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In past centuries, this took no convincing. Dysentery “has been more fatal to soldiers than powder and shot,” wrote William “Father of Modern Medicine” Osler in 1892. (“Dysentery” is an umbrella term for infections in which the pathogens invade the lining of the intestine, causing cells and capillaries to ooze their contents and creating dysentery’s hallmark symptom, the one that sounds like British profanity: bloody diarrhea.) For every American killed by battle injuries during the Mexican War of 1848, seven died of disease, mostly diarrheal. During the American Civil War, 95,000 soldiers died from diarrhea or dysentery. During the Vietnam War, hospital admissions for diarrheal diseases outnumbered those for malaria by nearly four to one.

Once germ theory gained acceptance and the mechanics of infection became known, microorganisms—and the filth they breed in, and the insects that deliver them—became targets of military campaigns. Suddenly there were Fly Control Units, sanitation officers, military entomologists. The US military has been involved in most of the major advances in preventing, treating, and understanding diarrheal disease. Cairo’s NAMRU-3, the parent unit of Mark Riddle’s humble container lab in Djibouti, has a four-star antidiarrheal pedigree. Its first director, Navy Captain Robert A. Phillips, figured out that adding glucose to rehydration fluids enhances intestinal absorption of salts and water. This meant rehydration could be achieved by drinking the fluids rather than making one’s way to a clinic to have them administered intravenously. This has been a lifesaver not only for people who fight in remote, medically underserved areas but for people who live there. A 1978
Lancet
editorial called Phillips’s discovery “potentially the most important medical advance this century.”

The full name of Riddle’s study is Trial Evaluating Ambulatory Treatment of Travelers’ Diarrhea (TrEAT TD).
*
“Travelers’ diarrhea” is another catch-all term. Most of it—at least 80 percent—is bacterial, with 5 to 10 percent viral (vomit typically joining the waterworks here) and a miscellaneous percentage from protozoa like amoeba or giardia. All of it is caused by contaminated food or water. There used to be a separate category called “military diarrhea” (
military
referring to the patients, not the explosive nature of their evacuations), but if you look at the responsible pathogens, the breakdown is almost the same. Military diarrhea is travelers’ diarrhea, because service members are travelers—in places where you don’t want to be drinking the water. A survey conducted by Riddle, David Tribble,
†
and others with the US Naval Medical Research Center revealed that from 2003 to 2004, 30 to 35 percent of military personnel in combat in Iraq experienced situations where they lacked access to safe food and water. In the early days of a conflict especially, combatants are like backwater backpackers, crapping in the dirt and waving the flies off whatever food the locals are peddling. In that same survey, 77 percent of combatants in Iraq and 54 percent in Afghanistan came down with diarrhea. Forty percent of the cases were serious enough that the person sought medical help.

For every person who shows up at morning sick call, four tough it out. Riddle would like to know why. The average bout of travelers’ diarrhea lasts three to five days. Why endure this, when some of the new antibiotics, Riddle’s data show, can have you back to normal in four to twelve hours? He’s been asking around, mostly at mealtimes. The tables in the hangar-size Dorie
‡
are arranged church basement–style, in long rows, so there’s always a friendly stranger across from you or at your elbow, someone new with whom to chat about loose bowel movements while you eat.

Riddle gets right into it this morning with the man to his left. The uniform identifies the man as a Marine sergeant, last name Robinson. “I’m in the Navy,” Riddle is saying, “and we’re looking at simplified treatment regimens for travelers’ diarrhea. We’re finding that a single dose of antibiotic and an anti-motility . . .”

Robinson looks up from his eggs. “Anti—?”

“Like Imodium,” I offer. “Stops you up.”

“Oh, absolutely not. You do
not
want to mess with Nature like that.” Robinson has the booming vocals and commanding bullnecked air of the actor Ving Rhames. One imagines Riddle going straight over to the lab after breakfast and tossing his data in the trash—
What was I thinking?

“You have something bad in you, bad water or what have you? You got to pass it.” It’s like discussing diarrhea with the Giant Voice. “Defeat the purpose if you mess with that.”

