NEW YORK — Demand from newly insured patients under the Affordable Care Act (ACA) will double the number of retail clinics in the next three years, management consulting firm Accenture has projected.

Walk-in clinics will drive $800 million in annual cost savings by 2015 and add capacity for 10.8 million patient visits per year, compared to 5.1 million in 2011, a new Accenture report says. The number of clinic visits is projected to account for 10% of nonprimary care outpatient visits by the end of 2015, the report adds.

Although the initial growth of clinics was halted short of market expectations in 2009, “health care reform will trigger a significant demand from millions of newly insured patients,” said Dr. Kaveh Safavi, managing director for Accenture’s North America health business. “The convergence of retail convenience with walk-in care services will provide a ‘release valve’ for strained health systems as they handle the influx of new patients.”

As the ACA produces a sudden spike in newly insured people seeking care, hospitals will be under tremendous pressure to keep pace, says the report, which is titled “Retail Medical Clinics: From Foe to Friend?” Demographic change exacerbates the challenge, with a steep increase in the ratio of elderly to young boosting demand.

“For stretched hospital operators, the answer may lie in an unexpected place, and one that, until recently, was considered a rival: retail health clinics,” the report says.

Historically, clinics experienced rapid growth from 2003 to 2008, ranging from 50% to 92% annually. However, growth stalled from 2008 to 2012, falling to just 2% per year.

The report blames the slowdown on low patient volumes for all but the narrowest range of services — particularly flu shots, which tend to be highly seasonal and generate relatively low reimbursements. Uncertainty over the ACA and the economic environment, along with “an unproven business model,” challenged clinics and slowed their growth, it notes. Added to this was the nearly complete failure of clinics and hospitals or primary care providers to forge partnerships — an important source of new patients and referrals.

But with the ACA’s implementation and a changed attitude from hospitals, the number of clinics is expected to increase 20% to 25% a year between now and 2015, more than doubling from 1,418 to 2,868, according to the report.

“Although primary care physicians and hospitals once regarded retail clinics as a business threat, in a post-reform landscape they are viewed as critical to facilitating future growth,” Safavi added. “In fact, retail clinics will reduce capacity constraints by referring lower-acuity patients to clinics while ensuring hospitals have capacity for more complex ­cases.”

For its part, CVS Caremark Corp. plans to add about 150 MinuteClinics this year, pushing its total to some 800, and by 2017 the company expects to have more than 1,700. MinuteClinics already have 25 affiliations with major health care systems. The relationships are based on system physicians serving as MinuteClinic medical directors. This fosters a variety of collaborative programs, including integration of electronic medical records and development of joint clinical programs.

Walgreen Co., meanwhile, announced in the spring that its more than 330 Take Care Clinics were expanding their scope to include assessment, treatment and management of such chronic conditions as hypertension, diabetes, high cholesterol and asthma, as well as additional preventive health services.

“With this service expansion, Take Care Clinics now provide the most comprehensive service offering within the retail clinic industry, and can play an even more valuable role in helping patients get, stay and live well,” said Dr. Jeffrey Kang, senior vice president of health and wellness services and solutions at Walgreens. “Through greater access to services and a broader focus on disease prevention and chronic condition management, our clinics can connect and work with physicians and other providers to better help support the increasing demands on our health care system today.”