Improved Sensitivity of Sputum Smear Microscopy after Processing Specimens with C ₁₈ -Carboxypropylbetaine To Detect Acid-Fast Bacilli: a Study of United States-Bound Immigrants from Vietnam

Abstract

The goal of this study was to evaluate the effect of the specimen-processing method that uses the detergent C 18 -carboxypropylbetaine (CB-18) on the sensitivity of acid-fast bacillus (AFB) staining. Vietnamese immigrants with abnormal chest radiographs provided up to three sputum specimens, which were examined for acid-fast bacilli by use of direct auramine and Ziehl-Neelsen staining. The remaining sputum was split; half was cultured, and the other half was incubated with CB-18 for 24 h, centrifuged, and examined for AFB by both staining methods. CB-18 processing improved the sensitivity of AFB staining by 20 to 30% (only differences in auramine sensitivity were statistically significant) but reduced specificity by Ϸ20% (P < 0.05). These findings have direct utility for overseas migrant tuberculosis screening programs, for which maximizing test sensitivity is a major objective.Sputum smear microscopy to detect acid-fast bacilli (AFB) is a rapid, inexpensive, and highly specific tool for identifying persons with active tuberculosis (TB) and represents a critical component of overseas screening for immigrants. The sensitivity of the AFB smear method is moderate (1, 2, 8, 10); a recent study of overseas TB screening for United States immigrant visa applicants reported the sensitivity of AFB smears to be approximately 34% (9). The goal of this study was to evaluate the effects of C 18 -carboxypropylbetaine (CB-18) (10, 16) specimen processing on AFB smear sensitivity and specificity for detecting TB disease (i.e., Mycobacterium tuberculosis complex [MTBC] culture-positive TB disease) among United Statesbound immigrants from Vietnam.A prospective cohort of United States-bound adult (Ն18 years) Vietnamese immigrants with abnormal chest X rays (CXRs) suggestive of TB was enrolled at Cho Ray Hospital in Ho Chi Minh City, Vietnam, between May 2000 and June 2001. Applicants with CXR findings suggestive of TB disease provided up to three sputum specimens (5); only specimens of 10 ml or greater were eligible for analysis.Specimens were examined by direct staining by use of both auramine and Ziehl-Neelsen (ZN) staining techniques according to recommended procedures (7). After staining, equal volumes of 50 mM NaOH containing 0.5% N-acetyl-L-cysteine (NALC) were used to homogenize the specimens, and specimens were split approximately equally. One half of each specimen was transferred to the Institute Pasteur in Ho Chi Minh City, where culture facilities are available, and was digested by using the standard oxalic acid (OxAC) procedure (7). After centrifugation at 3,046 ϫ g for 15 min, specimens were decanted and the residue neutralized by using 4% NaOH containing phenol red. Portions of each specimen were analyzed by culture (BACTEC 12B with PANTA Plus [Becton Dickinson, Sparks, MD] and Lowenstein-Jensen slants).Positive 12B bottles underwent ZN staining to confirm the presence of AFB. Lowenstein-Jensen slants were incubated at 35°C to 37°C for two months and inspected weekly for growth. Tubes were examined macroscopically; o...

Comparison of NALC-NAOH processing method with C18-carboxy propyl betaine method for the detection of mycobacterium in sputum

“…7 Our results are in parallel with Charles G. thornton 1998, K. F. Laserson 2005. 12,6 It has been shown CB-18 improves the recovery of mycobacteria other than tuberculosis among human respiratory specimens and also among animal products such as milk. [12][13][14][15] In present study, on processing the direct AFB negative sputum samples (N=279) using LJ medium culture had displayed an improvement in the positivity of AFB to 28.3% (N=79) indicating culture as a gold standard.…”

“…All processed specimens were decanted, resuspended in the remaining supernatant backwash, and transferred to microscope slides for staining. 6 …”

“…In this regard, few studies reported that C18-carboxypropylbetaine method of decontamination is superior to NALC-NaOH method. 6. But, there is inconsistency regarding the sensitivity of CB18 method in detection of sputum AFB 7 Therefore, this study has been designed with a main objective of evaluating the sensitivity of NALC-NAOH and Cb18 compared to the gold standard culture Lowenstein-Jensen medium.…”

Tuberculosis prevalence among underfive children in household contact with negative acid fast bacilli adult pulmonary tuberculosis

“…16,17 Thus, there was posibility of false negative sputum microscopically. Another possibility is that we also couldn't exclude the possibility of AFB positive adult TB living in the same house and the possibility of transmission from adult TB living not in the same house.…”

Bleach method in comparison with NALC-NaOH specimen processing method for the detection of mycobacterium in sputum specimen

“…2,4 In this regard, few studies reported that bleach method of concentration is cheaper and safer method for the detection of AFB. 5 There are very less comparison studies between the NALC-NaOH and bleach methods of AFB concentration. So, a study has been designed to compare standard NALC-NaOH method with cheaper bleach method in resource limited settings.…”