We’ve been hearing this a lot. People think diarrhea is the body’s attempt to rid itself of invaders, or to flush out the toxins they produce. They won’t take an antimotility drug like Imodium because they think it interferes with the purge. But diarrhea is not something you are doing to pathogens; it is something they are doing to you. In varied and dastardly ways. Shigella and campylobacter, two common causes of bacterial dysentery, wield a toxin-delivering “secretion apparatus”—a hypodermic-cum-bayonet that injects toxins into cells in the intestinal lining, killing them and causing the fluid inside them to spill out. That spillage is part of the watery-stool scenario, but there’s more! With enough of those cells out of commission, the large bowel can no longer perform its duty as an absorber of water. Instead of food waste getting drier and more solid as it moves along the gastrointestinal tract, it stays liquid all the way along. The bacterium called enteroaggregative
E. coli
produces the same effect, in a different manner. It becomes a living cling wrap, a bacterial phalanx that coats the intestine and blocks absorption. Vibrio cholera and enterotoxigenic
E. coli
, or ETEC, inflict chemical weapons: Both produce a toxin that hijacks the pump that maintains cellular homeostasis. The commandeered pump begins pulling water out of cells faster than patients can replace it by drinking.
§

Why do these creatures do this to us? Is there an evolutionary motive? Sure, says Riddle. There always is. By causing humans to produce liquid feces, feces that splatter and flow and coat a larger surface area, a pathogen speeds its spread. Cover the world! The bacterium that causes cholera is especially proficient. Cholera patients decant as much as five gallons of liquid a day. The efflux is so torrential that one of Dr. Phillips’s Navy colleagues was inspired to invent the cholera cot, an army-style cot with a hole cut out under the buttocks. (Bucket sold separately.) The cots, still made today, allow patients to “go to the bathroom without leaving the bed,” writes specialneedscots.com, taking euphemism into the realm of quantum physics.

Besides, enteric bacteria are not easily flushed out. They’ve evolved ways to hang on in the deluge. ETEC—the bacteria behind as much as half of all travelers’ diarrhea—are equipped with a hairlike grappling hook called a longus, which they use to pull themselves close to a cell wall. On receipt of a chemoelectrical signal from the cell, the bacteria sprout springy hairs called fimbriae, with suction cups at their ends. Your immune system, for its part, has more sophisticated defenses than simply hosing down the premises. It starts cranking out specially designed antibodies. One might target the suction cups and keep them from adhering. Another might gum up the longus or disable the toxin.

Sergeant Robinson has nothing more to say about diarrhea, but he would like Riddle to have a word with the people responsible for the packet of toilet paper in the combat field rations, or MREs (Meals, Ready-to-Eat). “It’s like this much.”
¶
He tears off a piece of napkin the size of a drink ticket. “To wipe your ass!” Riddle volunteers that Navy guys pack baby wipes. He may regret saying this, because Robinson counters that Marines just cut off a piece of their t-shirt. Which possibly sums up the whole Marine Corps–Navy relationship.

Riddle thanks Sergeant Robinson and makes to leave. He likes to get back to his quarters before 8:00 a.m., when the national anthems—first Djiboutian, then American—begin playing over the Camp Lemonnier public address speakers. All those outdoors have to stop what they’re doing and stand respectfully until the music stops.
#
The Djiboutian national anthem is a melodic, sweeping number, like the theme song to an old TV western. The whole thing isn’t played, but it can seem that way should you be having some “postprandial urgency.” Meals—particularly the big ones occasioned by all-you-can-eat chow-hall buffets—trigger the gastrocolic reflex, a major move-along of the contents of the large intestine. Ushering out dinner to make room for breakfast. If, on top of that, you have a touch of irritable bowel syndrome (IBS), there may be times when all the patriotism in the land won’t keep you standing through the final bars.

During his years at NAMRU-3 headquarters, in Cairo, Riddle regularly got hit with diarrheal infections, a result of “sampling the fecal veneer” at local eateries. Irritable bowel syndrome is a well-documented, little-publicized aftermath of diarrheal infections—especially severe or repeated bouts. If you talk to people who’ve recently been diagnosed with IBS, about a third of them will say that their symptoms began after a bad attack of food poisoning. Defense Department databases reveal a five-fold higher risk of IBS among men and women who suffered an acute diarrheal infection while deployed in the Middle East. Even the Veterans Administration recognizes IBS—as well as a form of arthritis called “reactive”—as one of the “post-infectious sequelae” of enteric infections. If patients can show that the condition developed following an infection with shigella, campylobacter, or salmonella during deployment, they’re entitled to benefits. Riddle estimates that the Defense Department could wind up spending as much money on these long-term consequences of food poisoning as it spends on post-traumatic stress disorder.

