Associated Press (02.10.2011) - Wednesday, February 16, 2011
A CDC analysis of data from five US laboratories that used an
alternative method of screening for syphilis found it returned
a higher number of false-positive results than expected.
Some labs seeking to reduce time and labor required for
syphilis screening have adopted a reverse sequence of
screening in which the treponemal enzyme and
chemiluminiescence immunoassays (EIA/CIA) is performed first,
followed by testing of reactive sera with a nontreponemal
test. CDC recommends screening with a nontreponemal test like
the rapid plasma reagin (RPR) or Venereal Disease Research
Laboratory (VDRL) test, followed by confirmation using one of
several treponemal tests.
From 2006 to 2010, CDC researchers looked at data on reverse
sequence testing in populations with high and low syphilis
prevalence. Three sites served patient populations with low
syphilis prevalence (large managed care organizations), and
two sites served populations with high prevalence (including
people with HIV and men who have sex with men).
A total of 140,176 specimens screened with EIA/CIA were
included; of these, 4,834 (3.4 percent) had a reactive test
result. Among them, 2,743 (56.7 percent) were RPR-nonreactive,
with additional confirmatory treponemal testing showing 866
(31.6 percent) were nonreactive, suggesting the initial
EIA/CIA result was false-positive.
According to CDC, "Among discordant sera, the rate of
nonreactive confirmatory treponemal tests was 2.9 times higher
in a population with low prevalence of syphilis, suggesting
that the low-prevalence population had a higher percentage of
Reverse sequence screening does have one advantage: "It
doesn't miss people who are infected," said Dr. Karen Hoover,
a CDC epidemiologist and study co-author.
"CDC continues to recommend that nontreponemal tests be used
to screen for syphilis and that treponemal testing be used to
confirm syphilis as the cause of nontreponemal reactivity. ...
However, if reverse sequence screening is used, CDC recommends
that a specimen with reactive EIA/CIA be tested reflexively
with a quantitative nontreponemal test (e.g., RPR or VDRL). If
test results are discordant, the specimen should be tested
reflexively using the [Treponema pallidum particle
agglutination] test as a confirmatory treponemal test," the
The report, "Discordant Results from Reverse Sequence Syphilis
Screening - Five Laboratories, Unites States, 2006-2010," was
published in CDC's Morbidity and Mortality Weekly Report