Last September a 49-year-old Qatari man who’d recently travelled to Saudi Arabia was hospitalised in Doha with a nasty respiratory illness. He deteriorated rapidly and doctors promptly airlifted him to a London hospital, where he wound up on life support with kidney and lung failure. From respiratory tract samples, investigators soon teased out an unknown coronavirus – the same one that had just killed an otherwise healthy 60-year-old in Saudi Arabia. For one tense moment, epidemiologists thought they might be witnessing a replay of the devastating 2003 SARS epidemic, also brought on by a coronavirus. But the threat this time looked worse: three million people were about to descend on Saudi Arabia for the hajj, a Muslim pilgrimage to Mecca already well known for the overnight global redistribution of illnesses via passenger jet.

Disease detectives of all specialties caught the next available flights into the heart of the potential outbreak. Epidemiologists tracked down anyone who had been even remotely associated with the victims. Veterinarians wearing protective gear went to a farm that one of the victims had visited; they took samples from hundreds of domestic and wild animals in order to identify the species from which the virus had jumped to humans. This effort, unseen by the public but involving hundreds of experts around the world, soon established that the disease did not, in fact, spread easily from one person to another. The hajj wasn’t a hot zone after all.

It was a lucky break. As of early March, the new virus had sickened only 14 people and killed eight. But the episode was also a reminder that the supply of emerging diseases in the modern world is almost eye-bleedingly endless, and that they can turn up anywhere. One such pathogen, West Nile virus, killed 243 people in the US last year. And a 2009 report in Emerging Infectious Diseases shows that West Nile virus is being overlooked as a cause of severe neurologic disease in South Africa. Health officials will tell you that the Big One, a disease outbreak on the order of the influenza pandemic of 1918, could happen any day – and that sooner or later it almost certainly will.

They’ll also tell you that men in particular need to pay attention to the potential hazards: we travel more than women, particularly for business. Our trips tend to take us to more-remote destinations. So maybe it shouldn’t come as a surprise that we also have a much higher incidence of malaria, dengue fever, hepatitis and Legionnaires’ disease – and perhaps other diseases yet unknown.

The good news? Science has become remarkably adept at identifying and containing potential outbreaks right at the start, even in the most remote locations, and often when only a handful of people – rather than hundreds – have become sick. In other words, they generally halt the outbreak before it can turn up on a 747 bound for New York City.

Some of the credit goes to rapidly advancing technologies, from Internet data mining to DNA fingerprinting. In the early 1980s, for instance, it took three devastating years to identify the virus that causes AIDS. With modern gene sequencing, says Columbia University virus hunter Dr W. Ian Lipkin, it would take just 48 hours today. And part of the credit belongs to governments, which have learned painful lessons about the consequences of allowing a new disease to get out of hand: since 1981, AIDS has killed more than 30 million people worldwide. And more than two-thirds (70%) of all people living with HIV, 25 million, live in sub-Saharan Africa, according to the Foundation for AIDS Research.

But if we are lucky enough to see another year pass without some pandemic lurching up out of nowhere to kill vast swaths of humanity, it’s mainly because of the people who now constantly watch for early signs of trouble – as well as the ones who parachute in when things go wrong to save lives and stop epidemics. They tend to be unusual characters, people who can chat casually about “flavors” of Ebola and about the addictive thrill of their work on the front lines of possible outbreaks. But
they also know firsthand what it takes to keep the world safe – and how to stay healthy themselves, even as people all around them die.

AT CDC HEADQUARTERS IN ATLANTA one day recently, as the coronavirus investigation was wrapping up, a daily map of trouble spots included an Ebola outbreak in the Democratic Republic of the Congo, Marburg fever in Uganda, cholera in Haiti, polio in Pakistan and dengue fever in Portugal. Hantavirus, which is transmitted through urine, droppings or saliva mainly from deer mice (and which also disproportionately affects men), had recently killed three vacationers at Yosemite National Park and a case of Crimean-Congo hemorrhagic fever had just turned up in, of all places, Glasgow, Scotland.

It is a dangerous world out there, especially because of the kinds of travel we now consider normal. In his office in the division of global migration and quarantine at the CDC, director Dr Martin Cetron, plays a computerised display tracking a single day’s passenger flights, streams of yellow lights gently flowing in from the farthest corners of the earth, coalescing in bright megalopolitan splotches of light, then radiating outwards again. “This is what makes me nervous,” he says.

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The Tracker: Dr Martin Cetron is the CDC’s man in charge of tracking the global migration of germs that infect, sicken and kill. As he watches his global flight tracker, he says, “This is what makes me nervous.”

