Limited Transmission of Multidrug-Resistant Tuberculosis Despite a High Proportion of Infectious Cases in Los Angeles County, California

Abstract

Preventing transmission of multidrug-resistant tuberculosis is critical because of treatment toxicity, cost, and the lack of effective therapy for latent infection. We attempted to determine the extent of transmission in Los Angeles County by comparing relatedness of multidrug-resistant tuberculosis cases using restriction fragment length polymorphism and by cross-matching contact information to the Tuberculosis Registry. Strain typing was done on isolates of 102 pulmonary multidrug-resistant cases identified between August 1993 and 1998. Seventy-one (70%) of the cases had cavitary lesions on chest radiograph, and 94 (92%) had sputa smear-positive for acid fast bacilli. Fifteen (15%) of the cases were known to be infected with human immunodeficiency virus. Four molecular clusters of two cases each and one closely related pair were identified among the 102 cases; contact investigation successfully identified all clusters but one. Among 946 contacts identified and cross-matched with the county's Tuberculosis Registry, one secondary case due to drug-resistant Mycobacterium bovis was found. To summarize, a very high proportion of pulmonary multidrug-resistant tuberculosis cases in Los Angeles County were infectious. Molecular strain typing indicated limited spread of disease, although it underestimated transmission compared with contact investigation. We believe aggressive surveillance and case management were critical to limiting the spread of multidrug- resistant tuberculosis.

Systematic Molecular Characterization of Multidrug-Resistant Mycobacterium tuberculosis Complex Isolates from Spain

“…The RFLP pattern of the strains in cluster tb5b had previously been described in the northwest of Russia, where these strains are highly prevalent (19). Immigrants play an important role in the spread of TB in some countries (5,9,21,40). However, relatively few of our patients (13.3%) were immigrants.…”

“…Spain has one of the highest incidences of TB in Western Europe. The incidences of pulmonary TB were 22.67, 21.05, and 19.64 per 100,000 inhabitants, respectively, in 1998, 1999, and 2000 (29). Standard restriction fragment length polymorphism (RFLP) analysis (30) revealed that 39% of isolates collected in Zaragoza (where the incidence of TB is similar to that in the whole of Spain) in 1993 were clustered (30), suggesting recent transmission.…”

“…A study with guinea pigs showed that mutations or deletions within the katG gene decrease the pathogenicity of isoniazid (INH)-resistant strains of Mycobacterium tuberculosis (16). A recent study in Los Angeles County showed that the transmission of MDR TB can be limited (7.8%) by aggressive surveillance (21). A recent study in The Netherlands showed that INH-resistant isolates harboring a mutation at amino acid 315 and INH-susceptible strains are equally likely to cluster (40).…”

Transmission of multidrug-resistant tuberculosis in the USA: a cross-sectional study

“…14 MDR tuberculosis has a substantial economic effect on programmatic activities, which is a result of treatment costs of long regimens, frequent admissions to hospital, and the necessary use of injectable drugs. 15 Although some control programmes have successfully reduced transmission of MDR tuberculosis, [16][17][18] the extent of MDR tuberculosis attributable to transmission in the USA is unknown. Previous studies 14,17,18 have not had wide geographical scopes or in-depth examination of epidemiological and clinical information that is necessary to confirm transmission.…”

Deciphering an Outbreak of Drug-Resistant Mycobacterium tuberculosis

“…Nitta et al describe limited transmission of MDR TB in Los Angeles, Calif. (16). Those authors concluded that a possible reason for this limited transmission could be the excellent TB control measures in Los Angeles.…”