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J Clin Microbiol. 2019 Aug 28. pii: JCM.00898-19. doi: 10.1128/JCM.00898-19. [Epub ahead of print]

Frequency and characteristics of biologic false positive tests for syphilis, reported in Florida and New York City, 2013-2017.

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Centers for Disease Control and Prevention, Atlanta, GA LNK1@CDC.GOV.
Florida Department of Health, Tallahassee, FL.
New York City Department of Health and Mental Hygiene, New York City, NY.
Centers for Disease Control and Prevention, Atlanta, GA.



Discordant syphilis test results, with a reactive non-treponemal test and non-reactive treponemal test are usually considered biological false positive test results (BFP), which can be attributed to other conditions. Syphilis surveillance laws mandate laboratory reporting of reactive syphilis tests which include many BFPs. We describe the frequency of BFP, titer distributions, and titer increases from reported test results in Florida and New York City (NYC).


Reactive non-treponemal tests for individuals with at least one non-reactive treponemal test and no reactive treponemal test, were extracted from STD surveillance systems in Florida and NYC from 2013 through 2017. Characteristics of individuals with BFPs were analyzed after selecting the observation with the highest titer from each individual. We next considered all results from individuals to characterize persons who had a four-fold titer increase between successive non-treponemal tests.


Among 526,540 reactive non-treponemal tests, there were 57,580 BFPs (11%) from 39,920 individuals. Over 90% (n=52,330) of BFPs were low titer (≤1:4), but 654 (1%) were high-titer BFPs (≥1:32). Very high-titer (≥1:128) BFPs were more common among individuals over 60 years of age (OR 2.68 95%CI 1.22-5.91). A four-fold increase in titer was observed among 1,863 (14%) individuals with more than one reported BFP.


Most BFPs detected by surveillance were low-titer but some were high-titer and some had a four-fold increase in titer. Review of patient histories might identify underlying conditions contributing to these high and rising titers.


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