A few months ago at a family reunion in Hawaii, Sue Ross' niece cut her foot while swimming in the ocean. When the foot turned red and swollen, Ross snapped a digital photo and e-mailed it to her family doctor in Minnesota. The physician noted the bright red streaks, a telltale sign of infection, and ordered the family to get immediate treatment.

"We found out it was a piece of sea urchin," said Ross, of Delano, whose niece quickly recovered after a round of antibiotics. "It's such a hard call. You're on vacation, you don't want to take the time and trouble to go in if you don't need to, but at the same time, you don't want it to get worse."

As mobile gadgets become more commonplace and doctors become more comfortable making simple diagnoses over the phone or Internet, the field of tele-medicine is expanding rapidly.

Doctor-to-patient interactions like Ross' are a small-but-growing slice of the $3.9 billion global tele-medicine market, which includes remote X-ray reading, apps for smartphones and in-home devices that monitor weight, blood pressure or glucose levels.

"In a couple of years, it's going to be what everybody expects from their physician," said Jonathan Linkous, of the Washington, D.C.-based American Telemedicine Association.

Dr. Douglas Smith, the physician who diagnosed the infected foot, is banking on it.

Smith operates a solo family practice in Plymouth, and was a co-founder of MinuteClinic. In his latest entrepreneurial venture, Smith is an investor and chief medical officer of Consult A Doctor, a company that operates a nationwide network of 300 licensed, board-certified doctors who are available 24 hours a day to consult and write basic prescriptions for patients via phone, e-mail or videoconference.

Consult A Doctor, based in Miami Beach, Fla., has done more than 200,000 consultations in the past six years over a secure, cloud-based, network compliant with HIPAA (Health Insurance Portability and Accountability Act).

More than 1,500 employers have signed up, including PepsiCo and window-shade maker Hunter Douglas, typically paying $1 or $2 a month per employee as part of a wellness package aimed at keeping a lid on health care costs. Consult A Doctor also is gaining ground with insurers. Independent brokers are selling the service as a way to differentiate one health plan from another, and as an add-on to travel insurance. Last year, Consult A Doctor took calls from Americans in 58 different countries.

Next week, the company will launch tele-health platforms aimed at helping hospitals and clinic workers get care. By July, it expects to introduce My Practice 24/7, which will be marketed to private-practice physicians who want to set up a service exclusively for their own patients.

The idea came from doctors who felt they were losing revenue to retail clinics or emergency rooms because of after-hours concerns, said Smith, who has been testing the My Practice service at his Orono Family Medicine clinic.

The reception is much different now than in 2000, when Smith launched MinuteClinic, now operated by CVS Caremark.

"Doctor groups threw tomatoes at me; they hated me over retail clinics," he said. "Doctors love this because they see it as expanding their capabilities. It's not seen as competition."

Consult A Doctor is one of many companies pushing into tele-medicine with online consultation. Insurers also are getting into the act.

In Minnesota, Bloomington-based HealthPartners launched Virtuwell in October 2010 and has handled more than 18,000 cases. Blue Cross and Blue Shield of Minnesota and Minnetonka-based UnitedHealth Group use American Well, a webcam service provided by a Boston company. Medtronic also offers American Well to employees.

Admirers say such Web-based house calls cut down on costly emergency room visits and encourage patients to take care of concerns earlier in the process because it's more convenient.

Skeptics worry that doctors could miss subtle clues when they don't see patients face-to-face. And privacy concerns persist, despite assurances of encrypted data and confidentiality. Data breaches of medical data rose more than 32 percent last year due to sloppy mistakes and unsecured mobile devices, according to the Ponemon Institute's annual report on health care providers' patient privacy practices.

Technology "is not the panacea some people think it is," Smith acknowledged. "I want to use it as an adjunct, not a replacement."

Technology will continue to drive growth in tele-medicine, however. The industry has been growing by about 10 percent a year, according to Datamonitor, but analysts predict a sixfold increase in the global market by 2016.

Federal health laws will pave the way for more doctors to get reimbursed for remote care. At least 13 states, including Minnesota, have passed laws mandating that providers get paid the same for tele-medicine consultation as they do for in-office visits.

Consult A Doctor CEO Wolf Shlagman said the company is poised for "explosive growth." It has a waiting list of doctors who want to be part of it, he said.

"Every large self-insured employer in the next 12 to 36 months is going to have some tele-medicine offering as part of their plan design to members and employers," Shlagman said.

Jackie Crosby • 612-673-7335