The prevalence of curable sexually transmitted infections (STIs) continues to increase globally with an estimated 376.4 million new infections in 2016.1 In the United States, the number of STIs reported to the Centers for Disease Control and Prevention (CDC) has increased each year for the last 5 years. In 2018, 1.8 million cases of chlamydia, 583,405 cases of gonorrhea, and 35,063 of syphilis were reported to the CDC, representing a 19%, 63%, and 71% increase from 2014, respectively.2 These increases in cases reflect a major public health threat. STI control requires timely diagnosis, treatment with effective antimicrobials, and appropriate reporting of cases for surveillance and case contact identification purposes.
In this issue of STD, Davis and Gaynor describe the results of a web-based survey of STI testing and practices by 105 state and local public health laboratories (PHLs) in the United States.3 Of the total number of chlamydia and gonorrhea cases reported to the CDC in 2016, 12% and 17%, respectively, were identified by the surveyed PHLs, highlighting the critical role of these laboratories in the diagnosis of STIs. In accordance with CDC recommendations, nucleic acid amplification tests (NAATs) were the most commonly performed tests by PHLs for the detection of chlamydia and gonorrhea. However, contrary to CDC recommendations, urine was the most common type of specimen received for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) NAAT for females. Public health laboratories should reconsider the practice of performing CT and NG NAAT in females using urine as this type of specimen might detect up to 10% fewer infections when compared with vaginal and endocervical swab samples.4 Approximately 10% of samples tested by PHLs were positive for syphilis. Trichomonas vaginalis (TV) testing was more routinely performed by local PHLs (73%) than state PHLs (23.5%), with wet mount and PCRs as the most common in-house tests.
The results of the survey by Davis and Gaynor not only enhance our understanding of STI testing and practices by PHLs but also provide support for the expansion of STI testing by PHLs. For example, given the extensive use of NAATs by PHLs for detection of NG and CT, existing platforms can be leveraged to test for TV in women, and Mycoplasma genitalium (MG), a major cause of nongonococcal urethritis in men.5 Furthermore, the results of the survey suggest that PHLs planned to add TV testing (36%) and MG testing (25%) within 12 months of completion of the survey further underscoring the recognized importance of these infections and the need to expand PHLs testing capacity. Although lymphogranuloma venereum (LGV) is less common than other STIs, 15% of surveyed PHLs received specimens for LGV testing. Considering the recent outbreaks and increase rates of LGV,6,7 PHLs should also increase their capacity for LGV testing, including NAATs for confirmation and differentiation from the more common serovars of CT.
The increasing rates of NG infections in the US coupled with the high rates of antimicrobial resistance represent a major challenge for management of these infections.2,8Neisseria gonorrhoeae has progressively developed resistance to all commonly prescribed antimicrobials9 and is considered as one of the top three urgent threats among antibiotic resistant bacteria. Surveillance, one of the strategies proposed by the WHO to combat antimicrobial resistance in NG,10 has been limited to a few specialized laboratories due to decreased capacity for performing antimicrobial susceptibility testing. Additionally, the use of NAAT for detection of NG prevents the collection of viable organisms required for antimicrobial susceptibility testing. Not surprisingly, only 25% of surveyed PHLs reported performing antimicrobial susceptibility testing for NG in 2016. The number of PHLs and other state laboratories performing antimicrobial susceptibility testing, however, is likely to increase as new surveillance programs are developed and implemented with funding from the CDC to combat antibiotic-resistant bacteria. These surveillance programs, such as the Strengthening the United States Response to Resistant Gonorrhea, the STI Surveillance Network, and the Enhanced Gonococcal Isolate Surveillance Project provide local and health departments with tools to enhance their capacity for antimicrobial susceptibility testing to test and monitor for antimicrobial-resistant gonorrhea.11
The use of algorithms for performing and reporting test results is also another important aspect of laboratory testing practices. In 2015, the CDC recommended a reverse syphilis test algorithm, which starts with the use of an assay to measure specific antibodies to Treponema pallidum, followed by a nontreponemal test.12 In comparison to the traditional algorithm (starting with a nontreponemal assay), the reverse algorithm is more specific for syphilis, more sensitive for detecting primary and secondary syphilis, and faster. Additionally, the reverse algorithm could also help to recognize untreated latent syphilis. Therefore, it is surprising that 80% of the PHLs surveyed in this study reported using the traditional algorithm for detection of syphilis. Furthermore, only 36% of the laboratories had a testing protocol for samples from subjects with a prior history of syphilis. Additional studies are warranted to determine why PHLs continue to use the traditional algorithm for detection of syphilis and how this might affect patient care. Furthermore, protocols need to be developed and implemented for testing samples from patients with a prior history of syphilis.
Consistent with the evolving nature and epidemiology of STIs, the number and type of tests performed by PHLs continue to evolve. As point-of-care tests for some STIs become more readily available, PHLs may stop offering certain tests or decrease the frequency of testing. For example, the Clinical Laboratory Improvement Amendments-waived OSOM (Genzyme Diagnostics, Cambridge, MA) test for TV is very sensitive, equipment-free, and can be performed in 15 minutes,13 allowing for TV testing to be performed in the clinic rather than in centralized laboratories. In contrast, for NG testing, PHLs should increase capacity for cultures and antimicrobial susceptibility testing to support ongoing surveillance programs for antimicrobial resistance and enhance antimicrobial stewardship. Finally, multiplex assays for STIs other than CT/NG need to be incorporated into the workflow of PHLs to differentiate STIs whose treatment may not be covered by empiric regimens. Central laboratories continue to have a key role in diagnosing and reporting STIs though the menu of tests will evolve as more rapid, portable devices are being developed for some STIs. Importantly, research on barriers to adoption and optimized workflows for testing at the point-of-need will be required to move away from algorithmic care and empiric treatment that increases the risk for continued evolution of multidrug-resistant organisms.
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