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Journal of Clinical Microbiology, April 2008, p. 1363-1368, Vol. 46, No. 4
0095-1137/08/$08.00+0 doi:10.1128/JCM.02180-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Phan Thi Hoang Anh,6
Dau Quang Tho,2
Estee Torok,2,3
Nguyen Thi Quynh Nhu,2
Nguyen Thi Hong Duyen,2
Phan Minh Duy,2
Jonathan Richenberg,5
Cameron Simmons,2,3
Tran Tinh Hien,4 and
Jeremy Farrar2,3
Centre for Molecular Microbiology and Infection, Imperial College, London, United Kingdom,1 Oxford University Clinical Research Unit, Hospital for Tropical Diseases, 190 Ben Ham Tu, District 5, Ho Chi Minh City, Vietnam,2 Centre for Clinical Vaccinology and Tropical Medicine, Churchill Hospital, Old Road, Headington, Oxford, United Kingdom,3 The Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam,4 Department of Radiology, Brighton, and Sussex University Hospitals, Eastern Road, Brighton, United Kingdom,5 Pham Ngoc Thach Hospital for Tuberculosis and Lung Diseases, Huong Vuong, District 5, Ho Chi Minh City, Vietnam,6 Institute for Systems Biology, 1441 N. 34th Street, Seattle, Washington7
Received 11 November 2007/ Returned for modification 23 December 2007/ Accepted 4 February 2008
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A further understanding of the relationship between mycobacterial genotype and clinical phenotype came with the advent of mycobacterial genotyping (1, 2). Tuberculosis outbreaks in the United States and United Kingdom provided epidemiological evidence that some genotypes of M. tuberculosis may be more transmissible and more capable of causing disease than others (22, 35). Many of these strains have now been extensively studied and shown to induce different patterns of host immune response and disease in cellular or animal infection models (8, 22). For example, the W-Beijing genotype—responsible for a large outbreak of drug-resistant tuberculosis in New York in the 1990s—was shown to disseminate more rapidly and caused more-severe disease than other strains (17, 33). These unusual characteristics have been partly explained by the ability of Beijing strains to produce a unique phenolic glycolipid that attenuates the host's innate immune response and ability to control the infection (25). Yet despite an increased appreciation of the genetic diversity of M. tuberculosis and the possible mechanisms underlying differences in virulence, the degree to which this variation influences disease severity and outcome in humans is still poorly understood.
Epidemiological studies have found some genotypes of M. tuberculosis may be associated with tuberculosis affecting different organs. For example, extrapulmonary disease has been associated with polymorphisms in the mycobacterial plcD gene (37) and the Beijing family of strains (14), but these associations appear to hold for some patient populations but not others. Investigators in South Africa failed to find any significant relationship between mycobacterial genotype and extrapulmonary tuberculosis (23).
A small number of studies have examined whether the mycobacterial genotype influences disease presentation and outcome, often with conflicting results. An association between pretreatment chest X-ray appearances has been reported by some (9) but not others (4). van Crevel et al. observed that Indonesian patients with pulmonary tuberculosis caused by Beijing strains had higher fevers than those infected with other strains (36), whereas the opposite was reported by Drobniewski et al. in Russia (9). Maree et al. failed to find a relationship between mycobacterial genotype and clinical presentation and outcome for 59 South African children with tuberculous meningitis (18).
Few studies have combined a detailed characterization of the bacterial genotype with presenting clinical features, disease severity, and response to treatment for a large number of patients. The purpose of this study was to examine the influence of the mycobacterial genotype on the clinical presentation, disease severity, and outcome in a large group of human immunodeficiency virus (HIV)-uninfected adults with tuberculous meningitis. We also examined the influence of the mycobacterial genotype on pretreatment chest X-ray appearances in a similarly sized group of HIV-uninfected adults with pulmonary tuberculosis from the same population.
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Briefly, patients with tuberculous meningitis were recruited at Pham Ngoc Thach Hospital for Tuberculosis and Lung Diseases and the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam, between March 2000 and April 2003. To enter the study, patients had to have clinical evidence of meningitis (nuchal rigidity and abnormal cerebrospinal fluid [CSF] parameters) with M. tuberculosis cultured from the CSF.