Nearly a billion people a year cross international borders, some of them inevitably carrying infections. Each international flight landing on US runways also carries, on average, 1.6 live mosquitoes. In 1999, one theory holds, some of these jet-setting mosquitoes may have delivered West Nile encephalitis to New York. West Nile has since spread to 48 American states and killed about 1 500 in the US. As bad as that outbreak was, afflictions that are far more widespread may yet come if what Cetron calls the “invisible infrastructure” of disease prevention ever falters.

Simon Richardson, now 29, spent much of the past six years backpacking his way from Australia, through Southeast Asia and India, and around Africa, never experiencing anything worse than “the odd tummy bug.” He was a rafting guide in New Zealand, a trekking guide in Thailand, and a scuba instructor in Mozambique. Finally, he returned home to England and joined the British Army, ranking in the top 2% on the fitness test. Then the pain hit, in the left side of his chest.

“I thought I pulled a muscle, so I stopped lifting weights for a few weeks. Then I thought it was flu. But it just kept getting worse and worse.” He went from being able to run a mile in under five minutes to a point where he couldn’t run at all. In the hospital, doctors took a sample of lung tissue with an endoscopic tube and gave him a diagnosis of tuberculosis that “was like getting punched in the stomach.” His friends just gave Richardson a blank stare when he told them. Most remembered tuberculosis only from old movies where pale victims coughed up blood and then died.

In fact, Richardson soon learned, TB is now resurgent, largely because delayed response to the AIDS epidemic gave it fresh ground to become active again, in the lungs of patients with weakened immune systems. The disease is treatable with an antibiotic cocktail, but the regimen is long and brutal. Some 1.4 million people die of TB each year, and 8.7 million new cases appear – more than triple the annual number of new HIV infections. In South Africa 530 000 incidences of TB were reported in 2012, according to the World Health Organisation. Air travel has contributed to London’s becoming an outpost of this new epidemic; even if Richardson had stayed home, he could have picked up the disease.

If Cetron grows nervous about this sort of thing, he also cites reasons for optimism: until a few years ago, the international community had to rely exclusively on national governments to report public health emergencies. But governments often didn’t realise they had a problem until it was too late; they were also sometimes reluctant to report a problem that might hurt trade or tourism. Now, though, listening posts like the CDC’s Global Disease Detection Operations Center constantly scan news and social media in almost every language for hints of trouble. And the National Institute for Communicable Diseases has a response team that supports all nine provinces. Moreover, regulations adopted in 2005 and backed by 194 nations allow outsiders to monitor internal media for public health emergencies. If a hospital is suddenly overwhelmed, the disease commandos are ready to spring into action.

“The ability to find an outlier, to detect an early event, has probably never been better,” says Cetron. Epidemiologists zoom in on “enigmatic events where we know that people are dying,” says Kira A. Christian, a CDC global disease analyst. “We know their signs and symptoms, their demographics. But we don’t know why.” Then they investigate. As with the coronavirus, it can mean that disease detectives must travel to some of the worst places on earth at the worst possible times.
Often these specialists come from the CDC’s Epidemic Intelligence Service, or EIS, an elite corps of young doctors, nurses, veterinarians, and other health professionals. In the apocalyptic 2011 movie Contagion, Kate Winslet plays the role of a fictional EIS officer, and real-life EIS officer Dr Kevin Clarke,, says he had to tell his mother to skip the film because (spoiler alert) “my character ends up in a body bag.”

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The Detective: When an unexplained rash of deaths hits an area, epidemiological sleuths like Dr Kevin Clarke parachute in to find causes and stop the threat. One recent project: a typhoid outbreak in Zambia.

Clarke, a 35-year-old pediatrician from Connecticut, recently returned from Zambia, where he’d been on the sort of mission the EIS undertakes 80 to 100 times a year. Doctors in Lusaka, the nation’s
rapidly growing capital city, had become alarmed when their clinics suddenly filled with stricken children. The symptoms indicated typhoid fever, probably from contaminated food or water. But where and why? The Zambian government called in the EIS to help.

In Lusaka, local medical staff provided the first clues about which of the city’s densely populated new neighborhoods the typhoid victims came from. Then Clarke went in with Zambian public health workers and teams of local college students. Narrowing down the possible causes of an outbreak is mostly a matter of methodical, even mathematical, evidence gathering, says Dr Eric Mintz, head of the CDC’s waterborne disease program. “But you have to know where to look and what to ask. And when you do, those John Snow moments are out there.”

Snow, now considered the father of epidemiology, was a pioneering physician during the London cholera epidemic of 1854. At a time when most doctors held their noses and blamed the disease on miasmas – foul air – Snow went door to door to map out exactly where the cholera was striking, and where it was passing by. His map led him to a single public well that had been contaminated with sewage – and the epidemic ended.

