[MoAb0101] ELISPOTs in the detection of Mycobacterium tuberculosis infection in a population with high prevalence of HIV and high exposure to BCG and environmental mycobacteria

16th International AIDS Conference

Toronto, Canada - August 13 - 18, 2006

ELISPOTs IN THE DETECTION OF MYCOBACTERIUM TUBERCULOSIS INFECTION IN A POPULATION WITH HIGH PREVALENCE OF HIV AND HIGH EXPOSURE TO BCG AND ENVIRONMENTAL MYCOBACTERIA

Int Conf AIDS. 2006 Aug 13-18;16 Abstract No. MoAb0101

Mutsvangwa J.¹, Corbett E.L.², Chaka-Boyd K.³, Vundla R.⁴, Muzangwa J.⁴, Mavhudzi T.⁴, Cheung Y.⁵, Mason P.R.⁶, Millington K.⁷, Ewer K.⁷, Lalvani A.⁷, Butterworth A.E.⁸
¹Biomedical Research and Training Institute, Harare, Zimbabwe, ²London School of Hygiene and Tropical Medicine & Biomedical Research and Training Institute, Department of Infectious Diseases, Harare, Zimbabwe, ³Biomedical Research and Training Institute, Laboratories, Harare, Zimbabwe, ⁴Biomedical Research and Training Institute, DetecTB, Harare, Zimbabwe, ⁵London School of Hygiene and Tropical Medicine, London, United Kingdom, ⁶Biomedical Research and Training Institute & University of Zimbabwe, Harare, Zimbabwe, ⁷Nuffield Department of Clinical Medicine,University of Oxford, Clinical Medicine, Oxford, United Kingdom, ⁸Biomedical Research and Training Institute & London School of Hygiene and Tropical Medicine, Department of Infectious Diseases, Harare, Zimbabwe

BACKGROUND: The tuberculin skin test (TST) remains the gold standard for the detection of new or latent infections with Mycobacterium tuberculosis (MTB), but has low sensitivity in HIV-infected subjects and lacks specificity in individuals vaccinated with BCG or exposed to environmental mycobacteria. The interferon-gamma ELISPOT response to peptides of defined MTB antigens has shown superior sensitivity and specificity in a number of settings. In this study we have compared TSTs and ELISPOTs among factory workers and their household contacts.

METHODS: Index cases (IX, n=75) and their household contacts (IXC, n=114) were recruited through a site-randomised study of VCT and health care delivery in factories in Harare. Index controls (CT, n=71) and their household contacts (CTC, n=85) were randomly selected from the same factories. TSTs were compared with ELISPOT responses to peptides and recombinant antigens of ESAT-6 and CFP10 (RD1 responses) and to PPD.

RESULTS: Positive TSTs and PPD responses were significantly more frequent than positive RD1 responses, both overall (TST 71%, PPD 83%, RD1 59%, p<0.001) and by case status. HIV prevalence was 79%, 32%, 18% and 9% among IX, IXC, CT and CTC respectively. TST and PPD responses were significantly lower among HIV+ than HIV- subjects, both overall (TST, 46% vs 79%, p<0.001: PPD, 61% vs 94%) and by case status. In contrast, RD1 responses were not affected by HIV status (overall, 59% positive for both HIV+ and HIV-).

CONCLUSIONS: A proportion of positive TSTs and PPD responses may be attributable to exposure to organisms other than MTB. Both TSTs and PPD ELISPOTs are substantially reduced in HIV-infected individuals, whereas RD1 ELISPOTs are unaffected. Thus, this study supports that the RD1 ELISPOT is a useful marker of MTB infection in individuals from areas with a high prevalence of HIV infection and high exposure to BCG or cross-reactive environmental mycobacteria.

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2006-08-13
MoAb0101

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