Exogenous reinfection in tuberculosis

CT Scan Differences of Pulmonary TB According to Presence of Pleural Effusion

BACKGROUND

Subpleural micronodules and interlobular septal thickening are common CT scan findings in TB pleural effusion. These CT scan features could help us differentiate between TB pleural effusion and nonTB empyema.

RESEARCH QUESTION

Does the frequency of subpleural micronodules and interlobular septal thickening correlate with the presence of pleural effusion in patients with pulmonary TB?

STUDY DESIGN AND METHODS

CT scan findings of pulmonary TB, micronodules and their distribution (peribronchovascular, septal, subpleural, centrilobular, and random), large opacity (consolidation/macronodule), cavitation, tree-in-buds, bronchovascular bundle thickening, interlobular septal thickening, lymphadenopathy, and pleural effusion were retrospectively analyzed. Patients were divided into two groups according to the presence of pleural effusion. Clinicoradiologic findings of the two groups were then analyzed. We presented Benjamini-Hochberg critical value for multiple testing correction of CT scan findings, with a false discovery rate of 0.05.

RESULTS

Of a total of 338 consecutive patients diagnosed with pulmonary TB who underwent CT scans, 60 were excluded because of coexisting pulmonary diseases. The frequency of subpleural nodules (47/68, 69% in pulmonary TB with pleural effusion vs 30/210, 14% in pulmonary TB without effusion, P < .001, Benjamini-Hochberg [B-H] critical value = 0.0036) and interlobular septal thickening (55/68, 81% vs 134/210, 64%, P = .009, B-H critical value = 0.0107) was significantly higher in the group of patients with pulmonary TB with pleural effusion than in the group without pleural effusion. In contrast, tree-in-buds (20/68, 29% vs 101/210, 48%, P = .007, B-H critical value = 0.0071) were less frequently seen in patients with pulmonary TB with pleural effusion.

INTERPRETATION

Subpleural nodules and septal thickening were more common in pulmonary TB patients with pleural effusion than in those without pleural effusion. TB involvement of the lymphatics in the peripheral interstitium could be associated with the development of pleural effusion.

Prevalence and incidence of tuberculosis infection among healthcare workers in chest diseases hospitals, Bangladesh: Putting infection control into context

BACKGROUND

Healthcare workers (HCWs) are at increased risk of tuberculosis infection (TBI). We estimated the prevalence and incidence of TBI and risk factors among HCWs in Bangladeshi hospitals to target TB infection prevention and control (IPC) interventions.

METHODS

During 2013-2016, we conducted a longitudinal study among HCWs in four chest disease hospitals. At baseline, we administered a questionnaire on sociodemographic and occupational factors for TB, tuberculin skin tests (TST) in all hospitals, and QuantiFERON ®-TB Gold in-Tube (QFT-GIT) tests in one hospital. We assessed factors associated with baseline TST positivity (induration ≥10mm), TST conversion (induration increase ≥10mm from baseline), baseline QFT-GIT positivity (interferon-gamma ≥0.35 IU/mL), and QFT-GIT conversion (interferon-gamma <0.35 IU/mL to ≥0.35 IU/mL). We included factors with a biologically plausible relationship with TBI identified in prior studies or having an association (p = <0.20) in the bivariate analyses with TST positivity or QFT-GIT positivity in multivariable generalized linear models. The Kaplan-Meier was used to estimate the cumulative TBI incidence rate per 100 person-years.

RESULTS

Of the 758 HCWs invited, 732 (97%) consented to participate and 731 completed the one-step TST, 40% had a positive TST result, and 48% had a positive QFT-GIT result. In multivariable models, HCWs years of service 11-20 years had 2.1 (95% CI: 1.5-3.0) times higher odds of being TST-positive and 1.6 (95% CI 1.1-2.5) times higher odds of QFT-GIT-positivity at baseline compared with those working ≤10 years. HCWs working 11-20 years in pulmonary TB ward had 2.0 (95% CI: 1.4-2.9) times higher odds of TST positivity, and those >20 years had 2.5 (95% CI: 1.3-4.9) times higher odds of QFT-GIT-positivity at baseline compared with those working <10 years. TBI incidence was 4.8/100 person-years by TST and 4.2/100 person-years by QFT-GIT. Females had 8.5 (95% CI: 1.5-49.5) times higher odds of TST conversion than males.

CONCLUSIONS

Prevalent TST and QFT-GIT positivity was associated with an increased number of years working as a healthcare worker and in pulmonary TB wards. The incidence of TBI among HCWs suggests ongoing TB exposure in these facilities and an urgent need for improved TB IPC in chest disease hospitals in Bangladesh.

Risk factors for types of recurrent tuberculosis (reactivation versus reinfection): A global systematic review and meta-analysis

BACKGROUND

The purpose of this meta-analysis (PROSPERO number: CRD42021243204) is to perform extensive and penetrating analyses on the risk factors associated with reactivation or reinfection.

METHODS

We searched PubMed and Embase using search terms. Risk factors (including sex, length of time between first onset and recurrent diagnosis, extrapulmonary tuberculosis, sputum smear, pulmonary cavity, Beijing family strains, diabetes, HIV infection, history of imprisonment, and immigration) were analyzed. The pooled risk ratio (RR) and 95% confidence interval (CI) were calculated with STATA 15.1. Heterogeneity was evaluated by I² and P values.

RESULTS

The meta-analysis included 25 studies with a total of 1,477 patients. After subgroup analysis, sensitivity analysis, and testing for publication bias, it was concluded that time spanning less than two years (RR=1.56, 95% CI: 1.33-1.85) was a risk factor for endogenous reactivation, while coinfection with HIV (RR=0.72, 95% CI: 0.63-0.83), Beijing family genotype (RR=0.46, 95% CI: 0.32-0.67), history of imprisonment (RR=0.36, 95% CI: 0.16-0.81) and immigration (RR=0.66, 95% CI: 0.53-0.82) were associated with exogenous reinfection.

CONCLUSIONS

The recurrence interval is a risk factor for the endogenous reactivation of tuberculosis. Infection with Beijing family strains, coinfection with HIV, imprisonment, and immigration contribute to the risk of exogenous reinfection.

Quantifying transmission fitness costs of multi-drug resistant tuberculosis

As multi-drug resistant tuberculosis (MDR-TB) continues to spread, investigating the transmission potential of different drug-resistant strains becomes an ever more pressing topic in public health. While phylogenetic and transmission tree inferences provide valuable insight into possible transmission chains, phylodynamic inference combines evolutionary and epidemiological analyses to estimate the parameters of the underlying epidemiological processes, allowing us to describe the overall dynamics of disease spread in the population. In this study, we introduce an approach to Mycobacterium tuberculosis (M. tuberculosis) phylodynamic analysis employing an existing computationally efficient model to quantify the transmission fitness costs of drug resistance with respect to drug-sensitive strains. To determine the accuracy and precision of our approach, we first perform a simulation study, mimicking the simultaneous spread of drug-sensitive and drug-resistant tuberculosis (TB) strains. We analyse the simulated transmission trees using the phylodynamic multi-type birth-death model (MTBD, (Kühnert et al., 2016)) within the BEAST2 framework and show that this model can estimate the parameters of the epidemic well, despite the simplifying assumptions that MTBD makes compared to the complex TB transmission dynamics used for simulation. We then apply the MTBD model to an M. tuberculosis lineage 4 dataset that primarily consists of MDR sequences. Some of the MDR strains additionally exhibit resistance to pyrazinamide - an important first-line anti-tuberculosis drug. Our results support the previously proposed hypothesis that pyrazinamide resistance confers a transmission fitness cost to the bacterium, which we quantify for the given dataset. Importantly, our sensitivity analyses show that the estimates are robust to different prior distributions on the resistance acquisition rate, but are affected by the size of the dataset - i.e. we estimate a higher fitness cost when using fewer sequences for analysis. Overall, we propose that MTBD can be used to quantify the transmission fitness cost for a wide range of pathogens where the strains can be appropriately divided into two or more categories with distinct properties.

