The results of the cake tests are expected to be available next week, according to local media.
On Friday, the police demanded the exhumation of the body of a man – the late husband of the woman who made the cake. He died in September of food poisoning, but police said his death was ruled natural at the time.
At this time, she is not considered a suspect in any of these cases, and the investigation is ongoing.
Six of the seven people at the Christmas party were eating cake on Monday afternoon, including the woman who baked it.
Police told Brazilian broadcasters that she was the only one believed to have eaten two slices of the homemade cake, and her tests showed high levels of arsenic.
Speaking to local media, police chief Marcos Vinicius Velaza said some family members complained that the pie had a “peppery” taste.
The family then developed symptoms such as vomiting and diarrhoea, and five of them sought medical attention at Nossa Senhora dos Navegantes Hospital at around 01:00 local time (04:00 GMT) on Tuesday.
Hours later, the two sisters died of cardiac arrest, the hospital said. Local media identified them as Maida Berenice Flores da Silva, 58, and Tatiana Denise Silva dos Santos, 43.
A third victim, whose blood test showed traces of arsenic, died later Tuesday evening of “shock after food poisoning,” the hospital said.
Local residents named her 65-year-old Neuza Denise Silva dos Anjus.
