Karin A. Nielsen, MD

Karin A. Nielsen, MD

Pediatric Infectious Diseases
Primary Location
Westwood Pediatrics
200 Medical Plaza
Los Angeles, California 90095


Link to Dr. Nielsen's complete CV >

Dr. Karin Nielsen is a Professor of Pediatrics in the Division of Infectious Diseases at UCLA Children's Hospital and a member of the UCLA faculty since 1996. She is an attending physician for Pediatric Infectious Diseases at Mattel Children's Hospital and co-director of the Care4Families HIV clinic at UCLA. Dr. Nielsen is a physician-scientist, originally from Rio de Janeiro, Brazil where she graduated in medicine from the University of Rio de Janeiro and completed pediatric residency training at the Hospital dos Servidores do Estado, also in Rio. At UCLA since 1991, she completed both clinical and research fellowships in pediatric infectious diseases and obtained a master's degree in Public Health/Epidemiology. Dr. Nielsen's main area of research has been pediatric infections particularly in the area of HIV and congenital infections. She is an internationally recognized expert in the field of pediatric HIV and Zika.

Dr. Nielsen has worked extensively in international clinical studies focused on both prevention of perinatal and sexual transmission of HIV and has published extensively on the treatment of this disease in children, adolescents and adults. She is a leading investigator in a number of studies conducted by NIH sponsored HIV networks such as IMPAACT, HPTN, ATN and ACTG, developing clinical trials in North and South America, Sub-Saharan Africa and Asia, many of which have changed management guidelines for HIV and more recently Zika. Dr. Nielsen has a very active collaboration with multiple sites in Brazil both on the field of HIV, congenital infections and more recently ZIKA virus, with active NIH grant funding for her studies. She is a key investigator in a large study of early treatment of HIV infection in at risk youth in Los Angeles and New Orleans and a co-investigator on a pediatric TB study in the Philippines. In addition, Dr. Nielsen is an active clinician licensed in both the U.S. and in Brazil with an interest in tropical and neglected infectious diseases. At UCLA she is an attending physician in Westwood and Santa Monica UCLA hospitals and an attending in the HIV care outpatient clinic and pediatric infectious diseases clinic. She is also s member of the UCLA Institutional Review Board and serves on several NIH study section panels. Dr. Nielsen lectures worldwide on multiple ID and Peds ID topics and has mentored multiple medical students, residents, graduate students and post-doctoral fellows from North, Central and South America, Europe, Africa and Asia.



UCLA School of Medicine, 1996


Hospital dos Servidores do Estado, 1989


Hospital dos Servidores do Estado, 1986


Universidade Federal do Rio de Janeiro, MD, 1986


Hospital Affiliations



  • Infectious Diseases Society of America (IDSA) Carolyn B. Hall 2019 lectureship award for outstanding contributions to pediatric infectious diseases.
  • Dr. Nielsen has been listed in the Consumer's Research Council of America as one of America's Top Physicians in Pediatric Infectious Diseases for many years.
  • Elected member in the Society for Pediatric Research, the American Pediatric Society, and the International AIDS Society.
  • Scientist investigator in the NIH HIV networks, for Pediatrics, Adolescent Medicine, Prevention and Treatment of HIV (IMPAACT, ATN, ACTG and HPTN networks funded by the NIH). International AIDS Society (IAS).
  • Diaspora Award for Best Health Professional in 2014 by the government of Brazil.