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Routine screening of pregnant women for Zika virus in the setting of local transmission—Miami−Dade County, Florida, 2016–2017

      Objective

      On July 29, 2016, the Florida Department of Health (FDOH) announced that active transmission of Zika virus (ZIKV) had been detected in a 1-square-mile area of Miami−Dade County. Centers for Disease Control and Prevention (CDC) guidance recommended ZIKV testing for asymptomatic pregnant women with an epidemiological link to that area,
      Centers for Disease Control and Prevention
      CDC guidance for travel and testing of pregnant women and women of reproductive age for Zika virus infection related to the investigation for local mosquito-borne Zika virus transmission in Miami−Dade and Broward Counties, Florida. Atlanta, GA.
      with testing recommendations expanded to include additional areas as identified. Miami−Dade was considered a Zika cautionary area through June 2, 2017, and screening was recommended for women in Miami−Dade who conceived up to 8 weeks after that date.
      Centers for Disease Control and Prevention
      Key messages—Zika Virus Disease. Atlanta, GA.
      Centers for Disease Control and Prevention
      Advice for people living in or traveling to South Florida. Atlanta, GA.
      From August 3, 2016, through July 2017, ZIKV testing was available to pregnant women free of charge via the Bureau of Public Health Laboratories (BPHL) and contracted commercial laboratories. Results of this screening program are described.

      Study Design

      Laboratory results were analyzed for 20,731 women aged 15–50 years who were tested for ZIKV in Miami−Dade with an initial date of specimen collection between July 29, 2016, and July 28, 2017. Results were matched on name, date of birth, and case identification number. Persons tested for ZIKV identified to the FDOH through means other than routine screening (eg, active surveillance initiated by a case, blood donation screening, provider report) were excluded.
      A positive screen was defined as a non-negative ZIKV immunoglobulin M (IgM) test in serum or cerebrospinal fluid and/or a presumptive positive reverse transcription−polymerase chain reaction (RT-PCR) result from a commercial laboratory in any specimen. Positive RT-PCR and non-negative IgM specimens from commercial laboratories received repeat testing at the BPHL or CDC; plaque reduction neutralization testing (PRNT) was performed on specimens with non-negative reference laboratory IgM results.
      Among patients who met epidemiologic and laboratory criteria, ZIKV infection or disease cases were classified as confirmed, probable, or suspected according to FDOH case definition.
      Florida Department of Health
      Zika virus disease and infection: reporting guidance for county health departments (CHDs) in disease reporting information for health care providers and laboratories.
      Additional data were obtained via chart review and patient interview for these cases.

      Results

      Between July 29, 2016, and July 28, 2017, a total of 20,731 women aged 15–50 years were tested for ZIKV in Miami-Dade, including 4664 women (22.5%) known to be pregnant at testing.
      Some demographic data, including pregnancy status, were not consistently reported to the FDOH’s surveillance database alongside laboratory results. Pregnancy status was not available for 15,059 women (72.6%) included in this study. It is likely that many of these women whose pregnancy status was not available were pregnant, because our screening program targeted this population and included controls to ensure that FDOH-funded tests went to pregnant patients.
      A total of 32 women (0.2%) had positive RT-PCR results at the BPHL and were considered to be confirmed ZIKV cases without screening positive (Table). In addition, 592 (2.8%) women had a positive screen result and required confirmatory testing; among these, 207 (35.0%) were classified as confirmed, probable, or suspected cases. The majority of women (385, 65.0%) who screened positive had negative confirmatory results.
      TableSummary of positive laboratory results for reproductive-aged women tested in Miami−Dade County, July 2016 to July 2017 (N = 624)
      Laboratory resultTotal (N = 624)
      Confirmed without screening positive32
      Screened positive592
      A total of 36 probable and suspected ZIKV cases had screening results that could not be matched to their confirmatory results. Thus, they are not included in the counts of women who screened positive by result type, although they are included in the total. In addition, some women may have screened positive on both IgM and RT-PCR, and thus may be counted in both the screened via RT-PCR and screened via non-negative IgM figures, although they were counted only once in the total number of individuals who screened positive
       Via RT-PCR (commercial laboratory)17
      A total of 36 probable and suspected ZIKV cases had screening results that could not be matched to their confirmatory results. Thus, they are not included in the counts of women who screened positive by result type, although they are included in the total. In addition, some women may have screened positive on both IgM and RT-PCR, and thus may be counted in both the screened via RT-PCR and screened via non-negative IgM figures, although they were counted only once in the total number of individuals who screened positive
       Via non-negative
      Non-negative IgM results included “positive,” “presumptive positive,” “possible positive,” “presumptive Zika virus positive,” “possible Zika virus positive,” “equivocal,” “indeterminate,” and “inconclusive,” as exact serology terminology varied by assay.
      IgM (commercial laboratory or BPHL)
      493
      A total of 36 probable and suspected ZIKV cases had screening results that could not be matched to their confirmatory results. Thus, they are not included in the counts of women who screened positive by result type, although they are included in the total. In addition, some women may have screened positive on both IgM and RT-PCR, and thus may be counted in both the screened via RT-PCR and screened via non-negative IgM figures, although they were counted only once in the total number of individuals who screened positive
      Screened positive with positive confirmatory testing207
       Confirmed ZIKV case (by RT-PCR and/or serologic testing)46
       Probable ZIKV case (by serologic testing)154
       Suspected ZIKV case (by serologic testing)7
      Total with positive confirmatory testing239
      BPHL, Bureau of Public Health Laboratories; IgM, immunoglobulin M; RT-PCR, reverse transcription−polymerase chain reaction; ZIKV, Zika virus.
      Logue. Routine screening of pregnant women for Zika virus in the setting of local transmission. Am J Obstet Gynecol 2019.
      a A total of 36 probable and suspected ZIKV cases had screening results that could not be matched to their confirmatory results. Thus, they are not included in the counts of women who screened positive by result type, although they are included in the total. In addition, some women may have screened positive on both IgM and RT-PCR, and thus may be counted in both the screened via RT-PCR and screened via non-negative IgM figures, although they were counted only once in the total number of individuals who screened positive
      b Non-negative IgM results included “positive,” “presumptive positive,” “possible positive,” “presumptive Zika virus positive,” “possible Zika virus positive,” “equivocal,” “indeterminate,” and “inconclusive,” as exact serology terminology varied by assay.
      Routine screening during July 2016 to July 2017 identified 181 pregnant women who were ZIKV cases; 171 (94.5%) had a possible exposure during pregnancy or less than 8 weeks before conception. Only 39 cases (21.5%) in pregnant women were locally acquired. Pregnancy outcome information was available for 164 (90.6%) of the 181 women identified through routine screening, none of whom has delivered an infant or fetus with congenital Zika syndrome or infection.

