Inferring COVID-19 testing and vaccination behavior from New Jersey testing data.

Characterizing the relationship between disease testing behaviors and infectious disease dynamics is of great importance for public health. Tests for both current and past infection can influence disease-related behaviors at the individual level, while population-level knowledge of an epidemic's course may feed back to affect one's likelihood of taking a test. The COVID-19 pandemic has generated testing data on an unprecedented scale for tests detecting both current infection (PCR, antigen) and past infection (serology); this opens the way to characterizing the complex relationship between testing behavior and infection dynamics. Leveraging a rich database of individualized COVID-19 testing histories in New Jersey, we analyze the behavioral relationships between PCR and serology tests, infection, and vaccination. We quantify interactions between individuals' test-taking tendencies and their past testing and infection histories, finding that PCR tests were disproportionately taken by people currently infected, and serology tests were disproportionately taken by people with past infection or vaccination. The effects of previous positive test results on testing behavior are less consistent, as individuals with past PCR positives were more likely to take subsequent PCR and serology tests at some periods of the epidemic time course and less likely at others. Lastly, we fit a model to the titer values collected from serology tests to infer vaccination trends, finding a marked decrease in vaccination rates among individuals who had previously received a positive PCR test. These results exemplify the utility of individualized testing histories in uncovering hidden behavioral variables affecting testing and vaccination.

Anxiety-related visits to New Jersey emergency departments after September 11, 2001.

The purpose of this study was to examine the effect of September 11, 2001 on anxiety-related visits to selected Emergency Departments (EDs). We performed a retrospective analysis of consecutive patients seen by emergency physicians in 15 New Jersey EDs located within a 50-mile radius of the World Trade Center from July 11 through December 11 in each of 6 years, 1996--2001. We chose by consensus all ICD-9 (International Classification of Diseases, 9th revision) codes related to anxiety. We used graphical methods, Box-Jenkins modeling, and time series regression to determine the effect of September 11 to 14 on daily rates of anxiety-related visits. We found that the daily rate of anxiety-related visits just after September 11th was 93% higher (p < 0.0001) than the average for the remaining 150 days for 2001. This represents, on average, one additional daily visit for anxiety at each ED. We concluded that there was an increase in anxiety-related ED visits after September 11, 2001.