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Screening for syphilis
Definition of syphilis
La syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. It remains fairly rare (around 500 cases in France in 2009), but it is on the rise everywhere in developed countries. It mainly affects gay men, nearly half of whom are HIV positive. However, the prevalence is increasing in all populations. The bacterium is very contagious if you have unprotected sex.
The manifestations of the disease vary greatly from person to person, and there are several distinct phases: incubation, primary, secondary and tertiary phases, interspersed with lag phases.
We distinguish as follows:
- la early syphilis (primary, secondary, early latent syphilis less than one year)
- la late syphilis (tertiary syphilis, which occurs without treatment after several years, and latent for more than a year)
Symptoms are variable and not all phases are mandatory.
About 3 weeks after infection, a small superficial wound 5 to 15 mm in diameter called chancre appears at the site of infection (mouth, penis, vagina or anus). The chancre is usually not painful and can go unnoticed, especially if it is inside the mouth, for example.
General signs are possible, including fever, headache, swelling of the glands, spleen and liver.
If the patient is not treated, the chancre disappears but the disease can progress to later stages.
Syphilis can cause serious complications in the long term (damage to the spinal cord, cranial nerves, eye damage).
When the disease affects the pregnant woman, complications for the fetus and the unborn child are also potentially serious (especially after 14-18 weeks of pregnancy). In addition, there is a significant risk of neonatal transmission. The death rate in the infected fetus or infant reaches 40%.
Why test for syphilis?
Syphilis can cause serious complications and in France it is a notifiable disease.
In addition, there is a risk of maternal-fetal transmission, so screening for the disease is systematic in pregnant women.
What results can we expect from a syphilis screening?
The diagnosis of syphilis is mainly based on serological analyzes (blood sample) aimed at detecting anti-treponema antibody (the bacteria in question). Several methods are used, mainly:
- la VDRL (Venereal Disease Research Laboratory), which is not specific for treponema
- la TPHA (Treponema pallidum Haemagglutination Assay), specific for treponema
- la FTA (Fluorescent Treponemal Assay), also specific for treponema. It is mainly used for diagnosis in newborns or in the presence of a chancre at the very beginning of the disease, if the VDRL and TPHA tests are negative.
The specific test (TPHA) and a non-specific test (VDRL) are usually combined to confirm the diagnosis of syphilis.
However, these two tests can be negative at the very beginning of the chancre (first 7 days). They are always strongly positive in the secondary syphilis stage.
Unfortunately, serological analyzes are not always easy to interpret (possibility of false positives) and do not make it possible to differentiate between the different sub types of Treponema pallidum (there are other non-venereal “treponematosis”). The diagnosis is however clear when several markers (VDRL + TPHA or FTA) are positive at high levels.
Other methods like dark field microscope or theimmunofluorescence allow for their direct detection of the treponema at the onset of the disease, after removal from the chancre.
Tests to look for the presence of other sexually transmitted infections such as HIV or hepatitis C will be systematically carried out.
What results can we expect from a syphilis screening?
When the diagnosis of syphilis is suspected (often even before being confirmed), treatment should be initiated.
It is primarily based on intramuscular injections of antibiotics (penicillin). Other antibiotics will be given in case of allergy to the penicillin.
The efficacy of the treatment should be checked by clinical and laboratory examination after 6, 12 and 24 months.
In pregnant women, biological and clinical monitoring is monthly.
Read also : Our fact sheet on syphilis |