Prospective evaluation of simply modified MODS assay: an effective tool for TB diagnosis and detection of MDR-TB

Figures & data

Figure 1 Design of MODS culture plates containing one well for PNB.

Abbreviations: C1, C2 are culture wells 1 and 2; MODS, microscopic-observation drug-susceptibility assay; PNB, para-nitrobenzoic acid identification well; INH, isoniazid well for INH susceptibility test; RIF, rifampicin susceptibility test well.

Figure 2 (A) Reading system of MODS plate inside bio-safety cabinet and (B) AM313T Dino-Lite PLUS Digital Microscope at viewer side of inverted microscope.

Abbreviation: MODS, microscopic-observation drug-susceptibility assay.

Figure 3 Daily reading and recording using digital microscope and software.

Figure 4 Cumulative culture positive rates of MODS assay, automated liquid culture by BACTEC™ MGIT™ 960 (Becton, Dickinson and Co, NJ, NY) and solid culture by Ogawa media.

Abbreviations: AFB+, acid fast bacilli positive sputum samples; AFB−, acid fast bacilli negative sputum samples; MODS, microscopic -observation drug susceptibility assay.

Table 1 Characteristic of the pulmonary TB patients at the study entry

Characteristics	Number	Percentage
Number	202	100
Sex
Male	155	76.73
Female	47	23.27
Age (years)
Median (IQR)	48 (37–59)
Race
Thai	117	57.92
Hill tribe	50	24.75
Myanmar and Lao	35	17.33
Type of patient
IPD	108	53.47
OPD	87	43.07
Unknown	7	3.47
Type of TB treatment
New case	178	88.12
Re-treatment	24	11.88
Sputum AFB status at TB diagnosis
Pulmonary AFB+	147	72.77
Pulmonary AFB scanty	12	5.94
Pulmonary AFB−	43	21.29

Abbreviations: AFB, sputum acid-fast bacillus smears; IPD, admitted as inpatient at the hospital; IQR, interquartile range; OPD, treated at TB clinic, outpatient department; TB, tuberculosis.

Table 2 Median time to culture growth in three different TB culture methods: Ogawa solid culture, BACTEC™ MGIT™ 960 liquid culture system and MODS assay in sputum samples of clinically diagnosed TB patients, Chiang Rai, Thailand 2010

N = 202 cases	Culture growth		Median time to culture positivity (days)	Interquartile range	Minimum/maximum	P value
	(n/N)	(%)
Solid culture
AFB-positive	130/147	88.44	28	22–42	12–58	<0.001S
AFB-negative	17/55	30.91	39	34–43	21–49	<0.001S
Total	147/202	72.77	30	23–42	12–58	<0.001S
Liquid culture
AFB-positive	138/147	93.88	6	5–8	3–37	<0.001L
AFB-negative	19/55	34.55	8	7–12	4–22	<0.001L
Total	157/202	77.72	6	5–9	3–37	<0.001L
MODS
AFB-positive	122/147	82.99	12	8–14	4–33
AFB-negative	13/55	27.67	19	13–20	11–26
Total	135/202	66.83	12	9–15	4–33

Notes: n = number of positive growth; N = total number;

S P value for comparison of microscopic-observation drug-susceptibility assay (MODS) versus solid;

L P value for comparison of MODS versus liquid. Growth means culture positive by seeing growth.

Table 3 DST performance result of MODS in reference to BACTEC™ MGIT™ 960 automated liquid culture for detection of drug-resistant M. tuberculosis in sputum

MODS	DST by MGIT
	Rifampicin		Isoniazid		MDR-TB
	Resistance	Sensitivity	Resistance	Sensitivity	Resistance	Sensitivity
Resistance	7	3	12	3	6	3
Sensitivity	0	119	4	111	1	116
Total	7	122	16	114	7	119

Abbreviations: DST, drug susceptibility test; MODS, microscopic-observation drug-susceptibility assay; MDR-TB, multidrug-resistant tuberculosis.

Table 4 Performance characteristic MODS assay compared to reference BACTEC™ MGIT™ 960 automated liquid culture for detection of drug-resistant M. tuberculosis in sputum, Chiang Rai, Thailand, 2010

	Rifampicin	Isoniazid	MDR-TB
Number of cases	129	130	126
Kappa value	0.8115	0.7437	0.7333
Agreement	97.67%	94.62%	96.83%
Area under ROC	0.988 (0.974–1)	0.862 (0.751–0.972)	0.916 (0.775–1)
Sensitivity (95% CI)	100 (59–100)	75 (47.6–92.7)	85.7 (42.1–99.6)
Specificity (95% CI)	97.5 (93–99.5)	97.4 (92.5–99.5)	97.5 (92.8–99.5)
PPV (95% CI)	70 (34.8–93.3)	80 (51.9–95.7)	66.7 (29.9–92.5)
NPV (95% CI)	100 (96.9–100)	96.5 (91.3–99)	99.1 (95.3–100)
Likelihood ratio (+)	40.7 (13.3–12.4)	28.5 (9.01–90.2)	34 (10.7–108)
Likelihood ratio (−)	0	0.257 (0.11–0.6)	0.147 (0.024–0.9)

Abbreviations: CI, confidence interval; MODS, microscopic-observation drug-susceptibility assay; MDR-TB, multidrug-resistant tuberculosis; NPV, negative predictive value; PPV, positive predictive value; ROC, receiver-operating characteristic curve.