Background

Zika virus (ZIKV) has spread rapidly in the Pacific and throughout the Americas and is associated with severe congenital and adult neurologic outcomes. Nucleic acid amplification technology (NAT) assays were developed for diagnostic applications and for blood donor screening on high-throughput NAT systems. We distributed blinded panels to compare the analytical performance of blood screening relative to diagnostic NAT assays.

Study design and methods

A 25-member, coded panel (11 half-log dilutions of a 2013 French Polynesia ZIKV isolate and 2015 Brazilian donor plasma implicated in transfusion transmission, and 3 negative controls) was sent to 11 laboratories that performed 17 assays with 2 to 12 replicates per panel member. Results were analyzed for the percentage reactivity at each dilution and by probit analysis to estimate the 50% and 95% limits of detection (LOD₅₀ and LOD₉₅ , respectively).

Results

Donor-screening NAT assays that process approximately 500 µL of plasma into amplification reactions were comparable in sensitivity (LOD₅₀ and LOD₉₅ , 2.5 and 15-18 copies/mL) and were approximately 10-fold to 100-fold more sensitive than research laboratory-developed and diagnostic reverse transcriptase-polymerase chain reaction tests that process from 10 to 30 µL of plasma per amplification. Increasing sample input volume assayed with the Centers for Disease Control and Prevention reverse transcriptase-polymerase chain reaction assays increased the LODs by 10-fold to 30-fold.

Conclusions

Blood donor-screening ZIKV NAT assays demonstrate similar excellent sensitivities to assays currently used for screening for transfusion-transmitted viruses and are substantially more sensitive than most other laboratory-developed and diagnostic ZIKV reverse transcriptase-polymerase chain reaction assays. Enhancing sensitivities of laboratory-developed and diagnostic assays may be achievable by increasing sample input.

Background

Dengue is a leading cause of morbidity throughout the tropics; however, accurate population-based estimates of mortality rates are not available.

Methods/principal findings

We established the Enhanced Fatal Acute Febrile Illness Surveillance System (EFASS) to estimate dengue mortality rates in Puerto Rico. Healthcare professionals submitted serum and tissue specimens from patients who died from a dengue-like acute febrile illness, and death certificates were reviewed to identify additional cases. Specimens were tested for markers of dengue virus (DENV) infection by molecular, immunologic, and immunohistochemical methods, and were also tested for West Nile virus, Leptospira spp., and other pathogens based on histopathologic findings. Medical records were reviewed and clinical data abstracted. A total of 311 deaths were identified, of which 58 (19%) were DENV laboratory-positive. Dengue mortality rates were 1.05 per 100,000 population in 2010, 0.16 in 2011 and 0.36 in 2012. Dengue mortality was highest among adults 19-64 years and seniors ≥65 years (1.17 and 1.66 deaths per 100,000, respectively). Other pathogens identified included 34 Leptospira spp. cases and one case of Burkholderia pseudomallei and Neisseria meningitidis.

Conclusions/significance

EFASS showed that dengue mortality rates among adults were higher than reported for influenza, and identified a leptospirosis outbreak and index cases of melioidosis and meningitis.