Innovative approaches to monitoring and tracking the COVID-19 epidemic are needed to assess the impact of community mitigation interventions, according to a study recently published in Clinical Infectious Diseases.
Earlier this year, New York State experienced the largest outbreak of COVID-19 in the United States, with cases outside of New York City (NYC) concentrated in 4 New York State Department of Health (NYSDOH) regions: Capital, Central, Western, and Metropolitan. In an attempt to slow the spread of COVID-19, state officials implemented a series of community mitigation strategies that led to an executive order for residents to stay at home and for all nonessential businesses to close. To track the epidemic and assess the impact of these interventions, innovative monitoring approaches are needed. Accurate monitoring is likely influenced by specimen collection supply, provider testing practices, and patient care-seeking behaviors. As the symptoms of COVID-19 are similar to those of influenza, monitoring influenza and influenza-like illness (ILI) as well as diagnostic trends for influenza and COVID-19 may provide a broader understanding of impact of COVID-19 on the community. Furthermore, early warnings of COVID-19 spread and local planning could be facilitated using a regional monitoring approach. Therefore, this study presented temporal data on ILI and influenza diagnoses, as well as COVID-19 cases for the aforementioned 4 regions of New York State, excluding NYC, through the first 6 weeks of the outbreak as a case study for other settings.
Data used for this analysis were obtained from 2 sources. The NYS Outpatient Influenza-like Illness Surveillance Network provided data on ILI derived from 140 outpatient providers in 49 of 57 NYS counties outside of NYC. Each week, the number of all-cause outpatient/emergency department visits and the total number of visits associated with ILI were aggregated. ILI was defined as a fever of ³100°F with cough and/or sore through in the absence of another known cause. The second source of data was mandatorily reported data on influenza types A-B and SARS-CoV-2 electronically reported by laboratories to the NYSDOH. The numbers of new COVID-19 and influenza cases were aggregated to calculate daily rates and average weekly rates by disease and region. The numbers of ILI visits and outpatient visits per region were aggregated to calculate the regional percent of visits for ILI.
ILI and laboratory-confirmed influenza tracked closely together and were declining up until the emergence of COVID-19. From the beginning of the 2020 calendar year until early February, the average rate of reported laboratory-confirmed influenza cases per 100,000 increased and then started declining through the end of March. From March 1st to April 4th, the average daily influenza case rate decreased by 98.9% in the Central region, by 98.7% in the Capital region, by 98.4% in the Western region, and by 96.9% in the Metropolitan region. The first confirmed COVID-19 case was reported in the Metropolitan region on March 2nd, and the other 3 regions reported cases a week later. From March 8th to March 21st, the slope of daily COVID-19 cases per 100,000 in each region was 3.6 (Metropolitan), 0.33 (Capital), 0.20 (Central), and 0.17 (Western); from March 22nd to April 10th, the slope was lower in all 4 regions. By April 12th, the weekly average rate of new reported COVID-19 cases per 100,000 was 63.3 (Metropolitan), 5.5 (Capital), 3.1 (Central), and 5.7 (Western).
The increase in ILI in the Central, Capital, and Western regions before the COVID-19 emergence might signal early COVID-19 activity in those regions without diagnosis. Overall, the study authors conclude that, “Together, these results support use of multiple sources for triangulation in regional monitoring of trends and impact of policies for COVID-19, particularly in locations where the disease is emerging, testing capacity is still being strengthened, and/or influenza is in decline.”
Rosenberg ES, Hall EW, Rosenthal EM, et al. Monitoring COVID-19 through trends in influenza-like illness and laboratory-confirmed influenza and COVID-19 – New York State, excluding New York City, January 1 – April 12, 2020. Clin Infect Dis. doi:10.1093/cid/ciaa684/5849237