Inference of Naturally Acquired Immunity Using a Self-matched Negative-Control Design

Host adaptive immune responses may protect against infection or disease when a pathogen is repeatedly encountered. The hazard ratio of infection or disease, given previous infection, is typically sought to estimate the strength of protective immunity. However, variation in individual exposure or susceptibility to infection may introduce frailty bias, whereby a tendency for infections to recur among individuals with greater risk confounds the causal association between previous infection and susceptibility. We introduce a self-matched "case-only" inference method to control for unmeasured individual heterogeneity, making use of negative-control endpoints not attributable to the pathogen of interest. To control for confounding, this method compares event times for endpoints due to the pathogen of interest and negative-control endpoints during counterfactual risk periods, defined according to individuals' infection history. We derive a standard Mantel-Haenszel (matched) odds ratio conveying the effect of prior infection on time to recurrence. We compare performance of this approach to several proportional hazards modeling frameworks and estimate statistical power of the proposed strategy under various conditions. In an example application, we use the proposed method to reestimate naturally acquired protection against rotavirus gastroenteritis using data from previously published cohort studies. This self-matched negative-control design may present a flexible alternative to existing approaches for analyzing naturally acquired immunity, as well as other exposures affecting the distribution of recurrent event times.

Recurrent TB: a systematic review and meta-analysis of the incidence rates and the proportions of relapses and reinfections

BACKGROUND

A recurrent tuberculosis (TB) episode results from exogenous reinfection or relapse after cure. The use of genotyping allows the distinction between both.

METHODS

We did a systematic review and meta-analysis, using four databases to search for studies in English, French and Spanish published between 1 January 1980 and 30 September 2020 that assessed recurrences after TB treatment success and/or differentiated relapses from reinfections using genotyping. We calculated person years of follow-up and performed random-effects model meta-analysis for estimating pooled recurrent TB incidence rates and proportions of relapses and reinfections. We performed subgroup analyses by clinical-epidemiological factors and by methodological study characteristics.

FINDINGS

The pooled recurrent TB incidence rate was 2.26 per 100 person years at risk (95% CI 1.87 to 2.73; 145 studies). Heterogeneity was high (I²=98%). Stratified pooled recurrence rates increased from 1.47 (95% CI 0.87 to 2.46) to 4.10 (95% CI 2.67 to 6.28) per 100 person years for studies conducted in low versus high TB incidence settings. Background HIV prevalence, treatment drug regimen, sample size and duration of follow-up contributed too. The pooled proportion of relapses was 70% (95% CI 63% to 77%; I²=85%; 48 studies). Heterogeneity was determined by background TB incidence, as demonstrated by pooled proportions of 83% (95% CI 75% to 89%) versus 59% (95% CI 42% to 74%) relapse for studies from settings with low versus high TB incidence, respectively.

INTERPRETATION

The risk of recurrent TB is substantial and relapse is consistently the most frequent form of recurrence. Notwithstanding, with increasing background TB incidence the proportion of reinfections increases and the predominance of relapses among recurrences decreases.

PROSPERO REGISTRATION NUMBER

CRD42018077867.

The predicted impact of tuberculosis preventive therapy: the importance of disease progression assumptions

BACKGROUND

Following infection with Mycobacterium tuberculosis (M.tb), individuals may rapidly develop tuberculosis (TB) disease or enter a "latent" infection state with a low risk of progression to disease. Mathematical models use a variety of structures and parameterisations to represent this process. The effect of these different assumptions on the predicted impact of TB interventions has not been assessed.

METHODS

We explored how the assumptions made about progression from infection to disease affect the predicted impact of TB preventive therapy. We compared the predictions using three commonly used model structures, and parameters derived from two different data sources.

RESULTS

The predicted impact of preventive therapy depended on both the model structure and parameterisation. At a baseline annual TB incidence of 500/100,000, there was a greater than 2.5-fold difference in the predicted reduction in incidence due to preventive therapy (ranging from 6 to 16%), and the number needed to treat to avert one TB case varied between 67 and 157. The relative importance of structure and parameters depended on baseline TB incidence and assumptions about the efficacy of preventive therapy, with the choice of structure becoming more important at higher incidence.

CONCLUSIONS

The assumptions use to represent progression to disease in models are likely to influence the predicted impact of preventive therapy and other TB interventions. Modelling estimates of TB preventive therapy should consider routinely incorporating structural uncertainty, particularly in higher burden settings. Not doing so may lead to inaccurate and over confident conclusions, and sub-optimal evidence for decision making.

Tuberculosis recurrences and predictive factors in a vulnerable population in Catalonia

BACKGROUND

Patients with a history of tuberculosis (TB) have a high probability of recurrence because long-term cure is not always maintained in successfully treated patients. The aim of this study was to identify the probability of TB recurrence and its predictive factors in a cohort of socially vulnerable patients who completed treatment in the TB referral center in Catalonia, which acts as the center for patients with social and health problems.

METHODS

This retrospective open cohort study included all patients diagnosed with TB who were admitted and successfully treated in Serveis Clínics between 2000 and 2016 and who remained disease-free for a minimum of 1 year after treatment completion. We calculated the incidence density of TB recurrences per person-years of follow-up. We also estimated the cumulative incidence of TB recurrence at 1, 2, 5, and 10 years of follow-up. Bivariate analysis was conducted using Kaplan-Meier curves. Multivariate analysis was conducted using Cox regression. Hazard ratios (HR) were calculated with their 95% confidence intervals (95%CI).

RESULTS

There were 839 patients and 24 recurrences (2.9%), representing 0.49 per 100 person-years. The probability of a recurrence was 0.63% at 1 year of follow-up, 1.35% at 2 years, and 3.69% at 5 years. The multivariate analysis showed that the predictive factors of recurrence were age older than 34 years (aHR = 3.90; CI = 1.06-14.34 at age 35-45 years and aHR = 3.88; CI = 1.02-14.80 at age >45 years) and resistance to at least one anti-TB drug (aHR = 2.91; CI = 1.11-7.65).

CONCLUSIONS

Attention should be paid to socially vulnerable persons older than 34 years with a previous episode of resistant TB. Surveillance resources should be directed toward adequately treated patients who nevertheless have a high risk of recurrence.