Patients with pulmonary tuberculosis were recruited between September 2003 and December 2004 at five district tuberculosis control units from Ho Chi Minh City and the surrounding districts, chosen to represent the geographic distribution of the patients with tuberculous meningitis. To enter the study, patients had to have a chest X-ray appearance consistent with active tuberculosis (without evidence of miliary or extrapulmonary tuberculosis), no clinical evidence of extrapulmonary disease, and M. tuberculosis cultured from sputum. Patients with a history of previous tuberculosis treatment were excluded.
The study protocols were approved by the human subject review committees at the Hospital for Tropical Diseases, Pham Ngoc Thach Hospital for Tuberculosis and Lung Disease, and the Health Services of Ho Chi Minh City in Vietnam. Ethical approval was also granted by the Oxfordshire Clinical Research Ethics Committee and the Oxford Tropical Research Ethics Committee.
Clinical phenotype. All clinical data were recorded by physicians without knowledge of the mycobacterial genotype results. Patients with pulmonary tuberculosis were not followed after the start of treatment. The results of chest radiography before the start of treatment were the only clinical data available from these patients. The chest radiographs were read by an independent radiologist following predefined criteria (see Table 1) and blind to the patient laboratory details.
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TABLE 1. Relationship between M. tuberculosis lineage and chest X-ray appearances at the start of treatment for 235 adults with pulmonary tuberculosis
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M. tuberculosis genotype and drug susceptibility. All M. tuberculosis isolates were genotyped by large sequence polymorphisms, following the method of Tsolaki et al. (34). Isolates were first characterized for RD105 and RD239 deletion, since it was anticipated that the majority of isolates would contain one of these two deletions. RD105-deleted isolates were further subdivided by examining deletions RD150, RD181, and RD142 (34). For isolates without RD105 or RD239, the pks gene was sequenced to identify the Euro-American lineage, using primers pksi (GCAGGCGATGCGTCATGGGG) and pksj (TCTTGCCCACCGACCCTGGC) to amplify a 520-bp fragment (7). After purification, the products were sequenced on the CEQ8000 system (Beckman Coulter, Singapore). Multiplex allele specific-PCR was used to screen other isolates for the pks15/1 7-bp deletion, using outer primers pks1i (3'-GCAGGCGATGCGTCATGGGG-5') and pks1j (3'-TCTTGCCCACCGACCCTGGC-5') (7) and an internal primer, pks1insR (3'-ACGGCTGCGGCTCCCGATGCT-5'). Isolates with the 7-bp deletion produced two bands, of 520 bp and 259 bp, while isolates without the deletion produce a single band of 520 bp, validated by comparison with sequencing data for 43 wild-type and 12 isolates with the pks15/1 7-bp deletion.
M. tuberculosis isolates were tested for susceptibilities to isoniazid, rifampin, ethambutol, and streptomycin by the proportion method (6). If the number of colonies growing on drug-containing medium (isoniazid, 0.2 µg/liter; rifampin, 40.0 µg/liter; ethambutol, 2.0 µg/liter; and streptomycin, 4.0 µg/liter) was
1% of that growing on drug-free medium, the isolate was considered to be resistant.
Statistical analysis. The clinical variables of disease caused by the different mycobacterial lineages were compared by the chi-square test if the data were categorical and the Kruskal-Wallis or Mann-Whitney U tests if the data were continuous. Multivariate analysis was performed using forward stepwise binary logistic regression (with a P value of <0.05 to enter and a P value of >0.055 to remove) to overcome the hazards of multiple univariate testing and to identify presenting clinical variables independently associated with mycobacterial lineage and outcome. Statistical analyses were performed using the SPSS software program, version 14.0 (SPSS, Inc.).
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Mycobacterial genotype and radiographic appearance of pulmonary tuberculosis. Table 1 presents a comparison of the pretreatment radiographic features of pulmonary tuberculosis caused by bacteria of the three lineages. The principal finding was that isolates of the Euro-American lineage were significantly more likely than isolates of the other two lineages to be associated with the radiographic appearances of lung consolidation (P = 0.006).
