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Table 1 Overview household contacts eligible for baseline analysis using different definitions of visit 1 QFT status

From: Interpretation of serial interferon-gamma test results to measure new tuberculosis infection among household contacts in Zambia and South Africa

  

Definition 1

(≥0.2)

 

Definition 2a

(≥0.35)

 

Definition 3

(≥0.7)

Definition 1 (≥0.2 IU/ml)

Zambia

n (%)

South Africa n (%)

Definition 2 (≥0.35 IU/ml)a

Zambia

n (%)

South Africa

n (%)

Definition 3 (≥0.7 IU/ml)

Zambia

n (%)

South Africa

n (%)

Positive

 

735 (54)

626 (76)

 

669 (49)

574 (70)

 

599 (44)

504 (61)

 Nil

≤8.0

  

≤8.0

  

≤8.0

  

 TBAgNil

≥0.2 & (≥25% of Nil value)

  

≥0.35 & (≥25% of Nil value)

  

≥0.7 & (≥25% of Nil value)

  

Negative

 

445 (33)

182 (22)

 

495 (36)

230 (28)

 

551 (40)

297 (36)

 Nil

≤8.0

  

≤8.0

  

≤8.0

  

 TBAgNil

< 0.2 or < 25% Nil

  

< 0.35 or < 25% Nil

  

< 0.7 or < 25% Nil

  

 MitogenNil

≥0.5

  

≥0.5

  

≥0.5

  

Indeterminateb

all other values

185 (14)

14 (2)

all other values

201 (15)

18 (2)

all other values

215 (16)

21 (3)

  1. Footnote: Nil negative control response; TBAgNil antigen response minus negative control response; MitogenNil positive control response minus negative control response
  2. a Manufacturer’s recommended assay cut-off
  3. b The number of indeterminate test results differs depending on the QFT definition used: if a positive value becomes a negative value using a stricter QFT definition, it will only be quantified as negative if the value is accompanied with MitogenNil≥0.5. If not, the value is quantified as indeterminate
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BMC Infectious Diseases

ISSN: 1471-2334

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