Escalating threat from tuberculosis: the third epidemic.

Abstract

A 1994 study reported on cases of drug-resistant tuberculosis (TB) at the Chest Service at Bellevue Hospital, in New York City. 20 years of TB laboratory susceptibility tests were reviewed in 4681 cases. Combined resistance to isoniazid and rifampicin rose from 2.5% in 1971 to 16% in 1991. Over 75% of these cases in 1991 were resistant to rifampicin, isoniazid, streptomycin, and ethambutol. Most of the patients belonged to one or more of the following groups: young, Black or Hispanic, unemployed, homeless, male, HIV-infected, and drug abuser. Clinical characteristics were: anergy, fever, cough, night sweats, weight loss, radiograph bilateral infiltrates, adenopathy, cavities, miliary shadowing, and normal chest radiograph. Overall, in 1993 in the US, 3% of all new cases and 6.9% of recurrent cases were resistant to both rifampicin and isoniazid. This resurgence of TB in industrialized countries has been ascribed to: 1) immigration of foreign populations at high risk of developing TB, 2) coinfection with HIV, and 3) an increase in high risk groups. The WHO stresses the importance of identifying meaningful denominators when discussing both primary and acquired drug resistance rates. Restriction fragment length polymorphism (RFLP) is the molecular technique that differentiates individual strains of Mycobacterium tuberculosis. Three recent studies from New York used RFLP to demonstrate the clustering of multidrug-resistant TB. Solutions to the problem consist of adequate infrastructure, i.e., a national TB program; prescription of combined preparations; inducement or enforcement of compliance using directly observed therapy (DOT) (a DOT protocol employed in Denver, Colorado, used 2 weeks of therapy followed by 24 weeks of twice weekly intermittent therapy); prevention of nosocomial spread by isolation of smear-positive cases during the first 2 weeks of treatment; rapid diagnosis of TB and drug susceptibility (within 10-21 days using radiometric culture, nucleic acid probes, and high performance liquid chromatography of mycolic acids); and treatment by five or six drugs.