local fish businessmen and wholesalers distribute the fresh fish to different parts of the country, hoping to make a quick profit in areas where people are not familiar with the larger marine variety of puffer fish and are not aware of its toxicity.
A catch of puffer fish in Cox's Bazaar.