In Lusaka, Clarke and his team used the same strategy and soon identified areas where the municipal water supply wasn’t being adequately chlorinated. Not coincidentally, they were the same areas where typhoid fever was occurring. The team alerted local authorities, and a month later the epidemic came to an end. It was, he admits, the kind of result that makes EIS work “pretty rewarding.”

So how do people like Clarke stay healthy in places like Lusaka or, another of his recent postings, South Sudan? And what can they teach the rest of us? You can protect yourself plenty of ways, epidemiologists say, and we’ll detail some of them below. But it’s worth remembering that what happens in the farthest corners of the earth may be at least as important to your survival. The viral diseases that make headlines – AIDS, SARS, Ebola and so on – almost always spill over from other species when people hunt animals for meat, turn them into pets, or otherwise make contact in ways that disturb habitats and disrupt the natural order. That’s happening far more rapidly now than at any time in our history, and we have few clues to what trouble we may stir up next. Scientists have so far identified about 2 000 virus species. But at least 3 000 more remain unidentified, and then there’s fungi and bacteria. The trick is to keep the bad stuff from spilling over into the human population.

“The old approach 10 years ago was that you just waited until lots of people started dying,” says William Karesh, a veteran of past Ebola outbreaks who now works with EcoHealth Alliance. “And then a lot of foreigners would show up wearing what looked like space suits, and that would just terrify everybody locally. A lot of them would run away because they didn’t know. Their family members were being taken away alive and never coming back. They were dying.”

The villagers who lived told stories that weren’t much different from those stories about spaceship abductions. But they were real. “Then somebody said, why don’t we talk to them between outbreaks? Why don’t we talk to them all the time? And that’s the solution – regular engagement and education,” says Karesh. So the strategy now is to have a continuing epidemiological presence out in the disease hot spots, teaching local people both to minimise environmental disturbances and to recognise trouble when it comes. Now, he says, if they run across a dead animal in the forest, they report it to health authorities instead of eating it. Local people have become the advance guards of surveillance.

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The Closer: The word “Ebola” is enough to strike fear in the hearts of many men. But Dr Stuart Nichol is not one of them. “Most of the cases that show up are not bleeding from every orifice,” he says calmly.

Outsiders still pour in to respond to an outbreak, but the approach now is more precise and less panicky. At the CDC, Dr Stuart Nichol, had just come back from an Ebola outbreak. Nichol downplayed the Hollywood “hot zone” reputation of hemorrhagic diseases: “Most of the cases that show up are not bleeding from every orifice. They are not melting down.”

But that actually makes diagnosis more difficult because the typical symptoms could just as easily be caused by common flu. So the response now is to set up a small field lab in the thick of an epidemic for rapid diagnosis. Patients are tested in the morning, “and by 5 o’clock in the evening we can tell people whether they’ll be going into the isolation ward or going home,” says Nichol, chief of the CDC’s Viral Special Pathogens Branch. “The basic approach to containing one of these outbreaks is to remove the infected people from the community and place them into isolation wards, to stop those chains of transmission.”

Is that enough? All of last year’s hemorrhagic fever outbreaks were limited to a few dozen cases, rather than the hundreds in past outbreaks. But the trouble with prevention is that you never know if you’ve done enough.

It’s still possible, says Nichol, that someone with Ebola or Marburg could catch a jet to New York or some other great megalopolitan splotch of light and start a chain of human-to-human transmission. “Would it kill a lot of people? Probably not. But the report of 10, 20, 100 cases in New York would cause significant panic. So we can’t be complacent.”

What about keeping yourself safe as an individual traveller in what can seem like a scary world? Epidemiologists going out on a posting typically consult the CDC’s own Yellow Book, the bible of recommended vaccines and medicines for countries worldwide. (Check out your destination at cdc.gov/travel.)

Men are far less likely than women to seek health advice before a trip, and that may be one reason they account for 71% of travel hospitalisations. It’s smart to visit a travel clinic to be certain that you have the right immunisations and to make sure false assumptions don’t get you into trouble. For example, some parents forgo measles immunisation for their children because they mistakenly believe it’s more dangerous than the disease. A large outbreak of measles involving around 1700 cases occurred in South Africa between 2003 and 2005 following its introduction from Mozambique. More recently, there was an outbreak between 2009 and 2011, with over 18 000 cases recorded, according to the WHO. But even an ostensibly safe destination like France reported 14 000 cases of measles in 2011, and some unprotected American travellers brought the disease home with them.

