Tuberculosis Disparity Between US-born African-Americans and Caucasians in Houston:

Transcription

1 Tuberculosis Disparity Between US-born African-Americans and Caucasians in Houston: A population-based study Jose A. Serpa 1, M.D.; Larry D. Teeter 2, Ph.D., James M. Musser 2, M.D., Ph.D. and Edward A. Graviss 1,2, Ph.D., MPH 1 Department of Medicine, Section of Infectious Diseases, Baylor College of Medicine, Houston, Texas 2 Center for Molecular and Translational Human Infectious Diseases Research, The Methodist Hospital Research Institute, Houston, Texas Corresponding Author: Edward A. Graviss, PhD, MPH Department of Pathology The Methodist Hospital Research Institute 6565 Fannin Street, Mail Stop MGJ Houston, TX eagraviss@tmhs.org Telephone number: Fax number: Word counts: Abstract : 150 words; Body of the text: 2576 words 1

2 Article Summary Line: An unsually high proportion of tuberculosis cases in Houston are caused by endemic strains being actively transmitted within the US-born non-hispanic Black population. Key Words: Mycobacterium tuberculosis, tuberculosis, epidemiology, minorities 2

3 ABSTRACT Background. Tuberculosis (TB) rates in the United States remain disproportionately high in certain ethnic minorities. Here we present a 9-year population-based study of TB among African-Americans in Houston. Methods. An analysis of US-born persons participating in the Houston TB Initiative ( ) was performed. Blacks were compared to non-hispanic Whites by univariate and multivariate analyses. All available Mycobacterium tuberculosis (MTB) isolates underwent susceptibility and genotype testing (IS6110-RFLP, spoligotyping and genetic grouping). Results Blacks and 565 Whites were included in the study. TB in Blacks was associated with younger age, residence in inner city, HIV seropositivity and drug resistance. Clustering was found in 82% and 72% of Blacks and Whites, respectively (P = 0.38). Three clusters had more than 100 patients each, including one with a predominance of Blacks. Conclusions. MTB cluster size was unexpectedly large in our population, which underscores the ongoing transmission of tuberculosis in Houston particularly among Blacks. 3

4 INTRODUCTION After the unprecedented resurgence in tuberculosis (TB) in the United States (US), the annual TB incidence steadily decreased from ; however, this decline has recently decelerated, raising concerns that the progress toward eliminating TB is slowing. In 2007, a total of 13,293 TB cases (4.4 cases per 100,000 population) were reported in the US, representing a 4.2% decline in the incidence from 2006 [1]. Despite this, the TB incidence continues to be higher in certain racial/ethnic minorities namely, Blacks, Hispanics, and Asians, when compared with non-hispanic Whites. For instance, US-born young Blacks probably generate the largest number of secondary cases of tuberculosis in the US [2]. In addition, non-hispanic Blacks continue to have TB rates eight times greater than non-hispanic Whites [3]. Hispanics and non-hispanic Blacks also accounted for nearly three quarters (73.9%) of 11,480 TB pediatric cases reported from 1993 to 2001, with more than half of these cases occurring in children younger than 5 years [4]. These findings clearly suggest recent ongoing transmission of Mycobacterium tuberculosis (MTB) in these ethnic groups rather than reactivation of remote infection. Recently, molecular epidemiologic studies, which estimate the proportion of clustered TB cases, have been used to support this hypothesis [5]. For instance, a molecular epidemiologic study of tuberculosis conducted in San Francisco during found clustered MTB strains in 191 (41%) of 471 studied patients that were distributed in 44 clusters. Interestingly, Hispanic or Black ethnicity, birth in the US, and a diagnosis of AIDS were found to be independent predictors of clustering [6]. Similarly, other 4

