Current Testing and Epidemiologic Surveillance for Zika Virus

Because commercial testing for Zika virus only recently became available, DOHMH coordinated diagnostic testing with health care providers and public health laboratories, particularly DOHMH’s Public Health Laboratory and the New York State Department of Health Wadsworth Center. The testing process has varied with the evolution of CDC guidelines regarding whom should be tested and as local capacity for testing expanded. Initially, medical epidemiologists screened all health care provider requests for Zika virus testing (based on CDC testing recommendations) for the presence of compatible symptoms and travel histories before authorizing testing (3).

On February 4, 2016, New York state testing criteria* were expanded to include asymptomatic pregnant women who traveled to an affected area at any time during pregnancy. This resulted in an increase in the number of patients for whom specimens were sent for reverse transcription–polymerase chain reaction (RT-PCR) and serology testing from a median of seven per day during January 21–February 3 to 52 per day during February 4–February 17. As a result of the increased volume of requests, DOHMH withdrew the requirement for medical epidemiologist authorization on February 12 and began permitting providers to submit specimens directly to the Public Health Laboratory. However, because of subsequent receipt of a large number of specimens that were mislabeled, mishandled, or improperly processed; had incomplete or missing laboratory requisition forms; or were obtained from patients who did not meet testing criteria, the pre-authorization requirement was reinstituted on March 21.

To manage the increased volume of testing requests and ensure adequate specimen processing, DOHMH rapidly established a Zika Testing Call Center using personnel, equipment, software, and physical space that had been used for the NYC Ebola active monitoring program (4). The call center triages calls and approves testing requests from providers, completes and faxes laboratory requisition forms to providers to include with the specimen, and arranges, when necessary, transportation of specimens to the Public Health Laboratory via a commercial courier.

During January 1–June 17, 2016, DOHMH coordinated laboratory diagnostic testing for 3,605 persons at the Public Health Laboratory, Wadsworth Center, and CDC. Among all persons tested, 3,319 (92.1%) had a Zika RT-PCR test, and 3,305 (91.7%) had Zika serology testing, which included immunoglobulin M (IgM) antibody capture enzyme–linked immunosorbent assay (MAC-ELISA) and, for some patients, plaque reduction neutralization testing (PRNT). A total of 182 (5.0%) confirmed cases of Zika virus infection were identified, based on positive results of urine or serum RT-PCR or serologic† testing. The majority of cases were confirmed by urine RT-PCR results (Table). Among all confirmed cases, 20 patients (11.0%) were pregnant at the time of diagnosis, nine of whom had symptoms compatible with Zika virus disease. Two cases of Zika virus–associated Guillain-Barré syndrome were diagnosed. Based on PRNT, 27 additional patients (0.7% of persons tested) were found to have unspecified recent flavivirus infection. All confirmed cases occurred in persons who had been in an area with ongoing Zika virus transmission.

To analyze possible undertesting based on residence, on March 1, DOHMH used U.S. Census American Community Survey, 2010–2014§ data to map by census tract 1) the number of persons living in NYC who were born in Mexico, the Caribbean, Central America, or countries in South America with active transmission of Zika virus (Figure 1), because these persons might travel frequently to areas with active Zika virus transmission, and 2) Zika virus testing rates among women aged 15–44 years during January–February 2016 (Figure 2). This mapping found little correspondence between census tracts with high rates of Zika virus testing and census tracts with high numbers of immigrants from countries with ongoing Zika virus transmission. The highest testing rates among women aged 15–44 years (104 per 100,000 population) occurred in census tracts in the lowest quartile of immigrants from these countries; whereas, the lowest rates of testing (29 per 100,000) occurred in census tracts in the highest quartile of immigrants from countries with ongoing Zika virus transmission. To address this apparent demographic disparity in testing, DOHMH personnel distributed educational materials in English, Spanish, and 10 other languages to practices of 170 health care providers in areas with large immigrant populations. To educate the public, DOHMH responded to dozens of media inquiries, including 25 one-on-one interviews with Spanish language media; distributed approximately 10,000 Zika testing informational cards throughout the city and approximately 6,000 travel warning flyers for pregnant women; and conducted approximately 100 presentations at social, community, and religious gatherings throughout the city regarding prevention of mosquito bites. During April–May 2016, the testing rate among women aged 15–44 years increased in census tracts with the highest quartile of immigrants (65 per 100,000) and decreased in census tracts with the lowest quartile of immigrants (40 per 100,000).

Pregnant women with confirmed Zika virus infection or inconclusive test results are followed for the duration of pregnancy by DOHMH medical epidemiologists in collaboration with their providers, and infants born to these women are periodically followed by DOHMH for the first 12 months of life. In mid-April, DOHMH convened a meeting with the City’s nine Regional Perinatal Centers to review DOHMH interim guidance and solicit input on improving Zika preparedness and response in NYC.