An increasing prevalence of Zika virus infection detected among blood donors in Puerto Rico using a highly sensitive, investigational nucleic acid test likely reflects an overall increase in the incidence of infection in the population at large, according to the Centers for Disease Control and Prevention.
“The implications and importance of this information are that in the coming months, it is possible that thousands of 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,” CDC Director Dr. Tom Frieden said in a telebriefing on June 17.
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“For the thousands of other infants born to women infected with Zika who don’t have microcephaly, we simply don’t know, and might not know for years, if there will be long-term consequences on brain development,” Dr. Frieden added.
The incidence of infection among blood donors in Puerto Rico the week of June 5-11 was 1.1%. This is the highest weekly incidence since testing using a newly developed nucleic acid test authorized by the Food and Drug Administration under an investigational new drug application that was implemented in Puerto Rico in April.
Between April 3 and June 11, 2016, a total of 68 presumptive viremic donors were identified from 12,777 donations tested. The incidence of positive findings has increased steadily over time (MMWR. 2016 Jun 17. doi: 10.15585/mmwr.mm6524e2).
In the wake of the finding, which was reported June 17 in an early release of the Morbidity and Mortality Weekly Report, Dr. Frieden and Dr. Matthew J. Kuehnert, director of the CDC Office of Blood, Organ, and Other Tissue Safety sought to allay concerns regarding transmission of the virus via blood transfusion.
“The test being used to test blood in Puerto Rico is extremely accurate,” Dr. Kuehnert said, noting the importance of this testing, as several mosquito-borne illnesses are know to be transmissible by blood transfusion and many infected individuals are asymptomatic.
Further, at least one case of transfusion-transmitted Zika infection has been reported in Brazil, Dr. Kuehnert said.
The blood supply in Puerto Rico is being protected by laboratory testing, and in most other areas – including the continental United States – it is being protected by deferral of people who report travel to areas with such transmission. Some centers are electing to implement blood testing, but this is not currently a requirement, he said.
All donations that test positive for Zika are removed from the blood supply, and donors who test positive are provided with information on how to prevent spreading the virus to others.
The larger concern is the increasing prevalence of infections, as the nucleic acid test results “may be the most accurate, real time, leading indicator of Zika activity in Puerto Rico,” Dr. Frieden said.
The 1% prevalence of infection suggests substantial ongoing community transmission, given that viral nucleic acid can be detected for only 7-10 days after acute infection, and it translates to a greater than 1% rate of infection each month in the community, he noted.
“Our concern here is about protecting pregnant women, and with this rate of infection the possibility that there could be thousands of pregnant women affected, leading to dozens to hundreds of affected babies, is what’s of most concern,” Dr. Frieden said, adding that efforts are underway to reduce risk.
“We’re working intensively, in addition to keeping the blood supply safe, with the Puerto Rico health department, the government, communities, and people throughout Puerto Rico, to provide services for pregnant women – DEET, long sleeves, measures in their homes to reduce mosquito exposure that might reduce their risk of getting infected, as well as to control mosquitoes,” he said.
Dr. Frieden explained that controlling the Aedes aegypti mosquito is very difficult, and that it requires the effort of the entire community working together to protect a pregnant woman.
“We can’t make the risk zero … but even if we can reduce it by 10%, 30%, or 50%, that is a significant number of tragedies that we can prevent, and we’re doing everything that we can to do that … so that we don’t look back in 3, 6, or 12 months and say we wish we had done more back in June,” he said.