5 population-based studies in New York City, and Tarrant and Harris Counties, Texas found MTB clustering that ranged between 36% and 52% [7-9]. Molecular studies of clustering and identification of risk factors that contribute to these racial/ethnic disparities have become crucial in our ongoing effort to eradicate TB in the US. Though differences in socioeconomic status and access to the health care system among non-hispanic Blacks have been postulated as the main barriers to diagnosis and treatment of TB in this ethnic group, further information remains to be elucidated [3, 10]. Here we present a study of the traditional and molecular epidemiology of tuberculosis in US-born African Americans (Blacks) enrolled in the Houston Tuberculosis Initiative over 9 years. 5

6 MATERIALS AND METHODS Study Population. The study population included patients recruited through the Houston Tuberculosis Initiative (HTI). The HTI is a population-based active surveillance and molecular epidemiologic study that enrolls tuberculosis cases reported to the City of Houston Department of Health and Human Services and the Harris County Public Health and Environmental Services. In this study, we examined data from TB cases enrolled by HTI who had been reported between October 1995 and September Study participants were interviewed by trained interviewers using a standardized questionnaire designed to gather details of participant demographics, living situation, transportation, travel and social contacts, tobacco and alcohol use, illicit drug use, sexual behaviors, history of incarceration and personal medical history. Clinical information was supplemented through record review of all available in-patient, out-patient, and public health medical records. Molecular characterization of MTB. M. tuberculosis isolates were analyzed with 3 molecular typing methods. First, isolates were characterized by an internationally standardized protocol of IS6110 RFLP profiling [11] and analyzed with BioImage Whole Band Analysis v3.2 software (BioImage, Ann Arbor, MI). Secondly, for isolates with fewer than five IS6110 copies, the spacer oligonucleotide type (spoligotype) was determined using a commercially available kit (Isogen Bioscience BV, Maarsen, The Netherlands) according to the manufacturer s instructions. A member of the Beijing family was defined as having an octal spoligotype pattern of (previously designated as S1) [12]. Thirdly, isolates were assigned to a principal genetic group based on polymorphisms at codon 463 of the katg gene, which encodes catalase 6

7 peroxidase, and codon 95 of the gyra gene, which encodes the A subunit of DNA gyrase [13]. Susceptibility testing was performed by using BACTEC 460 radiometric culture system at the hospital or reference laboratories supplying isolates to the HTI [14]. Definitions. Race/ethnicity assignation was based upon self-report. MTB isolates were defined as being clustered if they satisfied one of two criteria. Firstly, two or more isolates from the same principal genetic group with identical IS6110 banding profiles containing five or more copies of IS6110. Secondly, isolates with identical IS6110 banding profiles containing four or fewer copies of IS6110 and sharing the same spoligotype and principal genetic group. Clusters H03 and H33 were evaluated as a single cluster because they only differ in one band by IS6110 RFLP. Drug-resistant tuberculosis was defined as an isolate resistant to at least one drug including isoniazid, rifampin, ethambutol, pyrazinamide, or streptomycin. Multidrugresistant tuberculosis was defined by the presence of resistance to isoniazid and rifampin, with or without resistance to other agents. Data analysis. Questionnaire data were entered into a longitudinal database (initially Epi Info version 6.02b, Centers for Disease Control and Prevention, Atlanta, GA; and subsequently Microsoft Access, Redmond, WA) for storage and analysis. Statistical analyses were conducted with STATA version 8.0 SE (College Station, TX). Descriptive analysis was initially carried out and selected demographic, social, and clinical factors were studied by univariate logistic regression to test for differences between US-born Blacks and US-born Whites. The use of US-born Whites and not all Others as the comparison group was chosen due to the heterogeneity observed in the latter group, particularly among non US-born Hispanics and Asians. Variables that 7

