Larry Merlo, CEO of CVS and Mark Bertolini, CEO of AETNA appear on Squawk Box on Dec. 4th, 2017.

This week, investors could get a better picture of how this year's intense flu season is impacting health care firms, with three major health insurers and the nation's largest for-profit hospital operator set to report fourth quarter results.

Here's what to watch:

Hospital operator HCA reports Tuesday. With a large presence in Texas — where the flu outbreak has been especially severe — investors will be watching for the impact on HCA's admissions.

Aetna is also set to report results on Janaury 30th, but the bigger news for its investors this week will be the regulatory outlook for the CVS' proposed $69 billion acquisition of the health insurer.

The 30-day Hart-Scott-Rodino Act anti-trust waiting period on the CVS-Aetna deal expires on February 2nd. If regulators raise no objections to extend the review period, it would lift a big hurdle for the merger.

In regulatory filings, the companies said they expect the merger to be completed in the second half of this year. The deal carries a $2.1 billion break-up fee.