Reconstructing the population dynamics of foreign residents in Japan to estimate the prevalence of infection with Mycobacterium tuberculosis

Among newly notified tuberculosis cases in Japan, both the number and the proportion of foreign-born cases have steadily increased over time. As Japan prepares to introduce pre-entry tuberculosis screening for foreign-born persons entering Japan, various epidemiological evidence is needed to evaluate its effectiveness, including the prevalence of tuberculosis among current foreign residents in Japan, by country of birth. Yet as of today, even the underlying population dynamics has yet to be quantified. The present study therefore aimed to firstly reconstruct the demographic prevalence of foreign residents by the length of stay in Japan and by country of birth, and secondly, to estimate the prevalence of infection from notification data among foreign residents in Japan. We employed the McKendrick partial differential equation model to reconstruct the dynamics among six Asian countries which account for 80% of foreign-born tuberculosis patients notified in Japan i.e. China, the Philippines, Vietnam, Nepal, Indonesia, and Myanmar. Compared with China and the Philippines, the recent remarkable increase in the number of residents who had arrived within 5 years from Myanmar and Vietnam was identified. Assuming that the risk of primary tuberculosis given infection is 5%, the estimated prevalence of infection ranged from 3.5% to 21.3%, and all the estimates were more than three times greater than the crude estimate that ignored the time since immigration. The proposed method may be used to further estimate the prevalence by age, sex and residential status, which could potentially provide critical evidence towards establishing policies to control tuberculosis among foreign-born persons in Japan, and also possibly among migrants globally.

Older age at first tuberculosis diagnosis is associated with tuberculosis recurrence in HIV-negative persons

SETTING

Tuberculosis (TB) clinic in Durban, South Africa.

OBJECTIVE

To assess the factors associated with TB recurrence among human immunodeficiency virus (HIV) negative adults and children.

DESIGN

We conducted a retrospective longitudinal study from January 2000 to December 2012. We defined recurrence as a TB episode occurring within the study period after treatment completion or cure of a previous episode. We used a multivariable Poisson regression model to assess the factors associated with the number of recurrences among HIV-negative patients.

RESULTS

Among 17 941 patients with known HIV status, 3653 (20%) were HIV-negative; of these, 235 (6%) had one recurrence, 21 (1%) had two recurrences and 4 (0.1%) had three recurrences. The median follow-up time from the end of treatment for the first episode was 3.0 years (interquartile range 1.9-4.2). Age at the first TB episode was significantly associated with the number of TB recurrences: younger patients had the lowest rate of recurrence, with a steady increase in rates until age 40 years, after which rates stabilized.

CONCLUSIONS

TB recurrence rates among HIV-negative patients were higher at increased age at the first TB episode. Further translational studies are needed to clarify the factors that drive multiple TB recurrences in older age, including impaired immunity, the results of which have implications for TB vaccine development.

Polymorphisms in TLR4 and TNFA and Risk of Mycobacterium tuberculosis Infection and Development of Active Disease in Contacts of Tuberculosis Cases in Brazil: A Prospective Cohort Study

BACKGROUND

The role of genetic polymorphisms in latent tuberculosis (TB) infection and progression to active TB is not fully understood.

METHODS

We tested the single-nucleotide polymorphisms (SNPs) rs5743708 (TLR2), rs4986791 (TLR4), rs361525 (TNFA), rs2430561 (IFNG) rs1143627 (IL1B) as risk factors for tuberculin skin test (TST) conversion or development of active TB in contacts of active TB cases. Contacts of microbiologically confirmed pulmonary TB cases were initially screened for longitudinal evaluation up to 24 months, with clinical examination and serial TST, between 1998 and 2004 at a referral center in Brazil. Data and biospecimens were collected from 526 individuals who were contacts of 177 active TB index cases. TST conversion was defined as induration ≥5 mm after a negative TST result (0 mm) at baseline or month 4 visit. Independent associations were tested using logistic regression models.

RESULTS

Among the 526 contacts, 60 had TST conversion and 44 developed active TB during follow-up. Multivariable regression analysis demonstrated that male sex (odds ratio [OR]: 2.3, 95% confidence interval [CI]: 1.1-4.6), as well as SNPs in TLR4 genes (OR: 62.8, 95% CI: 7.5-525.3) and TNFA (OR: 4.2, 95% CI: 1.9-9.5) were independently associated with TST conversion. Moreover, a positive TST at baseline (OR: 4.7, 95% CI: 2.3-9.7) and SNPs in TLR4 (OR: 6.5, 95% CI: 1.1-36.7) and TNFA (OR: 12.4, 95% CI:5.1-30.1) were independently associated with incident TB.

CONCLUSIONS

SNPs in TLR4 and TNFA predicted both TST conversion and active TB among contacts of TB cases in Brazil.

Prospective 1-year follow-up study of all cured, new sputum smear positive tuberculosis patients under the Revised National Tuberculosis Control Program in Hyderabad, Telangana State, India

Background

Tuberculosis (TB) is one of the leading causes of mortality in India. The Revised National Tuberculosis Control Program (RNTCP) is a robust public health system to deal with TB in India. Unless the treated patient comes back to the system with signs and symptoms of TB due to relapse or re-infection, there is no mechanism of follow-up or any method to know the relapse rate in the population. We attempted to follow the patients declared as "Cured" as per the RNTCP guidelines for 1-2 years to identify the health status of the index cases and their household contacts in posttreatment phase.

Materials and Methods

In this prospective cohort study, 187 index cases, who were declared "Cured" in six randomly selected TB units of Hyderabad district, were followed up for 1-2 years through home visits by trained staff with structured data collection forms. Data were analyzed using SPSS v20.0.

Results

The mean age of the index cases was 33.64 (±16.10) years, and there were 75 females and 112 males. The study sample was homogenous for gender, age, smear grade, religion, marital status, smoking status, alcohol consumption, and human immunodeficiency virus status, etc., At 1-year posttreatment follow-up of 187 index cases, 143 (76.47%) were healthy and working without any symptoms of TB. Symptoms of TB were present in 26 (13.90%) cases, and seven index cases (4.06%) were re-diagnosed with TB. The 2-year posttreatment survival was 92%.

Conclusion

Long-term follow-up of cured, new smear-positive TB cases reinforce the effectiveness of anti-TB treatment under the RNTCP as assessed by improved health outcomes in more than two-thirds of cases and posttreatment survival of 92% of index cases. We recommend continuing such follow-up for all TB cases treated under the RNTCP for effective end-TB strategy.

Delineating the factors associated with recurrence of tuberculosis in programmatic settings of rural health block, Himachal Pradesh, India

BACKGROUND

Tuberculosis (TB) recurrence observed to be an important event in its treatment and has future implications under national TB control efforts. The present study was carried out to assess the recurrence rate along with its risk factors among patients undergoing treatment for TB under Revised National TB Control Program (RNTCP).

MATERIAL AND METHODS

Total 204 patients in health block of district Una, Himachal Pradesh were studied using pretested structured interviewer-administered questionnaire. Along with univariate a non-hierarchal multi-way frequency analysis (MFA) was done to study the one and multi-way effects between the discrete variables included in a hypothesized model. The variables were under-nutrition, pulmonary TB, injecting drug use (IDU), multi-drug resistant (MDR) TB, and past TB (recurrent cases).

