Dr. Delma Nieves loves solving puzzles.
It’s a passion that perfectly suits her relatively new role of division chief of Pediatric Infectious Diseases (ID) at CHOC, part of Rady Children’s Health.
On April 1, 2025, Dr. Nieves succeeded one of her mentors, Dr. Antonio Arrieta, who ran the ID division for 25 years and remains an attending infectious disease physician.
The two are part of a team whose members thrive in the problem-solving and detective work required of their specialty, which serves the entire CHOC enterprise.
Dr. Nieves, dual-board certified in general pediatrics and pediatric infectious diseases, completed her residency at CHOC (2002 to 2005) and credits Dr. Arrieta and another veteran ID team member, Dr. Jasjit Singh, CHOC’s medical epidemiologist and medical director of infection prevention and control, with igniting her passion to seek often elusive treatments for critically ill children and young adults.
“I saw how much Dr. Arrieta and Dr. Singh loved and continue to love what they do,” said Dr. Nieves, who grew up in Paramount and was a first-generation college student. “They were such great teachers; they completely inspired me.”
Innovative therapies
Members of the ID team have saved the lives of patients with innovative therapies, including two recent cases involving the use of phages — naturally occurring viruses that attack pathogenic bacterial infections when patients become resistant to antibiotics.
A 20-year-old patient of Dr. Nieves who has cystic fibrosis and whose leukemia is in remission is responding well to phage therapy. She’s the second CHOC patient to undergo such treatment, shortly after ID team member Dr. Erlinda “Chulie” Ulloa, a physician scientist, treated another young adult with phages in the first case of its kind in the nation.
Beyond phages, ID physicians at CHOC have acquired medications that are either restricted by the FDA or not approved for use in humans when all other alternatives had failed.
For example, they recently prescribed clofazimine, primarily used to treat leprosy, for three patients who acquired non-tuberculosis mycobacteria infections, which can attack the lungs, skin, bones, lymph nodes, and other organs. The ID specialists have used clofazimine numerous times before on other patients who did not have leprosy or tuberculosis.
Over the years, CHOC has been one of the main sites in the U.S. where most of the current anti-fungal agents were investigated for appropriate use for children. Fungal infections are uniquely dangerous and can be difficult to diagnose and treat — especially when the fungus invades the brain.
Dr. Arrieta recalls saving the lives of a few patients who had brain involvement with the mold Aspergillus, a highly fatal type of fungus, that mainly affects the lungs.
A young girl with leukemia was among them.
“She had a 90-percent chance of dying with the antifungal agents available at the time, but she recovered and became prom queen,” Dr. Arrieta recalled.
Following an outbreak in 2016 of children who developed jaw microbacterial infections from an Orange County dental clinic, Dr. Singh led a study that helped spur the Centers for Disease Control and Prevention to issue a health alert emphasizing the importance of maintaining and monitoring safe dental waterlines. The research led to a change in water standards for pediatric dental procedures in California.
In 2021, Dr. Singh and Dr. Arrieta were among 12 clinicians to be named fellows of the Pediatric Infectious Diseases Society (PIDS), the world’s largest organization dedicated to the treatment, control and eradication of infectious diseases affecting children.
“Most of the kids we treat get better,” Dr. Nieves says, “and it’s so special to be part of seeing them recover after being super sick.”
Groundbreaking research
CHOC ID doctors have made strides in the research of COVID-19 and related conditions. In a recent example, Dr. Nieves was first author of a study that examined the safety and tolerability of remdesivir, an antiviral agent with limited experience in children. It was used for severe infection and prevention of progression of disease in pediatric patients with SARS-CoV-2.
Members of the ID division participate in ongoing clinical trials and present groundbreaking research at multiple conferences, most recently the Congress of the European Society of Clinical Microbiology and Infectious Diseases in Vienna in April 2025 and the annual meeting of the European Society for Pediatric Infectious Diseases in Bucharest, Romania in May 2025.
At the Bucharest conference, Dr. Adam Lee, who recently completed his fellowship at CHOC, presented research concerning the optimization of oxacillin, an anti-staphylococcal agent that had not been previously studied in neonates, yet often is used to treat serious, life-threatening infections.
He, in collaboration with other members of the division, has also reported on an innovative way to use the antifungal agent voriconazole in the treatment of increasingly frequent serious Aspergillus infections in extremely premature newborns.
