Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Public Health
First Advisor
Parikh, Sunil
Abstract
Although there have been significant improvements in recent decades, emerging and established infections continue to represent a significant contribution to the global burden of disease. Diagnostics play a critical role at the population level for infectious disease surveillance and at the individual level for patient care decisions. However, adequate diagnosis can be challenging in high-risk populations and resource-limited settings. In my dissertation, I present work on repeat positive SARS-CoV-2 testing in nursing home residents and the detection and differentiation of hemozoin, a parasite-derived biomarker, produced by human malaria species. In the first year of the COVID-19 pandemic, little was known about SARS-CoV-2 reinfection or repeat positive tests. Concerns about disease and testing trends were especially heightened for nursing home residents, a highly vulnerable population due to communal living, demographic characteristics, and a high prevalence of co-morbidities. In my first chapter, I present the findings from a retrospective observational study of repeat positive RNA-based PCR SARS-CoV-2 tests ≥ 90 days after initial positive results in Connecticut nursing home residents from March 15, 2020 (first case reported) to December 15, 2020 (start of vaccination campaigns). Approximately 2.6% (156/6,079) of nursing home residents surviving beyond 90 days had a repeat positive SARS-CoV-2 PCR test, with a median time to repeat positivity of 135 days (range 90–245 days), with deaths following repeat positive in 12.8% (20/156) individuals. At the time of publication, the data from this work helped shed light on the duration of protective immunity following natural infection with the original viral strain in this subset of largely elderly and medically frail individuals. Additionally, our work helps highlight the importance of strong relationships between academia, government, and nursing home facilities for pandemic response and preparedness. Point-of-care malaria diagnostics are limited in their ability to detect low-density infections. Molecular tests allow for more sensitive detection, yet require equipment and infrastructure that present challenges in low-resource settings. In Chapter 2, I introduce the Cytophone, a photoacoustic (PA) flow cytometer that uses lasers and ultrasound transducers to noninvasively detect malaria-infected red blood cells. Our findings showed that the innovative diagnostic platform was able to detect the PA signals produced by hemozoin, an iron-containing biocrystal, in cultured samples of human malaria in vitro. In Chapter 3, I present the findings of our first-in-human assessment of the Cytophone for malaria detection in symptomatic Cameroonian adults. Diagnostic testing and safety assessments were performed during 132 visits: optimization of Cytophone parameters in a cross-sectional cohort, and evaluation of diagnostic performance in 94 visits in 20 adults over one month post-treatment. The Cytophone was safe with 90% sensitivity, 69% specificity, and excellent diagnostic performance based on a receiver-operator-curve-area-under-the-curve (ROC-AUC) of 0.84, as compared to microscopy. These findings and the device’s ability to assess large sample volumes suggest that the Cytophone could provide highly-sensitive malaria detection in point-of-care settings, a diagnostic advance urgently needed. Differentiation between the five human malaria species is integral for disease surveillance and patient treatment decisions. In my final chapter, I present the preliminary observations of an optical assessment of the hemozoin crystals produced by P. falciparum and P. knowlesi. Preliminary images from light microscopy and transmission electron microscopy suggest that there may be species-specific differences in the surface area covered and distribution of hemozoin within an infected cell. Additionally, initial spectrophotometry-derived absorbance spectra indicated that there may be species-specific absorbance peak shapes over the visible light spectrum. Although the preliminary observations we present are limited by the sample size and scope of parasite life stages and species assessed, they suggest that there are detectable and quantifiable species-specific optical differences in hemozoin that could be used for speciation in hemozoin-based diagnostics. Further optical and magnetic analyses are ongoing.
Recommended Citation
Armstrong, Jillian, "Evaluating Novel Diagnostics in COVID-19 and Malaria" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1021.
https://elischolar.library.yale.edu/gsas_dissertations/1021