RESULTS

Total 29 cases (14.2%) had recurrence (17.7/100,000 population) with significantly high fraction for alternate residence (Recurrent: 50.0%, Non-recurrent: 47.4%; p = 0.001), Multi-drug resistance (MDR) TB (Recurrent: 13.8%, Non-recurrent: 2.3%; p = 0.003), and sputum negative patients (Recurrent: 51.7%, Non-recurrent: 14.5%; p = 0.000). Non-recurrent cases had significantly high fraction for sputum positive cases (Recurrent: 48.3%, Non-recurrent: 72.1%; p = 0.011), and extra-pulmonary TB (Recurrent: 00.0%, Non-recurrent: 13.4%; p = 0.036). MFA observed all significant one-way effects. Significant two-way effects were IDU and pulmonary TB (p = 0.001), MDR and past TB (p = 0.004), IDU and past TB (p = 0.019), and IDU and MDR-TB (p = 0.039).

CONCLUSION

Proportion of TB recurrence was expected with a significant difference between the history of change of residence, MDR-TB, pulmonary and extra-pulmonary nature of the disease. Hypothesized model observed with a significant association of IDU, pulmonary TB, MDR-TB and past TB.

Modelling heterogeneity in host susceptibility to tuberculosis and its effect on public health interventions

A tuberculosis (TB) model that accounts for heterogeneity in host susceptibility to tuberculosis is proposed, with the aim of investigating the implications this may have for the effectiveness of public health interventions. The model examines the possibility that recovered individuals treated from active TB and individuals treated with preventive therapy acquire different levels of immunity. This contrasts with recent studies that assume the two cohorts acquire the same level of immunity, and therefore both groups are reinfected at the same rate. The analysis presented here examines the impact of this assumption when designing intervention strategies. Comparison of reinfection rates between cohorts treated with preventive therapy and recovered individuals who were previously treated for active TB provides important epidemiological insights. It is found that the reinfection rate of the cohort treated with preventive therapy is the one that plays the key role in qualitative changes in TB dynamics. By contrast, the reinfection rate of recovered individuals (previously treated from active TB) plays a minor role. Moreover, the study shows that preventive treatment of individuals during early latency is always beneficial regardless of the level of susceptibility to reinfection. Further, if patients have greater immunity following treatment for late latent infection, then treatment is again beneficial. However, if susceptibility increases following treatment for late latent infection, the effect of treatment depends on the epidemiological setting. That is: (i) in (very) low burden settings, the effect on reactivation predominates and the burden declines with treatment; (ii) in moderate to high burden settings the effect of reinfection predominates and burden increases with treatment. The effect is most dominant between the two reinfection thresholds, RT2 and RT1, respectively associated with individuals being treated with preventive therapy and individuals with untreated late latent TB infection.

Optimal control analysis of a tuberculosis model

In this paper, we extend the model of Liu and Zhang (Math Comput Model 54:836-845, 2011) by incorporating three control terms and apply optimal control theory to the resulting model. Optimal control strategies are proposed to minimize both the disease burden and the intervention cost. We prove the existence and uniqueness of optimal control paths and obtain these optimal paths analytically using Pontryagin's Maximum Principle. We analyse our results numerically to compare various strategies of proposed controls. It is observed that implementation of three controls is most effective and less expensive among all the strategies. Thus, we conclude that in order to reduce tuberculosis threat all the three controls must be taken into consideration concurrently.

Backward bifurcation and hysteresis in models of recurrent tuberculosis

An epidemiological model is presented that provides a comprehensive description of the transmission pathways involved for recurrent tuberculosis (TB), whereby cured individuals can become reinfected. Our main goal is to determine conditions that lead to the appearance of a backward bifurcation. This occurs when an asymptotically stable infection free equilibrium concurrently exists with a stable non-trivial equilibria even though the basic reproduction number R₀ is less than unity. Although, some 10-30% cases of TB are recurrent, the role of recurrent TB as far as the formation of backward bifurcation is concerned, is rarely if ever studied. The model used here incorporates progressive primary infection, exogenous reinfection, endogenous reactivation and recurrent TB as transmission mechanisms that contribute to TB progression. Unlike other studies of TB dynamics that make use of frequency dependent transmission rates, our analysis provides exact backward bifurcation threshold conditions without resorting to commonly applied approximations and simplifying assumptions. Exploration of the model through analytical and numerical analysis reveal that recurrent TB is sometimes capable of triggering hysteresis effects which allow TB to persist when R₀ < 1 even though there is no backward bifurcation. Furthermore, recurrent TB can independently induce backward bifurcation phenomena if it exceeds a certain threshold.

Trying to See the Forest through the Trees: Deciphering the Nature of Memory Immunity to Mycobacterium tuberculosis

The purpose of vaccination against tuberculosis and other diseases is to establish a heightened state of acquired specific resistance in which the memory immune response is capable of mediating an accelerated and magnified expression of protection to the pathogen when this is encountered at a later time. In the earliest studies in mice infected with Mycobacterium tuberculosis, memory immunity and the cells that express this were definable both in terms of kinetics of emergence, and soon thereafter by the levels of expression of markers including CD44, CD62L, and the chemokine receptor CCR7, allowing the identification of effector memory and central memory T cell subsets. Despite these initial advances in knowledge, more recent information has not revealed more clarity, but instead, has created a morass of complications—complications that, if not resolved, could harm correct vaccine design. Here, we discuss two central issues. The first is that we have always assumed that memory is induced in the same way, and consists of the same T cells, regardless of whether that immunity is generated by BCG vaccination, or by exposure to M. tuberculosis followed by effective chemotherapy. This assumption is almost certainly incorrect. Second, a myriad of additional memory subsets have now been described, such as resident, stem cell-like, tissue specific, among others, but as yet we know nothing about the relative importance of each, or whether if a new vaccine needs to induce all of these, or just some, to be fully effective.

The emergence of latent infection in the early evolution of Mycobacterium tuberculosis

Mycobacterium tuberculosis has an unusual natural history in that the vast majority of its human hosts enter a latent state that is both non-infectious and devoid of any symptoms of disease. From the pathogen perspective, it seems counterproductive to relinquish reproductive opportunities to achieve a détente with the host immune response. However, a small fraction of latent infections reactivate to the disease state. Thus, latency has been argued to provide a safe harbour for future infections which optimizes the persistence of M. tuberculosis in human populations. Yet, if a pathogen begins interactions with humans as an active disease without latency, how could it begin to evolve latency properties without incurring an immediate reproductive disadvantage? We address this question with a mathematical model. Results suggest that the emergence of tuberculosis latency may have been enabled by a mechanism akin to cryptic genetic variation in that detrimental latency properties were hidden from natural selection until their expression became evolutionarily favoured.

Recurrent tuberculosis in an urban area in China: Relapse or exogenous reinfection?

