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In 1979, a test to detect syphilis specific antibodies was added to the neonatal screening programme for metabolic diseases in Lower Saxony.1 We report test results for the period 1993 to the end of 2001 (684 156 samples). Analysis of data included calculation of annual incidence rates, dependency of maternal age, and birth weight of infants on the incidence of positive results.
Neonatal screening for syphilis specific antibodies does not aim (and is not able) to diagnose congenital syphilis. The goal of our test is to remind physicians responsible for the infants of the positive history of the mother, so they can check whether sufficient treatment of the maternal infection can be proved or whether further measures are necessary.2
Material was eluted from dried blood samples collected on filter paper. Syphilis specific antibodies were identified using Treponema pallidum haemagglutination (TPHA) test (Fujuzoki, Tokyo, Japan) or, since 1999, Treponema pallidum particle agglutination (TPPA) test (Fujirebio Inc, Tokyo, Japan). Extract and suspension of sensitised erythrocytes or particles were mixed at a dilution of 1:80. All samples showing a reaction at this dilution were assessed as being positive and retested for quantification of antibodies. Both test versions are based on indirect particle agglutination caused by 7S-IgG and 19S-IgM antibodies against Treponema pallidum.
During the observation period the incidence of infants with a positive test result increased significantly from 11.05 cases per 10 000 infants in 1993 to 19.73 cases per 10 000 children in 2001 (R2 for the linear regression: 0.75, p = 0.003) (fig 1⇓). The level of significance would be even higher if it took into account that the formerly used TPHA test produced a small but not exactly defined number of false positive results.
In former years, the incidence of syphilis antibodies in newborns increased with maternal age. Recently, age distribution of mothers of antibody positive babies changed: a large number of young mothers had babies with positive antibodies. Data for the years 1993-7 were compared with those of 1998–2001 by using the χ2 test (two tailed p values). The most obvious change occurred in the group of 20–24 years old and 25–29 year old mothers (p <0.001).
A significant correlation between birth weight and the probability of a positive test result was found. Data on birth weight were available for 405 786 newborns (81.2%). The incidence (cases per 10 000 tested infants) of syphilis antibodies in very low birthweight infants (<1500 g) and in low birthweight infants (<2500 g) was significantly higher (45.4 v 27.3, p<0.001 v 0.002) than in the total group (19.2).
Although the syphilis test was not introduced for epidemiological reasons, some conclusions can be drawn with respect to epidemiology. Firstly, there has been a significant rise in the incidence of syphilis antibody positive infants in the past 9 years, indicating an increasing number of young women who had or have a syphilis infection. Therefore, physicians in charge of newborn infants must be aware of the increasing probability of finding a congenital infection. Secondly, the probability of a positive test result is higher in low birthweight infants and in infants of younger mothers.
US, JS, and SS were responsible for evaluating the antibody test; US wrote the first draft of the manuscript and did the epidemiological and statistical analyses; JS and SS contributed to the interpretation and discussion of the data and revised the different versions of the paper; NJ adapted the test method for dried blood samples and guaranteed the quality of the testing; MA created the structure of the data system and helped with the analysis of the data.
Competing interests: None declared.
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