1 in 5 Syphilis Tests are Wrong

A feature on the MSNBC web site warns that health officials in the US have issued a press release to say that a fifth of cases diagnosed positively for syphilis since the 1980s were, in fact, negative.

The Centers for Disease Control and Prevention (CDC) issued a statement following a study of five different US laboratories. The studies showed that around 18% of patients that were diagnosed for syphilis were in fact clear. Previous estimates of the issue were around 7%, considerably lower than the results found by the study.

Syphilis tests detect the  antibodies to the bacteria that cause syphilis in blood, body fluid or tissue. There are a number of different tests that can be conducted for syphilis. The FTA-ABS test cannot be used to detect syphilis in the first 3 to 4 weeks following exposure to the bacteria. This test is harder to complete and is normally conducted when another test has previously indicated positive for the disease but further clarification is required. The TPPA test works on a similar basis. Darkfield microscopy, however, is a simpler test to take and uses a specially-designed microscope to examine a sample taken from an open sore. This test is used at an early stage. It is this Darkfield microscopy that is yielding the high margin of error.

The CDC recommendations outline that when Darkfield testing is undertaken, a follow-up test of FTA-ABS or TPPA is taken where a positive result occurs. It is not known how good the adherence is to these guidelines or whether patients are simply being advised to take anti-syphilis treatments to be safe. Treatment normally involves administering penicillin (largely via a very painful injection in the buttocks) but there is a risk of side-effects.

Syphilis testing is recommended in all pregnant women and in groups that are considered at high risk from sexually-transmitted diseases. The test doesn’t miss anybody that *is* infected but isn’t perfect at distinguishing syphilis antibodies from other proteins in the blood.

The incidence of syphilis infection in the US has been on the rise for the past eight years, according to the CDC, although chlamydia remains the most common sexually-transmitted disease in the country. Although it was once almost entirely eradicated in the developed world, changes in sexual behavior have left to a resurgence in western countries. This increase is largely attributed to unsafe sexual practices, largely among men who have sex with men. In 1999, 90% of cases were seen in the developing world, with more than 12 million people infected globally.

While syphilis can be treated with penicillin, the disease increases the risk of HIV transmission by between 2 and 5 times the normal rate. Co-infection is also common. Left untreated, syphilis can kill, with mortality rates of between 8% and 58%.