1,336 new cases of mosquito-borne virus Zika were reported in Puerto Rico last week.
Puerto Rico has been hit with the biggest weekly rise in Zika cases that the US territory has ever seen.
Health Secretary Ana Rius said on Friday that 1,336 new cases were reported in the past week, for a total of 4,437 cases since the mosquito-borne virus was first detected in December.
She said 76 of Puerto Rico's 78 municipalities now have Zika cases. A total of 553 pregnant women have Zika, which can cause severe birth defects.
Fifty-five people have been hospitalized for Zika-related illnesses, including 19 diagnosed with a temporary paralysis known as Guillain-Barre syndrome that has been linked to the virus. One person has died.
The spike comes a week after US health officials urged Puerto Rico to consider aerial spraying to fight the virus.