Just when you thought it was safe to get back in the water, the cruise industry is sick again. Literally. Figuratively. Indubitably.

Mysterious stomach viruses that broke out over the past few Holland America's Amsterdam sailings and the Disney(NYSE: DIS) Magic are putting a damper on the industry's efforts to bounce back after the 9/11 terrorist attacks.

Hoping to put the bon back in voyage, investors don't seem to be bothered with the recent wake of a Norwalk-like virus that has made roughly 500 passengers ill over the past three Holland America sailings. Shares of market leader Carnival(NYSE: CCL) have risen by nearly 30% off last month's lows. It has also been anchors away for rival Royal Caribbean(NYSE: RCL), whose stock has risen 50% over the past two months. The original Love Boat company, Princess(NYSE: POC), is in the middle of a love triangle, as Royal Caribbean and Carnival vie for its acquisitive affection. It's seen shares climb by almost 50% off summer lows.

But Love Boat's Doc is nowhere to be found, as the maladies aboard the Amsterdam and Magic will be more than just one-time hits after passenger refunds. As horror stories circulate about crews scrubbing and disinfecting to no avail, while buffets disappear and passengers rub elbows rather than shake hands, cruising aficionados may hold off on their next bookings.

The industry was one of the quickest to bounce back after 9/11. Cruise operators report slightly higher revenue this year, and new ships are still scheduled for delivery. Despite solid fundamentals still in place and all three cruising titans expecting double-digit earnings growth next year, it's not time to cash out of cruise stocks or sell the industry's players short. But keep an eye on the travel news. If the stomachaches, vomiting, and diarrhea continue, it will have an impact on industry capacity and the discounting of future voyages. Loose stools sink ships.