Cough Aerosols of Mycobacterium tuberculosis in the Prediction of Incident Tuberculosis Disease in Household Contacts

A cytoprotective role for optineurin during mycobacterial infection of macrophages

Autophagy has emerged as a critical innate immune mechanism for host elimination of intracellular pathogens, however, the role of the autophagy receptor Optineurin during mycobacterial infection is not fully understood. To address this lacuna, we infected bone marrow-derived macrophages (BMDMs) derived from Optn+/+ and Optn-/- mice with Mycobacterium smegmatis, and observed the infection outcome at sequential time points. While low multiplicity of infection (MOI) did not show any significant difference between BMDMs from the two groups, at high MOI Optn-/- mice-derived BMDMs showed significantly lower colony forming unit counts, as well as lower cell counts at 12 h and 24 h post-infection. Quantification of cell numbers and nuclear morphologies at various time points post-infection indicated a markedly higher cell death in the Optineurin-deficient macrophages. Optineurin-deficient BMDMs showed significantly lower levels of the autophagosomal protein LC3-II upon infection, indicating a potential role for Optineurin in regulating autophagy during mycobacterial infection. Moreover, when stimulated by bacterial LPS, Optineurin deficient macrophages, showed altered levels of the inflammatory cytokine pro-IL-1β. These observations taken together suggest a novel regulatory role for Optineurin during mycobacterial infection. Its deficiency leads to an impairment in macrophage responses, directly impacting the pathophysiology of infection.

HIV co-infection is associated with reduced Mycobacterium tuberculosis transmissibility in sub-Saharan Africa

Persons living with HIV are known to be at increased risk of developing tuberculosis (TB) disease upon infection with Mycobacterium tuberculosis (Mtb). However, it has remained unclear how HIV co-infection affects subsequent Mtb transmission from these patients. Here, we customized a Bayesian phylodynamic framework to estimate the effects of HIV co-infection on the Mtb transmission dynamics from sequence data. We applied our model to four Mtb genomic datasets collected in sub-Saharan African countries with a generalized HIV epidemic. Our results confirm that HIV co-infection is a strong risk factor for developing active TB. Additionally, we demonstrate that HIV co-infection is associated with a reduced effective reproductive number for TB. Stratifying the population by CD4+ T-cell count yielded similar results, suggesting that, in this context, CD4+ T-cell count is not a better predictor of Mtb transmissibility than HIV infection status alone. Together, our genome-based analyses complement observational household contact studies, and more firmly establish the negative association between HIV co-infection and Mtb transmissibility.

Tuberculosis Infectiousness is Associated with Distinct Clinical and Inflammatory Profiles

Interrupting transmission events to prevent new acquisition of infection and disease is a critical part of tuberculosis (TB) control efforts. However, knowledge gaps in understanding the biology and determinants of TB transmission, including poor estimates of individual infectiousness and the lack of accurate and convenient biomarkers, undermine efforts to develop interventions. Cough-generated aerosol cultures have been found to predict TB transmission better than any microbiological or clinical markers in cohorts from Uganda and Brazil. We hypothesized that highly infectious individuals with pulmonary TB (defined as positive for cough aerosol cultures) have elevated inflammatory markers and unique transcriptional profiles compared to less infectious individuals (negative for cough aerosol cultures). We performed a prospective, longitudinal study using a cough aerosol sampling system as in other studies. We enrolled 142 participants with treatment-naïve pulmonary TB in Nairobi, Kenya, and assessed the association of clinical, microbiologic, and immunologic characteristics with Mtb aerosolization and transmission in 143 household members. Contacts of the forty-three aerosol culture-positive participants (30%) were more likely to have a positive IGRA (85% vs 53%, P = 0.005) and a higher median IGRA IFNγ level (P < 0.001, median 4.25 IU/ml (0.90-5.91) vs. 0.71 (0.01-3.56)) compared to aerosol culture-negative individuals. We found that higher bacillary burden, younger age, and larger mean upper arm circumference were associated with positive aerosol cultures. In addition, novel host inflammatory profiles, including elevated serum C-reactive protein and sputum cytokines, were associated with aerosol culture status. Notably, we found pre-treatment whole blood transcriptional profiles associated with aerosol culture status, independent of bacillary load. Together, these findings suggest that TB infectiousness is associated with epidemiologic characteristics and inflammatory signatures and that these features may be used to identify highly infectious persons. These results provide new public health tools and insights into TB pathogenesis.

