Q&A: CDC publishes first recommendations for syphilis testing amid spike in cases
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Key takeaways:
- Recent CDC data showed a 17% increase in syphilis in the U.S. from 2021 to 2022.
- New syphilis testing recommendations from the CDC will set a baseline for syphilis testing in the U.S.
For the first time, the CDC has published recommendations on laboratory testing for syphilis.
The recommendations were published a week after the CDC released 2022 surveillance data on sexually transmitted infections, which showed that reported cases of chlamydia, gonorrhea and syphilis in the U.S. surpassed 2.5 million for the third time in 5 years.
There was a 17% increase of syphilis cases in all stages in 2022, and a 30.6% increase in cases of congenital syphilis, the data showed.
According to the CDC, the new syphilis testing recommendations are meant to be used by clinical laboratory directors, laboratory staff, clinicians and disease control personnel who “must choose from multiple testing methods, establish standard operating procedures for collecting and processing specimens, interpret test results for laboratory reporting, and counsel and treat patients for syphilis.”
We spoke with John R. Papp, PhD, a health scientist in the CDC’s the Division of STD Prevention, about how the new recommendations could impact syphilis testing in the U.S.
Healio: What is syphilis testing like now in the U.S.?
Papp: A survey published in 2021 by the Association of Public Health Laboratories reported that there were over 1.2 million syphilis tests performed by public health laboratories in 2016. There have not been any recent surveys published, and this number is an underestimate because it does not account for syphilis tests performed by private and hospital laboratories.
Most serologic-based testing for syphilis, which are tests that detect antibodies to the causative bacterium for syphilis, Treponema pallidum, are based on principles learned over 50 years ago. The technology has evolved to better detect these antibodies through increased sensitivity and/or automation.
Despite advances in serologic testing, there continues to be a dearth of direct detection tests (which confirm presence of the virus itself, eg, nucleic acid amplification tests) and point of care tests (which can provide results in minutes of the specimen being taken, and without sending a specimen to a lab).
Additional innovation, research and investment in diagnostics is critical to prevent and control STIs. Equitably stopping the syphilis epidemic and addressing the nation’s broader STI challenges require a coordinated and sustained effort shared by federal leadership, state and local health departments, health care systems, providers and private industry.
Healio: How might the recommendations improve it?
Papp: These lab recommendations for syphilis testing are the first published by the CDC, and they set a baseline for syphilis testing in the U.S. Serologic testing for syphilis is complicated because some tests detect antibodies that rise during infection and drop after treatment and other test types detect antibodies that remain high after infection despite treatment.
The CDC recommends that these different test types must be used in combination so that results can be better used by a health care provider when evaluating a patient for syphilis.
The recommendations also highlight the need for additional tests such as direct detection tests and point-of-care tests.
Healio: What are the major recommendations?
Papp: Specimens should be diluted in some serologic test types to reach an endpoint, that is, when no further antibodies are detected in the sample, so that the result represents the level of antibodies the patient has to syphilis. This is important because these antibody levels will drop if the patient is effectively treated, and health care providers use these results to monitor if the patient is cured of syphilis.
Serologic tests that detect different antibodies to the bacterium must be used in combination so that a health care provider can properly diagnose syphilis. There are different approaches to the sequence of serologic tests and the recommendations provide information for laboratories to consider when deciding on the most suitable approach.
Healio: The authors say wider availability of point-of-care tests could expand screening for syphilis and reduce time to treatment. A couple of these tests are cleared for use in the U.S. Why aren’t they being used more?
Papp: Some tests may not be able to distinguish from a past infection of syphilis that was effectively treated because they detect antibodies that do not decrease after treatment, so interpretation may be challenging by some health care providers. Studies on the use of these tests in field settings were limited, and with additional scientific evidence, further guidance may be provided on how these tests should be used in different communities.
Healio: How can we get these tests in the hands of more labs and screening programs?
Papp: Laboratories should use traditional tests as highlighted in the recommendations. Point-of-care tests should be reserved for field programs and not used in a laboratory setting. For screening, the current point-of-care tests cannot distinguish from a previous and successfully treated case of syphilis, so their application may be limited in some communities.
We know from the most recent STI data that the vast majority (86%) of syphilis cases were diagnosed outside of STI clinics in 2022. Health workers in a variety of settings — including primary care, EDs and community health, correctional and drug treatment programs — can play a vital role in stopping the syphilis epidemic when they expand efforts to test and treat people for syphilis.
To turn the syphilis epidemic around, we have to meet people where they are with syphilis screening and testing, and point-of-care tests have tremendous potential for helping with this — but they have to reach the people who need them.
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