We also examined whether the subdivisions of the East Asian/Beijing lineage described by Tsolaki et al. (34) were associated with specific radiological features. Subdivision data were unavailable from 14 of the 99 East Asian/Beijing isolates. Of the remainder, 3/85 (3.5%) had no RD181 deletion (group 1), 71/85 (83.5%) had RD181 deleted alone (group 2), and 11/85 (12.9%) had both RD181 and RD150 deletions (group 3). None of the isolates had the RD142 deletion. When the radiological features of pulmonary tuberculosis were compared across the subdivisions, there was a difference in the proportion with fibrosis: pulmonary fibrosis was observed in 2/3 (66.7%) of patients in group 1, 14/71 (19.7%) in group 2, and 0/11 in group 3 (P = 0.027). None of the other radiological features were significantly associated (P < 0.05) with the subdivisions (data not presented).
Mycobacterial genotype and presentation of tuberculous meningitis. Table 2 presents a comparison of the pretreatment clinical features of tuberculous meningitis caused by bacteria of the three lineages. The durations of illness before presentation to the hospital were significantly different across the lineages (P = 0.003), with patients with disease caused by the East Asian/Beijing lineage presenting with shorter illnesses than those with meningitis caused by the other lineages. This finding is unlikely to be caused by differences in presenting-disease severity between the groups, since there was a trend (P = 0.059) for patients with disease caused by East Asian/Beijing bacteria to present with disease more severe than those caused by other lineages. As with the pulmonary isolates, meningitis caused by the East Asian/Beijing lineage were far more likely to be resistant to one or more first-line antituberculosis drugs.
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TABLE 2. Univariate analysis of relationship between M. tuberculosis lineage and clinical features of tuberculous meningitis at start of treatmenta
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Data concerning the East Asian/Beijing subdivisions were available for all 74 isolates in the tuberculous meningitis group: 14/74 (18.9%) had no RD181 deletion (group 1), 35/74 (47.3%) had the RD181 deletion alone (group 2), and 25/74 (33.8%) had both the RD181 and RD150 deletions (group 3). No significant associations (P < 0.05) were found between the groups and the presenting clinical features of tuberculous meningitis (data not presented).
Mycobacterial genotype and outcome of tuberculous meningitis. Figure 1a to c shows the influence of mycobacterial genotype on the change in the CSF parameters of total leukocyte count, CSF glucose/blood glucose ratio, and CSF gamma interferon during treatment. No significant differences in response were observed between the bacterial lineages.
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FIG. 1. The influence of mycobacterial lineage on the response of CSF parameters to treatment for patients with tuberculous meningitis (error bars represent 95% confidence intervals). (a) Mycobacterial lineage and mean CSF total leukocyte count during treatment. (b) Mycobacterial lineage and mean CSF/plasma glucose ratios during treatment. (c) Mycobacterial lineage and log10 mean CSF gamma interferon concentration during treatment.
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Logistic regression was used to model the presenting clinical variables independently associated with death or severe disability (using disease caused/not caused by the East Asian/Beijing lineage as a covariable). We found that older age (odds ratio, 1.034; 95% CI, 1.010 to 1.060; P = 0.006), fewer CSF leukocytes (odds ratio, 0.998; 95% CI, 0.997 to 0.999; P = 0.026), and the presence of hemiplegia (odds ratio, 5.244; 95% CI, 1.824 to 15.082; P = 0.002) but not strain lineage were associated with death or severe disability.
Mycobacterial genotype and drug resistance. There was a strong association between isolates of the East Asian/Beijing lineage and drug resistance for both pulmonary and meningeal disease. Fifty-three of ninety-nine (53.4%) of East Asian/Beijing isolates causing pulmonary tuberculosis were resistant to one or more first-line drugs, compared to 21/104 isolates (20.2%) of the Indo-Oceanic lineage and 11/32 (34.4%) isolates of the Euro-American lineage (P < 0.001). The findings were similar for tuberculous meningitis (Table 2).
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We found that the clinical presentation of both forms of tuberculosis is influenced by the mycobacterial genotype. The radiological appearance of pulmonary consolidation was significantly more common in disease caused by the Euro-American lineage than in that caused by other lineages. Consolidation is caused by air spaces filled with inflammatory cells and exudate and therefore may reflect a differential inflammatory response between the lineages. However, the nature and extent of pulmonary disease may also be influenced by other factors, such as the duration of illness prior to diagnosis. We were not able to adjust the analysis for these covariables, and therefore, our conclusions concerning the influence of the mycobacterial genotype on pulmonary tuberculosis pathogenesis remain speculative.