Assessing vaccine-mediated protection in an ultra-low dose Mycobacterium tuberculosis murine model

Despite widespread immunization with Bacille-Calmette-Guérin (BCG), the only currently licensed tuberculosis (TB) vaccine, TB remains a leading cause of mortality globally. There are many TB vaccine candidates in the developmental pipeline, but the lack of a robust animal model to assess vaccine efficacy has hindered our ability to prioritize candidates for human clinical trials. Here we use a murine ultra-low dose (ULD) Mycobacterium tuberculosis (Mtb) challenge model to assess protection conferred by BCG vaccination. We show that BCG confers a reduction in lung bacterial burdens that is more durable than that observed after conventional dose challenge, curbs Mtb dissemination to the contralateral lung, and, in a small percentage of mice, prevents detectable infection. These findings are consistent with the ability of human BCG vaccination to mediate protection, particularly against disseminated disease, in specific human populations and clinical settings. Overall, our findings demonstrate that the ultra-low dose Mtb infection model can measure distinct parameters of immune protection that cannot be assessed in conventional dose murine infection models and could provide an improved platform for TB vaccine testing.

Primary Rifampicin Mono-Resistant Extrapulmonary Tuberculosis of the Knee Without Pulmonary Involvement: One of the First Cases of Its Type in an Immunocompetent Male

Tuberculosis presentation at sites other than the lungs is relatively infrequent, and isolated knee involvement without a pulmonary focus is exceptionally rare. Furthermore, there have been no reported cases of primary rifampicin mono-resistant extrapulmonary tuberculosis of the knee in males. In this case, a 24-year-old male patient presented with pain and swelling in his left knee after a fall five years ago. Given the absence of a history of tuberculosis, arriving at a diagnosis posed a significant challenge. However, the diagnosis was ultimately established through cartridge-based nucleic acid amplification tests and clinical link-up with radiometric techniques. Management was based on the latest national guidelines for anti-tuberculous treatment, which were tailored to his weight. To date, he has completed nine months of treatment with a significant improvement in his symptoms. This rare presentation emphasizes the need for a high degree of suspicion even in extrapulmonary tuberculosis cases.

A Rare Case of Tuberculous Nodular Breast Abscess in an Immunocompetent Indian Female

In underdeveloped countries, Mycobacterium tuberculosis infection is common and typically manifests as pulmonary tuberculosis. Nevertheless, reports of tuberculous extrapulmonary involvement are also documented. Tuberculous breast abscess is a rare presentation, especially in immunocompetent hosts. Herein, a case of primary tuberculous breast abscess is presented. The patient came with complaints of pain in her right breast and a discharging sinus. A thorough diagnostic workup resulted in the establishment of a diagnosis with the detection of Mycobacterium tuberculosis on smear microscopy of pus, a cartridge-based nucleic acid amplification test, a line probe assay, and culture. Ultimately, she was put on anti-tubercular treatment.

Primary Extrapulmonary Rifampicin Mono-Resistant Tuberculosis of the Knee in an Indian Female Without Pulmonary Involvement: The World's First Case

Extrapulmonary tuberculosis presentations are comparatively less frequent. Isolated involvement of the knee in the absence of pulmonary focus is extremely rare. Further, primary extrapulmonary rifampicin mono-resistant tuberculosis of the knee without pulmonary involvement is never reported in females. A case of a 26-year-old female is presented who came with complaints of pain, swelling, and discharging sinuses from her left knee. In the absence of a history of tuberculosis or trauma, the diagnosis was challenging. However, she was diagnosed based on the reports of cartridge-based nucleic acid amplification tests and clinical correlation with radiometric techniques and initiated anti-tuberculous treatment according to her weight per the national guidelines present in 2018.

Primary Tuberculosis of the Cuboid and Fifth Metatarsal Without Pulmonary Involvement: A Rare Case Report

Tuberculosis affecting the smaller bones of the foot is relatively infrequent. There is a paucity of data related to the tubercular involvement of cuboid and metatarsal bones. Diagnosis is challenging, especially in the absence of pulmonary involvement, a history of trauma, and contact with tuberculosis. We present a rare case of primary tuberculosis of the cuboid and fifth metatarsal without pulmonary involvement. The patient was started on anti-tubercular chemotherapy. A detailed literature search revealed that no such case with concomitant involvement of the cuboid and fifth metatarsal without pulmonary seeding has ever been reported.

