William E. Gilli, M.D., F.A.C.P.


Dr. Gilli is a Bakersfield native. He attended West High School and graduated from the USC School of Medicine in 1983. Dr. Gilli is Board Certified in Internal Medicine. He is an Assistant Professor of Medicine at UCLA teaching at Kern Medical Center since 1993. At KMC, he has help teach over 300 physicians in the last 25years. He is also a Fellow at the American College of Physicians. In early 2009, Dr. Gilli underwent a total hip replacement and has returned to running. He is an avid walker, runner, cyclist, and skier.

Kevin Nelson, FNP

Nurse Practitioner

Kevin Nelson obtained his Family Nurse Practitioner and Physician Assistant Certificates from Stanford University and worked in Family Practice in Taft and Bakersfield for 6 years prior to joining Mesa West. Kevin Nelson has been at Mesa West Medical since 2002. Kevin enjoys cycling and hiking.

Tracy Simonsen ACNP-C

Nurse Practitioner

Tracy Simonsen received her Bachelor’s Degree from Cal State University Bakersfield in Nursing. She then worked in Intensive Care Medicine for the next 7 years at Kern Medical Center. She obtain her Masters degree from UCLA in Nursing with a specialty as an Acute Care Nurse Practitioner. Tracy Simonsen has been at Mesa West Medical since 1996. Tracy enjoys tennis and golf.