A week before your trip to Mexico, the express mail van drops off a small package that might just save your vacation. You open it carefully and dial the number listed on the instruction sheet.
The nurse who answers gives you instructions on how to prepare, then drink the vaccine that's just been delivered.
You stir it into a flavored beverage and drink it, hoping it will protect you from traveler's diarrhea.
That scenario may sound like fantasy but could be closer to reality than you think. A liquid vaccine under study looks promising, says A. Louis Bourgeois, an associate research professor in the Center for Immunization Research at the Bloomberg School of Public Health's Department of International Health, part of Johns Hopkins University in Baltimore.
It's not perfect, Bourgeois acknowledges, but it shows promise in preventing or at least minimizing the misery of traveler's diarrhea. "The formula is being improved," he says. (The vaccine is probably five years away from market.)
Traveler's diarrhea, spread by organisms in contaminated food and beverages, affects up to 70% of travelers. Although it is generally benign and can go away without medication, it can ruin a trip.
Besides taking common-sense precautions — stay away from tap water, lettuce, ice cubes and undercooked foods in high-risk locations — you can take preventive antibiotics before your trip or pack them to take at the first symptom. But travel medicine specialists are divided about which medicinal approach is best.
"We arm every traveler [going to high-risk areas] with antibiotics," says Dr. Herbert L. DuPont, director of the Center for Infectious Diseases at the University of Texas School of Public Health, Houston, and chief of internal medicine at St. Luke's Episcopal Hospital, Houston.
For prevention, he prescribes rifaximin (Xifaxan), a drug that remains in the intestinal tract instead of being absorbed systemically throughout the body and is effective in blocking most of the organisms that cause traveler's diarrhea, he says. (DuPont helped develop the drug but has no financial connection with the manufacturer, he says.)
He recommends it for travelers to Mexico and Latin America, Southeast Asia and Africa if the trip is three weeks or less.
"If you're going longer, it's not a good idea," he says, because the drug is expensive — about $3.50 a pill — and because immunity will develop over time with repeated exposure.
But others, including the federal Centers for Disease Control and Prevention, don't recommend antibiotics as a preventive for traveler's diarrhea, even though some are 90% successful in staving off the condition with a once-a-day dose.
"Most travel medicine doctors don't give preventive medicine across the board," says Dr. Terri Rock, a travel medicine physician in Santa Monica. She generally prescribes preventive antibiotics for "those who have had a tough time with traveler's diarrhea or those who can't miss a single day of their trip," Rock says.
Another approach, which Rock and many other travel medicine doctors use, is to arm patients with emergency antibiotics such as Cipro (ciprofloxacin).
"I'm not saying Cipro works for every single" organism, she says, but often it does stop the diarrhea quickly.
Bourgeois, DuPont and Rock agree that preventing or even minimizing traveler's diarrhea is far from simple.
The vaccine Bourgeois is studying targets a bacteria called enterotoxigenic Escherichia coli, or ETEC, one of the main organisms causing traveler's diarrhea.
"Traveler's diarrhea is a complex problem. ETEC is a primary bacteria [causing it], but there are others and even some viruses," Bourgeois says. "Ultimately you would have to have a multicomponent vaccine."
In his study, Bourgeois and his colleagues gave 1,406 U.S. students headed to Guatemala or Mexico either the liquid vaccine or a placebo, and followed them for about six weeks.
About half of the 703 assigned to the vaccine group had the best response to the treatment, he says, and among them, the vaccine "was 84% effective at blocking severe diarrhea and 63% at blocking even mild illness."
Another problem: Organisms causing traveler's diarrhea can become resistant to medicines.
What's safe, what's not
BUT the biggest obstacle, says DuPont, is the abundance of contaminated foods in developing countries.
"We tell people to eat safe foods," he says. "It sounds ridiculously easy, but it is not. Safe foods are steaming hot, and those foods that are dry, like bread, because organisms like moisture. Foods that are peeled are safe."
Foods that "should have skull and crossbones on it are any foods with moisture and at room temperature."
In a developing country, that includes salad, cold meat and hamburgers.
Milk products in developing countries may not be pasteurized and should be avoided, Rock says. "Beer and wine are safe, but other alcohol diluted with water or ice is not."
Steer clear too of fruit juices served in a glass, because they could be diluted with contaminated water, she says.
And anyone on medications that reduce stomach acid — such as Prilosec (omeprazole), now over the counter — are at higher risk for traveler's diarrhea, Rock says, and should be even more careful.
Kathleen Doheny can be reached at firstname.lastname@example.org.