The health ministry said it had logged 745,900 cases nationwide in the first 15 weeks of the year - an annual increase of 234 per cent.
That equates to 367.8 people infected per 100,000 residents, which falls into the category of an epidemic under parameters used by the World Health Organisation.
The number of dengue deaths has climbed 44 per cent from the same period last year, and most of the diagnosed cases have occurred in business hub Sao Paulo.
Cases of the mosquito-borne infectious tropical disease increased in the wake of a serious drought last year, the worst in living memory.
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Severe water shortages led residents to store what they could in open receptacles, which facilitated the spread of dengue.
Last Thursday the city of Piracicaba, located 160 kilometres (100 miles) west of Sao Paulo, released its first batch of 100,000 transgenic male mosquitos in reaction to the growing crisis.
The genetically modified mosquitos pass on a modified gene during procreation that makes offspring incapable of reaching sexual maturity, causing the overall population to decline steadily.
Dengue symptoms include severe abdominal pain, persistent vomiting and circulatory system failure.