BACKGROUND: In 2016, Zika virus emerged as a mosquito-borne threat of international concern. Zika and dengue infections have similar clinical presentations, are transmitted by the same mosquito vectors, and occur in the same geographic regions globally. Therefore, distinguishing between dengue and Zika infections may be challenging without diagnostic tests. Threats like Zika have brought a heightened awareness to imported arbovirus infections. Patients approved by Georgia Department of Public Health (GDPH) epidemiologists for Zika testing at the state laboratory receive testing for both Zika and dengue either through RT-PCR or PRNT testing on samples with qualifying MAC-ELISA (IgM) results to distinguish between the similar viruses. Data on these results, compared with reporting information from previous years, may point to underreporting of dengue infections in years prior to the Zika outbreak.
METHODS: Data about suspect and confirmed Zika and dengue cases in Georgia are entered into Georgia’s State Electronic Notifiable Disease Surveillance System (SendSS). Data on investigations of dengue and Zika suspect cases from 2009 (the year dengue was made nationally notifiable)-2016 from SendSS were reviewed and analyzed. Cases were confirmed using standard CSTE case definitions. At the Georgia Public Health Laboratory (GPHL), Zika and dengue testing has been completed for over 1,200 Georgia citizens in 2016.
RESULTS: Between 2009-2015, no more than 20 suspect cases of dengue were investigated in a single year in Georgia (2010) and no more than 13 cases of dengue were confirmed (2012). During this period, the average number of dengue cases investigated was 12 per year and the average number of confirmed dengue cases per year was 9. In 2016, 48 cases of dengue were investigated, of which 27 were confirmed as dengue cases. Notably, 20 (74.0%) of the confirmed dengue cases in 2016 were identified in patients originally triaged for Zika testing only. In these cases, a physician suspected Zika and called GDPH based on a patient’s self-reported travel and symptoms.
CONCLUSIONS: The number of dengue cases confirmed in Georgia increased significantly in 2016 compared to the previous 7-year period. Most of the Georgia dengue cases from 2016 were originally triaged for Zika testing, indicating that these cases might not have been found if the awareness and capability to test for Zika were not available. This indicates that dengue reporting increased due to heightened awareness surrounding Zika and the testing protocols which include testing for both viruses in persons being considered for Zika testing.