Recurrent tuberculosis is an important indicator of the effectiveness of tuberculosis control and can occur by relapse or exogenous reinfection. We conducted a retrospective cohort study on all bacteriologically confirmed tuberculosis cases that were successfully treated between 2000 and 2012 in Shanghai, an urban area with a high number but a low prevalence rate of tuberculosis cases and a low prevalence of HIV infection. Genotyping the Mycobacterium tuberculosis from clinical isolates was used to distinguish between relapse and reinfection. In total, 5.3% (710/13,417) of successfully treated cases had a recurrence, a rate of 7.55 (95% CI 7.01-8.13) episodes per 1000 person-years, more than 18 times the rate of tuberculosis in the general population. Patients who were male, age 30-59, retreatment cases, had cavitation, diabetes, drug-resistant or multidrug-resistant tuberculosis in their initial episode of tuberculosis, were at high risk for a recurrence. Among 141 recurrent cases that had paired isolates, 59 (41.8%) had different genotypes, indicating reinfection with a different strain. Patients who completed treatment were still at high risk of another episode of tuberculosis and exogenous reinfection contributed a significant proportion of the recurrent tuberculosis cases. Targeted control strategies are needed to prevent new tuberculosis infections in this setting.

Tuberculosis cases caused by heterogeneous infection in Eastern Europe and their influence on outcomes

INTRODUCTION

Mycobacterium tuberculosis superinfection is known to occur in areas with high rates of tuberculosis (TB) and has a significant impact on overall clinical TB management.

AIM

We aimed to estimate the superinfection rate in cohorts of drug sensitive and multi-drug resistant tuberculosis (MDR TB) patients from Eastern Europe and the potential role of a second MDR TB strain infecting a patient with active non-MDR TB in treatment outcome.

METHODS

The study population included 512 serial M. tuberculosis isolates obtained from 84 MDR- and 136 non-MDR TB patients recruited sequentially at sites in Lithuania, Latvia and Russia in 2011-2013. Strains were genotyped using standardized 24-loci Mycobacterial Interspersed Repetitive Unit-Variable Number Tandem Repeat (MIRU-VNTR) typing.

RESULTS

Changes in two or more MIRU-VNTR loci suggesting superinfection were detected in 13 patients (5.9%). We found 4 initially non-MDR TB patients superinfected with an MDR TB strain during treatment and 3 of them had an unsuccessful outcome.

CONCLUSIONS

An unsuccessful treatment outcome in patients initially diagnosed with drug sensitive TB might be explained by superinfection with an MDR TB strain. Bacteriological reversion could be indicative of superinfection with another strain. Archiving of all serial isolates and their genotyping in case of culture reversion could support therapeutic strategies in high MDR TB burden settings if resources are available.

Exogenous Reinfection as a Cause of Late Recurrent Tuberculosis in the United States

RATIONALE

The etiology of recurrent tuberculosis is typically presumed to be reactivation of residual Mycobacterium tuberculosis infection, but reinfection may account for a greater proportion of recurrent tuberculosis than previously recognized.

OBJECTIVE

To use M. tuberculosis genotyping to characterize the etiology of recurrent tuberculosis occurring 12 months or more after treatment completion.

METHODS

The study population for this national population-based cohort was drawn from the estimated 3,039 persons reported to the National Tuberculosis Surveillance System with two episodes of tuberculosis in the United States during 1993-2011, 194 of whom had genotyping results from both the initial and subsequent episode. We analyzed the proportion of recurrent tuberculosis attributable to and risk factors associated with reinfection.

MEASUREMENTS AND MAIN RESULTS

Among 136 recurrences meeting inclusion criteria, genotypes between episodes were the same for 116 (85%) recurrences during 1996-2011; the 20 (15%) with differing genotypes were categorized as reinfections. Using exact logistic regression, factors associated with reinfection included Mexican birth with both TB episodes diagnosed in the United States within 12 years of immigration (adjusted odds ratio, 10.7; 95% confidence interval, 1.7-86.3) and exclusive use of directly observed therapy for treatment of the first episode (adjusted odds ratio, 4.5; 95% confidence interval, 1.0-29.2).

CONCLUSIONS

Reinfection was the cause of 15% of late recurrent tuberculosis cases in this U.S. cohort. The proportion caused by reinfection increased to 60% in certain subpopulations, such as recent immigrants from Mexico, suggesting that, despite successful treatment for tuberculosis during their first episode, these individuals remain in a social environment where they are reexposed to M. tuberculosis. Public health interventions to prevent novel reinfection might require a broader focus in these communities.

A two-strain TB model with multiple latent stages

A two-strain tuberculosis (TB) transmission model incorporating antibiotic-generated TB resistant strains and long and variable waiting periods within the latently infected class is introduced. The mathematical analysis is carried out when the waiting periods are modeled via parametrically friendly gamma distributions, a reasonable alternative to the use of exponential distributed waiting periods or to integral equations involving ``arbitrary'' distributions. The model supports a globally-asymptotically stable disease-free equilibrium when the reproduction number is less than one and an endemic equilibriums, shown to be locally asymptotically stable, or l.a.s., whenever the basic reproduction number is greater than one. Conditions for the existence and maintenance of TB resistant strains are discussed. The possibility of exogenous re-infection is added and shown to be capable of supporting multiple equilibria; a situation that increases the challenges faced by public health experts. We show that exogenous re-infection may help established resilient communities of actively-TB infected individuals that cannot be eliminated using approaches based exclusively on the ability to bring the control reproductive number just below 1.

Tuberculosis and HIV co-infection-focus on the Asia-Pacific region

Tuberculosis (TB) is the leading opportunistic disease and cause of death in patients with HIV infection. In 2013 there were 1.1 million new TB/HIV co-infected cases globally, accounting for 12% of incident TB cases and 360,000 deaths. The Asia-Pacific region, which contributes more than a half of all TB cases worldwide, traditionally reports low TB/HIV co-infection rates. However, routine testing of TB patients for HIV infection is not universally implemented and the estimated prevalence of HIV in new TB cases increased to 6.3% in 2013. Although HIV infection rates have not seen the rapid rise observed in Sub-Saharan Africa, indications are that rates are increasing among specific high-risk groups. This paper reviews the risks of TB exposure and progression to disease, including the risk of TB recurrence, in this vulnerable population. There is urgency to scale up interventions such as intensified TB case-finding, isoniazid preventive therapy, and TB infection control, as well as HIV testing and improved access to antiretroviral treatment. Increased awareness and concerted action is required to reduce TB/HIV co-infection rates in the Asia-Pacific region and to improve the outcomes of people living with HIV.

The Risk of Tuberculosis Reinfection Soon after Cure of a First Disease Episode Is Extremely High in a Hyperendemic Community

Elevated rates of reinfection tuberculosis in various hyperendemic regions have been reported and, in particular, it has been shown that in a high-incidence setting near Cape Town, South Africa, the rate of reinfection tuberculosis (TB) disease after cure of a previous TB disease episode is about four times greater than the rate of first-time TB disease. It is not known whether this elevated rate is caused by a high reinfection rate due, for instance, to living circumstances, or a high rate of progress to disease specific to the patients, or both. In order to address that question we analysed an extensive data set from clinics attended by TB patients in the high-incidence setting near Cape Town, South Africa and found that, in fact, the (average) rate of reinfection (as opposed to the rate of reinfection disease) after cure of a previous TB disease episode is initially about 0.85 per annum. This rate diminishes rapidly over time and after about ten years this rate is similar to the rate of infection in the general population. Also, the rate of progress to disease after reinfection is initially high but declines in subsequent years down to the figure typical for the general population. These findings suggest that the first few months after cure of a TB disease episode form a critical period for controlling reinfection disease in a hyperendemic setting and that monitoring such cured patients could pre-empt a reinfection progressing to active disease.

