The swine flu outbreak has prompted cruise line companies Carnival Corp. (CCL) and Royal Caribbean Cruises Ltd. (RCL) to alter routes, a small disruption now that could hurt earnings should conditions get worse.

For their part, both companies said it's too early to assess the impact on demand, although Royal Caribbean noted it hasn't seen an increase in cancellations.

Both companies have temporarily suspended visits to Mexican ports for some brands as a precautionary measure. These ports represent about 17% of each company's 2009 itineraries, according to UBS.

Of course, the outbreak's ultimate impact depends on how much the swine flu spreads. The disruption is just the latest setback for an industry already forced to discount trips to lure increasingly cost-conscious consumers.

"It's not helpful, but it's not cataclysmic," Susquehanna Financial Group analyst Robert LaFleur said.

Since the end of last summer, and before Wednesday, Carnival shares had fallen 36% and Royal Caribbean had lost 52%, each outpacing the S&P 500. Monday both stocks fell by double-digit percentages on swine-flu concerns. The shares rebounded Wednesday - Royal Caribbean gained 12% to $14.01, while Carnival added 3.8% to $26.53 - but remain lower for the week.

Mexican destinations represent about 17% of each company's 2009 deployments, UBS said, but that number goes down to 5% to 6% when easily reroutable cruises stopping at East Coast ports are taken out.

The concern is that the outbreak could reduce the number of passengers or force the cruise companies to lower ticket prices further. Either way, that could hurt passenger yields, a measure of ticket prices and onboard spending.

UBS estimates that it would take a 20% reduction in full-year passenger yields for the 5%-6% of the Mexican itineraries affected to impact company-wide yields on an annual basis by about 1%.

Cruise lines do have an advantage over other types of travel companies because they operate moveable and flexible assets. Similar to when a hurricane strikes, cruise lines are able to shift their itineraries to suit changing needs.

In the case of swine flu, ships previously scheduled to visit Mexico will go to another location, or in some instances, spend an extra day at sea, both companies said.

-By Kelly Nolan; Dow Jones Newswires; 201-938-4049; kelly.nolan@dowjones.com