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Tuberculosis Transmission in a State Correctional Institution -- California, 1990-1991

During September and October 1991, active tuberculosis (TB) was diagnosed in two inmates and one employee of a California state correctional institution (1991 average annual inmate population, 5421; employees, 1500). This report presents findings from an investigation by the California Department of Health Services (CDHS), the California Department of Corrections (CDOC), and CDC to determine whether ongoing transmission of Mycobacterium tuberculosis was occurring in the institution. Case-Finding Among Inmates

A case of TB was defined by using the CDC surveillance case definition for clinically or laboratory-confirmed TB (1) in any inmate diagnosed or treated for TB in the institution during 1991. Of 18 cases identified, 15 were culture confirmed. Of the 15 M. tuberculosis isolates, 12 were susceptible to all drugs tested, and three were resistant to a single drug (one to isoniazid, one to streptomycin, and one to ethambutol). For 10 (56%) of the 18 persons, onset of illness was recognized for the first time while they were in this institution during 1991, for an annual incidence of 184 per 100,000 population in the institution. For the remaining eight, seven had TB diagnosed before imprisonment, and one inmate had TB diagnosed in 1990.

Restriction fragment length polymorphism analysis performed on 12 available isolates revealed three distinct DNA patterns among eight M. tuberculosis isolates; the remaining four each had different patterns. However, inmates with similar isolates were not present at the institution at the same time and therefore could not be linked epidemiologically.

Because of limited clinical evaluation and prolonged time to sputum conversion, three case-patients may have been infectious for a total of 7 person-months during 1991. Other active cases were not considered infectious: three were not culture confirmed, six were diagnosed and the patients were started on adequate treatment before they entered the correctional institution, two were in persons who had no cough and had smear-negative pulmonary TB, and four were in persons who had only extrapulmonary TB.

Of the 10 inmates whose diagnoses of TB were made while in the institution in 1991, two had negative tuberculin skin tests (TSTs) documented on entry to the correctional institution 8 months before the diagnosis of TB. Neither patient had any known risk factors for anergy; one was negative for antibody to human immunodeficiency virus (HIV), and the other was not tested but did not report HIV risk behaviors. Tuberculin Reactivity Among Inmates

The point prevalence of tuberculin positivity and the incidence of TST conversion among inmates were estimated from inmate skin test results in November 1991 and correctional institution medical records. A positive TST was defined as a reaction of greater than or equal to 10-mm induration in response to 5 tuberculin units of tuberculin purified protein derivative administered by the Mantoux method.

Of 3070 inmates in the prison at the end of November 1991, TST results were available for 2944 (96%). Of these, 873 (30%) were TST positive: 549 had a history of a prior positive test and were not retested in November 1991, and 324 tested positive for the first time at the prison in November 1991.

Of the 324 who tested positive at the prison, 155 had no record of an earlier TST; for 21, results had been recorded as positive but the size of their TST reaction was not recorded. The remaining 148 TST-positive inmates had documented skin test conversions. Of these, 106 (72%) entered the state prison system with a negative TST and had skin test conversions while in the state prison system; for 97 of the 106, skin test conversion occurred within the previous 2 years. The remaining 42 persons who had skin test conversions spent some time outside the prison system during the conversion intervals. Because of frequent inmate movement between correctional institutions, conversions could not be attributed specifically to the institution under investigation.

The 2-year conversion incidence was estimated to be 5.9 per 100 person-years spent in the prison system. Case-Finding and Prevalence Among Employees

The employee identified as one of the three index case-patients was diagnosed with culture-negative pulmonary TB in September 1991; the source of the employee's infection is undetermined. This employee worked as a counselor on the prison's HIV unit and recalled exposure to one of the three infectious inmates. The employee did not report any exposure to TB outside the prison. The employee's most recent negative multipuncture skin test for TB had been in May 1989, 1 year before employment at the prison.

Records regarding employees' current or past TST status were incomplete. However, two other employees had documented skin test conversions during the previous 2 years while working at the prison; one reported exposure to an inmate with possible TB. Neither reported any known exposures to M. tuberculosis outside the prison. Reported by: F Schwartz, MD, Marin County Health Dept, San Rafael; S Singh, PM Small, MD, Howard Hughes Medical Institute, Stanford; D Cashman, MD, R Campbell, DO, N Khoury, MD, California Dept of Corrections; S Coulter, S Royce, MD, R Roberto, MD, GW Rutherford, III, MD, State Epidemiologist, California Dept of Health Svcs. Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: The incidence of active TB among inmates of this prison was more than 10 times the crude incidence of TB in California (17.4 per 100,000 population) for 1991. In addition, the number of incident cases was three times what would have been predicted for a population of this size and demographic profile. Although the incident cases apparently were not linked, two findings from this investigation suggest that transmission of M. tuberculosis may have occurred in the prison: first, at least two inmates with active TB may have become infected at the prison; and second, a substantial number of TST conversions were documented among asymptomatic inmates. The prolonged infectiousness of the three active cases in the prison illustrates the potential for M. tuberculosis to be propagated in the prison system.

Although it cannot be proven that the 97 inmates who had TST conversions within the previous 2 years were infected while in prison, the 2-year conversion incidence of 5.9 per 100 person-years in prison probably underestimates the risk for new M. tuberculosis infection. No information was available regarding the timing of conversion and the potential for acquisition of infection in the state prison system for at least 155 inmates.

The findings in this report, as well as previous findings of the potential for introducing multidrug-resistant TB into correctional systems (2), emphasize the need to improve infection-control practices in these settings. State health departments can assist correctional system officials in implementing control measures in correctional facilities (3), including 1) regular and systematic TB screening of inmates and staff, with HIV testing and TB preventive therapy (PT) for those who test positive for TB and are eligible for PT; 2) rapid identification, isolation, and treatment of suspected cases of TB; 3) directly observed therapy and PT, and rigorous follow-up and recordkeeping to ensure completion of treatment; and 4) follow-up to assure continuity of care both inside and outside the correctional facilities.

Recent California legislation, supported by the CDOC, the CDHS, and state employee organizations, requires inmate and employee TB skin testing, requires reporting of results to the CDHS, and designates that treatment for TB may be required as a condition of parole for inmates with active TB. The CDHS and the CDOC are cooperating in implementing the mandates of the legislation. The CDOC is addressing infection-control issues in its facilities, and its staff members are participating on the California Tuberculosis Elimination Task Force and the Interagency Working Group on Tuberculosis.


  1. CDC. Case definitions for public health surveillance. MMWR 1990;39(no. RR-13):39-40.

  2. CDC. Transmission of multidrug-resistant tuberculosis among immunocompromised persons in a correctional system -- New York, 1991. MMWR 1992;41:507-9.

  3. CDC. Prevention and control of tuberculosis in correctional institutions: recommendations of the Advisory Committee for the Elimination of Tuberculosis. MMWR 1989;38:313-20,325.

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