RESUMO
Objective: To evaluate direct drug susceptibility testing on MGIT 960 system for detection of multidrug resistant tuberculosis from smear positive pulmonary specimens
Study Design: Cross-sectional analytical study
Place and Duration of Study: Microbiology Department, Armed Forces Institute of Pathology, Rawalpindi, from July 2016 to September 2017
Methodology: Smear positive specimens were pretreated according to guidelines and then tested on MGIT 960 TB system for direct drug susceptibility testing [DST] of isoniazid and rifampin. Samples were also processed by gold standard indirect method, which comprises culture and then DST from positive growth by MGIT 960 TB system
Results: Out of 108 specimens, 95 [88%] DST results were reportable. Out of 95 reportable specimens, 17 isolates were resistant to both isoniazid [INH] and rifampin [RIF] by direct DST. The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy for INH were 92%, 93%, 82%, 97% and 92.6%, respectively; and 95%, 96%, 86.3%, 98.6% and 95.7%, respectively for RIF. Average time to report DST by indirect method was 23.6 +/-3.9 days, while it was 11.4 +/- 2.7 days for the direct method
Conclusion: Direct susceptibility testing on MGIT 960 system showed very good agreement when compared with indirect method. Time saving is crucial factor in initiation of early effective therapy, especially in drug resistant cases. Further studies on large scale are required for more accurate evaluation of this method
RESUMO
Objective: To evaluate the performance of nitrate reductase assay on smear positive pulmonary specimens for detection of multi and extensively drug resistant tuberculosis simultaneously. Study Design: Cross-sectional analytical study. Place and Duration of Study: Microbiology Department, Armed Forces Institute of Pathology, Rawalpindi from June to December 2016
Methodology: Smear positive pulmonary samples were processed both by nitrate reductase method on Lowenstein Jenson medium and also inoculated on gold standard Bactec MGIT 960 TB system. All the specimens were first digested and decontaminated according to standard protocol before inoculation
Results: Out of total 76 samples, three did not give color and, therefore, were excluded from the final data analysis. Among the remaining 73 samples, mycobacterial index was: 28 specimens were having 1+ [1-9 bacilli/100 fields], 26 samples were 2+ [1-9 bacilli/ field], and 19 samples were having 3+ index [>9 bacilli/field]. The respective sensitivity and specificity were 84% and 100% for isoniazid [INH]; 82% and 100% for rifampin [RIF]; 67% and 100% for amikacin [AK]; and both 100% for ofloxacin [OFX]. Overall agreement in case of INH, RIF, AK, and OFX was 94.5%, 97.2%, 98.6% and100%, respectively. Overall average agreement was 97.5%
Conclusion: Nitrate reductase assay is a reliable, low cost and accurate method that can be used for early for diagnosis of multi and extensively drug resistant tuberculosis
RESUMO
To evaluate the diagnostic efficiency of microscopic examination of Gram stained uncentrifuged drop of urine for presumptive diagnosis of urinary tract infections [UTI]. 250 samples collected from March 2005 to August 2005 comprising of both in patient and out patient samples were analyzed. Urine sample was homogenized and a nickel-chrome loop, calibrated to 10 micro l was used to take a drop of urine and was applied on glass slide [25mm x 75mm]. The drop was allowed to dry in air at room temperature [25°C approx.] without spreading. The slides after drying were stained with Gram method of staining. The microscopic examination was carried out with a 100x oil immersion objective, 30 fields were examined. Observation of one or more microorganism per high power oil immersion lens was taken as a positive reading. Culture of urine was taken as reference method and performed by using filter paper strips applying 2micro l of urine on cystine-lactose-electrolyte-deficient agar. Culture results obtaining a mixed growth of >/= 2 organisms were excluded out of the study. Only those cultures were taken as positive and made part of the study which yielded more than 10[5] or 10[4] to 10[5] CFU of pure single type /ml of urine. Sensitivity, specificity, positive and negative predictive values were calculated by using appropriate formulas. A total of 250 samples were processed for the study. Out of which 39 [15.6%] samples yielded mixed growth of > 2 organisms. All these samples were excluded out of the study [remaining 211 samples]. Microscopic examination of 97[45.9%] samples showed no organism and no growth was obtained on subsequent culture of these samples [true negative]. 61 [28.9%] samples were found to have >/= 1 organism in Gram stained smear of uncentrifuged single drop of urine and their culture yielded growth of > 10[5] or 10[4] to 10[5] CFU of pure single type /ml of urine [true positive]. No organism was detected on microscopic examination of 9 [4.2%] samples however pure growth of single organism was obtained on their culture [false negative]. >/= 1 organisms were seen on the microscopic examination of 44 [20.8%] samples which failed to grow on culture media [false positive]. Sensitivity [87.1%], specificity [61 .39%], positive predictive value [58.09%], negative predictive value [91.5%] was calculated by using respective formulas. This method provides a good negative predictive value and helps to rule out the presence of UTI efficiently when bacteria are not seen on microscopic examination. A very simple method without the use of laboratory centrifuge and culture media makes it an ideal practice in peripheral laboratories devoid of adequate resources and facilities to deal with one of the most commonly received specimens