Bedbugs Aren’t as Contagious as You Think

Health and medicine explained.
Oct. 6 2011 7:16 AM

The Brown Peril

How contagious are bedbugs, really?

Illustration by Robert Neubecker.

Illustration by Robert Neubecker.

In the months after the Civil War, the New York Times sent several writers to the South. Between covering horse theft in Richmond and pondering whether one could tell a “yank” from a “reb” based on physiognomy, the reporters grumbled about an odious feature of their hotels: bedbugs. One wrote that he had come “from frequent experience” to view bedbugs as a Southern institution no less entrenched than slavery. Another begged readers for the name of a decent North Carolina inn, complaining that the “natives” there allowed bedbugs “full sway” such that “they now rule the State during the hours usually devoted to slumber without opposition.” He said he had tried to adopt the local custom of thinking “them’s only chinch-bugs” but failed. “[A]nd now at 8 o’clock in the morning of the 13th day of March, 1866, I am seated at my table, having been driven out of bed four times already … writing to soothe my rage and drown the blasphemy which wells up from my heart on account of ‘them chinch-bugs.’”

Not to doubt the yank reporters, but it is not clear chinch conditions were really less blasphemous to the North; one 1865 article said it was common to see bedbugs “crawling about the clothing of lawyers” in D.C. courtrooms. In that era, housewives swapped extermination tips alongside pudding recipes in newspaper household columns. Everyone had bugs, and it was very embarrassing. In 1908, a doctor with the New York City Department of Health had the temerity to declare in the Times that bedbugs had sacked Gotham. He assured readers that “a short zoological excursion” through any apartment or hotel suite would yield evidence of the “brown peril.” He exhorted New Yorkers to admit they had bedbugs, and stop insisting that the insects on the guestroom sheets “of course had been brought in from outside.”

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Blame the guests, blame the rebs, blame any other unfamiliar person or place. Amid the current outbreak, this fear of catching bedbugs from strangers has reached new heights. In August, Animal Planet ran a show called “Bedbug Apocalypse” that warned, “There’s really nowhere to hide" and interviewed a woman so addled by biting houseguests that she insisted on steam-cleaning her chairs before she would sit. One talking head said that if we don’t act fast, “pretty much you can be guaranteed that you are going to take bedbugs home with you.” It’s a contagious fear: According to common belief, bedbugs are “world-class hitchhikers”—they spread so readily that sufferers get treated like outcasts. But is it true? Is a case of bedbugs really that easy to catch?

Investigating the question entails a consideration of bedbug epidemiology. Public health experts often consider three key factors when estimating whether a plague will spread or die out: the rate at which people come into contact with the pathogen, the duration over which an infection remains contagious, and the inherent transmissibility of the bug. Multiply these three factors together, and you get a value, called R0 (the basic reproduction number), that tells you the average number of people who will be infected by any one case. If R0 is less than 1, the contagion peters out. If it is greater than 1, the infection can spread.

We already know that R0 for bedbugs is above 1, since the plague has been spreading. In the current epidemic, hotel infestations have been key sentinel cases. Budget inns in West London became early prey for Cimex lectularius in 1997. Four years later, in 2001, outbreaks in big-city U.S. hotels popular among international travelers hinted that the resurgence was global—and caused some to conclude the bugs came from abroad. Looking back at the equation above, hotels have a high “contact rate”—they welcome a lot of strangers into bed—so rooms there are at elevated risk of infection. Some of these early outbreaks tended to linger, boosting R0, because exterminators at that point had little bedbug experience and infestations were not always completely eliminated.

But what about the last factor—the natural infectiousness of the pathogen? If you stayed in a hotel that had bedbugs—if you curled up in one of its bug-infested beds—what would be your chances of bringing them home with you? That is to say, are bedbugs highly “contagious,” like chicken pox? Or are they harder to pass along, like poison ivy? If we knew exactly how transmissible bedbugs are, we’d have a better sense of whether the Bedbug Apocalypse is really nigh. More importantly, we’d know how wary to be of motel beds, movie theater seats, and hugs from bug-afflicted buddies.

Scientists have examined the medical consequences of bedbug bites and investigated their potential to spread disease. (There is no evidence they do, though bedbugs have been accused, over the years, of spreading everything from cholera to polio to bubonic plague.) Few have studied their infectiousness, however. Many of the bedbug stats we hear originate from data gathered before World War II—complete with tales of zombie bedbugs surviving for three or four years without food—or ominous press releases from the pest-control industry (dutifully transcribed by leading newspapers) warning of bedbugs on trains, bedbugs in taxis, bedbugs everywhere! The average media consumer might be excused for thinking bedbugs are as unstoppable as the contagions spawned in Hollywood’s gray matter. Fortunately, it’s not true.

Clive Boase, a British pest consultant who works with one of the U.K.’s largest hotel chains, says managers of busy properties often assume there’s no way they can avoid catching bedbugs. They may note with a wink that some of their guests come from other European countries or otherwise have questionable hygiene. If you move enough grubby strangers through a bedroom, they say, then one of them will surely infect it. So Boase ran a test: He selected several hotels with bad bedbug problems, assiduously eradicated the pests with insecticides, and then monitored the premises for 12 months to see how long it took for the bugs to be reintroduced. The plague never came back, not even after one property had served nearly 100,000 new customers. “I’m not disputing the fact that bedbugs are spread by people. … But I believe that the reinfestation rate is much lower than the pest-control industry would often have us believe,” he says.

Another data point comes from New York City’s Department of Education, which maintains a kind of bedbug surveillance over its schools: teachers and staff are required to report bug sightings to the city, even if they've seen just one lonely insect. During the 2010-11 year, there were 3,590 confirmed reports of bedbugs in the school system’s 1,200 buildings, which are used by a little over a million students daily. How many of these cases resulted in the establishment of a full-blown colony on school grounds? Only once did an infestation bloom—seven bedbugs were discovered making whoopee in the closet of a Queens high school last December. Gotham’s vaunted serum-suckers thus gained a foothold in only 0.03 percent of their known school forays. Even this low figure may be an overestimate. No doubt other trespassers went undetected, ending their days in a quiet corner crack, gasping for a sup of blood. (Although bedbug lore says they can go for years without feeding, in reality they may last only a month or two.)

The notion that it may be harder for bedbugs to bivouac in dwellings than we have often imagined is supported by preliminary research into bedbug population genetics presented at a recent pest conference in Brazil. North Carolina State University entomologist Ed Vargo has gathered bedbug specimens from dozens of sites up and down the East Coast and analyzed their DNA to trace the outbreak’s origins and spread. In the infested apartment buildings he studied, he found that all resident bedbugs were close kin, even across widely divergent floors. That suggests they all arose from a single pregnant female or a handful of her eggs following a one-time hitchhike onto the premises. If successful bedbug invasions were common, Vargo says, he should see more genetic diversity. “It’s not like these things are being introduced constantly … it seems like these introduction events are probably kind of rare,” says Vargo.