I am a postdoctoral research fellow focusing on spatial data modeling and infectious disease epidemiology, specifically typhoid fever, in the Division of Infectious Diseases and Geographic Medicine at Stanford University's School of Medicine under the mentorship of Dr. Jason Andrews.
My research focuses on
(i) applying geospatial techniques to understand spatial burden of typhoid fever
(ii) developing spatial and temporal data models to simulate typhoid fever surveillance

Professional Education

  • Doctor of Philosophy, University of Maryland College Park (2019)
  • Master of Science, S.U.N.Y. State University at Buffalo (2014)

Stanford Advisors


All Publications

  • Determining spatial access to opioid use disorder treatment and emergency medical services in New Hampshire JOURNAL OF SUBSTANCE ABUSE TREATMENT Cao, Y., Stewart, K., Wish, E., Artigiani, E., Sorg, M. H. 2019; 101: 55?66


    This research presents an analysis of spatial access to both opioid use disorder treatment facilities and emergency medical services in New Hampshire during 2015-2016, a period during which there was a steep increase in unintentional overdoses involving fentanyl. For this research, spatial access was computed using the enhanced two-step floating catchment area model combined with the Huff model to assess access across New Hampshire and gives attention to supply-side parameters that can impact spatial access. The model is designed to measure access to healthcare services for opioid use disorder patients offered at treatment centers or from buprenorphine treatment practitioners, as well as from emergency medical services across New Hampshire. A composite index of accessibility is proposed to represent overall access to these different treatment services for opioid use disorder patients. Geospatial determinants of spatial access included street network distances, driving times and distance decay relationships, while other key factors were services availability and population demand. Among the towns with the highest composite access scores, approximately 40% were metropolitan locations while 16% were rural towns. The insights from this research showed that for this period, while the opioid crisis was impacting many towns in New Hampshire, high levels of access to treatment services were not uniform across the state. When comparing the access results with data on the towns of residence for individuals who died from unintentional overdoses involving fentanyl during 2015 and 2016, estimates found that approximately 40% of the towns were not estimated to be in the highest class of access to treatment services at the time. This research provides information for local public health officials to support planning strategies to address opioid use disorder treatment access in high-risk regions.

    View details for DOI 10.1016/j.jsat.2019.03.013

    View details for Web of Science ID 000472123800008

    View details for PubMedID 31174714

    View details for PubMedCentralID PMC6557292

  • Geospatial Analysis of Drug Poisoning Deaths Involving Heroin in the USA, 2000-2014 JOURNAL OF URBAN HEALTH-BULLETIN OF THE NEW YORK ACADEMY OF MEDICINE Stewart, K., Cao, Y., Hsu, M. H., Artigiani, E., Wish, E. 2017; 94 (4): 572?86


    We investigate the geographic patterns of drug poisoning deaths involving heroin by county for the USA from 2000 to 2014. The county-level patterns of mortality are examined with respect to age-adjusted rates of death for different classes of urbanization and racial and ethnic groups, while rates based on raw counts of drug poisoning deaths involving heroin are estimated for different age groups and by gender. To account for possible underestimations in these rates due to small areas or small numbers, spatial empirical Baye's estimation techniques have been used to smooth the rates of death and alleviate underestimation when analyzing spatial patterns for these different groups. The geographic pattern of poisoning deaths involving heroin has shifted from the west coast of the USA in the year 2000 to New England, the Mid-Atlantic region, and the Great Lakes and central Ohio Valley by 2014. The evolution over space and time of clusters of drug poisoning deaths involving heroin is confirmed through the SaTScan analysis. For this period, White males were found to be the most impacted population group overall; however, Blacks and Hispanics are highly impacted in counties where significant populations of these two groups reside. Our results show that while 35-54-year-olds were the most highly impacted age group by county from 2000 to 2010, by 2014, the trend had changed with an increasing number of counties experiencing higher death rates for individuals 25-34 years. The percentage of counties across the USA classified as large metro with deaths involving heroin is estimated to have decreased from approximately 73% in 2010 to just fewer than 56% in 2014, with a shift to small metro and non-metro counties. Understanding the geographic variations in impact on different population groups in the USA has become particularly necessary in light of the extreme increase in the use and misuse of street drugs including heroin and the subsequent rise in opioid-related deaths in the USA.

    View details for DOI 10.1007/s11524-017-0177-7

    View details for Web of Science ID 000406482700012

    View details for PubMedID 28639058

    View details for PubMedCentralID PMC5533669

  • Geographic patterns of end-stage renal disease and kidney transplants in the Midwestern United States APPLIED GEOGRAPHY Cao, Y., Stewart, K., Kalil, R. 2016; 71: 133?43

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