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The role of the interferon gamma release assay in assessing recent tuberculosis transmission in a hospital incident.

Bradshaw L, Davies E, Devine M, Flanagan P, Kelly P, O'Connor K, Drobniewski F, Nikolayevskyy V, Abubakar I - PLoS ONE (2011)

Bottom Line: We also described within-patient variability of IGRA results.Among patients and staff, increasing age of patients was the only factor associated with IGRA positivity.Greatest within-subject variability of IU/mL in serially-tested patients/staff was seen in those with a positive IGRA test and this did not correlate with increased exposure to the index case.

View Article: PubMed Central - PubMed

Affiliation: Tuberculosis Section, Respiratory Diseases Department, Health Protection Agency Centre for Infections, London, England. louise.bradshaw@hpa.org.uk

ABSTRACT
In 2007, an extensive contact screening investigation into onward transmission of tuberculosis was instigated at a hospital in Northern Ireland following diagnosis of pulmonary multi-drug resistant TB in a healthcare worker. Interferon gamma release assays (IGRAs) were used to test 333 patients and 98 staff. We investigated for evidence of onward transmission and recent infection based on analysis of clinical, demographic and IGRA data. We also described within-patient variability of IGRA results. Among patients and staff, increasing age of patients was the only factor associated with IGRA positivity. Greatest within-subject variability of IU/mL in serially-tested patients/staff was seen in those with a positive IGRA test and this did not correlate with increased exposure to the index case. IGRA positivity being largely explained by increasing age in patients and previous TB contact in staff lends weight to the conclusion that IGRA positivity reflected previous infection rather than recent transmission.

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Related in: MedlinePlus

Study IGRA results.A, Interpretative patient IGRA result by days exposure to index case. *Serially IGRA-tested patients only. B, Within-subject variability of patients by days exposure to index case. C, Patient conversion/reversion.
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pone-0020770-g002: Study IGRA results.A, Interpretative patient IGRA result by days exposure to index case. *Serially IGRA-tested patients only. B, Within-subject variability of patients by days exposure to index case. C, Patient conversion/reversion.

Mentions: Among 333 patients, 30 (9.01%) had a positive IGRA test, and 41 (12.31%) had an indeterminate result, while seven of 98 staff tested were positive and one had an indeterminate test. The median age of patients was 65 years (inter-quartile range 48–76) and 54.7% were male. Staff had a lower median age (41 years, inter-quartile range 33–46) and 8.16% were male. Only one patient converted from IGRA negative to IGRA positive, however, they later reverted (patient 3 in Figure 2c: conversion plus known exposure to the index case could potentially be interpreted as indicative of recent transmission). This patient had 4 days potential exposure to the index case. Patients 1 and 2 (also Figure 2c, with 2 days and 15 days exposure respectively, and positive interpretative results) also reverted. No patient or staff member has been identified with active TB up to 1 June 2010 which is three years after last possible exposure to the index case.


The role of the interferon gamma release assay in assessing recent tuberculosis transmission in a hospital incident.

Bradshaw L, Davies E, Devine M, Flanagan P, Kelly P, O'Connor K, Drobniewski F, Nikolayevskyy V, Abubakar I - PLoS ONE (2011)

Study IGRA results.A, Interpretative patient IGRA result by days exposure to index case. *Serially IGRA-tested patients only. B, Within-subject variability of patients by days exposure to index case. C, Patient conversion/reversion.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3113857&req=5

pone-0020770-g002: Study IGRA results.A, Interpretative patient IGRA result by days exposure to index case. *Serially IGRA-tested patients only. B, Within-subject variability of patients by days exposure to index case. C, Patient conversion/reversion.
Mentions: Among 333 patients, 30 (9.01%) had a positive IGRA test, and 41 (12.31%) had an indeterminate result, while seven of 98 staff tested were positive and one had an indeterminate test. The median age of patients was 65 years (inter-quartile range 48–76) and 54.7% were male. Staff had a lower median age (41 years, inter-quartile range 33–46) and 8.16% were male. Only one patient converted from IGRA negative to IGRA positive, however, they later reverted (patient 3 in Figure 2c: conversion plus known exposure to the index case could potentially be interpreted as indicative of recent transmission). This patient had 4 days potential exposure to the index case. Patients 1 and 2 (also Figure 2c, with 2 days and 15 days exposure respectively, and positive interpretative results) also reverted. No patient or staff member has been identified with active TB up to 1 June 2010 which is three years after last possible exposure to the index case.

Bottom Line: We also described within-patient variability of IGRA results.Among patients and staff, increasing age of patients was the only factor associated with IGRA positivity.Greatest within-subject variability of IU/mL in serially-tested patients/staff was seen in those with a positive IGRA test and this did not correlate with increased exposure to the index case.

View Article: PubMed Central - PubMed

Affiliation: Tuberculosis Section, Respiratory Diseases Department, Health Protection Agency Centre for Infections, London, England. louise.bradshaw@hpa.org.uk

ABSTRACT
In 2007, an extensive contact screening investigation into onward transmission of tuberculosis was instigated at a hospital in Northern Ireland following diagnosis of pulmonary multi-drug resistant TB in a healthcare worker. Interferon gamma release assays (IGRAs) were used to test 333 patients and 98 staff. We investigated for evidence of onward transmission and recent infection based on analysis of clinical, demographic and IGRA data. We also described within-patient variability of IGRA results. Among patients and staff, increasing age of patients was the only factor associated with IGRA positivity. Greatest within-subject variability of IU/mL in serially-tested patients/staff was seen in those with a positive IGRA test and this did not correlate with increased exposure to the index case. IGRA positivity being largely explained by increasing age in patients and previous TB contact in staff lends weight to the conclusion that IGRA positivity reflected previous infection rather than recent transmission.

Show MeSH
Related in: MedlinePlus