      Conclusion

      Most women with a positive ZIKV screen result during July 2016 to July 2017 had negative confirmatory results. A low rate of predictive value positive is not uncommon when the prevalence of a disease is low; the FDOH has reported 288 locally acquired ZIKV cases in Miami−Dade since 2016.
      Zika Free Florida
      Total statewide cases: local cases; c2017.
      Although federal testing guidance has been updated,
      • Oduyebo T.
      • Polen K.D.
      • Walke H.T.
      • et al.
      Update: interim guidance for health care providers caring for pregnant women with possible Zika virus exposure—United States (including U.S. territories), July 2017.
      the Miami−Dade experience with ZIKV demonstrates challenges of screening in low-prevalence settings.

      Acknowledgments

      The authors would like to thank the epidemiology staff at Department of Health (DOH) Miami−Dade and the Bureau of Epidemiology; clinical staff at DOH Miami−Dade’s Zika testing clinics; and laboratory staff at the Bureau of Public Health Laboratories−Miami, the Bureau of Public Health Laboratories−Tampa, and the Bureau of Public Health Laboratories−Jacksonville.
      The Florida Department of Health received federal funding for Zika response and preparedness activities in 2016 and 2017. Some of the laboratory work described in this study was supported by federal funding, although the contents of this report are solely the responsibility of the authors and do not necessarily represent the official position of any other agencies.

      References

        • Centers for Disease Control and Prevention
        CDC guidance for travel and testing of pregnant women and women of reproductive age for Zika virus infection related to the investigation for local mosquito-borne Zika virus transmission in Miami−Dade and Broward Counties, Florida. Atlanta, GA.
        US Department of Health and Human Services, CDC. 2016; (Available at:)
        https://emergency.cdc.gov/han/han00393.asp
        Date accessed: June 16, 2019
        • Centers for Disease Control and Prevention
        Key messages—Zika Virus Disease. Atlanta, GA.
        US Department of Health and Human Services, CDC. 2017; ([updated 2017 June 8; cited 2019 June 16]. Available from:)
        • Centers for Disease Control and Prevention
        Advice for people living in or traveling to South Florida. Atlanta, GA.
        US Department of Health and Human Services, CDC. 2017; ([posted 2016 Oct 1; revised 2017 June 2]. Available at:)
        • Florida Department of Health
        Zika virus disease and infection: reporting guidance for county health departments (CHDs) in disease reporting information for health care providers and laboratories.
        (Available at:)
        • Zika Free Florida
        Total statewide cases: local cases; c2017.
        (Available at:)
        • Oduyebo T.
        • Polen K.D.
        • Walke H.T.
        • et al.
        Update: interim guidance for health care providers caring for pregnant women with possible Zika virus exposure—United States (including U.S. territories), July 2017.
        MMWR Morb Mortal Wkly Rep. 2017; 66: 781-793