Measuring indirect transmission-reducing effects in tuberculosis vaccine efficacy trials: why and how?

Tuberculosis is the leading bacterial cause of death globally. In 2021, 10·6 million people developed symptomatic tuberculosis and 1·6 million died. Seven promising vaccine candidates that aim to prevent tuberculosis disease in adolescents and adults are currently in late-stage clinical trials. Conventional phase 3 trials provide information on the direct protection conferred against infection or disease in vaccinated individuals, but they tell us little about possible indirect (ie, transmission-reducing) effects that afford protection to unvaccinated individuals. As a result, proposed phase 3 trial designs will not provide key information about the overall effect of introducing a vaccine programme. Information on the potential for indirect effects can be crucial for policy makers deciding whether and how to introduce tuberculosis vaccines into immunisation programmes. We describe the rationale for measuring indirect effects, in addition to direct effects, of tuberculosis vaccine candidates in pivotal trials and lay out several options for incorporating their measurement into phase 3 trial designs.

Isolated Tuberculous Mediastinal Lymphadenopathy in an Immunocompetent Child Without Pulmonary Involvement: A Case Report

Tuberculosis continues to be a big challenge to public health. Isolated cases of tuberculous mediastinal lymphadenopathy in an immunocompetent child without pulmonary involvement are relatively rare. Compared to adults, children are susceptible to such infections; however, due to a lack of specific clinical features and the involvement of invasive techniques in establishing the diagnosis, there are chances of a diagnostic delay. A case of a nine-year-old girl who reported having chest pain for one month is presented. In the absence of the constitutional signs and symptoms of tuberculosis, a diagnosis was confirmed with computed tomography, histopathology, and cartridge-based nucleic acid amplification of samples obtained from endobronchial ultrasound-guided transbronchial needle aspiration. She was put on anti-tuberculous treatment for her weight.

Primary Isoniazid Mono-Resistant Extrapulmonary Tuberculosis Presenting as Cervical Lymphadenitis: The World's First Case of Its Type

Tuberculosis is commonly seen in endemic countries. Cases of primary drug resistance are rare. There is a paucity of data related to primary drug resistance at extrapulmonary sites. Herein, a case of primary isoniazid mono-resistant extrapulmonary tuberculosis of the multiple right cervical lymph nodes is presented. This patient reported multiple swellings and discharging sinuses. A battery of investigations with an eye for finding drug resistance led to a definite diagnosis. He was initiated on an anti-tubercular regimen per the national guidelines. A detailed literature search revealed that no such case of primary isoniazid mono-resistant extrapulmonary tuberculosis presenting as cervical lymphadenitis has ever been reported.

Primary Tubercular Breast Abscess in an Indian Female: A Rare Case

Tuberculosis is widespread in developing countries, which usually presents as pulmonary tuberculosis. However, cases of extrapulmonary tuberculosis at sites other than the lungs are also reported. The present case is a rare variety of extrapulmonary tuberculosis presenting as a primary tubercular breast abscess in an Indian female with no pulmonary involvement and no history of tuberculosis. A detailed clinical workup led to the final diagnosis, and she was put on anti-tuberculous treatment per the national guidelines.

Isolated Tuberculosis of the First Metatarsal of the Right Foot Without Pulmonary Involvement: A Rare Case

Tuberculosis of the small bones of the foot is a rare clinical condition. Oftentimes, there is a delay in diagnosis, which could adversely affect the results. Isolated cases of tuberculosis of the first metatarsal of the right foot without pulmonary involvement are seldom reported. Herein, a case of a 13-year-old Indian female who presented with complaints of pain, swelling, and discharge from her right foot is presented. A diagnostic workup led to a definite diagnosis of isolated tuberculosis of the first metatarsal of the right foot without pulmonary involvement, and she was put on anti-tubercular treatment.

Disease Transmission by Patients With Subclinical Tuberculosis

BACKGROUND

Subclinical tuberculosis has been increasingly recognized as a separate state in the spectrum of the disease. However, evidence on the transmissibility of subclinical tuberculosis is still inconclusive.