8 showed a P-value < 0.2 in the univariate analysis were considered in the elaboration of a multivariate logistic regression model to identify with factors independently associated with black race among TB patients. Covariates were not included in the model if they substantially decreased the sample size due to missing data. The variable injection drug use was used in our final model instead of drug use due to colinearity and a strong association with the former variable. Covariates that were no longer significant after adjustment for other significant variables in the full model were dropped from the final parsimonious model. Ethical approval. Individual participants gave written informed consent prior to enrollment in the study. Parental consent and case assent were obtained for subjects aged 13 years or older but younger than 18 years, and the parent served as a proxy for the interview of cases younger than 13 years old. Proxy permission and interview were also utilized for subjects who were deceased or not mentally capable of giving informed consent. The study was approved by the Institutional Review Board of Baylor College of Medicine, Houston, Texas and affiliated hospitals, and the University of Texas Health Science Center-Houston, Committee for the Protection of Human Subjects. 8

9 RESULTS Study Population. A total of 4312 cases of tuberculosis were reported in Harris County between October 1995 and September Of those, 3662 (85%) agreed to participate in the study and were interviewed by trained staff personnel of the HTI. There were 1318 (36%) US-born Blacks, 1220 (52%) Hispanics, 565 (24.1%) US-born Whites, 463 (19.8%) Asians and 85 (4%) foreign-born Blacks. Among interviewed cases, 3064 (84%) had a positive culture for MTB, and 2806 (92%) of those isolates underwent molecular characterization by the methods described above. Interviewed subjects were more likely to be younger, Black, HIV seropositive, and MTB culture positive than those who refused to participate or could not be located (P < 0.01 for first three comparisons and P = 0.03 for the last comparison). Rates of tuberculosis during the study period. Although the overall US incidence of tuberculosis decreased from 8.0 to 4.9 cases per 100,000 persons in the period , TB incidence in Harris County, Texas has remained fairly stable since the year 2000 after an initial decrease in (Figure 1). Stratification by ethnicity showed that African Americans consistently had the highest TB incidence in Harris County. In fact, for the year 2004, African-Americans accounted for approximately 56% of all TB cases among US-born cases despite representing only 18% of the Harris County population (Texas State Data Center and Office of the State Demographer. US-born Blacks versus US-born Whites. Table 1 displays relevant demographic and clinical variables according to ethnicity. Variables which were more likely to occur among US-born Blacks than US-born Whites included younger age, not being married, 9

10 fewer years of education, unemployment, inner city residence, lower income, use of public transportation, renal disease, HIV seropositivity, extra-pulmonary disease, MTB culture positivity, MTB clustering, and MTB resistance. There were a total of 614 HIV-infected tuberculosis patients in our study population, reflecting a 28% rate of co-infection among US-born Blacks and 20% among US-born Whites (P < 0.001). Hispanics and Asians had markedly reduced rates of HIV co-infection (9.1% and 1.7%, respectively). Pulmonary disease was the predominant clinical presentation in the study population; however, extra-pulmonary disease was reported more frequently among US-born Blacks than US-born Whites (P < 0.01). Resistance to at least one anti-tuberculosis agent was recorded in 80 (7.3%) isolates from US-born Blacks compared with 22 (4.5%) isolates from US-born Whites (P = 0.04). Multi-drug resistance tuberculosis represented only 1% of all cases. Mortality defined as death within 180 days of diagnosis of TB was approximately 10% and it was similar among US-born Blacks and US-born Whites. Clustering of cases within groups. Among all reported cases (4312) during the study period, 3578 (including enrolled and non-enrolled cases) had at least one positive MTB culture. Isolates from 3227 (90%) were genotyped, including 1984 (61.5%) that had matching genotypes with at least one other isolate. A total of 242 clusters were identified and the cluster size varied from 2 to 172 patients (mean: 57.2; median: 27). Analysis of isolates from enrolled cases (2807) revealed that 1765 (63%) isolates were clustered including 822 of 1007 (82%) isolates from US-born Blacks and 349 of 448 (77%) isolates from US-born Whites (P = 0.05). Significantly lower rates of clustering were observed among Hispanics and Asians (52% and 28%, P < 0.01, 10