Why not prescribe antibiotics more widely? First, there’s the issue of antibiotic-resistant strains developing, though this is less of a concern with some of the newer regimens that wipe out infections in a single day—likely not enough time for a resistant strain to evolve and thrive. More worrisome, perhaps, is recent research showing that the colons of overseas travelers who treat their diarrhea with antibiotics, particularly in Southeast Asia, tend to become colonized with two species of “bad” bacteria that they then carry home and can spread around town. Both bugs may inhabit a traveler’s gut only briefly and cause no problems while they’re there, but they are dangerous to patients with weak immune systems. Here again, with the newer single-dose regimens, it may not be an issue.

These are largely first-world concerns. The week I returned from Djibouti, the World Health Organization released a statistic for annual deaths from diarrhea worldwide: 2.2 million. The estimate for ETEC alone is 380,000 to 500,000 deaths per year. Children especially are at risk because they dehydrate dangerously fast. The Centers for Disease Control and Prevention puts the daily toll for deaths from diarrhea in children under five at 2,195—more than from malaria, AIDS, and measles combined. (The Gates Foundation is funding the Navy’s efforts to develop an ETEC vaccine.)

Riddle traveled a lot in his twenties and recalls being hit by a realization. So much of people’s lives—their opportunities, their health and longevity—comes down to where they were born. “It’s so random,” he says. We’re over at his office, which is downstairs from his lab, in the same container. “It shouldn’t be that way. It shouldn’t matter where your parents happened to live.” He pauses for a jet ripping through a takeoff. At certain times of day, you get this every few minutes. It’s like having a desk under the tarmac at Heathrow. The commotion fades and Riddle resumes. “I went into medicine wanting to help the greatest number of people.” And then, just when I thought he’d gone all earnest on me: “I happened to fall into diarrhea.”

A
T CAMP
Lemonnier there is often a quicker route to where you’re going, but to follow it you’d need to be shot. You’d need to scale a twelve-foot-high Cyclone fence and the barbed-wire Slinky along top of it, ignore the sign—Stop! Deadly Force Authorized!—and cross into the secure zone. Camp Lemonnier is the hub of counter-extremism activities in north Africa and Yemen. A fleet of drones resides in the zone, along with Navy SEALs and other Special Operations ghosts who pass in and out on their way from one classified gig to the next.

These are the people I want to speak with. I’m interested in diarrhea as a threat to national security. How would the takedown of Osama bin Laden have played out had one of the SEALs been fighting the forces of extreme urgency? How often is food poisoning the cause of a “mission fail”?

Yesterday I convinced the droll and adorable Camp Lemonnier public affairs officer, Lieutenant Seamus Nelson, to put a request in the daily email feed that goes out to everyone on base. (“. . . Mary is looking for individuals who would be willing to share a story about how a case of diarrhea has impacted them while engaged in operations. . . .”) Because really, how do you step into that conversation? The men of Special Operations are easy to spot—the beards, the build, the air of stony omnipotence—but they are not easy to talk to. They keep solidly to themselves. You don’t find them in the bar or the Combat Café. No one from Special Ops showed up at the LGBT barbeque or competed in the Fourth of July Cardboard Boat Regatta. Nor will you find them at the gym. They have their own equipment and trainers inside the zone.

“They only come out to eat,” says Riddle. We are sitting in Seamus’s office, waiting to talk to one of the four people who replied to the now infamous diarrhea email.

Seamus nods. “And to steal our women.”

The interviews have been scheduled back-to-back, one man coming in as another leaves, the Public Affairs container having taken on the quiet, hangdog air of a Catholic confessional. We just listened to the commanding officer of an inshore boat unit that protects Navy ships from USS
Cole
–type terrorist attacks in the port of Djibouti City. He demonstrated the maneuvers using Seamus’s stapler as the “high-value asset” kept safe by a tape dispenser and a bottle of allergy pills, zigzagging across each other’s paths. An inopportune bathroom break would leave the stapler vulnerable to attack. Even if crew stick to their posts, their vigilance is compromised; “illness preoccupation” is an overlooked military liability of diarrhea.