Drs. Nieves and Arrieta are collaborating with other national and international experts to better understand how the pneumococcus, a simple bacterium easily treated with penicillin, continues to evade effective vaccines to remain a leading cause of mortality worldwide in children younger than 5 years of age.
Another member of the division, Dr. Negar Ashouri, is engaged in active collaboration with national experts in Kawasaki disease as well as a national collaborative to investigate new treatment and diagnostic techniques for serious neonatal infections.
The list of accomplishments for the ID division goes on.
“Every single member of this division plays a very necessary role,” Dr. Nieves says.
Memories on the wall
Dr. Arrieta’s office is full of stories, and the stories never get old.
They flow from him as he points out some of the numerous photos of current and former patients plastered on three bulletin boards in his office.
One note from a young girl reads: “Thank you Dr. Arrieta for helping me get better.”
Another from a parent reads: “Thank you for always taking such good care of our daughter we really appreciate everything you do for her, God Bless.”
Dr. Arrieta points to a photo of a young woman in a wedding dress.
“She has cystic fibrosis and was supposed to die at age 5,” he says.
Born in Peru, where many children come down with community-acquired infections such as typhoid fever and malaria, Dr. Arrieta has been at CHOC for 34 years and is married to Cheryl Arrieta, a nurse here.
Like other members of the ID team, Dr. Arrieta’s passion for doing all he can to save the lives of sick children is apparent.
“We all love this work,” Dr. Nieves says.
Dr. Arrieta points to a photo of a boy who died of a fungal infection.
“That one broke my heart,” he says.
San Diego collaboration
To treat her 20-year-old patient with phage therapy after she developed a multi-drug-resistant infection, Dr. Nieves collaborated with nationally known ID specialist Dr. John Bradley, at the time medical director of the Division of Infectious Diseases at Rady Children’s Hospital-San Diego and a distinguished professor at the UC San Diego School of Medicine.
Dr. Bradley had treated a similar patient.
Dr. Nieves also connected with Dr. Anca Segall, Ph.D., who engages in phage studies at San Diego State University.
For years, CHOC and Rady Children’s Hospital-San Diego have collaborated on ID patients.
Recently, Dr. Segall, Dr. Nieves and Dr. Bradley presented a study that showed how phage therapy in conjunction with antibiotics holds promise for patients with cystic fibrosis who develop chronic antibiotic-resistant bacterial infections in their airways, lungs, other mucosal surfaces, and in some cases, bloodstream.
That study was accepted for oral presentation in October 2025 at the Conference on Bacteriophages: Biology, Dynamics, and Therapeutics, inWashington, D.C.
Dr. Nieves is hopeful that her patient will get well enough to undergo a lung transplant.
Plans for growth
In addition to her clinical and division director duties, Dr. Nieves runs the pediatric infectious diseases fellowship program at CHOC and UC Irvine. The ID division is also very active in the pediatric residency program at CHOC.
Dr. Nieves hopes to expand those programs and add more ID physicians to her team.
“We want to make sure we keep up with the growth of the hospital and that we’re able to continue to meet the needs of our existing and future patients,” she says.
Meet the team
Members of the ID team say they feel like family.
Here are brief snapshots of members:
Dr. Delma Nieves
Division chief and Fellowship Program Director, Pediatric Infectious Diseases
Years at CHOC: 16 (19 if counting residency here)
Interests: Medical education; team building; research interests including pneumococcal infections, pertussis and neonatal infections.
Quote: “Being part of the Infectious Diseases division at CHOC has been such a gift in my life. It is always exciting and challenging in a good way. I know that my work matters. When I feel tired at the end of a day at work, I know it is worth it if I can make a positive impact in someone’s life whether it be a patient, a colleague, or a trainee.”
Dr. Antonio Arrieta
Former division chief, Pediatric Infectious Diseases; Director of Infectious Diseases Division Research
Years at CHOC: 35
Research interests: Fungal infections, immunocompromised hosts, pneumococcal infections
Quote: “I wish someday, with the help of my colleagues at CHOC, I could make a difference in the lives of children everywhere in the world, from our little corner in Orange County. We have helped to better understand how to dose antibiotics and antifungal agents in children of different ages and sizes, remembering that children are not just small adults. This has improved the survival of children with serious infections. We hope to continue helping to learn how to defeat the pneumococcus, the most common cause of death in children worldwide outside of the neonatal period. I always tell my residents and medical students that a pediatrician needs to know the pneumococcus better than their girlfriend or boyfriend!”
