Clues to how stomach
bacterium spreads found in unsavory places
BY KRISTIN WEIDENBACH
Stanford researchers are
searching in some unsavory places to solve the riddle of
how a common bacterium that causes stomach ulcers and
perhaps some kinds of stomach cancer jumps from one human
to another. The most obvious places the bacteria may be
hiding are the vomit, feces and saliva of infected
people.
"One of the real
dilemmas of this organism is how it gets into people; how
they get infected," said Julie Parsonnet, MD,
associate professor of infectious diseases and geographic
medicine in the department of medicine and of
epidemiology in the department of health research and
policy. "We want to figure out how it's transmitted,
and the first step is to see how it's getting out of
people. Since it lives in the gut, we presume it's
getting out through the mouth or in stools,"
Parsonnet said.
Sixteen healthy people
infected with Helicobacter pylori, which is carried by 50
percent of the population, volunteered for Parsonnet's
study. Like the majority of those carrying the bug, these
people showed no signs of infection, but evidence of the
bacteria in their breath and antibodies in their blood
confirmed H. pylori's presence. Ten people who tested
negative for the bacteria were also studied as controls.
The volunteers were
admitted to Stanford's General Clinical Research Center
for 24 hours, and Parsonnet and her team collected all
manner of biological samples for analysis.
The researchers first
screened normal feces from each of the 26 volunteers.
Helicobacter thrives in the stomach's acidic
surroundings, but its survival outside this environment
is limited. Normal stools can take days to traverse the
colon and, not surprisingly, the researchers found no
live bacteria in these samples. But, when given a
substance that induced diarrhea, 11 of the 16 infected
people passed stools from which the bug could be grown.
Parsonnet believes that
diarrheal stools are expelled so quickly from the small
bowel and stomach that live bacteria can be transported
into the external environment. According to Parsonnet, H.
pylori can survive outside the body for a few hours,
which may be sufficient time to infect anyone who
contacts the sample.
The researchers also gave
the infected people, and one uninfected volunteer, a
substance to make them vomit. The results showed that
vomiting is a potent way of discharging millions of
infectious H. pylori into the environment. The
researchers found live bacteria in samples from all of
the infected individuals. The concentration of
Helicobacter in vomit was also much greater than in
feces.
Transmission of H. pylori
by this route supports what scientists already know about
Helicobacter infection. Close living quarters, the
presence of many siblings and poor household hygiene are
factors known to increase the risk of infection.
Children, who tend to vomit and "spit up" more
frequently than adults, are particularly likely to
transmit the bug to other children, said Parsonnet.
"Imagine children in day care together; one throws
up and another child is right next to him or her. Or
contaminated toys are not cleaned up properly," she
said.
Infection during childhood
leads to more opportunities to pass the bug on to others
and also increases the likelihood of serious disease,
said Parsonnet. Although many people carry the bug
without symptoms, a combination of factors -- such as the
particular strain of H. pylori and the person's diet and
genetics -- can lead to ulcers and/or stomach cancer.
Infection at an early age gives the bacteria more time to
wreak havoc.
Analysis of air and saliva
samples completed Parsonnet's battery of tests. Although
the researchers could detect traces of bacteria in the
saliva of approximately half of the people carrying H.
pylori, mouth-to-mouth transmission is not considered a
primary route of infection. Sampling the air surrounding
infected volunteers confirmed the pivotal role of
vomiting in the potential spread of the bacteria. The
researchers found no evidence of the bug until the onset
of vomiting, when air sampled from approximately a foot
in front of the volunteers yielded Helicobacter that had
been exhaled in tiny aerosol droplets.
Scientists who study H.
pylori around the world believe that the rate of
infection is declining, and the results of Parsonnet's
study suggest that a reduction in gastrointestinal
diseases that cause vomiting and diarrhea may be an
important cause of that decline. "H. pylori is very
common in developing countries where diarrheal diseases
are common," said Parsonnet. "Less
child-to-child contact and better hygiene means that
opportunities for getting diarrheal disease and
transmission of H. pylori are decreasing."
Parsonnet is continuing
her research with a follow-up study to determine if H.
pylori is shed more readily from people with low levels
of acid in their stomach. She also plans to find out if
some strains of H. pylori are more transmissible than
others.
The results of the study
were published in the December 15 issue of the Journal of
the American Medical Association. Thomas Haggerty, a
research technician, and Haim Shmuely, MD, a visiting
scholar in Parsonnet's lab, were co-authors of the study.
Volunteers were paid $250 for participating. Funding for
the study was provided by the National Institutes of
Health and the Centers for Disease Control and
Prevention. SR
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