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Abstract
Diagnostic testing for M. tuberculosis infection has advanced with QuantiFERON and GeneXpert, but simple cost-effective alternatives for widespread TB screening has remained elusive and purified protein derivative (PPD)-based tuberculin skin testing (TST) remains the most widely used method. PPD-based tests have reduced performance, however, in BCG vaccinees and in individuals with immune deficiencies. We compared the performance of skin testing with the recombinant DPPD protein against that of a standard PPD-based skin test. Our data indicates similar performance of DPPD and PPD (r2 = 0.7689) among HIV-negative, active TB patients, all of whom presented greater than 10 mm induration following administration. In contrast to results demonstrating that PPD induced indurations greater than 5 mm (i.e., the recommended threshold for positive results in this population) in only half (19 of 38) of the HIV positive TB patients, 89.5% (34 of 38) of these participants developed indurations greater than 5 mm when challenged with DPPD. Importantly, none of the patients that were positive following PPD administration were negative following DPPD administration, indicating markedly improved sensitivity of DPPD among HIV-infected individuals. Our data indicate that DPPD has superior performance in skin testing than the current TST standard.
Highlights
Tuberculosis (TB) was the primary cause of 1.3 million deaths in 2017, making it the second most common cause of death from infectious diseases (WHO 2018a)
Performance of DPPD in skin testing among target populations We evaluated the diagnostic capacity of DPPD as a skin test antigen by comparing against that of the gold standard, purified protein derivative (PPD)
There was a moderate correlation between PPD and DPPD results (r2 = 0.6303), an induration of greater than 10 mm was observed in a lower proportion of healthy participants following administration of DPPD than following injection with PPD (13.6% versus 57.9%, respectively) (Fig. 1a)
Summary
Tuberculosis (TB) was the primary cause of 1.3 million deaths in 2017, making it the second most common cause of death from infectious diseases (WHO 2018a). Estimates are that nearly 2 billion people latently infected with Mycobacterium tuberculosis and 5–10% of infected individuals will progress to TB disease during their lifetime (Getahun et al 2015; Houben and Dodd 2016; WHO 2018a). M. tuberculosis infection is especially problematic in immune compromised individuals that have an increased likelihood of progression to disease such that TB is among the leading cause of death in HIV/ AIDS patients. A wide variety of strategies are utilized to diagnose TB Indirect methods such as chest X-rays are commonly used to confirm symptoms. Direct detection systems have included culture of M. tuberculosis from sputum samples, and modern technologies such as nucleic acid amplification tests (i.e., GeneXpert) have revolutionized the diagnosis of active TB by allowing faster generation of more sensitive and specific results that improve patient care (Boehme et al 2011; Nicol et al 2011). Given difficulties in sputum collection etc., these tests still have limited overall sensitivity, and even with generous subsidies and concessional pricing they remain too expensive for routine use in the majority of resource-limited settings
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