TABLE 1.
Rate of mycobacterial detection by Bactec MGIT 960 system and rate of false-negative signalsa
| Protocol no. | Sample-processing protocol | No. of samples with positive signal | No. of samples with negative signal | No. of negative smears | No. of false-negative results/no. of samples classified as negative by Bactec MGIT 960 system (%) |
|---|---|---|---|---|---|
| 1 | Processed without CPC (n = 60) | 59 | 1 | 1 | 0/1 (0) |
| 2 | Mixed with CPC and washed (n = 60) | 53 | 7 | 2 | 5/7 (71.4) |
| 3 | Mixed with CPC and not washed (n = 60) | 50 | 10 | 3 | 7/10 (70.0) |
a
P values: for protocols 1 and 2, <0.0001; for protocols 1 and 3, <0.0001; and for protocols 2 and 3, >0.5. Each of the 60 samples was divided into three parts, and one aliquot had no CPC, another had CPC but was washed, and the third aliquot had CPC and was processed without being washed. The Bactec MGIT 960 result was labeled false negative when the tube gave a negative signal but was shown to contain mycobacteria upon smear examination.