A new study suggests that care provided by nurse practitioners (NP) and physician assistants (PA) for low-acuity ailments is comparable to the care provided by physicians for the same health issues.

The number of retail health clinics in the U.S. continues to increase at a rapid clip along with the scope of services they provide, according to a new study from RAND Corporation. 

The study, titled “The Evolving Role of Retail Clinics,” found that nearly three-quarters of retail clinics are located in the South and Midwest. It also found that 35% of the U.S. urban population lives within a 10-minute drive of a retail clinic and that clinics have a higher concentration in higher-income urban and suburban areas.

Keeping wait times for appointments to a minimum is a cardinal rule for medical practices, but one that’s becoming more difficult to achieve. Since 2013, more than 20 million new patients have joined the U.S. healthcare system, straining the resources of some practices that were already at volume before the debut of the Affordable Care Act (ACA).

The time it takes for a new patient to see a physician is on the rise, according to a study conducted by Merritt Hawkins.

The “2017 Survey of Physician Appointment Wait Times and Medicare and Medicaid Acceptance Rates” showed the average wait time for new patients to see a physician in the U.S. increased 30% from 2013 to 2016. The study found the average wait time for new patients was 24 days in 2016, an increase from an average of 18.5 days in 2014 and 20.5 days in 2009.

As retail clinics expand in number and in scope of services, they could emerge as a threat to some primary care practices.

Though industry estimates vary, the United States has approximately 2,500 retail-based health clinics, and that number is on pace to exceed 2,800 locations by the end of 2017. CVS was the market leader with 1,040 locations as of January 2016, followed by Walgreens Healthcare Clinics with 403 locations. Kroger ranked third with 194 Little Clinics, while Wal-Mart, Target, and Rite-Aid all had fewer than 100 locations, according to a 2016 study from the Drug Channels Institute.