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American Samoa experience may guide Zika testing in asymptomatic pregnant women
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A recommended timeline in American Samoa for discontinuing Zika virus screening in asymptomatic pregnant women could guide efforts in similarly sized populations, researchers reported.
“The surveillance processes outlined and the timeline established for American Samoa might have implications for jurisdictions where small populations and similar population immunity following widespread Zika virus exposure can facilitate interruption of transmission,” the study authors wrote in MMWR.
By developing the timeline, health officials sought to avoid undue Zika-testing burdens on the health care system and “psychosocial repercussions on pregnant women” in America Samoa after local mosquito-borne transmission of the virus had ceased.
Zika infection was first documented in the territory in January 2016. In response, health officials there implemented vector control measures, strategies to protect pregnant women, surveillance through EHR reports, testing of symptomatic patients and routine testing of all asymptomatic pregnant women, according to the researchers.
The last Zika case in the U.S. territory confirmed by real-time reverse transcription-polymerase chain reaction (rRT-PCR) had symptom onset on June 19, 2016. With help from the CDC, the America Samoa Department of Health (ASDoH) conducted surveillance from Aug. 31 to Oct. 15 to determine whether local transmission was still occurring.
That included the use of rRT-PCR testing, which researchers deemed more reliable than serology.
“Because of the serologic cross-reactivity between Zika virus and other flaviviruses (eg, dengue virus) circulating in American Samoa, and the possible long duration of anti-Zika immunoglobulin M (IgM) antibody positivity, serology was considered a less reliable indicator of ongoing Zika virus transmission,” they wrote.
In all, 32 patients had a fever, rash, arthralgia or conjunctivitis, or any combination of those Zika virus symptoms. Thirty of these patients (94%) tested negative for the virus by rRT-PCR, whereas specimens from the remaining two patients were not sufficient to test.
Researchers also tested 277 asymptomatic pregnant women for the virus, 86 (31%) of whom tested positive or the equivalent for anti-Zika IgM by serology. Yet all 86 tested negative by rRT-PCR.
Researchers found no rRT-PCR–positive tests in pregnant or nonpregnant patients during the 45-day surveillance period, which equals the Zika virus’ three 15-day extrinsic incubation periods. That led the researchers to set Oct. 15 as the end date for potential mosquito-borne transmission.
Their timeline maintained testing for the following:
- anyone with Zika virus signs and symptoms;
- asymptomatic pregnant women with a due date or last menstrual period on or before Dec. 10, 2016;
- pregnant women with prenatal signs of congenital Zika virus syndrome;
- infants whose mothers had laboratory evidence of Zika virus infection during pregnancy;
- infants with abnormalities associated with congenital Zika virus syndrome;
- asymptomatic pregnant women who lived in or traveled to an area with active transmission outside American Samoa; and
- those who had unprotected sex with someone who had lived in or traveled to such areas.
The researchers added that such a timeline frees up valuable health care resources otherwise used on testing.
“Establishing a timeline for discontinuing screening of asymptomatic pregnant women allows ASDoH to allocate resources appropriately toward early interventions for children and families affected by Zika virus,” they concluded. – by Joe Green
Disclosure: The researchers report no relevant financial disclosures.
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