2 Articles about TB
December 1, 1997 5 minutes read
[Editor’s note: In light of ongoing discussions regarding the recently proposed tuberculosis standard by the Occupational Safety and Health Administration, we detail two recent TB articles by the Centers for Disease Control and Prevention.]
Agerton T, Valway S, Gore B, et al.
Transmission of a highly drug-resistant strain (strain W1) of Mycobacterium tuberculosis: Community outbreak and nosocomial transmission via a contaminated bronchoscope.
JAMA 1997; 278:1,073-1,077.Inadequate cleaning and disinfection of the bronchoscope after diagnostic procedures performed on a patient with multidrug-resistant TB set off a cascade of events that included false-positive cultures on two subsequent patients, transmission of TB infection to another, and development of active MDR-TB in a third patient, investigators report.
In 1995, eight patients with multidrug-resistant tuberculosis were identified in South Carolina, and upon investigation it appears that three of them may have been infected nosocomially during bronchoscopy procedures. All cases were resistant to seven drugs and had matching DNA fingerprints (strain W1). Community links were identified for five patients (Patients 1-5). However, no links were identified for the other three patients (Patients 6-8), except for being hospitalized at the same hospital as one community patient.
Patient 5 (community patient) and Patient 8, diagnosed April 1995 and November 1995 respectively, had clinical courses consistent with MDR-TB, with smear-positive and culture-positive specimens and cavitary lesions on chest radiograph. Both died of MDR-TB less than 1 month after diagnosis. Patients 6 and 7 (diagnosed May 1995) each had 1 positive culture for MDR-TB. The specimens were collected during bronchoscopy. Patient 6 had a skin-test conversion after bronchoscopy. Neither Patient 6 nor Patient 7 had a clinical course consistent with MDR-TB; neither was treated for MDR-TB; and both are alive and well. No evidence of laboratory contamination of specimens, transmission on inpatient wards, or contact among patients was found. All 4 received bronchoscopies in May 1995; Patients 6, 7, and 8 had bronchoscopies 1, 12, and 17 days, respectively, after Patient 5. Observations revealed that bronchoscope cleaning was inadequate, and the bronchoscope was never immersed in disinfectant.
"Inadequate cleaning and disinfection of the bronchoscope after the procedure performed on Patient 5 led to subsequent false-positive cultures in Patients 6 and 7 and transmission of infection to Patient 6 and active MDR-TB to Patient 8," the authors concluded.
To prevent transmission of pathogens through bronchoscopes, bronchoscopies should not be performed on patients with active TB unless absolutely necessary, they advise, recommending that the clinicians follow the cleaning and decontamination protocol recommended by the Association for Professionals in Infection Control and Epidemiology. The protocol includes the following recommendations:
• Vigorous manual cleaning of bronchoscopes is essential because it has been shown that without proper prior manual cleaning, even immersion for 60 minutes in 2% glutaraldehyde will not eliminate TB from a bronchoscope.
• All surfaces of the instrument should be rinsed with 70% alcohol to reduce the risk of contamination with microbes such as Mycobacterium gordonae, which often are present in ordinary tap water. This will also facilitate drying, which is necessary because a moist environment allows any microbes present in the scope to remain viable.
• Bronchoscopes should be hung vertically and not coiled, to minimize potential accumulation of residual moisture and incubation of microbes.
A troubling aspect of the investigation is that TB transmission via a contaminated bronchoscope was only identified because the cluster involved transmission of strain W1, a highly resistant strain of M. tuberculosis not commonly seen outside New York state.
"In general, transmission of TB through bronchoscopes is difficult to assess for a variety of reasons," the authors conclude. "The time between infection with TB and the onset of symptoms is long, usually months to years after infection has occurred, thus a particular exposure in the past might never be identified as the source of infection."
Additionally, most people infected with TB never develop active disease. If persons who underwent bronchoscopies in sequential order became infected with fully susceptible TB and developed disease as a result of a contaminated bronchoscope, the possible link between their infections and their bronchoscopies may not be suspected. For those reasons, it is important to implement infection control protocols to recognize possible cross-contamination or transmission through bronchoscopes, they recommend.
Moore M, Onorato M, McCray E, et al.
Trends in drug-resistant tuberculosis in the United States, 1993-1996.
JAMA 1997; 278:833-837.Isoniazid resistance in tuberculosis remained relatively stable for the 1993-1996 period, and the percentage of multidrug-resistant TB decreased due to implementation of infection control and public health measures, the authors report. The findings were compared to surveys conducted U.S. surveys in 1991 and 1992, though differences in the surveys limit full comparison of the data.
National trends were significantly influenced by the marked decrease of MDR-TB cases in New York City. The foreign-born, HIV-positive patients, and those with prior TB have higher rates of resistance. In addition, the widespread extent of isoniazid resistance confirms the need for drug susceptibility testing to guide optimal treatment of patients with culture-positive disease.
The percentage of U.S. MDR-TB case patients from New York City dropped from 62% in the first quarter of 1991 to 30% in 1996. In the early 1990s, the New York City epidemic demonstrated the disastrous results of weakened TB control, they emphasize.
"However, dramatic improvement, including a 44% decrease in the number of MDR-TB case patients, was achieved by securing adequate resources and emphasizing basic principles of TB control under strong leadership," they note.
Patients reported to the national TB surveillance system as confirmed TB cases with culture-positive disease from 1993 through 1996 by the 50 states, New York City, and Washington, DC. Overall resistance to at least isoniazid was 8.4%; rifampin, 3.0%; both isoniazid and rifampin (i.e., MDR TB), 2.2%; pyrazinamide, 3.0%; streptomycin, 6.2%; and ethambutol hydrochloride, 2.2%.
Rates of resistance were significantly higher for case patients with a prior TB episode. Among those without prior TB, isoniazid resistance of 4% or more was found in 41 states, New York City, and Washington, DC. A total of 1457 MDR TB cases were reported from 42 states, New York City, and Washington, DC; however, 38% were reported from New York City.
"Our findings confirm that resistance to anti-TB drugs among reported TB cases in the United States remains a serious public health concern," the authors note. ". . . To prevent the development of MDR-TB, an increased suspicion for isoniazid resistance is important to ensure that initial treatment regimens are adequately supervised and include four first-line drugs."
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