METHODS

We re-analyzed the data from the 2007 combined tuberculosis prevalence and tuberculin surveys in Vietnam. Poisson regression with robust standard errors was conducted to assess the effect of clinical presentation of individuals with tuberculosis in the household on tuberculin skin test (TST) positivity among children aged 6-14 years who participated in the tuberculin survey, adjusting for child's age, smear status of the index patient, and other covariates.

RESULTS

In the multivariate analysis, we found significantly increased risks for TST positivity in children living with patients with clinical, smear-positive tuberculosis, compared with those living with individuals without tuberculosis (adjusted risk ratio [aRR]: 3.04; 95% confidence interval [CI]: 2.00-4.63) and with those living with patients with subclinical tuberculosis, adjusting for index smear status (aRR: 2.26; 95% CI: 1.03-4.96). Among children aged 6-10 years, those living with patients with clinical, smear-positive tuberculosis and those living with patients with subclinical, smear-positive tuberculosis had similarly increased risks of TST positivity compared with those living with individuals without tuberculosis (aRRs [95% CI] of 3.56 [1.91-6.62] and 3.11 [1.44-6.72], respectively).

CONCLUSIONS

Our findings support the hypothesis that smear-positive subclinical tuberculosis contributes to Mycobacterium tuberculosis transmission. To eliminate tuberculosis in 2035, control strategies need to address subclinical presentations of the disease.

Comparison of two diagnostic intervention packages for community-based active case finding for tuberculosis: an open-label randomized controlled trial

Two in every five patients with active tuberculosis (TB) remain undiagnosed or unreported. Therefore community-based, active case-finding strategies require urgent implementation. However, whether point-of-care (POC), portable battery-operated, molecular diagnostic tools deployed at a community level, compared with conventionally used POC smear microscopy, can shorten time-to-treatment initiation, thus potentially curtailing transmission, remains unclear. To clarify this issue, we performed an open-label, randomized controlled trial in periurban informal settlements of Cape Town, South Africa, where we TB symptom screened 5,274 individuals using a community-based scalable mobile clinic. Some 584 individuals with HIV infection or symptoms of TB underwent targeted diagnostic screening and were randomized (1:1) to same-day smear microscopy (n = 296) or on-site DNA-based molecular diagnosis (n = 288; GeneXpert). The primary aim was to compare time to TB treatment initiation between the arms. Secondary aims included feasibility and detection of probably infectious people. Of participants who underwent targeted screening, 9.9% (58 of 584) had culture-confirmed TB. Time-to-treatment initiation occurred significantly earlier in the Xpert versus the smear-microscopy arm (8 versus 41 d, P = 0.002). However, overall, Xpert detected only 52% of individuals with culture-positive TB. Notably, Xpert detected almost all of the probably infectious patients compared with smear microscopy (94.1% versus 23.5%, P = <0.001). Xpert was associated with a shorter median time to treatment of probably infectious patients (7 versus 24 d, P = 0.02) and a greater proportion of infectious patients were on treatment at 60 d compared with the probably noninfectious patients (76.5% versus 38.2%, P < 0.01). Overall, a greater proportion of POC Xpert-positive participants were on treatment at 60 d compared with all culture-positive participants (100% versus 46.5%, P < 0.01). These findings challenge the traditional paradigm of a passive case-finding, public health strategy and argues for the implementation of portable DNA-based diagnosis with linkage to care as a community-oriented, transmission-interruption strategy. The study was registered with the South African National Clinical Trials Registry (application ID 4367; DOH-27-0317-5367) and ClinicalTrials.gov (NCT03168945).

Exhaled Mycobacterium tuberculosis Predicts Incident Infection in Household Contacts

BACKGROUND

Halting transmission of Mycobacterium tuberculosis (Mtb) by identifying infectious individuals early is key to eradicating tuberculosis (TB). Here we evaluate face mask sampling as a tool for stratifying the infection risk of individuals with pulmonary TB (PTB) to their household contacts.

METHODS

Forty-six sputum-positive PTB patients in The Gambia (August 2016-November 2017) consented to mask sampling prior to commencing treatment. Incident Mtb infection was defined in 181 of their 217 household contacts as QuantiFERON conversion or an increase in interferon-γ of ≥1 IU/mL, 6 months after index diagnosis. Multilevel mixed-effects logistical regression analysis with cluster adjustment by household was used to identify predictors of incident infection.

