One such company is Omada Health, which connects those suffering with issues like diabetes to Web-based support groups. Sean Duffy, the company's CEO, said start-ups like his are attracting attention and money, in part because there is now a new generation of entrepreneurs who are passionate about health care and tech.

"I worked at Google before going to medical school," Duffy said. "I love technology. I love health care. You have entrepreneurs who are able to combine both. The venture capital and investing community sees the chance for the next wave of folks to take health care to a digital era."

So, which start-ups in this space are most likely to go public this year?

Those tracking the space point to several candidates, including Fitbit, the maker of fitness trackers; ZocDoc, which allows users in all 50 states to find and book appointments online with doctors; Practice Fusion, a cloud-based electronic health records provider; Proteus, which makes ingestible sensors; and 23andMe, which provides genetic reports about users' ancestry and family history. (Fitbit, 23andMed and ZocDoc declined comment. A spokesperson for Practice Fusion said: "An IPO could definitely be in Practice Fusion's future.")

One note of caution for investors.

Five digital health companies went public in 2014, according to Rock Health, raising a total of $1.7 billion. But three of those five stocksCare.com, Castlight Health, and Imprivataare now selling at below their offering price, in two cases well below. The other two, Everyday Health and IMS Health Holdings, remain above their offering prices. (Care.com declined comment; the chairman of Castlight said "opportunity is tangible and large in healthcare right now, so both the entrepreneurial and VC community will focus on the market and business model dynamics inherent in businesses they believe can be the next...Castlight, rather than short term stock prices.")

Analysts note that enthusiasm for this sector could cool if that downtrend continues this year.

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Updated to reflect the comments of Practice Fusion and Fitbit.

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Health care start-ups rake in money