Utah Zika Infection Continues to Stump Health Officials

A Zika infection case in Utah has raised more questions about virus transmission.

Officials in the state informed the Centers for Disease Control and Prevention (CDC) that a patient had presented to a physician with Zika-like symptoms. This patient had not traveled to a region with an ongoing outbreak, had not had sexual contact with a person who had traveled, and had not received a blood transfusion or organ transplant nor sustained any mosquito bites.

The patient, who was assessed in July, was herself a healthcare worker, and she had been providing care to an elderly family friend who had contracted Zika abroad, as confirmed via blood tests obtained 2 days before his death from causes not related to the mosquito-borne virus. According to the CDC report on the case, published on September 19, the elderly male had a level of viremia "approximately 100,000 times higher than the average level reported in persons infected with Zika virus."

The caregiver's Zika virus was confirmed via rRT-PCR performed on a blood sample collected 7 days after symptom onset. A serum specimen collected 11 days after symptom onset, and after symptoms had resolved, was positive for antibodies to Zika virus, based on MAC-ELISA results.

Because of the unusual nature of the case, health officials in Salt Lake City and Davis County, Utah, working with the Utah Department of Health, requested CDC assistance on an investigation to determine exposures and "determine a probable source of infection." The ensuing investigation included an epidemiologic evaluation of the patient's family contacts, a serosurvey of other healthcare workers who had provided care to the elderly male traveler, a community survey of those living within a 200-meter radius of the elderly male traveler, and vector surveillance near the residences of the patient and the elderly male traveler. A family contact was defined as "a person who resided in the same household as the [elderly male] or had direct contact with his body fluids (ie, tears, conjunctival discharge, saliva, vomitus, urine, or stool) during the period when he was most likely viremic."

In all, 19 family contacts, including 13 who reported "hugging and kissing" the elderly male's face and 5 who reported being present while stool, urine, or vomitus was being cleaned, were identified and interviewed, and provided blood or urine specimens for testing. Other than the female caregiver, who reported hugging and kissing the male and being present when stool was cleaned (without having direct contact with the stool), all family contacts were negative for Zika virus infection by rRT-PCR or MAC-ELISA on specimens obtained roughly 2 to 3 weeks after last exposure. All healthcare workers and neighboring residents tested, through August 22, were negative for Zika (although testing is ongoing). To date, vector surveillance has revealed no Aedes aegypti or Aedes albopictus mosquito populations in the area.

In the report on the case, CDC officials noted, "It remains unclear how [the] patient was infected, [although she] was known to have had close contact (ie kissing and hugging) with the index patient while [his] viral load was found to be very high. 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."

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.