RESULTS

Mtb was detected in 91% of PTB mask samples with high variation in IS6110 copies (5.3 × 102 to 1.2 × 107). A high mask Mtb level (≥20 000 IS6110 copies) was observed in 45% of cases and was independently associated with increased likelihood of incident Mtb infection in contacts (adjusted odds ratio, 3.20 [95% confidence interval, 1.26-8.12]; P = .01), compared with cases having low-positive/negative mask Mtb levels. Mask Mtb level was a better predictor of incident Mtb infection than sputum bacillary load, chest radiographic characteristics, or sleeping proximity.

CONCLUSIONS

Mask sampling offers a sensitive and noninvasive tool to support the stratification of individuals who are most infectious in high-TB-burden settings. Our approach can provide better insight into community transmission in complex environments.

Contribution of Reinfection to Annual Rate of Tuberculosis Infection (ARI) and Incidence of Tuberculosis Disease

BACKGROUND

Modeling studies have concluded that 60-80% of tuberculosis (TB) infections result from reinfection of previously infected persons. The annual rate of infection (ARI), a standard measure of the risk of TB infection in a community, may not accurately reflect the true risk of infection among previously infected persons. We constructed a model of infection and reinfection with Mycobacterium tuberculosis to explore the predictive accuracy of ARI and its effect on disease incidence.

METHODS

We created a deterministic simulation of the progression from TB infection to disease and simulated the prevalence of TB infection at the beginning and end of a theoretical year of infection. We considered 10 disease prevalence scenarios ranging from 100/100 000 to 1000/100 000 in simulations where TB exposure probability was homogeneous across the whole simulated population or heterogeneously stratified into high-risk and low-risk groups. ARI values, rates of progression from infection to disease, and the effect of multiple reinfections were obtained from published studies.

RESULTS

With homogeneous exposure risk, observed ARI values produced expected numbers of infections. However, when heterogeneous risk was introduced, observed ARI was seen to underestimate true ARI by 25-58%. Of the cases of TB disease that occurred, 36% were among previously infected persons when prevalence was 100/100 000, increasing to 79% of cases when prevalence was 1000/100 000.

CONCLUSIONS

Measured ARI underestimates true ARI as a result of heterogeneous population mixing. The true force of infection in a community may be greater than previously appreciated. Hyperendemic communities likely contribute disproportionally to the global TB disease burden.

Compound lidocaine/prilocaine cream combined with tetracaine prevents cough caused by extubation after general anaesthesia: a randomised controlled trial

BACKGROUND

Coughing caused by tracheal extubation is common following general anaesthesia. Heavy aerosol production by coughing during recovery from general anaesthesia in patients with respiratory infections (especially COVID-19) may be one of the highest risk factors for infection in healthcare workers. The application of local anaesthetics to the endotracheal tube is an effective method to reduce coughing. The most commonly used anaesthetics are compound lidocaine/prilocaine cream and tetracaine spray. However, coughing still occurs when the two anaesthetics are used alone. We speculated that the application of compound lidocaine/prilocaine combined with tetracaine spray would better prevent coughing caused by tracheal extubation.

METHODS

Patients scheduled for laparoscopic cholecystectomy or cholecystectomy combined with common bile duct exploration under general anaesthesia were randomly assigned to Group C (saline spray), Group L (2 g compound lidocaine/prilocaine cream contains 5 mg of lidocaine and 5 mg prilocaine)), Group T (tetracaine) and Group F (compound lidocaine/prilocaine cream combined with tetracaine). The incidence of coughing, the endotracheal tube tolerance assessment, the incidence of agitation, the active extubation rate, the incidence of postoperative pharyngeal pain and the incidence of postoperative cough were recorded and analysed. Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and the plasma concentrations of epinephrine and norepinephrine were measured immediately before extubation and 1 min after extubation.

