Adults between ages 20 and 29 accounted for the greatest portion of new coronavirus cases — just over 20% — between June and August, according to a report released Wednesday by the U.S. Centers for Disease Control and Prevention. The findings suggest young adults are likely contributing to community spread of the virus and are not as protected as previously believed.

The elderly and ill were disproportionately affected by COVID-19 in the early months of the coronavirus pandemic, but the average age of confirmed COVID-19 patients dropped from 46 years in May to 38 years in August, as a growing number of young adults contracted the virus, according to the newly released CDC data.

In the Philadelphia area, public health experts have said they believe college students returning to school have contributed to an uptick in cases among young adults.

The findings are “preliminary evidence” that young adults contribute to community spread of the virus to older adults, the CDC stated. In Southern states in June, for instance, the report’s authors found that an increase in infection among young adults was followed several days later by an increase in infection among older adults.

Rising rates of COVID-19 among young adults is concerning because their job preferences may put them at greater risk of exposure to the virus. The report’s authors point out that young adults account for a large portion of jobs in business with high potential for exposure, such as retail stores, restaurants and bars, entertainment and child-care services.

At the same time, young adults may be less likely than older adults — who have been made well aware of their risk factors for contracting the virus — to follow safety protocol, such as social distancing and avoiding group gatherings. Young adults are more likely to have mild or no symptoms, which could add to their belief that they are not at risk, while contributing to asymptomatic spread of the virus to others, according to the report.

The report’s authors urged public health officials to continue emphasizing strategies to reduce spread, such as restricting the size of in-person gatherings, mask requirements and social distancing. The authors also recommended “age-appropriate” educational materials that can convey why it is important for young adults to follow safety guidelines, the risks of asymptomatic transmission and the role young adults may play in unknowingly spreading the virus.