New York-based private equity firm Tailwind Capital purchased an undisclosed stake in SDI Health, a healthcare analytics provider. Terms of the transaction were not disclosed.

The healthcare sector continues to see significant private equity interest, even as smaller transactions in other sectors struggle, amidst lender troubles.

In speaking with MergersUnleashed, Douglas M. Karp, managing partner and co-chief executive officer at Tailwind Capital, said the mid-market firm was interested in the business since SDI acquired Verispan in July 2008. Verispan was previously a joint venture between Quintiles and the pharmaceutical giant McKesson Corp. In discussing SDI’s purchase of its larger competitor, he said, “Andrew Kress and his management team completed a very difficult and complex acquisition.”

LLR Partners, a Philadelphia, Pennsylvania-based private equity firm backed the earlier transaction. Tailwind Capital and LLR will now both maintain “a significant, material investment” in SDI, Karp said.

He also noted that the current management “is in place,” but said he expects “material hires in terms of numbers and talent.” Karp said SDI will “for the time being be focused on internal growth.”

Karp expects Tailwind’s additional investment into the Plymouth Meeting, Pennsylvania-based company will enable SDI to compete against industry competitors IMS Health and Netherlands-based Wolters Kluwer Health. Last week, TPG Capital and the CPP Investment Board agreed to a $5.2 billion acquisition of purchase IMS.

SDI was founded in 1982. According to reports, Verispan employed 500 and SDI employed 200, as of July 2008.

Several healthcare transaction have been announced in recent months. In October, HIG Capital agreed to purchase Allion Healthcare Inc., a listed, New York-based provider of specialty pharmacy and disease management services for ailments including AIDS. In September, Cortec Group bought a control  stake in 180 Medical Inc. In addition, Miguel Fernandez, chairman of Florida-based private equity firm MBF Healthcare Partners, LP, committed $100 million in capital to invest in a new managed care healthcare platform, Simply Healthcare Plans, also in September.

Tailwind previously invested in the healthcare space. In partnership with San Francisco firm Telegraph Hill Partners, the firm acquired a stake in Freedom Innovations in April 2008. In April 2006, Tailwind Capital sold Aircast Incorporated to dj Orthopedics, Inc. for $290 million. Tailwind bought the portfolio company in December 2004.