Puerto Rico is in the grip of an epidemic of dengue fever that has killed six people, according to the territory's health secretary.

The number of reported cases was above the epidemic threshold for 2 weeks in a row in mid-September, Lorenzo Gonzalez Feliciano, MD, said in a statement Monday.

There were 342 cases reported in the most recent week for which figures are available, Sept. 9 to 15, up from 274 the previous week, according to the CDC.

More than half the reported cases had laboratory confirmation, Gonzalez Feliciano reported.

"The trend of increase in reported cases could continue in coming weeks," he said, leading health officials to declare an epidemic.

There have been six deaths from the mosquito-borne disease this year, with the most recent being two children from the San Juan area, Gonzalez Feliciano told a local radio station.

All told, there have been 4,816 suspected cases of dengue fever reported on the island this year, although many of those occurred last winter. The CDC said there have been a total of 21 cases of the serious hemorrhagic form of the disease.

Dengue is endemic in Puerto Rico, with between 3,000 and 9,000 cases reported yearly, except in epidemic years.

Since 1990, according to the CDC, there have been three large epidemics – 24,700 suspected cases in 1994, 17,00 cases in 1998, and 10,708 in 2007.

The epidemic threshold is set at 75% of the historical average for the years 1986 through 2011, according to the agency.

Puerto Rico attempts to control dengue by mosquito control measures, such as eliminating pools of standing water, and personal protection such as using insect repellent.

Gonzalez Feliciano emphasized the need for citizen cooperation in such measures during what he called the "most active time" for dengue fever – the winter months.

He also urged people who have symptoms of dengue -- fever, headache, muscle and joint pain, and skin rash -- to seek medical help quickly rather than waiting 3 or 4 days.