Pathology and immune reactivity: understanding multidimensionality in pulmonary tuberculosis

Heightened morbidity and mortality in pulmonary tuberculosis (TB) are consequences of complex disease processes triggered by the causative agent, Mycobacterium tuberculosis (Mtb). Mtb modulates inflammation at distinct stages of its intracellular life. Recognition and phagocytosis, replication in phagosomes and cytosol escape induce tightly regulated release of cytokines [including interleukin (IL)-1, tumor necrosis factor (TNF), IL-10], chemokines, lipid mediators, and type I interferons (IFN-I). Mtb occupies various lung lesions at sites of pathology. Bacteria are barely detectable at foci of lipid pneumonia or in perivascular/bronchiolar cuffs. However, abundant organisms are evident in caseating granulomas and at the cavity wall. Such lesions follow polar trajectories towards fibrosis, encapsulation and mineralization or liquefaction, extensive matrix destruction, and tissue injury. The outcome is determined by immune factors acting in concert. Gradients of cytokines and chemokines (CCR2, CXCR2, CXCR3/CXCR5 agonists; TNF/IL-10, IL-1/IFN-I), expression of activation/death markers on immune cells (TNF receptor 1, PD-1, IL-27 receptor) or abundance of enzymes [arginase-1, matrix metalloprotease (MMP)-1, MMP-8, MMP-9] drive genesis and progression of lesions. Distinct lesions coexist such that inflammation in TB encompasses a spectrum of tissue changes. A better understanding of the multidimensionality of immunopathology in TB will inform novel therapies against this pulmonary disease.

Exogenous reinfection of tuberculosis in a low-burden area

PURPOSE

Recurrence of tuberculosis (TB) can be the consequence of relapse or exogenous reinfection. The study aimed to assess the factors associated with exogenous TB reinfection.

METHODS

Prospective cohort study based on the TB database, maintained at the Division of Infectious Diseases, Luigi Sacco Hospital (Milan, Italy). Time period: 1995-2010.

INCLUSION CRITERIA

(1) ≥2 episodes of culture-confirmed TB; (2) cure of the first episode of TB; (3) availability of one Mycobacterium tuberculosis isolate for each episode. Genotyping of the M. tuberculosis strains to differentiate relapse and exogenous reinfection. Logistic regression analysis was used to assess the influence of risk factors on exogenous reinfections.

RESULT

Of the 4682 patients with TB, 83 were included. Of these, exogenous reinfection was diagnosed in 19 (23 %). It was independently associated with absence of multidrug resistance at the first episode [0, 10 (0.01-0.95), p = 0.045] and with prolonged interval between the first TB episode and its recurrence [7.38 (1.92-28.32) p = 0.004]. However, TB relapses occurred until 4 years after the first episode. The risk associated with being foreign born, extrapulmonary site of TB, and HIV infection was not statistically significant. In the relapse and re-infection cohort, one-third of the patients showed a worsened drug resistance profile during the recurrent TB episode.

CONCLUSIONS

Exogenous TB reinfections have been documented in low endemic areas, such as Italy. A causal association with HIV infection could not be confirmed. Relapses and exogenous reinfections shared an augmented risk of multidrug resistance development, frequently requiring the use of second-line anti-TB regimens.

Latent tuberculosis infection in rural China: baseline results of a population-based, multicentre, prospective cohort study

BACKGROUND

Prophylactic treatment of individuals with latent Mycobacterium tuberculosis infection is an essential component of tuberculosis control in some settings. In China, the prevalence of latent tuberculosis infection, and preventive interventions against this disease, have not been systematically studied. We aimed to assess the prevalence of latent tuberculosis and its associated risk factors in rural populations in China.

METHODS

Between July 1, and Sept 30, 2013, we undertook a baseline survey of a population-based, multicentre, prospective cohort study of registered residents (≥5 years old) at four study sites in rural China. Eligible participants were identified by door-to-door survey with a household sampling design. We screened participants for active tuberculosis and history of tuberculosis then used a tuberculin skin test and an interferon-γ release assay (QuantiFERON [QFT]) to test for latent infection. We used odds ratios (ORs) and 95% CIs to assess variables associated with positivity of QFT and tuberculin skin tests.

FINDINGS

21,022 (90%) of 23,483 eligible participants completed a baseline survey. Age-standardised and sex-standardised rates of skin-test positivity (≥10 mm) ranged from 15% to 42%, and QFT positivity rates ranged from 13% to 20%. Rates of positivity for the tuberculin skin test and the QFT test were low in study participants younger than 20 years and gradually increased with age (p for trend <0·0001). Rates of latent tuberculosis infection were higher for men than women (p<0·0001). Overall agreement between the tuberculin skin test and the QFT test was moderate (81·06%; kappa coefficient 0·485), with skin-test-only positive results associated with the presence of BCG scar, male sex, and ages of 60 years and older, and QFT-only positive results associated with male sex and ages of 60 years and older.

INTERPRETATION

On the basis of findings showing that the performance of the tuberculin skin test might be affected by various factors including BCG vaccination and age, our results suggest that the prevalence of latent tuberculosis in China might be overestimated by skin tests compared with interferon-γ release assays.

FUNDING

The National Science and Technology Major Project of China, the Program for Changjiang Scholars and Innovative Research Team in University of China.

Tuberculosis vaccine types and timings

Traditionally, the design of new vaccines directed against Mycobacterium tuberculosis, the most successful bacterial pathogen on the planet, has focused on prophylactic candidates that would be given to individuals while they are still young. It is becoming more apparent, however, that there are several types of vaccine candidates now under development that could be used under various conditions. Thus, in addition to prophylactic vaccines, such as recombinant Mycobacterium bovis BCG or BCG-boosting vaccines, other applications include vaccines that could prevent infection, vaccines that could be given in emergency situations as postexposure vaccines, vaccines that could be used to facilitate chemotherapy, and vaccines that could be used to reduce or prevent relapse and reactivation disease. These approaches are discussed here, including the type of immunity we are trying to specifically target, as well as the limitations of these approaches.

Inhaled corticosteroids and the increased risk of pulmonary tuberculosis: a population-based case-control study

AIMS

The association between inhaled corticosteroid (ICS) use and pulmonary tuberculosis (TB) development is uncertain. We conducted a population-based case-control study to investigate whether ICS use increases the risk of developing TB.

METHODS

Tuberculosis patients aged 18 years and older were identified using the National Health Insurance Research Database (NHIRD) in Taiwan between 2002 and 2010. Each TB patient was frequency matched to four control patients according to age, sex and index year. We retrospectively followed up the medications and comorbid medical conditions for the 5 years prior to the index date. We calculated the odds ratios (ORs) and 95% confidence intervals (CIs) of TB development using multiple logistic regression models.

