title: Trends in Pertussis Incidence in Georgia from 2010 – 2020 Based on the 2020 CSTE/CDC Case Definition
Creators: name: Raderalazasoa, Gina
Publisher: name: Georgia State University
Year: 2021

description: INTRODUCTION: Pertussis is a highly contagious respiratory infection transmitted from person to person in close contact. Its burden is high among unvaccinated infants (< 1 year) due to age appropriateness, and the number of cases has been on the rise among adolescents and adults in the past ten years. In 2020, a change in pertussis case definition (CD) was issued by the Council of State and Territorial Epidemiologists (CSTE), classifying PCR-positive cases as confirmed cases regardless of cough duration. This study aims to assess whether the change in pertussis CD affects the number of confirmed and probable pertussis cases reported in Georgia from 2010 -2020 and evaluate its effectiveness.
METHODS: Epidemiologic data were obtained from the State Electronic Notifiable Disease Surveillance System (SendSS). Based on the 2020 CSTE/CDC case definition, reported pertussis cases were re-evaluated as confirmed, probable, and not-a-case (NAC). A cross-sectional study was performed. The characteristics of all reported pertussis cases were first described. Then, the incidence rates were compared under the old and new CDs. Last, sensitivity, specificity, predictive value positive (PVP), and predictive value negative (PVN) of the new CD were estimated.  
RESULTS: From 2010 to 2020, there were 3,882 reported pertussis cases in Georgia. About 22% (n=867) of reported pertussis cases were among infants < 1 year. Cough duration was inconsistent across case classification. PCR was ordered in 62.28% (n=2,176), whereas culture in 8.67% (n=303) only. More than half of the laboratory-confirmed cases were obtained from PCR. Between 2010 and 2020, 2,765 (71.23%) reported cases were considered as pertussis cases (confirmed and probable), and 1,117 (28.77%) were NACs, using the previous CDs issued in 2010 and 2014. After reclassification based on the 2020 CSTE/CDC case definition, 3,213 (82.77%) were considered as cases, whereas 669 (17.23%) were NACs. Fifty-eight percent (n=137, 95% CI: [50.79% – 65.31%] of pertussis cases would have been missed in 2020 if the 2014 CSTE/CDC case definition was still in use. The incidence rate of pertussis cases was 1.16 times higher with the new CD than the old CD. The new CD was estimated to have 83.80% [95%CI: 82.42 – 85.17] sensitivity and 72.11% [95%CI: 70.56% – 73.66%] predictive value positive.
CONCLUSION: Pertussis is a remerging infectious disease that needs better control and surveillance. Changing the clinical criteria of illness of cough ? 2 weeks to cough of any duration and accounting PCR-positive cases as laboratory-confirmed cases were found to be effective in capturing more pertussis cases in Georgia. Despite the limitations of this study, it demonstrates the usefulness of updating case definitions with reliable diagnostic tools. These findings can be used to reinforce the capacity of health districts and public health departments to identify pertussis cases accurately and deploy the necessary resources. Standardized and evidence-based tools are essential for notifiable diseases surveillance to monitor trends and stop epidemics on time. Future research could expand on adopting an integrated approach to surveillance of emerging infectious diseases.