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What is going to happen to us? Even in the short term,
with diseases we know a lot about, that's a tough question to
answer. Besser, Davis, and Call run a surveillance project aimed at
detecting rising strains of Salmonella and perhaps heading
off the next outbreak. The microbe's biology makes that difficult;
human actions make it even harder. Salmonella is a
"reportable" disease in humans, which means that doctors are
legally required to report it to public health authorities when
they diagnose it; but if the patients don't come in, the doctors
have nothing to report.
"If you get diarrhea and the cramping and all that, how many
people go to the doctor?" asks Call. Most likely, he says, "You
wait it out, and you're fine again [after a few days], and you
never know what it was."
"It's way underdiagnosed and underreported," agrees Davis. She
says the rule of thumb is that Americans experience 38 times more
cases of Salmonella infection than are ever reported.
Monitoring of livestock infections is even more haphazard.
Salmonella infections in animals are not reportable, so the
WSU team relies on voluntary collections by vets and livestock
owners for those samples.
"It's called 'passive surveillance," Besser says. "Farmer A
might be really attuned and send in [samples from] the first animal
that looks cross-eyed at all, and Farmer B might lose 10 animals
before he thinks it's important enough to call a vet. A lot of
farmers don't even have an established relationship with a vet. So
we know we're probably missing an awful lot."
The team also monitors healthy cattle herds and water and
waste-management systems. What they've found there complicates the
picture even more.
On-farm waste lagoons often contain Salmonella, which
makes sense, since they receive feces from hundreds or thousands of
cattle and other farm animals. But Salmonella isn't just a
denizen of cattle farms.
"When we go down to the Pullman sewage treatment plant and get
untreated water coming in, more often than not it's positive for
Salmonella," says Besser. So does the water coming out of
Pullman homes has as much Salmonella in it as the water in
farm waste ponds? "At least as much, if not more. A little bit
different composition of strains," he says. "It's there. It's
passing through us all. We find E. coli O157:H7 too, in
Pullman's untreated sewage. It's not as common as
Salmonella, but it's also going through us on a regular
basis."
E. coli O157:H7. That's the bug that tainted burgers at
Jack in the Box in 1993, and that imperiled our spinach salads in
2006. In humans it causes symptoms ranging from cramping and
diarrhea to a potentially lethal form of kidney failure. O157:H7 is
especially dangerous for kids. It appears to infect us more easily
than Salmonella; with E. coli the infectious dose
appears to be just a few hundred cells.
Besser says measures taken since the Jack in the Box incident
have greatly reduced our chances of getting meat tainted with E.
coli (or Salmonella or other pathogens as well). A major
source of contamination was found to be dust on the animals' hides;
when cattle were skinned at the slaughterhouse, dust (and harmful
bacteria) settled on the meat. Now, carcasses receive a
pasteurizing wash after skinning.
That may be our best line of defense, because Besser's work
shows that it's unlikely we can ward off E. coli outbreaks
by identifying the bug in cows before slaughter. Nearly every herd
his team has examined carries it.
"Most of the work I've been doing has been going out, working
with farmers to find things they can do to reduce the chances that
their cattle are carrying O157:H7," he says. "We haven't found any
magic bullets after 15 years of work."
He says the often-heard claim that hay- or grass-fed cattle are
less likely to carry O157:H7 than cattle that are fed grain is
"just not true, in our experience. Grass-fed cattle are as likely
to be positive as grain-fed herds." He says numbers of E.
coli vary with the season (more in summer than winter) and age
of the cow (more in calves than in adults), but that's about it for
trends.
So O157:H7 simmers harmlessly along in the cow population, every
now and then bursting out in humans. In the summer of 2006, a
couple of hundred people across the nation were sickened by E.
coli from fresh spinach, in an episode that may say more about
our ability to spot trouble in a hurry than it does about dangers
in our food supply.
"There were 200 cases scattered in 50 states, and it was picked
up after the first 20 or 30 cases," marvels Besser. "We would never
have detected it in the past. Never. To put that in perspective, in
the average year the CDC [Centers for Disease Control] thinks that
there's somewhere over 50,000 cases of E. coli O157:H7
disease in the United States. The vast majority of them don't get
reported."
He says the CDC's report on the incident found that the E.
coli originated on a cattle farm half a mile from the spinach
field; the bugs were probably carried to the spinach by feral pigs
walking through on their way to a water hole.
Now that we know where it came from, what does that tell us
about how to stop another outbreak? Not much, says Besser.
"There's not a single thing we can tell that farmer to do to
reduce the likelihood that his cattle will carry E. coli
O157:H7. It seems to me that identifying him as a culprit in the
outbreak is really not fair."
Although the strain that caused the outbreak was especially
nasty, with a lot of sufferers requiring hospitalization, Besser
thinks the panic that ensued was a bit overblown. He, for one,
didn't stop eating spinach.
"I think people shouldn't bear unnecessary risks, but there are
some risks we accept every day, like crossing busy streets or
driving a car," he says. "To some extent, we can afford to worry
about 200 cases of ill people out of 250 million, because we've got
lots of resources and not very many other scary things to worry
about. Throughout history, I presume that that level of risk would
have been just ignored most of the time. And in most parts of the
world now, it would be ignored."
In most parts of the world, the number of people who die from
infectious diseases is beyond comprehension. Malaria alone kills
about a million people every year, most of them young children.
"It just dwarfs what we're talking about," says Besser. Then he
adds, "But you know, this bug [E. coli O157:H7] sometimes
kills our kids. That's a terrible thing, even if it only happens
once."
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