RESULTS

Most of the study participants were men (68.7%), and the mean age among the 8091 TB patients and 32,364 comparison participants was 61.3 ± 18.6 years. After adjusting for potential covariates, ICS use caused a 2.04-fold increased risk of developing TB (adjusted OR: 2.04, 95% CI: 1.78-2.33). When considering dose-response and adjusting for potential covariates, ICS and oral corticosteroids (OCS) use remained independent risk factors and exhibited a dose-response relationship of TB development. The multiplicative increased risk of TB was also significant in patients using ICS and OCS compared with patients not using ICS and OCS (adjusted OR: 4.31, 95% CI: 3.39-5.49). Previous TB history exhibited the greatest risk of TB development among the comorbidities (adjusted OR: 8.50, 95% CI: 7.52-9.61).

CONCLUSION

Long-term ICS use may increase the risk of TB.

How do we manage and treat a patient with multiple sclerosis at risk of tuberculosis?

Tuberculosis continues to be a serious health problem worldwide. The disease continues to be underdiagnosed and not properly treated. In conditions that affect the immune system, such as multiple sclerosis (MS), latent tuberculosis may thrive and reactivate during the use of immunomodulatory and immunosuppressive drugs. Among the best treatment options for patients with latent or active tuberculosis who have MS are IFN-β, glatiramer acetate and mitoxantrone. Drugs leading to a reduced number and/or function of lymphocytes should be avoided or used with caution. Tuberculosis must always be investigated in patients with MS and treated with rigor.

Modeling the potential impact of host population survival on the evolution of M. tuberculosis latency

Tuberculosis (TB) is an infectious disease with a peculiar feature: Upon infection with the causative agent, Mycobacterium Tuberculosis (MTB), most hosts enter a latent state during which no transmission of MTB to new hosts occurs. Only a fraction of latently infected hosts develop TB disease and can potentially infect new hosts. At first glance, this seems like a waste of transmission potential and therefore an evolutionary suboptimal strategy for MTB. It might be that the human immune response keeps MTB in check in most hosts, thereby preventing it from achieving its evolutionary optimum. Another possible explanation is that long latency and progression to disease in only a fraction of hosts are evolutionary beneficial to MTB by allowing it to persist better in small host populations. Given that MTB has co-evolved with human hosts for millenia or longer, it likely encountered small host populations for a large share of its evolutionary history and had to evolve strategies of persistence. Here, we use a mathematical model to show that indeed, MTB persistence is optimal for an intermediate duration of latency and level of activation. The predicted optimal level of activation is above the observed value, suggesting that human co-evolution has lead to host immunity, which keeps MTB below its evolutionary optimum.

The temporal dynamics of relapse and reinfection tuberculosis after successful treatment: a retrospective cohort study

BACKGROUND

There is increasing evidence from tuberculosis high-burden settings that exogenous reinfection contributes considerably to recurrent disease. However, large longitudinal studies of endogenous reactivation (relapse) and reinfection tuberculosis are lacking. We hypothesize a relationship between relapse vs reinfection and the time between treatment completion and recurrent disease.

METHODS

Population-based retrospective cohort study on all smear-positive tuberculosis cases successfully treated between 1996 and 2008 in a suburban setting in Cape Town, South Africa. Inverse gaussian distributions were fitted to observed annual rates of relapse and reinfection, distinguished by DNA fingerprinting of Mycobacterium tuberculosis strains recultured from diagnostic samples.

RESULTS

Paired DNA fingerprint data were available for 130 (64%) of 203 recurrent smear-positive tuberculosis cases in the 13-year study period. Reinfection accounted for 66 (51%) of 130 recurrent cases overall, 9 (20%) of 44 recurrent cases within the first year, and 57 (66%) of 86 thereafter (P < .001). The relapse rate peaked at 3.93% (95% confidence interval [CI], 2.35%-5.96%) per annum 0.35 (95% CI, .15-.45) years after treatment completion. The reinfection tuberculosis rate peaked at 1.58% (95% CI, .94%-2.46%) per annum 1.20 (95% CI, .55-1.70) years after completion.

CONCLUSIONS

To our knowledge, this is the first study of sufficient size and duration using DNA fingerprinting to investigate tuberculosis relapse and reinfection over a lengthy period. Relapse occurred early after treatment completion, whereas reinfection dominated after 1 year and accounted for at least half of recurrent disease. This temporal relationship may explain the high variability in reinfection observed across smaller studies. We speculate that follow-up time in antituberculosis drug trials should take reinfection into account.

Genotyping of ancient Mycobacterium tuberculosis strains reveals historic genetic diversity

The evolutionary history of the Mycobacterium tuberculosis complex (MTBC) has previously been studied by analysis of sequence diversity in extant strains, but not addressed by direct examination of strain genotypes in archaeological remains. Here, we use ancient DNA sequencing to type 11 single nucleotide polymorphisms and two large sequence polymorphisms in the MTBC strains present in 10 archaeological samples from skeletons from Britain and Europe dating to the second–nineteenth centuries AD. The results enable us to assign the strains to groupings and lineages recognized in the extant MTBC. We show that at least during the eighteenth–nineteenth centuries AD, strains of M. tuberculosis belonging to different genetic groups were present in Britain at the same time, possibly even at a single location, and we present evidence for a mixed infection in at least one individual. Our study shows that ancient DNA typing applied to multiple samples can provide sufficiently detailed information to contribute to both archaeological and evolutionary knowledge of the history of tuberculosis.

Data needs for evidence-based decisions: a tuberculosis modeler's 'wish list'

Infectious disease models are important tools for understanding epidemiology and supporting policy decisions for disease control. In the case of tuberculosis (TB), such models have informed our understanding and control strategies for over 40 years, but the primary assumptions of these models--and their most urgent data needs--remain obscure to many TB researchers and control officers. The structure and parameter values of TB models are informed by observational studies and experiments, but the evidence base in support of these models remains incomplete. Speaking from the perspective of infectious disease modelers addressing the broader TB research and control communities, we describe the basic structure common to most TB models and present a 'wish list' that would improve the evidence foundation upon which these models are built. As a comprehensive TB research agenda is formulated, we argue that the data needs of infectious disease models--our primary long-term decision-making tools--should figure prominently.

The next 10 years for tuberculosis vaccines: do we have the right plans in place?

The control of TB is a global health priority. Over the last decade, considerable progress has been made in the field of TB vaccines with numerous vaccine candidates entering the clinic and two candidates now in Phase IIb efficacy trials. Nevertheless, the lack of predictive animal models and biomarkers of TB vaccine efficacy prevents rational vaccine down-selection and necessitates prolonged and expensive clinical efficacy trials in target populations. Advances in molecular technology and progress in the development of human as well as animal mycobacterial challenge models make the identification of one or more immune correlates of protection a genuine prospect over the next decade. Moreover, the increasing pace, extent and coordination of global research efforts in TB promises to broaden understanding and inform the next generation of vaccine candidates against TB as well as related globally important pathogens.

