The man had been caring for an elderly family member who contracted the virus while abroad in June. The elderly patient was extremely ill and developed septic shock, according to the CDC. Further testing found his levels of virus were "approximately 100,000 times higher than the average level reported in persons infected with Zika virus," according to the report.
The elderly patient died on June 25, and less than a week later, the family member started to exhibit symptoms of the virus, even though he had not traveled to an area with Zika transmission. After a thorough investigation, health officials remained unsure how the virus spread.
The Zika virus is known to spread through mosquito bites, sexual contact and blood transfusions. But none of those means of transmission were documented in this case.
"Patient A was known to have had close contact (i.e., kissing and hugging) with the index patient while the index patient's viral load was found to be very high," CDC researchers said in the report. "Although it is not certain that these types of close contact were the source of transmission, family contacts should be aware that blood and body fluids of severely ill patients might be infectious."
Now CDC officials are investigating whether bodily fluids in some patients with extremely high levels of the Zika virus could transmit it in a way not previously documented.