In contrast, we were able to characterize the presenting features and response to treatment of tuberculous meningitis in greater detail. The principle findings arising from the multivariate analysis were that tuberculous meningitis caused by the East Asian/Beijing lineage was independently associated with a shorter duration of illness and lower numbers of leukocytes in the CSF at presentation. This suggests the mycobacterial genotype influences disease progression and the development of the intracerebral inflammatory response.
Tuberculous meningitis develops following the release of small numbers of bacteria into the subarachnoid space from small subpial or subependymal granuloma (Rich foci) formed during an earlier bacteremia (26). Symptoms develop slowly, dependent upon the numbers of initial bacteria, their speed of replication, and the immune response they invoke. The outcome is intimately associated with treatment before the onset of coma (13), but the relationship between coma severity, the duration of symptoms, and the intracerebral inflammatory response is poorly defined. Previous studies have failed to show a linear relationship between the duration of illness and coma and have suggested other unknown factors may influence this relationship (29, 32). Mycobacterial lineage appears to be one of those factors: patients with meningitis caused by the East Asian/Beijing lineage have more rapidly progressive disease with a shorter duration of symptoms independent of disease severity at presentation.
In addition, the independent association between the East Asian/Beijing lineage and low CSF leukocyte numbers supports the proposal that the mycobacterial lineage influences the intracerebral inflammatory response. CSF cytokine concentrations were measured for a small proportion of the patients, but this failed to show any significant relationship with the mycobacterial lineage. However, previous studies have shown CSF cytokine concentrations correlate poorly with coma and outcome from tuberculous meningitis (27). Instead, this and previous studies have shown that a low CSF leukocyte count is an independent predictor of death (32). We were not able to show that meningitis caused by the East Asian/Beijing lineage was an independent risk factor for a poor outcome—perhaps because the study was not sufficiently powered to demonstrate such an effect—but the bilateral relationship between a low CSF leukocyte count, the East Asian/Beijing lineage, and a poor outcome suggests the bacteria differentially influence a critical part of disease pathogenesis.
There are additional ways in which the mycobacterial genotype may influence the outcome for tuberculosis. Although we did not find a clear relationship between mycobacterial lineage and outcome from tuberculous meningitis when those with multidrug-resistant disease were excluded from the analysis, there was a clear association between the East Asian/Beijing lineage and resistance to one or more first-line drugs (including multidrug resistance). The same association was found for the pulmonary isolates. Multidrug resistance is a strong independent risk factor for a poor outcome for all forms of tuberculosis (21) and, when strongly linked to mycobacterial genotype, provides a clinically important influence of the bacterial genotype on the outcome. We recently reported a strong association between the Beijing genotype and drug resistance for HIV-infected Vietnamese adults with tuberculous meningitis (5). This study suggests the relationship holds for HIV-uninfected adults with pulmonary disease, and similar findings have been reported from Russia (9) and Kazakhstan (15).
In summary, we have found that the genotype of M. tuberculosis has important clinical consequences since it influences the presenting features of pulmonary and meningeal tuberculosis. In particular, meningitis caused by the East Asian/Beijing lineage presented with a shorter duration of symptoms independent of disease severity and was associated with fewer CSF leukocytes, which in turn was an independent risk factor for death or severe disability. These findings suggest the East Asian/Beijing lineage alters disease presentation by influencing the intracerebral inflammatory response. In addition, the East Asian/Beijing lineage was strongly associated with drug-resistant pulmonary and meningeal disease, providing an additional mechanism by which the bacterial genotype influences the clinical outcome.
We thank the clinical and laboratory staff of Pham Ngoc Thach Hospital for Tuberculosis, the Hospital for Tropical Diseases, and the District Tuberculosis Units for assistance with patient recruitment and isolate collection and identification. We thank Dick van Soolingen, Kristin Kremer, and Marianne van der Sande of the Tuberculosis Reference Laboratory, National Institute for Public Health, The Netherlands, for their help and advice with bacterial genotyping. We also thank all of the patients who took part in the study.
None of the authors has any conflict of interest to declare.
Published ahead of print on 20 February 2008. ![]()
Present address: Division of Mycobacterial Research, Medical Research Council, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom. ![]()
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