The Centers for Disease Control says one person who was infected with the Zika virus has died in Puerto Rico.

In the Morbidity and Mortality Weekly Report, the CDC said the patient died because of immune thrombocytopenia purpura, a condition in which the patient has a low blood platelet count as a result of another illness. The condition can cause dangerous internal bleeding in rare cases.

CNN is reporting that the patient was a 70-year-old man from San Juan who contracted Zika, was treated for the symptoms, but then returned to the hospital with signs of the bleeding disorder.

The CDC said although the man had some underlying health conditions, they were not life-threatening and should not have led to his death.

A spokesman for the CDC says there have been other cases of bleeding in adults who contracted Zika. The spokesman said researchers do not yet know whether there are risk factors associated with ITP in people infected with Zika.

They are noticing a similar relationship between Zika and Guillain-Barre Syndrome.

Symptoms of Zika are normally mild and don't last longer than a week. The CDC says people rarely die of Zika or even get sick enough to go to the hospital. People may not even know they are infected.

Symptoms include fever, rash, joint or muscle pain and conjunctivitis.

Sen. Bill Nelson, D-Florida, who has sponsored legislation to push for more funding for Zika research, issued this statement Friday:

"The death of an American citizen should serve as a wake-up call to all those in Congress who continue to block our efforts to stop the spread of this virus. While this may be the first Zika-related death in our country, it won’t be the last if Congress does not start taking this virus seriously.”

Information from CNN contributed to this report.