Risk Factors for Tuberculosis Conversion in a State Prison

A case-control study determined the risk factors for latent tuberculosis (TB) conversion among Oregon Department of Correction (ODOC) inmates from July 2000 July 2001. The first objective was to identity the converters. These were inmates who tested negative for the Purified Protein Derivative (PPD) skin test on entry and subsequently tested positive on annual testing. The second objective was determining the risk factors for conversion by comparing the converters with randomly selected controls. The Correctional Information System (CIS) and Mental Health databases were accessed to obtain health and demographic information. With ninety-nine percent of PPD positive inmates on anti-tuberculosis medications, nearly all male inmates who tested positive from July 00-01 (n = 307) were identified through the ODOC pharmacy records. A medical chart review (276 of 307 or 90%) separated the converters (n = 72) from the reactors who tested positive on entry (n = 123) and the prior positives on medications (n = 81). The conversion rate was 5.0 per 1,000 person-years. Differences between the cases (converters) and controls were analyzed using multivariate logistic regression. The converters were 6 times more likely to be Latino (p < .005) vs. Caucasian, over 19 times less likely to live in medium vs. minimum (p < .001) or maximum vs. minimum (p < .001) security prisons, and over 5 times less likely to live in a medium vs. low (.012 < p < .031) or high vs. low (.002 < p < .007) density prison. They had 1.4-1.5 times fewer PPD skin tests (.002 < p < .009) and lived in 1.5-1.7 times fewer prisons (.005 < p < .017). Age, education, county of incarceration, number of incarcerations, and number of visitors were not found to be significant variables. The results revealed a low conversion rate compared to other U.S. prisons. Prison health officials should consider performing two-step skin testing in order to distinguish the booster phenomenon from intramural conversion. INTRODUCTION Worldwide, tuberculosis (TB) is the second leading cause of death from a single infectious agent (1). Onethird of the world population is infected with Mycobacterium tuberculosis and causes were multifactorial: decreased funding for tuberculosis surveillance, increased immigration from areas of high TB prevalence, the unfortunate rise in HIV/AIDS, and major outbreaks in congregate settings such as prisons. Prisons had three times the rate of pulmonary TB than the general population and in some New York, New Jersey, and California prisons, the incarcerated were 6-11 times more likely to develop active TB than the non-incarcerated (3-5). In response to the outbreaks, the Centers for Disease Control (CDC) developed guidelines for correctional facilities in 1989 and again in 1995 (6-7). In the first guideline, the increased risk for active TB due to coinfection with HIV was highlighted. In the second guideline, the same principles of surveillance, namely screening, containment, and assessment, were emphasized. The basic principles revolved around yearly PPD skin testing, treatment with prophylactic * To whom correspondence should be addressed: 255 SW Harrison Street, #7G, Portland Oregon, U.S.; Email: hungr@ohsu.edu. Tuberculosis in Prison 27 Vol. 7 No. 1 medications, containment of active cases, and periodic assessments through incidence studies such as this one. Based on these recommendations, the ODOC instituted yearly PPD skin testing in 1990. With increased surveillance of high-risk populations such as inmates, immigrants, minorities, and the immuno-suppressed, the incidence of active TB in the U.S. decreased from 9.8 cases per 100,000 in 1993 (n = 25,287) to 5.2 cases per 100,000 in 2002 (n = 15,078). (8) In Oregon, the incidence was even lower, with a rate of 3.2 per 100,000 in 2002 (n = 111) (9). Only a few active cases were found in the Oregon Department of Corrections (ODOC). From 1995-2001, there was only one case in each of 1997, 1998, and 2001 (9). The decrease in incidence ushered a new paradigm with regards to TB control. In May 2000, the Institute of Medicine (IOM) issued a report entitled, "Ending Neglect: The Elimination of Tuberculosis in the United States" (10). The report detailed the multi-factorial strategies necessary to prevent TB resurgence and decisively eradicate TB in the U.S.. Eradication was defined as < 0.1 case per 100,000 person-years. The basic principles revolved around surveillance, applied research, prevention and control, and infrastructure. A shift from active to latent TB screening was emphasized. The focus was on preventing active TB by detecting and treating latent TB. By doing so, the reservoir of Mycobacterium tuberculosis could be essentially eliminated. In the ODOC, health officials wished to know the extent of TB transmission and the risk factors for latent TB conversion. The known risk factors in other prisons and jails were the following: 1) exposure to an active case, 2) increased crowdedness, 3) increased duration of stay, 4) being housed in multiple institutions, and 5) being incarcerated multiple times (11-13). With this information, they could increase the frequency of skin testing in the high-risk inmates. In addition, the baseline conversion rate could be established and the possible reasons for conversion explored. Of note, the booster phenomenon has been known to cause initial false negative tests. A 'booster' is a person with TB whose immune system is unable to elicit a positive response until the second skin test. They are erroneously mistaken for converters. METHODS Study Population The ODOC consisted of twelve institutions and one intake center during the study period from July 00-01 (14). The inmate population ranged from n = 166 at the Oregon Women's Correctional Center to n = 2,794 at the Snake River Correctional Institution. Men comprised 95% (n = 9,746) of the inmate population and women 5% (n = 573). Three-quarters of the inmates were Caucasian, 11% Latino, 11% Black, and 3% other. One-third of the inmates were between the ages of 18-30, almost half between 31-45 and one-fifth between 45 and 70. Due to the demographic preponderance of men, women were excluded from the study. Confidentiality Institutional Review Board (IRB) approval was obtained and inmate names stripped from the records. A unique identifier was used and all the data presented in aggregate form. Case Selection Pharmacy records revealed that 307 men were on anti-TB medications during the study period. This captured 99% of men with a recent or past positive skin test. Ninety percent of their medical charts containing skin test data were reviewed (n = 276) and the men separated into converters (n = 72), reactors (n = 123), and prior positives on medications (n = 81). Converters were inmates who tested negative at entry and positive on annual testing. Some of them were positive before the oneyear period (n = 23). Reactors were inmates who tested positive at entry, and priors on medications were positive before entry. Ten percent of the records (n = 31) were not reviewed and accounted for a potential of 8 missing converters. Control Selection A database manager at the ODOC randomly selected 305 male inmates from all 12 institutions who were never on anti-TB medications. All of these inmates resided in the ODOC from July 00July 01. Seventy-seven percent (n = 234) of the controls were verified through a medical chart review. Demographic Information The demographic variables seen in table 1 were collected from two sources. All the variables were derived from the Correctional Information System (CIS) database except for "drug abuse potential" that came from the mental health computer database. Inmate psychiatric assessments provided the data for that variable. Data Analysis The conversion rate was calculated by dividing the number of converters from the estimated inmateyears during the study period. For the case-control study, univariate analysis was performed with the use of chi-square for categorical 28 McGill Journal of Medicine 2003 Table 1. Demographic characteristics of the cases and verified controls. Characteristics Cases Verified Controls