ATLANTA -- The CDC no longer recommends serial ultrasounds to check for fetal abnormalities in asymptomatic Zika virus patients with a negative IgM test, according to the president of the Society of Maternal Fetal Medicine (SMFM).
At its meeting here, SMFM held a special session to discuss how the may impact their clinical practices, covering such topics as asymptomatic travelers, symptomatic travelers, and women from endemic areas.
The panel was led by , SMFM president. In an interview with 番茄社区, Riley said that the CDC was no longer recommending serial ultrasounds to check for fetal abnormalities in asymptomatic patients with a negative IgM test. The latter detects the first antibodies produced in response to a viral infection.
"The guidance is more on serology, but we're still using ultrasound to see if the baby is affected," she explained. "The main difference is that instead of going straight to ultrasound, there is still that patient who might be able to avoid multiple ultrasounds if, in fact, she is asymptomatic, has been exposed, has a negative IgM and a negative ultrasound; she might be able to just be done because the likelihood that she has infection is incredibly low."
Asymptomatic Travelers
Despite the guidance from the CDC to begin with an IgM test, a meeting attendee from Houston said that, in her area, the plan is to go to straight to polymerase chain reaction (PCR) testing, which can detect the virus within 7 days of exposure.
"We admit we don't have perfect testing right now, and there's an argument in either direction," the attendee stated.
But panelist , of the Duke University School of Medicine in Durham, N.C., cautioned that after 7 days -- 11 at most -- the virus will no longer be in the patient's system, which is why the CDC had recommended testing for antibodies with serology testing versus testing for the virus.
"If you traveled and it's a week later, you've already cleared organisms," he said. "In an asymptomatic population, serology is way to go."
There is currently no IgG test, which can be done later after exposure, for Zika virus so clinicians were concerned about the potential for cross-reactivity in an IgM test with similar flaviviruses transmitted by mosquitoes.
"A patient may have been immunized for Japanese encephalitis or had previous exposure to dengue or yellow fever," said panelist , of the CDC's Division of Reproductive Health in Atlanta. "So a positive IgM should be followed up with another test for clarification, and it's not going to be perfect."
When another meeting attendee asked why serial ultrasounds shouldn't be done to avoid the potential for false-positive tests, Riley pointed to the expense involved in serial testing, as well as the small likelihood that an asymptomatic patient, with a negative IgM test and a normal ultrasound 4 weeks on, would have a fetus who would suddenly develop microcephaly at a later stage.
"Do we want to do ultrasounds every 4 weeks on someone who is highly, highly unlikely to have anything going on?" Riley said. "That's going to be a healthcare expenditure."
Symptomatic Travelers
In symptomatic patients who had traveled to affected areas, panelists and participants discussed amniocentesis in the case where a mother had two positive tests, to see if the Zika virus had been transmitted to the fetus.
When an attendee pointed out the greater risk of pregnancy loss with amniocentesis even in a normal pregnancy, Heine said that clinical judgment would be important, because the risk of infection varied greatly, depending on the gestational age of the fetus. A fetus infected in the first trimester would be worse off than one who was infected in the third trimester, where it would be able to have some immunity from its mother.
"If I have a 26-week fetus and the mother seroconverted, I may think back, knowing that a fetus in the third trimester can mount an immune response and mom can transfer antibodies," he said. "We know there are loss rates; we know if we do thousands of amnios, we're going to have some losses of normal kids. There is a sweet spot for viruses crossing the placenta that will cause damage, which is somewhere in second trimester, but I don't know if that's going to hold true for Zika."
Another attendee asked if a patient tested positive for Zika, should an amniocentesis be done right away? Panelist , of Women & Infants' Maternal Fetal Medicine in Providence, R.I., said she would wait a few weeks.
However, the panel had no answer as to whether an amnio should be done if a patient has a positive serology test, but a negative ultrasound.
Riley then reminded the attendees that patients are not really concerned whether their baby has Zika virus, but whether their baby will have normal development.
"At the end of the day, the patient doesn't want to know is my baby infected, but is my baby affected?" she said. "Even if you stick a needle in there and get back a virus, you don't know."
Another concern was about transmission in semen through symptomatic partners. The CDC suggestion that people use condoms, or practice abstinence throughout the remainder of the pregnancy, was met with with great skepticism, with one participant noting that the recommendation would not win favor with patients.
"Couldn't we do a PCR assay on the partner's semen instead, and then if that's negative, they're good to go?" he asked.
Callaghan advised against this. "The big studies that are going to have to happen are in endemic countries where we're going to learn about the virus' existence in semen," he said. "I can't emphasize the...uncertainty about this enough -- this is really unprecedented."
Endemic Areas
Meeting attendees expressed concerns about cases of Zika virus in the U.S. "What will constitute an endemic area if it starts coming to the [U.S.] -- will it be five cases of transmission or will it be latitude-based...," one participant asked.
Callaghan said that the CDC would provide guidance when appropriate, but guessed that "the threshold will be low" for declaring an endemic area.
One attendee who had recently returned from a conference in Brazil reported that maternal fetal medicine doctors were pulling out their cell phones to show ultrasounds of fetuses with microcephaly from potential Zika virus exposure.
But Heine pointed out that there may have been some overreporting of microcephaly cases in Brazil due to a changing definition of microcephaly.
"The put out a table with all the cases on it, and Brazil was reporting on 33 cm [head circumference] or less, which is our 10th percentile," he said. "On December 10, they changed it so it's now 32 cm or less, which is our third percentile. So, did this happen? Yes, I've seen the pictures on the news, but there was probably some overreporting going on."
Overall, the panel said the first thing clinicians should do when they return home from the conference is to call their state epidemiology departments to find out the testing procedures, as all of the testing for Zika virus is going through individual state health agencies. Results will then be sent to the CDC.
"Everyone should keep a log, because more information may come out next month, and these guidelines may change," Riley stressed. "If you need to call patients back, it'd be easier to know who you counseled."