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Date: Tuesday, Dec. 3, 1996 FOR IMMEDIATE RELEASE Contact: John Bowsersox (301) 402-1663, jbowsersox@nih.gov
Using sensitive new diagnostic techniques, National
Institute of Allergy and Infectious Diseases (NIAID) researchers
have shown that men and women are equally likely to contract Chlamydia
trachomatis from infected sex partners. Previous studies had
suggested that male-to-female transmission of chlamydia, the most
common sexually transmitted pathogen in the United States, occurred
more often than female-to-male transmission.
"Within heterosexual partnerships, the transmission
efficiency of chlamydia appears to be bidirectional and equal,"
says Thomas C. Quinn, M.D., M.Sc., of NIAID's Laboratory of Immunoregulation
and The Johns Hopkins University School of Medicine in Baltimore,
Md.
Dr. Quinn and colleagues from Johns Hopkins and the
Baltimore City Health Department studied chlamydial infection
and transmission among couples attending sexually transmitted
disease (STD) clinics in Baltimore. The study results appear
in the Dec. 4 issue of the Journal of the American Medical Association.
Over a four-year period, 958 individuals -- STD clinic
visitors and their sex partners --enrolled in the study. The
researchers tested each individual for chlamydial infection using
two different diagnostic techniques: cell culture, which involves
incubating tissue samples from a man's urethra or a woman's cervix
for several days, and a polymerase chain reaction (PCR) test designed
to detect minute traces of chlamydial DNA.
As previous studies have shown, cell culture revealed
a significant gender difference in chlamydial infection - approximately
13 percent of women and 8 percent of men in the study tested positive
for the pathogen. PCR testing of the same samples, however, detected
chlamydia in about 15 percent of both men and women. More than
40 percent of infected men and nearly 80 percent of infected women
had no symptoms of infection.
Further evidence that chlamydia is an equal opportunity
pathogen came from analyzing the infection status of sex partners
of individuals who tested positive for chlamydia by PCR. The
researchers found that two-thirds of male sex partners of infected
females and two-thirds of female sex partners of infected males
were themselves infected with chlamydia. Women younger than 20
and those who had greater than 25 percent cervical ectopy, a condition
in which the lower cervix is covered by a type of tissue susceptible
to chlamydial infection, were most likely to contract chlamydia
from infected male sex partners. In contrast, the researchers
identified no variables associated with men's risk for contracting
chlamydia from infected female sex partners.
"These data agree with what we already know
about chlamydia - it tends to affect women in their young adult
or teenage years, when ectopy is most common," explains Dr.
Quinn. "The degree of ectopy varies among young women.
The more ectopy you have, the more susceptible you are to chlamydia.
We know that women over 20 have less ectopy and less chlamydial
infection. The big unknown in this relationship is the role that
immunity plays in susceptibility to chlamydial infection. By
the time some women have reached age 20, have they acquired sufficient
immunity to resist chlamydia? That will be the focus of the next
study."
"The similar rates of infection in men and women
in this study suggest that our thoughts about women being more
susceptible to infection may be incorrect," adds Penny Hitchcock,
D.V.M., chief of NIAID's sexually transmitted diseases branch.
"And the fact that many infected individuals were asymptomatic
underscores the need to prospectively screen for chlamydial infection,
especially to prevent pelvic inflammatory disease (PID) in women."
PID, an infection of the upper reproductive tract
that often leads to infertility, tubal pregnancy and other serious
complications, affects more than 1 million women in the United
States each year. Most cases are caused by chlamydial infection,
which is diagnosed in 4 to 5 million people in this country each
year. The actual number of cases probably is much higher, since,
as the current study shows, chlamydial infections often produce
no symptoms and thus frequently go undiagnosed. Earlier this
year, NIAID-supported researchers reported that women who were
screened and treated for asymptomatic chlamydial infections were
nearly 60 percent less likely to develop PID than women who received
treatment only after they showed clinical signs of chlamydial
infection.
The U.S. Centers for Disease Control and Prevention
(CDC) recommends widespread testing and treatment for chlamydial
infections among sexually active individuals and their partners.
In a recent report, the Institute of Medicine, a private, gateway.html
organization that provides health policy advice to the federal
government, also called for comprehensive screening for chlamydia
and other STD pathogens.
Dr. Quinn notes that diagnostic tests that use PCR
or ligase chain reaction (LCR), a similar method for amplifying
and detecting trace amounts of genetic material, could prove to
be important tools for controlling the spread of chlamydia. Since
the current study was begun, two such tests for detecting chlamydia
in urine samples have become available commercially. Because
they do not require patients to undergo an invasive tissue-sampling
procedure, urine-based tests could lead more people to be tested
for chlamydial infection.
"It's clear that PCR and LCR tests are significantly
more sensitive compared to culture," says Dr. Hitchcock.
With these new, non-invasive tests, coupled with single dose
antibiotics for treating infected individuals, we have an extremely
effective approach to chlamydia prevention and control."
Dr. Hitchcock adds that NIAID is committed to supporting
research aimed at applying PCR and LCR technology to the development
of even better non-invasive and inexpensive diagnostic tests for
chlamydia and other STD pathogens.
NIAID is a component of the National Institutes of
Health. NIAID conducts and supports research to prevent, diagnose
and treat illnesses such as AIDS and other sexually transmitted
diseases, tuberculosis, asthma and allergies. NIH and the CDC
are agencies of the Public Health Service, U.S. Department of
Health and Human Services.
NIAID press releases, fact sheets and other materials
are available on the Internet via the NIAID home page at www.niaid.nih.gov.