False-negative BD MGIT™ TBc Identification Test results in routine tuberculosis diagnosis: a New Zealand perspective.

>We previously reported on a comparison of the AccuProbe(®) Gen-Probe(®) MTBC assay (AccuProbe) (BioMérieux, Marcy L'Etoile, France) with the Becton Dickinson (BD) MGIT™ TBc Identification (TBc) Test (BD, Franklin Lakes, NJ, USA) in our laboratory. In the period following the shift from the AccuProbe assay to the TBc test, we obtained six false-negative results. On sequencing the mpt64 gene, we found that these false-negative cases had mutations in the mpt64 gene due to deletion, insertion or substitution. Despite the occurrence of false-negative results, we found that the reduced cost and minimal technical expertise, combined with a new testing algorithm, still make this test the preferred option for rapidly identifying Mycobacterium tuberculosis complex in MGIT cultures in a low TB burden country such as New Zealand.

Clinical failures associated with rpoB mutations in phenotypically occult multidrug-resistant Mycobacterium tuberculosis.

SETTING: Recently, Mycobacterium tuberculosis isolates have been described that test phenotypically susceptible to rifampicin (RMP) yet harbour genotypic rpoB mutations. OBJECTIVE: 1) To investigate the impact of such mutations on clinical outcomes among RMP-susceptible isolates, and 2) to determine the prevalence of rpoB mutations among isoniazid (INH) monoresistant isolates at our laboratory and to describe the association between the presence of these mutations and clinical outcomes. METHODS: M. tuberculosis isolates were screened for mutations in the rpoB gene using the Cepheid Gene-Xpert® MTB/RIF assay. Clinical correlation was made by reviewing patient case notes. RESULTS: Isolates from 94 patients were found to have INH-resistant, RMP-susceptible profiles. Clinical information was available for 52 patients, including three whose isolates had rpoB mutations. All three of these patients had treatment failures, compared to two of 49 patients whose isolates did not have rpoB mutations (P = 0.0005). DISCUSSION: We demonstrate a significant association between the presence of rpoB gene mutations that are not detected at the current RMP critical concentration and treatment failure. We suggest that a review of the current RMP critical concentration is warranted to ensure that RMP is not used inappropriately for the treatment of phenotypically occult multidrug-resistant tuberculosis.

Epidemiological features of drug resistant tuberculosis in Harare, 1994 to 1996.

OBJECTIVES: To characterise the prevalence, clinical and radiological features of drug resistant tuberculosis in selected patients with pulmonary tuberculosis in Harare between 1994 and 1996. DESIGN: A retrospective review of medical and microbiological records. SETTING: Beatrice Road Infectious Diseases Hospital, Harare, Zimbabwe. SUBJECTS: 381 smear-positive tuberculosis patients who had samples submitted to the National Tuberculosis Reference Laboratory for culture and susceptibility testing. MAIN OUTCOME MEASURES: Prevalence of resistance of isolated cultures of Mycobacterium tuberculosis to anti-tuberculosis drugs; clinical, radiological and microbiological response to treatment with recommended anti-tuberculosis regimens. RESULTS: Resistance to one or more drugs was detected in 16 isolates (16/165, 9.7%), single drug resistance in five (3.0%) and resistance to two or more drugs in 11 (6.7%). There were no distinctive clinical or radiological features of drug-resistant tuberculosis, although a higher percent of drug resistant cases had evidence of pleural disease (25% vs 2.5%, p = 0.005). Neither past history of tuberculosis or known or suspected HIV infection was associated with the presence of drug resistance. CONCLUSIONS: In spite of the resurgence of tuberculosis and the high prevalence of HIV infection in Zimbabwe, the rates of drug resistance have remained relatively low, even among a selected population at high risk of resistance. A significant proportion of cases of drug-resistant tuberculosis appear to be due to new transmission of drug resistant strains, which reinforces the importance of maintaining a surveillance system for the monitoring of drug susceptibility. Ongoing prospective studies should provide more reliable estimates of the prevalence and determinants of drug resistance in Zimbabwe.

The use of monoclonal antibodies to identify mycobacteria grown in culture in Zimbabwe.

Monoclonal antibodies (Mabs) were used in an ELISA system to identify 462 mycobacterial isolates from clinical specimens in Zimbabwe. Cultures of mycobacteria were either sonicated or mechanically homogenised and used to coat the wells of microtitre plates. The mouse Mabs used reacted to lipoarabinomannan, an antigen common to all species of mycobacteria, to a 16 kDa protein specific to members of the Mycobacterium tuberculosis complex, to a glycolipid found in the cell wall of M. kansasii and to a glycolipid found in the cell wall of members of the M. avium-intracellulare complex. On the basis of serologic reactivity 443/462 (94%) isolates were identified as M. tuberculosis, 6/462 (1%) were identified as M. avium-intracellulare and 7/462 (2%) were identified as M. kansasii. The remaining 16 isolates gave negative reactions with each of the monoclonals, except that reactive with lipoarabinomannan. On the basis of biological tests on the 13 of the isolates that were available, 6 were identified as M. tuberculosis and 3 as M. bovis. In each of these the optical densities in the ELISA with at least one of the Mabs directed against the 16 kDa protein, was within 0.2 units of the cut off value. 4 isolates were not identifiable using biological tests in our laboratory. Each of the available isolates identified serologically as M. avium-intracellulare or M. kansasii gave biological reactions consistent with this identification. This study has shown Mab-ELISA to be a reliable means of rapidly identifying large numbers of mycobacterial isolates in a reference laboratory in Zimbabwe.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the autistic patient's dental needs and ability to undergo dental examination.

A successful clinical examination was achieved on the first attempt for 50 percent of the autistic patients. In general, autistic patients had a lower hygiene level than those in the control group, but a comparable caries index. Behavior management techniques included positive reinforcement; tell, show and do; and negative reinforcement.