Nosocomial tuberculosis: an outbreak of a strain resistant to seven drugs.

OBJECTIVE: To evaluate nosocomial transmission of multidrug-resistant (MDR) tuberculosis (TB). DESIGN: Outbreak investigation: review of infection control practices and skin test results of healthcare workers (HCWs); medical records of hospitalized TB patients and mycobacteriology reports; submission of specimens for restriction fragment length polymorphism (RFLP) typing; and an assessment of the air-handling system. SETTING: A teaching hospital in upstate New York. RESULTS: Skin-test conversions occurred among 46 (6.6%) of 696 HCWs tested from August through October 1991. Rates were highest on two units (29% and 20%); HCWs primarily assigned to these units had a higher risk for conversion compared with HCWs tested following previous incidents of exposure to TB (relative risk [RR] = 53.4, 95% confidence interval [CI95] = 6.9 to 411.1; and RR = 37.4, CI95 = 5.0 to 277.3, respectively). The likely source patient was the only TB patient hospitalized on both units during the probable exposure period. This patient appeared clinically infectious, was associated with a higher risk of conversion among HCWs providing direct care (RR = 2.37; CI95 = 1.05 to 5.34), and was a prison inmate with TB resistant to seven antituberculosis agents. The MDR-TB strain isolated from this patient also was isolated from other inmate and noninmate patients, and a prison correctional officer exposed in the hospital. Mycobacterium tuberculosis isolates from all of these patients had matching RFLP patterns. Infection control practices closely followed established guidelines; however, several rooms housing TB patients had marginal negative pressure with variable numbers of air changes per hour, and directional airflow was disrupted easily. CONCLUSIONS: These data strongly suggest nosocomial transmission of MDR-TB to HCWs, patients, and a prison correctional officer working in the hospital. Factors contributing to transmission apparently included prolonged infectiousness of the likely source patient and inadequate environmental controls. Continued urgent attention to TB infection control is needed.

Modified method for testing the quality of albumin-containing enrichments used in growth media for mycobacteria.

Many commercially available media for cultivation of mycobacteria have failed to support the growth of these organisms. This is especially true of media prepared with albumin-containing enrichments. Earlier, we developed a method for rapid identification of good albumin enrichments for agar-based media used to test the susceptibility of tubercle bacilli to pyrazinamide. The method was modified to make testing of the acceptability of albumin enrichments for primary isolation media for mycobacteria possible. We describe here a simple turbidimetric test using a specific Bacillus subtilis strain to assay quickly (24 h) different lots of albumin-containing enrichments that may be used in the preparation of growth media for mycobacteria.

High-performance liquid chromatography analysis of mycolic acids as an aid in laboratory identification of Rhodococcus and Nocardia species.

High-performance liquid chromatography analysis of the p-bromophenacyl esters of mycolic acids from whole organisms gave chromatographic patterns that were useful in differentiation of Rhodococcus and Nocardia species. Rhodococcus equi, R. erythropolis, and R. rhodochrous contained more-polar mycolic acids and were easily separated from the less-polar mycolic acid-containing species of R. sputi, R. bronchialis, R. corallinus, R. rubropertinctus, and R. terrae. The less-polar mycolic acid-containing Rhodococcus species showed chromatographic patterns that partially overlapped (in elution times) the patterns of Nocardia asteroides, N. otitidiscaviarum, and N. brasiliensis, but the larger number of peaks in the last species made separation between the genera possible. Distinct chromatographic patterns were found for most species, except for R. equi strains that showed two different patterns. Strains of R. rubropertinctus and R. terrae appeared identical. N. asteroides and N. otitidiscaviarum showed similar mycolic acid patterns.

Nosocomial mycobacterial pseudoinfection in a Georgia hospital.

Nosocomial pseudoepidemics may be detected when clustering of pseudoinfections occur or when artificial clusters of real infection are observed. Nontuberculous mycobacteria were reportedly isolated from specimens obtained from seven patients at one hospital from October 1980 to January 1981. Because the patients' clinical illnesses were not uniformly consistent with mycobacterial disease, we hypothesized that pseudoinfections had occurred and searched for a common source of contamination. The investigation suggested that specimen contamination was associated with one microbiology laboratory technician: 6 of 22 (27%) specimens processed by that person were positive compared with 1 of 103 (1%) specimens processed by the other five technicians. However, a specific mechanism of contamination was not identified. Nosocomial pseudoepidemics associated with false infections should be suspected and investigated when clinical features and laboratory findings do not agree.

Preservation of mycobacteria at -70 degrees C: survival of unfrozen suspensions in transit.

Mycobacteria stored at -70 degrees C retain 100% viability and maintain their definitive taxonomic, serologic, immunologic, and pathogenic properties. When shipped at ambient temperatures, however, suspensions of all mycobacteria lose viability in transit, with those species having a narrow temperature range for growth (Mycobacterium tuberculosis and M. bovis) being most severely affected. In spite of these losses, all strains retain their definitive taxonomic properties. If care is taken in pre-testing and post-testing the microbial populations being preserved, mycobacteria are probably best shipped in the lyophilized state, and this procedure has been successfully used for several international studies.

