The first retail health clinic opened in 2000, and there are around 500 in the U.S. The figure is expected to zoom as more and more people patronize them.
The MinuteClinic, for instance, expects to have 400 locations by year end and ultimately as many as 2,500 locations.
Michael Howe, its chief executive, was confident many of the concerns raised would die down as doctors became more acquainted with the clinic concept.
He refuted as groundless a resolution passed by the American Medical Association in June asking state and federal authorities to investigate whether there was a conflict of interest in drug-store chains that both write and fill prescriptions.
"We make it very clear to the patients they have a right to go where they want," he said.
He also insisted that the CVS chain that acquired the MinuteClinic last year focused on offering high-quality care. "We're fully accredited for all of the services we provide. We meet the same standards that other healthcare organizations meet."
As it happens it is nurse practitioners (NPs)— nurses with advanced degrees who can write prescriptions — staff most clinics. They reduce costs because they charge, on average, less than half of what family doctors do.
Nurse practitioners have at least six years of schooling and use proprietary software that helps them examine and question patients.
They not only diagnose ailments but also input computer data, process payments, dispense tip sheets on how to avoid future illness and send patients thank-you notes.
While there is always room for error in diagnosing illness, clinic operators say there is little that can go wrong.
Of course they treat common ailments only — such as ear infections, allergies, or pink eye — and offer an alternative to packed doctors' offices and pricey emergency rooms.
If clinics cannot treat someone because an ailment is too serious, such as bronchitis that's advanced to pneumonia, most clinics refer clients free of charge to a local doctor or emergency room. Clinic operators say they refer out about 10 per cent of clients.
The growth of clinics in retail stores comes amid a shortage of family physicians that only promises to worsen.
Medical groups predict a shortage of 200,000 doctors in the United States by 2020. About 20 percent of Americans live in areas with a shortage of primary medical care.
Wal-Mart operates 78 in-store clinics in 13 states, where the cost of a "get well" visit ranges between $40 and $65.
A few months ago the American Academy of Pediatrics (AAP) opposed retail-based clinics as an appropriate source of medical care for infants, children, and adolescents.
In a statement, the AAP said it "strongly discourages" the use of retail-based clinics for babies, kids, and teens because the clinics aren't a "medical home" providing consistent long-term care for patients.
But in a country where healthcare is said to be collapsing, becoming unaffordable for large sections of the people, any cheaper option is welcome.
About half of those surveyed who visit Wal-Mart clinics have no insurance, according to spokeswoman Deisha Galberth. Another 15 percent said if there had not been a clinic, they would have gone to an emergency room instead.
Sandy Ryan, Take Care Health's chief nurse practitioner officer, said about 30 percent of patients who visit a Take Care clinic do not have a regular doctor. Another 30 percent are uninsured. And 15 to 20 percent of patients seen at the clinics are referred elsewhere for additional care.
"What we are doing is providing an access point that doesn't exist," Ryan said.