SAN JUAN, Puerto Rico (AP) — Puerto Rico's Health Department is reporting 201 confirmed Zika cases amid warnings the U.S. territory could face an epidemic of the mosquito-borne virus.

Officials said Friday that 21 of those cases involve pregnant women. This concerns health authorities because Zika may be linked to microcephaly, which causes babies to have unusually small heads and brain damage.

The director of the U.S. Centers for Disease Control and Prevention visited the island on Tuesday as federal officials stepped up efforts to help prevent the spread of Zika in Puerto Rico.

Health officials say they expect thousands of pregnant women in Puerto Rico to become infected. They also warn that more than 20 percent of the island's 3.5 million people overall could be affected.