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A correction has been published: N Engl J Med 1998;338(24):1783.

Original Article
Volume 338:633-639 March 5, 1998 Number 10
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An Outbreak Involving Extensive Transmission of a Virulent Strain of Mycobacterium tuberculosis
Sarah E. Valway, D.M.D., M.P.H., Maria Pia C. Sanchez, R.N., F.N.P., M.P.H., Thomas F. Shinnick, Ph.D., Ian Orme, Ph.D., Tracy Agerton, B.S.N., M.P.H., Debbie Hoy, B.S.N., M.S.E., J. Scott Jones, B.A., Harriet Westmoreland, R.N., and Ida M. Onorato, M.D.

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ABSTRACT

Background and Methods From 1994 to 1996, there was a large outbreak of tuberculosis in a small, rural community with a population at low risk for tuberculosis. Twenty-one patients with tuberculosis (15 with positive cultures) were identified; the DNA fingerprints of the 13 isolates available for testing were identical. To determine the extent of transmission, we investigated both the close and casual contacts of the patients. Using a mouse model, we also studied the virulence of the strain of Mycobacterium tuberculosis that caused the outbreak.

Results The index patient, in whom tuberculosis was diagnosed in 1995; the source patient, in whom the disease was diagnosed in 1994; and a patient in whom the disease was diagnosed in 1996 infected the other 18 persons. In five, active disease developed after only brief, casual exposure. There was extensive transmission from the three patients to both close and casual contacts. Of the 429 contacts, 311 (72 percent) had positive skin tests, including 86 with documented skin-test conversions. Mice infected with the virulent Erdman strain of M. tuberculosis had approximately 1000 bacilli per lung after 10 days and about 10,000 bacilli per lung after 20 days. In contrast, mice infected with the strain involved in the outbreak had about 10,000 bacilli per lung after 10 days and about 10 million bacilli per lung after 20 days.

Conclusions In this outbreak of tuberculosis, the growth characteristics of the strain involved greatly exceeded those of other clinical isolates of M. tuberculosis. The extensive transmission of tuberculosis may have been due to the increased virulence of the strain rather than to environmental factors or patient characteristics.


Source Information

From the Division of Tuberculosis Elimination, National Center for HIV, STD, and TB Prevention (S.E.V., T.A., I.M.O.), Epidemic Intelligence Service, Epidemiology Program Office (M.P.C.S., T.A.), and the Division of AIDS, STD, and TB Laboratory Research, National Center for Infectious Diseases (T.F.S.), Centers for Disease Control and Prevention, Atlanta; the Department of Microbiology and Immunology, Colorado State University, Fort Collins (I.O.); the Tennessee Department of Health, Upper Cumberland Region, Cookeville (D.H., H.W.); and Kentucky Department for Health Services, Frankfort (J.S.J.).

Address reprint requests to Dr. Valway at the Division of TB Elimination, Mailstop E-10, Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA 30333.

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