11 respectively) probably underscoring a higher proportion of reactivation of remote infection in these patients. The cluster size for US-born Blacks was larger (mean: 69.3, median: 45) than for US-born Whites (mean: 46.7, median: 14) (P < 0.001). TB strains belonging to the Beijing family represented 26% and 29% of isolates from US-born Blacks and US-born Whites, respectively (P = 0.25). Two (H03/H33 and L16) of the nine largest clusters containing at least 30 patients had a predominance of US-born Blacks when compared with US-born Whites (Table 2 and Figure 2). Multivariate logistic regression analysis. In our final model (Table 3), factors independently associated with Black race among TB patients included younger age, fewer years of education, inner city residence, use of public transportation, prison history, renal disease and HIV seropositivity. US-born blacks were significantly less likely to report current homelessness, smoking, alcohol abuse, injection drug use and same sex behavior. Although male gender, not being married, MTB culture positivity, employment, and extra pulmonary disease were significant in the univariate analysis, they were no longer significant in the full model and therefore were dropped from the final parsimonious model. Because including certain covariates significantly decreased the sample size (and the representativeness of the dataset), we developed a second model (data not shown) by adding drug resistance and clustering to the final model. In this model, drug resistance remained significantly higher in US-blacks than US-born Whites (OR: 1.76, 95% CI: , P = 0.04); however MTB clustering did not remain statistically significant (OR: 1.13, 95% CI: , P = 0.44). 11

12 DISCUSSION Although the 2007 tuberculosis rate in the United States was the lowest recorded since national reporting began in 1953, the decline has slowed from an average of 7.1% per year ( ) to an average of 3.8% per year ( ) [1]. In this report, we present a population-based study of tuberculosis in a large US metropolitan city emphasizing the epidemiologic, molecular, and clinical characteristics of US-born Black cases. During the 9-year study period, we found a dramatic reduction in the overall incidence of tuberculosis in Harris County, Texas; however, analysis by ethnicity revealed that the incidence among African-Americans had remained fairly stable ( cases per 100,000) over the last five years of the study. This incidence is 4 to 5 times the US national TB incidence [1]. Numerous factors have been postulated to explain the disproportionately high tuberculosis rate in Black individuals including socio-economic characteristics, biased presence of co-morbidities, and even genetics. Our evaluation of socioeconomic characteristics demonstrated that younger age, fewer years of education, use of public transportation and inner city residence were independent factors associated with black race among TB patients. These associations support the concept that tuberculosis remains predominantly a disease of the disadvantaged and marginalized [15, 16]. Contrary to a recent report [16], our population-based study showed that US-born Whites with TB were more likely to be homeless than US-born Blacks with TB. In addition, certain clinical conditions such as renal disease and HIV seropositivity were more likely to occur among US-born Blacks with TB. 12

13 Susceptibility testing revealed that M. tuberculosis isolates from US-born Blacks were more likely to be resistant than those from US-born Whites, which was in accordance with a former report [17]. However, foreign born individuals, particularly Hispanics and Asians still represent the largest burden of drug resistant tuberculosis in Houston [18]. Mortality (death due to any cause within 6 months of TB diagnosis) reported in our study population was approximately 10%. No difference in TB-associated mortality between US-born Blacks and Whites was noted. Clustering of TB strains was observed in a high proportion of US-born Blacks and US-born Whites (81.6% and 77.2% respectively, P = 0.38). Our group had previously demonstrated that ethnicity was not a significant covariate for strain clustering after adjustments for factors related to socio-economic status [19]. Clustered isolates belonging to the Beijing genotype family were present in 26% and 29% of US-born Blacks and US-born Whites, respectively (P = 0.25). Indeed, this genetically highly conserved family, reported worldwide but particularly prevalent in Asia and the territories of the former Soviet Union [20, 21], is frequently associated with large outbreaks of tuberculosis, increased virulence, and multidrug resistance [22, 23]. One of the most striking findings of our study is the markedly large size of clusters seen in our case population. Previous US-based studies had reported cluster sizes not exceeding 30 to 78 patients each [6, 8, 9]. We reported 9 clusters that had more than 30 patients each and 3 clusters with more than 100 patients each including one that had a predominance of Blacks. We hypothesize that this may be due to the longer surveillance period used here as well as endemic spread of highly transmissible strains including several of the Beijing family. We estimated that at least 54 percent [( ) / 3227] 13

