Get To Know UsLeadership Team
Edward Kan, M.D. - Managing Partner
Dr. Kan graduated from Northwestern University Medical School in 2001 and was Chief Resident at Long Island Jewish Medical Center where he completed his Emergency Medicine residency in 2005. He is an Adjunct Clinical Professor Assistant Professor with Stanford Medicine. He has worked with PEMG since 2005, and has been Managing Partner since 2017. He has interests in Emergency Medicine practice management, patient experience, and student instruction.
Gerald Nazareno, M.D.
Dr. Johnson has been working in the Emergency Department at Stanford Tri-Valley since 2005 and currently serves as the Vice Chief of the Emergency Department. She is board-certified in Emergency Medicine and has been elected Fellow of the American College of Emergency Physicians. Before working at Stanford Tri-Valley, she was on faculty at University of California, San Francisco as a Clinical Professor in the Department of Emergency Medicine. She completed her Emergency Medicine Residency at Alameda County Medical Center/Highland Hospital in Oakland, California in 2005. She obtained her medical degree from Stanford University School of Medicine, in Palo Alto, California in 2001. Dr. Johnson graduated Summa Cum Laude with B.A. in Political Science from West Chester University in Pennsylvania and completed post-baccalaureate studies at San Francisco State University before medical school. When away from the Emergency Department Dr. Johnson enjoys time with family and friends, gardening, running, rowing, yoga, hiking, and card or board games of any nature. She also loves to read literary classics, particularly obscure Dickens novels.
Andreas Tjoe, M.D.
Dr. Tjoe graduated from Temple University School of Medicine, Philadelphia, in 2009. He went to Beth Israel Medical Center, Manhattan, for residency and graduated in 2012. He has been with PEMG since 2013. He is an adjunct clinical assistant professor with Stanford Medicine and actively teaches physician assistants in training. When not working, Dr. Tjoe enjoys spending time with his family and road cycling.
Alexander Hoang, M.D.
Advance Practice Providers
Heather DeMars, P.A.
Heather Elliott DeMars graduated from Massachusetts College of Pharmacy and Health Sciences with a masters degree In Physician Assistant Studies in 2009. She started her career as a PA in Maine working in Emergency Medicine and moved to California in 2012. She aquired her certification of added qualification in Emergency Medicine and has been working in the ER and Urgent care since that time. She has been working with PEMG since 2014. Heather enjoys music, staying active and spending time with her family.
Christina Arieta, P.A.
Christina Arieta graduated from Western University of Health Sciences’ PA program in 2015, followed by a 14 month Emergency Medicine fellowship at Arrowhead Regional Medical Center in Colton, CA. She returned home to the Bay Area in 2017 and has been with PEMG since 2018. When away from work, Christina enjoys spending time with family and friends, practicing yoga, traveling, playing soccer and getting into a good book.
Elaine Yang, M.D.
Dr. Yang graduated from USC Keck School of Medicine in 2016, loving the community of East LA and the patients of LA County. She completed training in Emergency Medicine and a fellowship in Emergency Ultrasound at Highland Hospital-Alameda Health System. She has been with PEMG since 2022. When not practicing medicine she enjoys time in the garden, exploring outdoors, and traveling.
Saajan Bhakta, D.O.
Michael Costello, M.D.
Dr. Costello graduated from Rush Medical College (Chicago) in 1992. He completed his residency in Emergency Medicine at Detroit Receiving Hospital in 1995. He is Board Certified by the American Board of Emergency Medicine and he is an Adjunct Clinical Assistant Professor with Stanford Medicine. He has worked with PEMG since 2000. He has interests in Emergency Medicine and student/resident instruction.
Yen-Hua Yu, D.O.
Dr. Yu graduated from Lake Erie College of Osteopathic Medicine in 2009, and completed emergency medicine residency at Albert Einstein Medical Center in Philadelphia in 2013. She has been with PEMG since 2016. Outside of work, Dr. Yu enjoys being outdoors and spending time with the family.
Tian Mi, M.D.
Dr. Mi graduated from Saint Louis University and went to residency at Allegheny General Hospital. He has worked with PEMG since 2019. In his spare time he likes to spend time with his family and friends.
Matthew Conlin, P.A.
Matt Conlin is a physician assistant that has been with PEMG for the past three years. He graduated from the Stanford Physician Assistant program in 2016. He is a former paramedic, currently focusing on expanding from emergency medicine into urgent care. He is a Bay Area native and enjoys spending time with his family and friends.
Daniel Mizwicki, P.A.
Daniel Mizwicki graduated from Rosalind Franklin University in Chicago in 2013. Upon completion of their PA program, he worked primarily in Emergency Medicine with 2 years spent in an Orthopedic Surgery position prior to moving to the Bay area in 2020. Daniel has since worked in the Urgent Care setting in San Francisco. He joined the team at Stanford Tri-Valley Urgent Care in 2024. Daniel enjoys travel, cooking, running, camping in his spare time.
Chris Malek, P.A.
Christopher Malek graduated from the Stanford School of Medicine’s MSPA program in June 2024. Prior to his training, he gained valuable experience working as an EMT, where he developed a passion for patient care. With a strong interest in education, Chris enjoys teaching and aspires to transition into academia, where he hopes to contribute to the training and development of future healthcare professionals.
Spencer Knapp, P.A.
Kellie Amador, NP
Ngoc Hoang, M.D.