Evaluation of the potential role of a new mutation in mabA in modifying the response of Mycobacterium tuberculosis to isoniazid

A new mutation in mabA, Thr4Ile, was identified in a Mycobacterium tuberculosis isolate from a patient whose culture remained positive after treatment. The same mutation was found in another 5 patients infected by different strains. A putative role for this mutation in the process of diminishing susceptibility to isoniazid is evaluated.

Co-infection with Mycobacterium tuberculosis and human immunodeficiency virus: an overview and motivation for systems approaches

Tuberculosis is a devastating disease that accounts for a high proportion of infectious disease morbidity and mortality worldwide. HIV-1 co-infection exacerbates tuberculosis. Enhanced understanding of the host-pathogen relationship in HIV-1 and Mycobacterium tuberculosis co-infection is required. While reductionist approaches have yielded many valuable insights into disease pathogenesis, systems approaches are required that develop data-driven models able to predict emergent properties of this complex co-infection system in order to develop novel therapeutic approaches and to improve diagnostics. Here, we provide a pathogenesis-focused overview of HIV-TB co-infection followed by an introduction to systems approaches and concrete examples of how such approaches are useful.

The re-emergence of tuberculosis: what have we learnt from molecular epidemiology?

Tuberculosis (TB) has re-emerged over the past two decades: in industrialized countries in association with immigration, and in Africa owing to the human immunodeficiency virus epidemic. Drug-resistant TB is a major threat worldwide. The variable and uncertain impact of TB control necessitates not only better tools (diagnostics, drugs, and vaccines), but also better insights into the natural history and epidemiology of TB. Molecular epidemiological studies over the last two decades have contributed to such insights by answering long-standing questions, such as the proportion of cases attributable to recent transmission, risk factors for recent transmission, the occurrence of multiple Mycobacterium tuberculosis infection, and the proportion of recurrent TB cases attributable to re-infection. M. tuberculosis lineages have been identified and shown to be associated with geographical origin. The Beijing genotype is strongly associated with multidrug resistance, and may have escaped from bacille Calmette-Guérin-induced immunity. DNA fingerprinting has quantified the importance of institutional transmission and laboratory cross-contamination, and has helped to focus contact investigations. Questions to be answered in the near future with whole genome sequencing include identification of chains of transmission within clusters of patients, more precise quantification of mixed infection, and transmission probabilities and rates of progression from infection to disease of various M. tuberculosis lineages, as well as possible variations in vaccine efficacy by lineage. Perhaps most importantly, dynamics in the population structure of M. tuberculosis in response to control measures in high-prevalence areas should be better understood.

Modeling the spread of tuberculosis in semiclosed communities

We address the problem of long-term dynamics of tuberculosis (TB) and latent tuberculosis (LTB) in semiclosed communities. These communities are congregate settings with the potential for sustained daily contact for weeks, months, and even years between their members. Basic examples of these communities are prisons, but certain urban/rural communities, some schools, among others could possibly fit well into this definition. These communities present a sort of ideal conditions for TB spread. In order to describe key relevant dynamics of the disease in these communities, we consider a five compartments SEIR model with five possible routes toward TB infection: primary infection after a contact with infected and infectious individuals (fast TB), endogenous reactivation after a period of latency (slow TB), relapse by natural causes after a cure, exogenous reinfection of latently infected, and exogenous reinfection of recovered individuals. We discuss the possible existence of multiple endemic equilibrium states and the role that the two types of exogenous reinfections in the long-term dynamics of the disease could play.

Mixed-strain mycobacterium tuberculosis infections and the implications for tuberculosis treatment and control

Numerous studies have reported that individuals can simultaneously harbor multiple distinct strains of Mycobacterium tuberculosis. To date, there has been limited discussion of the consequences for the individual or the epidemiological importance of mixed infections. Here, we review studies that documented mixed infections, highlight challenges associated with the detection of mixed infections, and discuss possible implications of mixed infections for the diagnosis and treatment of patients and for the community impact of tuberculosis control strategies. We conclude by highlighting questions that should be resolved in order to improve our understanding of the importance of mixed-strain M. tuberculosis infections.

Investigation of endobronchial tuberculosis diagnoses in 22 cases

BACKGROUND

Endobronchial tuberculosis (EBTB) is a special form of pulmonary tuberculosis. In spite of much progress in the diagnosis of this disease in past years, delayed or mistaken diagnosis is still commonly seen.

OBJECTIVE

The aim of this study is to try to find out some useful clues for the diagnosis of EBTB, especially the early diagnosis.

METHODS

The medical records of patients with EBTB were analyzed retrospectively.

RESULTS

The male-to-female ratio was 1:2.2 out of 22 patients. Patients aged below 60-years-old constituted 72.7% of the cases. 22.7% of these patients were smokers. The male-to-female ratio of smokers was 4:1. 68.2% of these patients tested all showed negative result for the HIV test. The frequent complaints were cough, sputum, shortness of breath and fever, and antibiotic treatments were usually inefficacious. Multiple lobes lesion, exudative shadow and atelectasis were the frequent radiological findings. Acid-fast bacilli staining for sputum smear was positive in only 13.6% of these patients. Tuberculin skin test was positive in 59.1% of these patients. Granular lesion was the most common bronchoscopic appearance in these patients. Histological changes showed distinctive tuberculose lesion in 72.2% of 18 patients undergoing bronchoscopic biopsy.

CONCLUSION

The diagnosis of EBTB is easily delayed or mistaken because of nonspecific clinical manifestations and the low incidence of positive acid-fast bacilli staining. A high index of awareness of this disease is required for diagnosis. Bronchoscopy should be performed as soon as possible in suspected patients, especially when patients present positive tuberculin skin test or no response to antibiotic treatments.

Translating basic science insight into public health action for multidrug- and extensively drug-resistant tuberculosis

Multidrug (MDR)- and extensively drug-resistant (XDR) tuberculosis (TB) impose a heavy toll of human suffering and social costs. Controlling drug-resistant TB is a complex global public health challenge. Basic science advances including elucidation of the genetic basis of resistance have enabled development of new assays that are transforming the diagnosis of MDR-TB. Molecular epidemiological approaches have provided new insights into the natural history of TB with important implications for drug resistance. In the future, progress in understanding Mycobacterium tuberculosis strain-specific human immune responses, integration of systems biology approaches with traditional epidemiology and insight into the biology of mycobacterial persistence have potential to be translated into new tools for diagnosis and treatment of MDR- and XDR-TB. We review recent basic sciences developments that have contributed or may contribute to improved public health response.

QUALITATIVE STUDY FOR A MULTI-DRUG RESISTANT TB MODEL WITH EXOGENOUS REINFECTION AND RELAPSE

One tuberculosis transmission model is formulated by incorporating exogenous reinfection, relapse, and two treatment stages of infectious TB cases. The global stability of the unique disease-free equilibrium is obtained by applying the comparison principle if the effective reproduction number for the full model is less than unity. The existence and stability of the boundary equilibria are given by introducing the invasion reproduction numbers. Furthermore, the existence and local stability of the endemic equilibrium are addressed under some conditions.