Positive Xpert MTB/RIF Ultra Tests on CSF specimens stored at −20˚C or −80˚C

(SR 2:1)/15min

Spiked

CFU/mL

Drug-susceptible MTBC

Stored for 35 days (n = 54)

Rifampin-resistant MTBC

Stored for 50 days (n = 36)

−20˚C (n = 23)

−80˚C (n = 31)

−20˚C (n = 15)

−80˚C (n = 21)

n

(%)

(Trace)

Avg

Ct value

(Range)

n

(%)

(Trace)

Avg

Ct value

(Range)

n

(%)

(Trace)

Avg

Ct value

(Range)

n

(%)

(Trace)

Avg

Ct value

(Range)

10¹

6/8 (75%)

(1)

31.1

(26.2 - 33.7)

6/10 (60%)

(1)

28

(26 - 30.6)

5/5

(100%)

27.4

(24.1 - 31.7)

7/7

(100%)

24.7

(22.5 - 27.4)

10²

8/8 (100%)

(3)

29.2

(29.4 - 31.2)

10/10 (100%)

(3)

28.1

(24.8 - 30.4)

5/5

(100%)

23.1

(21.5 - 24.4)

7/7

(100%)

22.4

(21.1 - 24.2)

10⁶

7/7

(100%)

20.1

(18.5 - 22)

11/11 (100%)

19.7

(18.4 - 22.1)

5/5

(100%)

18.5

(17.2 - 19)

7/7

(100%)

18.6

(17.4 - 19.9)