Preservation of mycobacteria st -70 degrees C: persistence of key differential features.

The advantages of long-term preservation of suspensions of mycobacteria by storage at -70 degrees C established in earlier studies are reinforced by present evidence that freezer storage does not alter key taxonomic features used to identify mycobacteria. Occasional discrepancies in biochemical test characteristics of mycobacteria that have been stored in the freezer and reconstituted at 37 degrees C reflect only sluggish metabolic activity, which is restored to normal on repeat testing.

Laboratory services for mycobacterial diseases.

The philosophy of the recently proposed "Levels of Laboratory Service" program, which will be so vital to the conduct of a successful outpatient tuberculosis treatment and control program, is presented. The hallmark of this program is the decentralization of the diagnostic/monitoring services as they involve laboratory participation. In the long run this could mean more efficient operation, more reliable reporting, and probably less work for the participating laboratories. The greater emphasis on smear examination (Level I) as a monitoring tool will mean fewer cultures, thereby lessening the load for those laboratories that once went through countless clinically requested exercises of repetitively proving by culture the existence of M. tuberculosis in a given patient. Doubtless, the bulk of the work will be conducted in Level II laboratories; but here, too, identification of the most easily defined pathogen, M. tuberculosis, will minimize the over-all workload for these investigators while decreasing their concern about mycobacteria other than tubercle bacilli. Expertise gained in frequent repetitions of a limited number of tests (niacin, nitrate reduction, and pH 7/68 degrees C catalase) will ensure reliable speciation of the clinically most important Mycobacterium. The work of Level III laboratories should eventually be reduced primarily to organisms other than M. tuberculosis, thereby ensuring that a number of highly competent reference institutions will not only attain proficiency in taxonomic aspects of mycobacteria, but will also reflect the regional picture of the changing patterns in mycobacterial pathogens of man. Participation of laboratories in proficiency testing programs will encourage top-level performance in all areas. Additionally, such testing programs will serve a teaching role; a laboratory need not feel "locked in" at a given service level, but may increase its proficiency and move up a step in terms of the service it provides. In contrast, no laboratory need feel compelled to increase its activities; if daily workloads limit the extent of their involvement with mycobacteria, these laboratories can be confident that other institutions are providing needed services. The success of the entire "Levels of Laboratory Service" program depends on the recognition by individual laboratories of their own workload limitation, the directed motivation of personnel, and the maintenance of a free and open pipeline of communication to laboratories at the next higher level of service.

Comparison of two commercial formulations of the MacConkey agar test for mycobacteria.

Recent evaluations of the MacConkey agar test for differentiation of rapidly growing mycobacteria have revealed that certain strains of Mycobacterium fortuitum and M. chelonei that were expected to grow on MacConkey agar failed to do so. Investigation of two formulations of MacConkey agar showed that these two species grew better on the medium when the crystal violet dye was omitted. Several possible reasons for this difficulty are discussed. It is recommended that clinical laboratories engaged in differential identification of mycobacteria utilize commercial MacConkey agar without crystal violet when testing rapidly growing species of this genus.

Preservation of mycobacteria: 100 percent viability of suspensions stored at -70 C.

Our earlier studies on long-term preservation of mycobacteria have been expanded to include other species in this genus. Mycobacterium kansasii and M. marinum, like mammalian tubercle bacilli and BCG, survive much better when stored at -70 C. By statistical analysis, M. gordonae, M. scrofulaceum, M. xenopi, M. avium, M. intracellulare, M. terrae, M. fortuitum, and M. smegmatis survived equally well at -20 C or -70 C; however, viable counts of all strains stored at -20 C were always lower than those of paired suspensions stored at -70 C, suggesting that the lower temperature is preferable for prolonged storage periods. Advantages of preservation at -70 C in Tween-albumin liquid medium are: (i) 100% viability of bacterial populations for long periods, (ii) highly reproducible inocula for animal experiments, (iii) minimal clonal selection of undesirable mutants, (iv) maintenance of genetic characteristics, and (v) adaptability to a "seed lot" system. On the basis of available information, a discussion of lyophilization versus freezer storage is presented.

Response of hypersensitive mice to the footpad injection of living homologous or heterologous mycobacteria: preliminary report.

Mice sensitized by the injection of viable mycobacteria into one of the hind footpads responded to a second injection of mycobacteria (3 to 4 weeks later), introduced into the contralateral foot, with a degree of footpad swelling that was both accelerated and exaggerated beyond that observed after the first inoculation. The degree of specificity of this reaction (i.e., response to homologous versus heterologous mycobacteria) was comparable to that previously reported for dermal reactions of hypersensitive guinea pigs to tuberculin or tuberculin-like antigens from mycobacteria. In preliminary studies it was impossible to achieve this state of specific sensitization by vaccinating mice subcutaneously with water-in-oil emulsions of heat-killed mycobacteria; reasons for the failure are discussed. It is suggested that this tool could prove useful in both taxonomic and immunological investigations. Advantages and disadvantages of the mouse footpad test in relation to the dermal skin test in guinea pigs are discussed.