You may also mistakenly regard immunisations and anti-malarial drugs as superfluous. “You don’t even think about it,” says Rish Sanghvi, a 36-year-old biotech market researcher in California. He grew up in India until he was 16, and on a return trip there in 2011 he figured he was just going home to visit family. So he didn’t take any precautions, except to avoid raw foods and drink only filtered water. “I guess if I were going to Africa, I’d be more careful.” But it turns out that his risk was real enough.

One day early in his visit, Sanghvi was playing soccer with friends and he felt exhausted. “I thought I was going to pass out,” he says. Then the stomach problems started, followed by mild hallucinations. His brother, a physician, recognised typhoid fever and immediately put him on antibiotics. Even so, Sanghvi couldn’t keep his food down, and he was laid up for a month. Back in the US, with his weight down 30%, he spent another two months unable to do more than “sit at home and chill. Man, that’s the last time I don’t take my drugs,” he says.

Sanghvi figures he picked up the disease from the less visible things – the dairy products in a lassi drink, the chutney served with a dosa pancake, the raw onions in a sandwich. Even for experienced epidemiologists, it’s not always easy to follow the familiar advice for eating in foreign
countries – boil it, cook it, peel it or forget it. “We commonly work in refugee camps and remote settings,” says the CDC’s Clarke, “and sometimes the only food to come by is some goat stew and rice, and you may not have full control over how it was prepared.”

Foreign visitors also often end up feeling social pressure to fit in by drinking the water or eating the food. “It’s a 100-degree day, and somebody’s offering you a nice tall glass of iced lemonade, and it’s a big deal for them to offer ice because it’s hard to get,” says Jason Love, a Peace Corps volunteer in the Dominican Republic. “It’s hard to turn down from a desire point of view, and it’s hard to turn down for social reasons.” But Love ended up with a six-month case of giardia, a nasty way to say goodbye to a quarter of your body weight.

For those kinds of emergencies, a travel clinic will typically send you out with a powerful antibiotic. But antibiotics can also cause serious side effects. You may just want to wait it out. Carry salt packets and mix them with clean water to help you retain fluids. As for the social pressure, Dr Cyrus Shahpar, another EIS officer, tries to make his preference for his own water bottle seem quirky rather than rude.

Keeping yourself fit on the road can also stave off disease, or minimise the symptoms. The novelist George Orwell, in frail health and an enthusiastic smoker, wrote that his TB treatment was like “sinking the ship to get rid of the rats,” and he died of the disease 20 months later. Simon Richardson, on the other hand, took on a fundraising challenge three months into his TB treatment. On behalf of a group called TB Alert, he logged 34 000 metres on a rowing machine – the equivalent of crossing the English Channel – in just over three hours. In rowing parlance, that’s an average split time of 2:41, well on the way to recovery.

Even if exercise isn’t always possible, Lipkin (just off the plane from investigating the coronavirus in Saudi Arabia) recommends relaxation exercises to shake off the stress of travel. Eat well and stay hydrated, he says, to keep the protective tissues of the nose and mouth moist. Avoid shaking hands, and because that’s not always possible, wash your hands frequently and carry a hand sanitiser. Don’t touch your face, and for pity’s sake, don’t pick your nose or touch your eyes, especially after shaking hands. People touch their noses and other parts of the face far too many times an hour. He says you’re basically “inoculating your nose with what was in somebody else’s nose.”

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Going Viral: If a bug escapes into the human population, they’ll find and crack it here: the CDC’s Emergency Operations Center executive boardroom in Atlanta.

What about the travel nightmare of being stuck beside a passenger who’s coughing up a lung on a sold-out flight? You may wish you had tucked a paper face mask in your carry-on. But even in the middle of an epidemic, people often end up wearing such masks on top of their head because they’re so uncomfortable. The flimsy ones with a single blue rubber band also will not protect you, according to a doctor who works with tuberculosis patients. Try the more expensive filtering masks, available at hardware stores, that have two elastic straps to pull the mask snug around your nose and mouth. Accept the fact that you will look like a fool. And since you probably won’t see anybody on that flight ever again, you won’t have the pleasure of laughing last. Plus, if you end up avoiding illness, you may not even remember to thank yourself for having done the smart thing.

And there in a nutshell is the frustrating conundrum of disease prevention in a dangerous age on a shrinking planet. Doctors who cure us when we are sick no doubt deserve the glory and gratitude we lavish on them. But the bigger achievement of keeping us from getting sick in the first place goes almost unnoticed. The virus hunters and disease detectives who spend their lives at it are a kind of ghost service, engaged in shadowy, uncertain, inglorious work. Ideally, if they succeed, we never even know they were there. Or as Clarke puts it, in a philosophical moment, “If something was prevented, how do you report that it never happened?”