14 of TB cases in Houston were due to recent infection that had progressed to active disease during the nine-year study period [6]. We believe this is a conservative estimate as a strict definition of identical IS6110 RFLP bands was used for clustering and several of the RFLP patterns in our study were similar but with +/- 1 band (Figure 2). In summary, several tuberculosis genotypes remain endemic in Houston, particularly among minorities such as US-born Blacks. A high proportion of cases associated with endemic MTB strains continue to be actively transmitted within this population. Further research focusing on the dynamics of the disease including possible delays in presentation and/or diagnosis in this ethnic group, is of paramount importance to achieve our national goal of TB elimination. 14

15 Disclosure of Financial Support This project was funded in part with federal funds from the National Institute of Allergy and Infectious Diseases and the National Institute of Drug Abuse, National Institutes of Health, under contract N01-A and DA Conflict of Interest No authors have conflicts of interest to report Preliminary analysis of data contained in this paper was presented at the 45 th Annual Meeting of IDSA, October 4-7, 2007 at San Diego (Abstract # 346). 15

16 REFERENCES 1. Trends in tuberculosis--united States, MMWR Morb Mortal Wkly Rep, (11): p Borgdorff, M.W., et al., Transmission of tuberculosis in San Francisco and its association with immigration and ethnicity. Int J Tuberc Lung Dis, (4): p Racial disparities in tuberculosis--selected southeastern states, MMWR Morb Mortal Wkly Rep, (25): p Nelson, L.J., et al., Epidemiology of childhood tuberculosis in the United States, : the need for continued vigilance. Pediatrics, (2): p Barnes, P.F. and M.D. Cave, Molecular epidemiology of tuberculosis. N Engl J Med, (12): p Small, P.M., et al., The epidemiology of tuberculosis in San Francisco. A population-based study using conventional and molecular methods. N Engl J Med, (24): p Driver, C.R., et al., Molecular epidemiology of tuberculosis after declining incidence, New York City, Epidemiol Infect, (4): p Weis, S.E., et al., Transmission dynamics of tuberculosis in Tarrant county, Texas. Am J Respir Crit Care Med, (1): p El Sahly, H.M., et al., Epidemiologic differences between United States- and foreign-born tuberculosis patients in Houston, Texas. J Infect Dis, (3): p Marinac, J.S., et al., Knowledge of tuberculosis in high-risk populations: survey of inner city minorities. Int J Tuberc Lung Dis, (10): p van Embden, J.D., et al., Strain identification of Mycobacterium tuberculosis by DNA fingerprinting: recommendations for a standardized methodology. J Clin Microbiol, (2): p Soini, H., et al., Characterization of Mycobacterium tuberculosis isolates from patients in Houston, Texas, by spoligotyping. J Clin Microbiol, (2): p Sreevatsan, S., et al., Restricted structural gene polymorphism in the Mycobacterium tuberculosis complex indicates evolutionarily recent global dissemination. Proc Natl Acad Sci U S A, (18): p Woods, G.L., Susceptibility testing for mycobacteria. Clin Infect Dis, (5): p Grange, J., A. Story, and A. Zumla, Tuberculosis in disadvantaged groups. Curr Opin Pulm Med, (3): p Haddad, M.B., et al., Tuberculosis and homelessness in the United States, Jama, (22): p Bloch, A.B., et al., Nationwide survey of drug-resistant tuberculosis in the United States. Jama, (9): p El Sahly, H.M., et al., Drug-resistant tuberculosis: a disease of target populations in Houston, Texas. J Infect, (1): p De Bruyn, G., et al., The contribution of ethnicity to Mycobacterium tuberculosis strain clustering. Int J Tuberc Lung Dis, (7): p