Dr. Coleen Cunningham
Pediatrician in chief, CHOC
Years at CHOC: Five
Research interests: Prevention and treatment of pediatric HIV (plus a few studies re: other viruses, mostly vaccines)
Quote: “This is a truly knowledgeable, hard-working, and supportive team – a really great group of people.”
Dr. Erlinda “Chulie” Ulloa
Attending physician, CHOC
Assistant professor, UCI School of Medicine, Department of Pediatrics, Microbiology & Molecular Genetics
Years at CHOC: Five
Research interests: Translating laboratory discoveries into better treatments for children with the most challenging bacterial infections — cases where standard therapies have failed or don’t exist. Her lab works on three fronts: drugs that enhance the immune system’s antibacterial activity, innovative treatment strategies including drug repurposing, and improved antimicrobial testing methods.
Quote: “What makes CHOC’s Infectious Diseases division truly special is the people. Everyone — from faculty to staff — shares a deep commitment to our patients and a genuine curiosity that drives innovation. It’s a team where collaboration, mentorship, and compassion come together every day, making it an inspiring place to work.”
Dr. Jasjit Singh
Assistant division chief, Infectious Diseases
Medical director, CHOC Infection Prevention and Epidemiology
Clinical professor, UCI Department of Pediatrics
Strong vaccine advocate. Immediate past president and treasurer of the California Immunization Commission
Chairperson of infection prevention within the CHOC system
Years at CHOC: 30 years
Research interests: Vaccines, vaccine-preventable diseases, global health, primary immunodeficiencies, infection prevention and control.
Quote: “Our division is like a family. With our shared vision of providing exceptional care to children with infectious disease issues, being up to date on the latest literature, and being a resource for community pediatricians, we always try to help each other out as much as we can.”
Dr. Negar Ashouri
Medical chair of the antimicrobial stewardship program, chief of staff-elect, Rady Children’s Hospital Mission
Years at CHOC: 23 years (a former resident here)
Research interests: Kawasaki disease, congenital/perinatal infections, antimicrobial stewardship
Quote: “I get to spend the day with a group of physicians who inspire me, support me, and have become my second family.”
Dr. Adam Lee
Title: Attending physician
Years at CHOC: Six months as an attending. He came in 2019 to start his residency and stayed at CHOC in 2022 for his fellowship.
Research interests: Pharmacometrics and pharmacokinetic modeling, which involves studying dosing of drugs to determine if patients are receiving adequate therapeutic doses. His fellowship project was a study on oxacillin in young infants and he was able to find that prior dosing regimens were not optimally devised for young infants.
Quote: “I love working here. Aside from being colleagues, we are all friends. The division here has always been a very welcoming family, and it is a pleasure to come to work each day.”
Dr. Aaron Shaw
Title: Attending physician at CHOC
Years at CHOC: Two
Quote: “It’s an honor to be a part of such a caring and supportive division. These doctors care so deeply about the children we serve, and I’m grateful I get to be here and serve alongside them.”
Dr. Matthew Zahn
Title: Attending physician at CHOC and member of the prestigious Committee on Infectious Diseases (COID) of the American Academy of Pediatrics and collaborator on the writing of “The Red Book”, published by the committee.
Years at CHOC: Three months
Research interests: Public health response to infectious diseases, Candida auris (a multidrug-resistant fungus common in healthcare settings)
Quote: “It’s an honor to participate in the care of children at CHOC.”
Stephanie Osborne
Assistant nurse manager, clinical research, infectious diseases
Years at CHOC: 27
Research interests: Pneumonia, investigational new drug treatments, anti-infectives
Quote: “The ID team has been a family to me. As such, we treat each other with dignity, respect, and kindness, and sometimes a little spunk!”
Jennifer Strickland
Physician assistant
Years at CHOC: 11
Research interests: Pneumonia, investigational new drug treatments, anti-infectives
Quote: “It has been a pleasure working with this ID team and it truly feels like a family. Everyone is dedicated, hard-working, and very kind.”
