A virus with a “terrible” hacking cough eclipsed Deirdre Girard’s recent South American cruise on the Viking Sun. But for the playwright and her husband, the real disappointment set in after they got home.

"Once we started getting better, we heard from other passengers that half the ship had had the same virus, and that there were lines of people at the ship doctor's office," Girard, of Newbury, Mass., says. Girard's doctor asked for more information about the virus. Viking refused to tell the couple what it knows, citing the federal Health Insurance Portability and Accountability Act, which protects patient privacy, she says.

“Are ships avoiding notification of passengers regarding an outbreak and causing them unnecessary illness?” she wonders.

Getting reliable health information when you travel isn’t easy. And it’s not just the safety of your cruise ship that’s of concern.

“Travelers don’t have enough information,” says Carolyn Fernandes, an infectious diseases physician with the University of Pittsburgh Medical Center’s travel program, adding that they need reliable health information that includes guidance on vaccinations and the safety of food and water.

Viking says it fully complies with Centers for Disease Control and Prevention requirements to log and report illnesses on board. When 2 percent or more of the ship’s passengers or crew are ill with the same symptoms, the captain also notifies all guests through a public announcement, according to the company.

Viking says that fewer than 12 passengers and not as many crew members were infected on Girard’s cruise. It also says it has no record of her seeking medical attention while on the Viking Sun. Around the time of her cruise, two other Viking ships — the Star and the Sea — reported minor outbreaks, but her ship did not.

Girard says that she tried to report her illness but on the day she fell ill, the ship’s doctor canceled his office hours. During office hours the next day, she says, there was a medical evacuation that required the staff’s attention.

Passengers who are concerned about health conditions on cruise ships can consult the CDC’s list of outbreak updates for international cruise ships. But using it for planning purposes can be problematic. A quick look at the cruise lines on the list suggests that there’s no real pattern. Avoiding a cruise ship or a cruise line that seems to have a hygiene problem is no guarantee that you won’t end up flat on your back in your cabin during the voyage.

In many cases, the dreaded norovirus is brought aboard by infected passengers. “So while the cruise ship itself may be 100?percent clean in the CDC reports, there still may be outbreaks aboard,” says John Gobbels, chief operating officer of Medjet, an air-medical transport and travel security program. “When that happens, it is very contagious, and affected passengers may be quarantined or removed from the ship entirely and admitted to a local land facility if that’s warranted.”

Travelers can get useful information from unofficial sources before a trip, says Katherine Harmon, who oversees health analysis for WorldAware, a firm specializing in travel risk management. “Much of this information is garnished from crowdsourcing — sites like TripAdvisor, Yelp and Cruise Critic,” she says. “They’re not official, but they can still be useful if people read the comments and have a healthy skepticism.”

What about health information on your destination? Jamie Wells, director of medicine for the American Council on Science and Health, a nonprofit advocacy organization in New York, says the CDC has a lot of useful information that travelers often miss. For example, the online resource Travelers’ Health includes comprehensive information about vaccination requirements and medications, as well as guidance on food and water safety, personal safety and other concerns.

“Printing out their recommendations for the places you will go and bringing them to your physician for further discussion is a wise initial step,” Wells says. Some vaccines aren’t routinely stocked, and may require referrals to travel health clinics, he says.

If you’re wondering why there isn’t an app for this — well, actually, there is. It’s called My Travel Health, and it includes information from three sources: Mayo Clinic, the State Department’s travel safety system and the CDC.

“So it brings together validated travel and safety information in one place, along with storing medical records, doctor contact info and embassy information,” says Rashid Fehmi, a Mayo Clinic senior financial analyst who helped develop the app.

Resources like these can help you plan a vacation, but they aren’t enough, experts say. For instance, Jacquie Schwoerke, vice president of global patient services at Sharp HealthCare, a hospital system in San Diego, says too many people assume that their health insurance will cover them outside the country. It might not.

“Medical emergencies occur every day, and having a plan could save you, your family and travel companions from a lot of stress and financial devastation,” says Schwoerke, whose employer deals with many travel-related problems because it’s near the U.S.-Mexico border.

But why is reliable health information so difficult to find? Travel companies and vacation destinations don’t want to alarm their customers with potentially off-putting health statistics. And while downplaying the dangers may benefit the travel industry, it won’t keep you healthy when you’re on the road.