17 20. Jou, R., C.Y. Chiang, and W.L. Huang, Distribution of the Beijing family genotypes of Mycobacterium tuberculosis in Taiwan. J Clin Microbiol, (1): p Drobniewski, F., et al., Drug-resistant tuberculosis, clinical virulence, and the dominance of the Beijing strain family in Russia. Jama, (22): p Lillebaek, T., et al., Mycobacterium tuberculosis Beijing genotype. Emerg Infect Dis, (12): p Glynn, J.R., et al., Worldwide occurrence of Beijing/W strains of Mycobacterium tuberculosis: a systematic review. Emerg Infect Dis, (8): p

18 Table 1: Univariate analysis of selected epidemiologic and clinical characteristics US-born Blacks US-born Whites Hispanics Asians US-born Blacks vs. Whites n % n % N % n % OR P I. Demographics Age * <0.001 Male gender % % % % Not married % % % % 1.56 <0.001 Years of education * % % 0.90 <0.001 Employed % % % % Inner city residence a % % % % Household size * II. Social History Income < $ 10K/year % % % % 1.90 <0.001 Use of public % % % % 2.11 <0.001 transportation Current homelessness % % % 4 0.9% Stayed in a shelter b % % % 5 1.1% Current smoking % % % % 0.52 <0.001 Alcohol abuse c % % % % 0.63 <0.001 Drug use b % % % 4 0.9% Injection drug use b % % % % Same sex behavior % % % 2 0.4% 0.54 <0.001 Commercial sex % % % 2 0.4% Prison history % % % 5 1.1% III. Medical History 18

19 Known TB exposure % % % % Previous TB % % % % Asthma % % % % Diabetes % % % % Renal Disease % % % % HIV seropositivity % % % 8 1.7% IV. Diagnosis and Prognosis Pulmonary TB % % % % 0.42 <0.001 Extrapulmonary TB % % % % 2.01 <0.001 Cavitation % % % % Smear positive % % % % pulmonary TB MTB culture positivity % % % % MTB clustering % % % % Drug resistance % % % % Multi-drug resistance 3 0.3% 1 0.2% % 9 0.9% Mortality d % % % % Note: Stratification based upon race shown here does not include information on foreign-born Blacks * Continuous variable, mean and median presented a Defined according to specific zip codes b Within six months prior to diagnosis of tuberculosis c Drinks alcohol daily or nearly daily d Death within 180 days of diagnosis of TB 19

20 Table 2: Characteristics of the nine largest MTB clusters Cluster IS6110 CDC Spoligotype Genetic US-born US-born Hispanics Asians US-born Blacks Copy designation group Blacks Whites vs. Whites number n % n % n % n % OR P H % % % % H03/H33 20/ % % % % H % % % % H % 7 1.5% % % H % % % % H % 8 1.8% % % H % % % % 0.10 <0.001 L % % % % L % 2 0.4% % %

21 Table 3. Factors associated with black race in multivariate analysis among US-born TB patients in Houston, Texas, Risk Factor Odds Ratio 95% CI P-value Age 0.98 a <0.001 Years of education 0.93 a <0.001 Inner city residence b Use of Public transportation <0.001 Current homelessness <0.001 Current smoking <0.001 Alcohol abuse c Injection Drug use d <0.001 Same sex behavior <0.001 Prison history Renal disease HIV seropositivity <0.001 a Odds ratios per additional year at risk b Defined according to specific zip codes c Drinks alcohol daily or nearly daily d Within six months prior to diagnosis of tuberculosis 21

22 Figure Legends Figure 1. Plot of tuberculosis rates for the period Figure 2. IS6110 Profiles of the ten largest MTB clusters 22