Lab Matters Winter 2017 - Page 28

infectious diseases

The TB Iceberg : Finding the Underwater Infections by Paul Zell , MPH , specialist , TB and Anne M . Gaynor , PhD , manager , HHST

Bacteria Mycobacterium tuberculosis

Tuberculosis ( TB ) caused by Mycobacterium tuberculosis can be classified as active TB disease or latent TB infection . The 9,557 1 US cases reported in 2015 were persons with active TB disease , meaning they are symptomatic and potentially contagious . But active TB disease is just the tip of the TB “ iceberg ;” the Centers for Disease Control and Prevention ( CDC ) Division of Tuberculosis Elimination ( DTBE ) estimates that there are up to 13 million persons with latent TB infection in the United States . 2

The project demonstrated that bringing testing in-house will decrease turnaround time and cost , and increase the populations that can be tested by IGRA .
Latent TB infections , representing the remainder of the “ iceberg ,” can be difficult to identify as the bacteria are present in the body yet inactive . Additionally , the person does not exhibit symptoms and they cannot spread the bacteria to others . However , a latent TB infection may develop into an active case at any time ; one study suggested that approximately 80 % of all active TB cases in the United States arise from latent TB infection . 3 , 4
The next step in public health ’ s effort to eliminate TB in the United States is to better identify and track latent TB infections . As an early step in that effort , APHL selected 11 sites to receive awards aimed at expanding public health access to the interferon gamma release assay ( IGRA ), a test used to detect TB infection .
The two diagnostic tests commonly used to detect TB infection are the tuberculin skin test ( TST ) and IGRA . Both have limitations including the interpretation of the test , the populations that should receive that test , and how the testing is executed . However , use of IGRA has advantages that make it desirable , including a one-time visit and lack of false reactivity due to previous BCG vaccination . Unlike TST , IGRA is a laboratory-based test requiring special equipment and adherence to strict sample processing and handling
requirements that can make implementation challenging in a public health setting . In order to expand access to the use of IGRAs , APHL , in partnership with CDC , solicited applications from public health laboratories and their related jurisdictional TB control programs to bring on or expand their testing for TB infection using this method .
The selected sites began work on their IGRA expansion proposals in January 2016 and completed work in September 2016 . Collectively , participating sites reported at least 100 newly trained laboratory and clinical staff qualified to perform steps associated with IGRA , decreased turnaround time ( TAT ) by an average of three days from previous IGRA TATs , and a 104 % increase in overall IGRAs performed . As a result of the project , two sites were able to expand their IGRA testing program within correctional facilities located within their state by increasing the number of inmates screened , representing a large advantage in identifying latent TB infection among an inherently high-risk population .
One particularly encouraging result of the project was that a participating site that had been utilizing a third party for IGRA testing moved their testing program in-house after completing the project . The project demonstrated that bringing testing in-house will decrease turnaround time and cost , and increase the populations that can be tested by IGRA . The project also increased cooperation and collaborations between laboratory and programmatic staff as both parties worked closely for the project ’ s duration . While a complete evaluation of the project has not yet been completed , early indications are that the project was a success in the expansion of the use of IGRA in the fight to uncover more of the TB iceberg . Further evaluations will focus on whether expanded access had the broader goal of preventing TB disease by ensuring persons with TB infection are offered and complete treatment .
Bacille Calmette-Guerin ( BCG ) is a vaccine for TB disease . Many foreign-born persons have been BCG-vaccinated . BCG is used in many countries with a high prevalence of TB to prevent childhood tuberculous meningitis and miliary disease .
References 1 . Centers for Disease Control and Prevention ( CDC ). Reported Tuberculosis in the United States , 2015 . Atlanta , GA ; US Department of Health and Human Services , CDC : 2016 . Available at : https :// www . cdc . gov / tb / statistics / reports / 2015 / pdfs / 2015 _ surveillance _ report _ fullreport . pdf 2 . Miramontes R , Hill AN , Yelk Woodruff RS , Lambert LA , Navin TR , Castro KG , LoBue PA . Tuberculosis Infection in the United States : Prevalence Estimates from the National Health and Nutrition Examination Survey , 2011-2012 . Plos One 2015 Nov
4 ; 10 ( 11 ) e0140881 . 3 . Shea KM , Kammerer JS , Winston CA , Navin TR , Horsburgh CR Jr . Estimated Rate of Reactivation of Latent Tuberculosis Infection in the United States , Overall and by Population Subgroup . Am J Epidemiol 2014 Jan 15:179 ( 2 ): 216-25 . 4 . Yuen CM , Kammerer JS , Marks K , Navin TR , France AM . Recent Transmission of Tuberculosis — United States , 2011-2014 . PLoS One . 2016 Apr 15 ; 11 ( 4 ): e0153728 .
LAB MATTERS Winter 2017
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