Blood Test Shows Zika Rising 'Rapidly' in Puerto Rico

Troy Brown, RN

June 17, 2016

A US Food and Drug Administration (FDA)-authorized blood test used to detect the Zika virus in donated blood in Puerto Rico is keeping the blood supply safe, but by providing real-time information about Zika activity, it is showing a rapid rise of the virus in the US territory that is posing a greater risk for birth defects among newborns.

The test is currently being used in at least one blood donation center in the United States, according to information presented at a Centers for Disease Control and Prevention (CDC) media teleconference today.

"We're sharing information on what may be our most accurate real-time leading indicator of Zika activity in Puerto Rico.... Based on the best information available, Zika infections appear to be increasing rapidly in Puerto Rico," CDC Director Tom Frieden, MD, said at the teleconference.

"The implication of this and the real importance of this information is that in the coming months, it's possible that thousands of pregnant women in Puerto Rico could become infected with Zika. This could lead to dozens or hundreds of infants being born with microcephaly in the coming year, and for the thousands of other infants born to women infected with Zika who don't have microcephaly, we simply don't know, and may not know for years, if there will be long-term consequences on brain development," he said.

Since April 3, blood centers in Puerto Rico have screened locally donated blood for the Zika virus, using a highly sensitive, highly specific, nucleic acid amplification test (Roche) that measures the Zika virus in the blood as part of a blood safety program that is keeping the virus out of the blood supply there.

So far, there have been no confirmed cases of Zika spread through a blood transfusion anywhere in the United States, Puerto Rico, or the other US territories. However, 68 of 12,777 blood donations in Puerto Rico have tested positive for the virus, and that proportion has steadily increased. "Even though there is an increase in infection rates, there is no known risk from a transfusion because of this highly sensitive test being used," Dr Frieden said.

Infected Blood Donations Reflect Infection in Population at Large

The highest weekly incidence of Zika virus in donated blood in Puerto Rico was 1.1% for the latest week of reporting (June 5 - June 11), according to a June 17 report published in the Morbidity and Mortality Weekly Report. That incidence has steadily increased over time.

"Although the blood donor population doesn't represent the general population, the increasing prevalence of blood donations that test positive for Zika likely reflects an overall increase in infections in the population at large," Dr Frieden explained.

This test does not show how long the virus remains in the blood and only shows the presence of the virus at the time of testing. Other tests show the presence of the virus for just a few days after the onset of illness, but because this test is so sensitive, it may show the presence of the Zika virus for a week or 2.

"Priority Is to Protect Pregnant Women"

Dr Frieden said that a 1.1% positivity rate in donated blood at any given time translates "into a more than 1%, perhaps 2%...rate of infection each month." This means that during a 9-month pregnancy, there is a substantial chance that a woman would become infected.

"The bottom line is we're seeing a steady increase in infection in blood donors; that blood is being removed from the blood supply, so there's no need to think that there's a risk from blood transfusions in Puerto Rico or anywhere else. It does reflect a concerning trend in Puerto Rico," he said.

"[The] priority is to protect pregnant women, to reduce infants affected with microcephaly. It's going to take the full community, and anything we can do to reduce those numbers will be critically important," Dr Frieden added.

The CDC is working intensively with Puerto Rico to provide services to pregnant women, including DEET, long sleeves, and measures in the home to reduce mosquito exposure, but controlling this mosquito is very difficult.

FDA Recommendations

At this time, in the contiguous United States, the test is only being used by the Gulf Coast Regional Blood Center in Houston, Texas, where it has been in use since May 23, but other blood centers plan to begin screening.

"The test is being used in Texas currently...through an investigational new drug application the FDA authorized. Although the recommendation by FDA is that the test be used as an option in Zika areas where there is active transmission of Zika, there is an option for blood centers anywhere to use it," Matthew J. Kuehnert, MD, director, CDC Office of Blood, Organ, and Other Tissue Safety, said in the teleconference.

"Initially, when the threat of Zika first emerged, the FDA put out recommendations to say that in an area of active transmission, that blood centers should either use pathogen-reduced blood through a pathogen reduction technology, which is only FDA-approved for apheresis platelets and plasma; to use a screening test; or to outsource the blood. Until the Roche test was available, the option was to only outsource blood, because most blood transfused are red blood cells, which is not FDA-approved for pathogen reduction technology," Dr Kuehnert explained.

Blood donation centers in the United States are not required to test blood at this time. Centers already screen by asking potential donors about possible exposure to the Zika virus, particularly through travel to affected areas.

In Puerto Rico, all donated blood that tests positive is removed from the blood supply, and donors who test positive are given information about how to avoid spreading Zika to others.

"Zika and Blood Transfusion." CDC. Updated June 1, 2016. Full text

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