A beaming, 2½-year-old girl recently came to see me because her parents were concerned that she still could speak only a few words, and was having tantrums at a rate excessive even for a toddler.

Julissa, as I'll call her, is very affectionate and friendly, but I quickly saw why her parents were worried. She had only a few words in Spanish, her parents' native language, and in English, learned primarily from a speech therapist.

During our visit, she wasn't able to play peek-a-boo with me, a game I would have expected her to master before age 2. Plenty of toddlers are strong-willed, but she flies into tantrums when even minor things don't go her way. By the end of the evaluation, it was clear that Julissa has trouble communicating, as well as restricted and repetitive behaviors, which are core features of autism.

When I made the diagnosis, I explained to Julissa's parents that autism spectrum disorder is a neuro-developmental condition, defined by differences in how a child experiences the world.

Last week, the Centers for Disease Control and Prevention released new estimates for the prevalence of autism spectrum disorder. In the 11 states included in the monitoring network, 1 in 59 school-age children is estimated to have autism. This rate represents an approximately 15 percent increase from data released in 2016, when it was estimated that 1 in 68 children had ASD. In New Jersey, it is estimated that 1 in 34 school-age children has ASD, the highest rate among the states in the study.

So what do these numbers mean?

First, it is important to understand that the CDC study reviews records to count children diagnosed with autism, or who have enough symptoms recorded in school or medical records to suggest a diagnosis.  There is no specific test for autism, so we must rely on trained clinicians to recognize its hallmarks. Unfortunately, there is no way to determine a comprehensive count of every child who may have autism, so even the rigorous methodology used in this study may miss some kids.

>>READ MORE: As autism prevalence grows, so do awareness and special places to play

When you look more closely at prevalence rates by sex, race and ethnicity, differences emerge. Across the 11 sites in the CDC study, for every school-age girl diagnosed with autism, four boys are diagnosed. And for every 100 Hispanic children, like Julissa, who are diagnosed, 120 non-Hispanic white children are diagnosed.

We are still trying to understand what is driving these differences.

Likely, there are differences in the development of boys' and girls' brains that leave boys at greater risk of autism. In addition, subtle differences in the presenting symptoms for girls may make it more challenging to recognize the condition in girls.

Ethnic variations likely are driven more by recognition than risk. We know this because Hispanic children who exhibit similar symptoms to non-Hispanic peers are less likely to get an autism diagnosis. The same situation has been true for African American children, who historically have had lower rates of autism diagnosed than white children.

There are no biologic differences that explain why ethnicity affects autism risk. It is encouraging that this study found that gaps in the rates of diagnosis have narrowed compared to prior studies. This narrowing gap suggests that the recognition of autism is improving, meaning that more children can get the treatment they need.

Given that autism is a relatively unusual diagnosis for a young Hispanic girl, Julissa's pediatrician and parents were astute in noticing differences in the way she was developing from a very young age. So they sent her for appropriate evaluations and interventions to get her the support that she needs. Like her parents, I also speak Spanish, which I hope makes them feel more comfortable with my caring for their daughter.

To Julissa's family, friends and community, she is more than a data point in an autism study. She is a bright, loving girl with incredible potential. With the appropriate diagnosis, support and intervention, we expect that she will make tremendous progress.

Kate Wallis, MD, MPH, is a pediatrician in Philadelphia and a fellow in developmental-behavioral pediatrics, a specialty that focuses on caring for children with developmental disabilities and autism spectrum disorder.