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|Posted: Fri Jul 07, 2006 9:35 pm Post subject:
Tests for mumps prove unreliable
Tests for mumps prove unreliable
DAVID WAHLBERG firstname.lastname@example.org
July 6, 2006
Wisconsin's mumps outbreak has turned into a mystery: Many of the 251 people
thought to have contracted the rare disease this spring may not have had
mumps after all.
Tests at the state Laboratory of Hygiene have produced numerous false
positives, said state health officials who are reviewing the results with
the U.S. Centers for Disease Control and Prevention.
State officials are also checking medical charts of patients thought to have
had mumps to see if their symptoms fit.
Mumps usually causes swollen glands in the cheeks, along with fever,
headache and muscle pain. Its rare complications include brain inflammation,
deafness and swelling of the testicles, ovaries or breasts.
Some people who tested positive may have had a different virus related to
the flu, officials said.
Another factor is complicating the situation: Other test results may have
been false negatives, so some people with actual mumps may have been
Test results from other states are also under review, CDC officials said.
The true extent of the Iowa- centered outbreak - which hit several
Midwestern states, peaked in late April and wound down last month - may
never be known. Most of those stricken were in their late teens or early
But even if many of the more than 4,700 cases reported nationally are found
invalid, it appears a real outbreak did occur, officials said. The country
has seen fewer than 300 annual cases of mumps in recent years, after routine
childhood immunization started in 1977 and was expanded in 1989.
"We know we had mumps," said Dan Hopfensperger, immunization program manager
for the Wisconsin Division of Public Health. "But our numbers are likely to
Of Wisconsin's 251 cases, 204 had been confirmed by lab testing,
Hopfensperger said. Dane County had 76 reported cases, half of those in
David Warshauer, assistant director of communicable diseases at the state
lab, said the confusion stems from different testing kits used by various
labs. Since labs hadn't tested much for mumps in many years, they had little
opportunity to assess the reliability of the kits until this year, he said.
"No laboratory test is 100 percent specific," Warshauer said. "You start
running large numbers of tests and you start finding these problems."
The state lab has shipped several patient samples to the CDC and to a lab in
Iowa. Scientists in both locations found fewer positives than the Wisconsin
lab did, meaning some of Wisconsin's positive results are wrong, Warshauer
The CDC is reviewing results from Wisconsin and other states, a process that
could take several months, said Paul Rota, a microbiologist with the
Some false positives may have been from people infected by a parainfluenza
virus, which commonly causes respiratory disease, Rota said.
Workers at Wisconsin's state lab, on the UW-Madison campus, became
suspicious about the tests in late April, Warshauer said. About 100 samples
were positive for antibodies to mumps at the time, but in a different
cell-culture test the virus grew in only two or three of the samples.
Yet when lab workers checked the medical records of the patients, most had
the signature swollen cheeks, Warshauer said, so the lab continued the
Later, after doctors said some patients testing positive appeared to not
have mumps, the state lab investigated further, Warshauer said. Workers
tested 30 samples collected last year for possible West Nile virus; 19 were
positive for mumps, a highly unlikely finding.
"That's what put us over the edge," Warshauer said.
On May 10, the lab discontinued antibody testing for mumps.
False positives are the main problem under review, but Warshauer and Rota
said some people with mumps - in particular, those who have been
vaccinated - may have tested negative.
The vaccine is considered to be 80 percent to 90 percent effective, so some
people who have been immunized can get the disease. They are unlikely,
however, to produce the fresh antibodies to a new infection that are
detected in the test, the scientists said.
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