LETTER
Routine repeat testing of specimens with a low-positive result for Chlamydia trachomatis and Neisseria gonorrhoeae by nucleic acid amplification test (NAAT) is not recommended (5) because of the following. (i) The majority of positive specimens that are negative on confirmatory testing are true positives. (ii) Infected patients will go untreated. In August 2010, the Centers for Disease Control and Prevention (CDC) disseminated a Laboratory Outreach Communication System (LOCS) advisory specifying that low-positive NAAT results should be reported as positive (3). In September 2010, we conducted a follow-up online survey of licensed laboratories respondents to the 2007 California Clinical Laboratory Survey (2) that reported routine repeat testing of specimens with low-positive C. trachomatis and N. gonorrhoeae NAAT results.
Of 108 laboratories contacted, 63% responded (15 public laboratories and 53 private laboratories). Of 52 laboratories repeating low-positive results, 22 (42%) reported the unconfirmed results as negative; 19 of these laboratories were private-sector laboratories. At least 40 (77%) did not report cases for public health surveillance. Public health laboratories were more likely than private-sector laboratories to have received the LOCS advisory (14/15 [93%] versus 11/53 [21%]; P < 0.0001).
These results are troubling, since most laboratories that repeat low-positive specimens are not reporting a disease that is reportable in all states. The public health implications are that chlamydia control efforts are undermined, as cases go untreated and continue to transmit infections to sex partners. The magnitude of this practice is amplified by private-sector laboratories that test the vast majority of specimens for C. trachomatis and N. gonorrhoeae in California; specifically, among the 108 laboratory respondents that reported repeating low-positive specimens, the private-sector test volume was over 3 million chlamydia tests compared with the public health test volume of 158,000 chlamydia tests, an order of magnitude smaller (2). Although we did not quantify the number of low-positive tests that were not confirmed and we did not determine the proportion of all positives that were low positives and repeated in this survey, the proportion of all positives that fall into the low-positive range as indicated by the manufacturer is likely very low (1, 4), particularly if clinicians are testing higher-prevalence populations according to national screening guidelines.
Failure to correctly inform patients of positive results due to repeat testing practices is related to the failure to reach all laboratories with current guidelines. We have a public health obligation to address these failures by expanding the LOCS to include private-sector laboratories and state sexually transmitted disease (STD) program promotion of best laboratory practices across public-private laboratory sectors.
ACKNOWLEDGMENTS
The STD Control Branch thanks Carol Kong and Lindsey Apodaca for their assistance with survey implementation and the California laboratory respondents for their insight and comments.
Footnotes
Published ahead of print 23 November 2011
REFERENCES
- 1. Becton, Dickinson and Company 2010. ProbeTec package insert. Becton, Dickinson and Company, Sparks, MD: http://www.bd.com/ds/technicalCenter/inserts/L008195(201001).pdf [Google Scholar]
- 2. California Department of Public Health 2009. Sexually transmitted diseases testing in California 2007: clinical laboratory summary. California Department of Public Health, Sacramento, CA: http://www.cdph.ca.gov/data/statistics/Documents/STD-Data-LabSurvey.pdf [Google Scholar]
- 3. Centers for Disease Control and Prevention 16 August 2010. “Dear Colleague” letter from Kevin Fenton, Director, National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA: http://wwwn.cdc.gov:80/dls/locs/ViewUploadedDocument.aspx?DLS_Upload_Files_id=542 [Google Scholar]
- 4. GenProbe Inc 2006. Aptima Combo 2 package insert. GenProbe Inc., San Diego, CA: http://www.gen-probe.com/pdfs/pi/501798RevA.pdf [Google Scholar]
- 5. Schachter J, Chow JM, Howard H, Bolan G, Moncada J. 2006. Detection of Chlamydia trachomatis by nucleic acid amplification testing: our evaluation suggests that CDC-recommended approaches for confirmatory testing are ill-advised. J. Clin. Microbiol. 44:2512–2517 [DOI] [PMC free article] [PubMed] [Google Scholar]