Epidemiologic Surveillance

In response to the introduction of Zika virus, PRDH and CDC Dengue Branch incorporated Zika virus case reporting and diagnostic testing into existing dengue and chikungunya virus surveillance systems and developed a laboratory-based Passive Arboviral Diseases Surveillance System.† Health providers submit serum specimens to PRDH from patients with a clinical suspicion of Zika, chikungunya, or dengue virus infection using a case report form.§ Depending on the number of days between onset of illness and specimen collection, specimens are tested for the three arboviruses by a Trioplex RT-PCR assay, for evidence of Zika and dengue virus infection by IgM ELISA, or by both assays (4).¶ Zika virus–infected patients were defined by positive results from either RT-PCR (confirmed) or IgM ELISA with negative dengue virus IgM ELISA (presumptive positive). Zika virus testing has been incorporated into the Sentinel Enhanced Dengue Surveillance System, which tests specimens from all febrile patients treated at either one outpatient clinic or one hospital emergency department in Ponce. Tissue and blood specimens collected during autopsy from patients who died after an acute febrile illness are tested for Zika virus infection through the Enhanced Fatal Acute Febrile Illness Surveillance System.** Following CDC interim guidance (6), symptomatic pregnant women are tested using the diagnostic algorithm, and asymptomatic pregnant women are tested for evidence of Zika and dengue virus infection by IgM ELISA. Initiated in February 2016, the Guillain-Barré syndrome Passive Surveillance System allows health providers from across the island to report clinically suspected Guillain-Barré syndrome cases by sending a case report form and serum specimen to PRDH.†† Specimens from patients with suspected Guillain-Barré syndrome are tested by both RT-PCR and IgM ELISA for all three arboviruses. Diagnostic test results are managed through an integrated data management system. Results are reported to providers, and aggregate data are available online in a weekly arboviral report.§§

During November 1, 2015–April 14, 2016, specimens from 6,157 suspected arbovirus-infected patients were evaluated and 683 (11%) were either laboratory-confirmed or presumptive positive for Zika virus infection (Table). Of these 683 Zika virus laboratory confirmed or presumptive patients, 581 (85%) were confirmed by RT-PCR, 73 (11%) were presumptive positive by IgM ELISA, and 29 (4%) were positive by both RT-PCR and IgM ELISA. Dengue, chikungunya, or unspecified flavivirus infection was identified in 110 (2%), 61 (1%), and 32 (<1%) suspected arbovirus-infected patients, respectively. No patients with evidence of coinfection with Zika, dengue, or chikungunya viruses were identified by RT-PCR. Of all identified Zika virus–infected patients, 646 (95%) were reported to the Passive Arboviral Diseases Surveillance System. Thirty-two (5%) Zika virus–infected patients were reported through the Sentinel Enhanced Dengue Surveillance System. Five (1%) suspected cases of Guillain-Barré syndrome reported to the Guillain-Barré syndrome Passive Surveillance System were presumptive positive for Zika virus infection, and two had unspecified flavivirus infection.

Weekly Zika virus disease case counts gradually increased since late November 2015, whereas incidence of dengue and chikungunya cases remained comparatively low (Figure 1). Zika virus–infected patients were reported from 50 (64%) of the 78 total municipalities (Figure 2); 146 (21%) patients were residents of the San Juan metropolitan area. Among all identified Zika virus–infected patients, 436 (64%) were female, and median age was 34 years (range = 35 days–89 years). The most frequently reported signs and symptoms were rash (74%), myalgia (68%), headache (63%), fever (63%), and arthralgia (63%). Thrombocytopenia (defined as blood platelets levels <100,000 cells/mm3) was reported in nine (1%) cases. Sixty-five (10%) symptomatic pregnant women were Zika virus–infected patients. Seventeen (2%) patients required hospitalization, including five (1%) suspected Guillain-Barré syndrome cases. In one (<1%) identified Zika virus–associated case, the patient died of complications related to severe thrombocytopenia.

To ensure the safety of the blood supply, Puerto Rico imported all blood products from the United States during March 5–April 14 (7). On April 2, blood collection resumed with donor screening using a Food and Drug Administration–approved Zika virus investigational nucleic acid detection test (Roche Molecular Systems, Inc., Pleasanton, California). Emergency blood imports ended on April 15. During April 2–14, nine (<1%) of 1,910 screened donated blood units had positive test results. These units were removed from the blood supply, and testing is pending to confirm presumptive Zika virus infection.