Dr. Hoang graduated from The University of Queensland Medical School in 2009 and completed her residency at New York Presbyterian Queens in 2014. After several years working at Long Island Jewish Valley Stream, a busy community hospital in New York, she started a family and moved home to California to be closer to her family. She has been with PEMG since early 2024. In her free time, she enjoys spending time with family and friends, hiking and traveling.
Brian Kaminski, M.D. - Managing Director
Dr. Brian Kaminski graduated Summa Cum Laude with a B.S. in Biology from Duke University in 1997, then graduated from Duke University School of Medicine in 2001. He proceeded to graduate from the Stanford Emergency Medicine Residency Program in Palo Alto, CA, in 2004. He has been with PEMG since 2010. At Stanford Health Care Tri-Valley, Dr. Kaminski served as Chair of the Medical Staff Quality Committee (2020-2023), and currently serves as the Medical Director and Chief of the Emergency Department (2020-present). Outside of medicine, Dr. Kaminski enjoys hiking, trail running, board games, and spending quality time with his wife and 3 children.
Physicians
Douglas Yoshida, M.D.
Douglas Yoshida MD received his undergraduate degree at UC Berkeley and medical degree at UC San Diego. He completed his Emergency Medicine residency at Highland Hospital in Oakland, California. He has worked in a variety of medical environments including the Kaiser system, over 10 years in the academic settings of UCSF, NYU and Stanford University, and international work in Nepal, Bosnia and Zambia. He has found his “forever home“ at Stanford Tri-Valley. In his free time he enjoys the diverse food culture of the Bay Area with his wife Jennifer, swimming and various other sorts of exercise, theater, walking his dog Mochi, and traveling to unusual destinations.
Sania Zubair, M.D.
Dr. Zubair graduated from Medical College of Wisconsin in 2007 and completed her Emergency Medicine residency in 2010 from Johns Hopkins Hospital in Baltimore, Maryland. She has worked with PEMG since 2018. In her spare time, Dr.Zubair likes to read, garden and spend time in nature.
Ranvir Dhillon, M.D.
Dr. Dhillon graduated from Harvard University in 2009 and went on to UCSF Medical School, where he graduated in 2013, and continued his residency at UCSF Fresno in Emergency Medicine. He has worked with PEMG since 2021. His interests at work include providing quality care and he serves on the Medical Staff Quality Committee.
Kelly Morrill, N.P. - Lead Provider, UC
Kelly Shannon graduated from University of Texas San Antonio Health Science Center in 2007 with Bachelors of Science in Nursing. After working in the Emergency Department as a Registered Nurse, she competed her Masters Degree and Nurse Practitioner license. As a Nurse Practitioner, she is able to diagnose conditions, prescribe medications, and provide treatments. Kelly joined PEMG in 2017. She enjoys spending time with her family, hiking, and traveling.
Adam Morris, P.A.
Adam Morris graduated from Midwestern University in 2008 masters degree in physician assistance studies. His worked as a PA in emergency medicine urgent care medicine since that time. He has worked around the United States and moved to California in 2017. He joined PEMG in 2017. Adam enjoys music, movie trivia, mountain biking, and working out.
Michael Liao, M.D.
Dr. Liao graduated from Northwestern University Feinberg School of Medicine in 2002 then completed residency in Emergency Medicine at Long Island Jewish Medical Center in 2006. After residency he joined the faculty at Washington University in St Louis until 2008. He then completed fellowships in both Clinical Ultrasound and Clinical Research at Denver Health Medical Center in 2011 during which he also obtained a Masters in Clinical Sciences at the University of Colorado Denver. He joined the Pleasanton Emergency Medical Group in 2023. His interests are in medical informatics, medical education, prediction instruments, and quality improvement. He enjoys playing ultimate frisbee and spending time with his two children.
Colleen Johnson, M.D.
Jeremy Estrada, M.D.
Dr. Estrada is a Board Certified and California licensed Emergency Physician. He received his MD degree from Eastern Virginia Medical School in 2015 and completed residency training in Emergency Medicine in Pittsburgh, PA. He has practiced as an attending physician in the Emergency Department and Urgent Cares since 2018. He is a proud husband and father of 3 girls.
Alan Ly, D.O.
Dr. Ly graduated from Midwestern University in 2018 and went to residency at SUNY Upstate in Syracuse, New York until 2021. Dr. Ly has been working with PEMG since 2021. Dr. Ly has Interest in emergency medicine as well as academics, administration and quality control.
Christina Halldorson, M.D.
Dr. Halldorson graduated from the University of Washington in 2013. She moved to Pittsburgh, PA and graduated from emergency medicine residency at Allegheny General Hospital in 2016. Since then she has worked in Sacramento and New Zealand and has been with PEMG since 2024. She also has a masters in public health and has interests in international medicine and disaster medicine.
Kelley Lang, P.A.
Kelley Lang is a physician assistant who graduated from Heritage University with a masters in Physician Assistant Studies in 2018. She has worked with PEMG since 2023.
Stephanie Nguyen, D.O.
Dr. Nguyen graduated from Philadelphia College of Osteopathic Medicine in 2017 and completed her Emergency Medicine residency in 2024 at Inspira Health Network in Vineland, New Jersey. She joined PEMG right after residency. She enjoys spending time with her family and friends and venturing out to new restaurants and boba places during her free time.
Desmond Chee, P.A.
Desmond graduated from Rocky Vista University and started with PEMG in July 2024. He has worked at Stanford Trivalley and John Muir Concord previously as an emergency department technician for two years. He has also served as an emergency medical technician for Contra Costa County and teaches EMT students in his free time.