However, the agency stopped short of issuing a warning to consumers to avoid eating the popular fish.
“Tuna is something that we all eat and there’s no reason to stop eating it,” Sofie Ivarsson, an epidemiologist at the agency, told The Local.
She added that the issue is something that those who handle fish professionally, such as distributors and restaurants, need to be aware of, as it is during the shipping and preparation process that the fish can become contaminated.
According to Ivarsson, there’s not much the individual consumer can do.
She added that reason the rise in reports is limited to Stockholm may be due to the introduction in 2009 of a system allowing Stockholm residents to report suspected food poisonings online.
Since then, nine out of ten reports of histamine poisoning in 2010 originated from the Swedish capital.
It is fairly uncommon to get histamine poisoning, sometimes called scombroid poisoning, from fish. When it happens, however, it is usually when eating fish from the scombridae family, which includes tuna, mackerel and wahoo fish.
These fish naturally contain histidine, which is an essential amino acid for humans and other mammals, but if food is not refrigerated or stored cold enough, bacteria can turn the amino acid into the more poisonous histamine.
The sudden rise in reports in Stockholm has also led researchers to believe that there are probably many cases across the country that go undetected and unreported.
“We believe there is a large number of unreported cases of food poisoning in general,” she said, adding that many don’t take the trouble to report sudden stomach ache or nausea.
Recently a middle aged couple in Skåne sought medical assistance when experiencing a red, burning and itching rash on their upper bodies.
About an hour earlier they had both eaten a tuna salad from a pizzeria, and doctors concluded that as the source of their poisoning.
The couple recovered after a few hours, which is usually the case with histamine poisoning, but symptoms might also last for several days, and include nausea, dizziness, headache, palpitations, stomach ache and diarrhea.
Ivarsson explained that histamine poisoning is not a contagious disease, and for most people it will appear almost as an allergic reaction.
“People might just assume they are allergic to fish when they experience the symptoms,” she said, “but that might not be the case if you’ve never had allergic reactions before.”
Histamine poisoning only amounts to five percent of reported food poisonings In Sweden annually, with 124 individual cases reported between 2003 and 2010.