RESULTS

A total of 211 patients were randomly assigned to Group C (53 cases), Group L (52 cases), Group T (52 cases) and Group F (54 cases). The primary result is assessment of the incidence of cough. The patients emerged from general anaesthesia, 96% of Group C had cough, which was significantly reduced in Group L (61.5%, P < 0.001), Group T (75%, P < 0.05) and Group F (22.2%, P < 0.001). Group F had a significantly reduced incidence of cough compared to Group L and Group T (P < 0.05 or P < 0.01, respectively). The secondary results were assessed. The endotracheal tube tolerance score in Group C ((1, 3) 4, P < 0.001) was higher than Group L ((0, 1) 2), Group T ((0, 1.25) 3) and Group F ((0, 0) 1). Group F had a significantly lower score than Group L and Group T (P < 0.05, P < 0.01, respectively). The incidence of agitation and the active extubation rate were also higher in Group C (96.2% and 71.7%, respectively, P < 0.001) than Group L (48.1% and 15.4%, respectively), Group T (61.5% and 26.9%, respectively) and Group F (17.3% and 7.7%, respectively). Blood pressure, HR and plasma concentrations of epinephrine and norepinephrine were significantly higher in Group C than in all other groups at the time of extubation and 1 min after extubation (P < 0.001). Group F exhibited significantly reduced blood pressure, heart rate and plasma concentrations of epinephrine and norepinephrine compared to Group L and Group T (P < 0.05, P < 0.01 or P < 0.001, respectively). The incidence of postoperative pharyngeal pain and the incidence of postoperative cough were not significantly different among the groups.

CONCLUSIONS

Compound lidocaine/prilocaine cream combined with tetracaine may be a more effective approach for preventing coughing and stabilising circulation during extubation following general anaesthesia. This may play an important role in preventing medical staff from contracting respiratory infectious diseases.

TRIAL REGISTRATION

Chinese Clinical Trial Registry: ChiCTR2200058429 (registration date: 09-04-2022) "retrospectively registered".

BIS-guided sedation prevents the cough reaction of patients under general anaesthesia caused by extubation: a randomized controlled trial

Background

The multiple modes of SARS-CoV-2 transmission including airborne, droplet, contact and faecal–oral transmissions that cause coronavirus disease 2019 (COVID-19) contribute to a public threat to the lives of people worldwide. Heavy aerosol production by coughing and the big peak expiratory flow in patients with respiratory infections (especially SARS-CoV-2) during recovery from general anaesthesia are the highest risk factors for infection in healthcare workers. To perform sedation before extubation significantly reduced the incidence of coughing during recovery from general anaesthesia. However, there are few studies on endotracheal tube removal under BIS-guided sedation in postanaesthesia care unit (PACU). We speculated that the BIS-guided sedation with dexmedetomidine and propofol would better prevent coughing caused by tracheal extubation and reducing peak expiratory flow.

Methods

Patients with general anaesthesia were randomly assigned to Group S (dexmedetomidine was infused in the operating room for 30 min, and the bispectral index (BIS) value was maintained 60–70 by infusion propofol at 0.5~1.5 μg/ml in the PACU until the endotracheal tubes were pulled out) and Group C (no dexmedetomidine and propofol treatment, replaced with the saline treatment). The incidence of coughing, agitation and active extubation, endotracheal tube tolerance and the peak expiratory flow at spontaneous breathing and at extubation were assessed.

Results

A total of 101 patients were randomly assigned to Group S (51 cases) and Group C (50 cases). The incidence of coughing, agitation and active extubation was significantly lower (1(51), 0(51) and 0(51), respectively) in Group S than (11(50), 8(50) and 5(50), respectively) in Group C (p < 0.05 or p < 0.01, respectively); the scores of cough were significantly reduced (1(1, 1)) in Group S than (1(1, 2)) in Group C (p < 0.01); and the endotracheal tube tolerance was significantly improved (0(0, 1)) in Group S than (1(1, 3)) in Group C (p < 0.001). The peak expiratory flow at spontaneous breathing and at extubation was significantly reduced (5(5, 7) and 6.5(6, 8), respectively) in Group S than (8(5, 10) and 21(9, 32)) in Group C (p < 0.001).

Conclusions

BIS-guided sedation with dexmedetomidine and propofol significantly prevented coughing and reduced peak expiratory flow during recovery from general anaesthesia, which may play an important role in preventing medical staff from contracting COVID-19.

Trial registration

Chinese Clinical Trial Registry: ChiCTR2200058429 (registration date: 09-04-2022) “retrospectively registered”.

Aerosolization of Mycobacterium tuberculosis by Tidal Breathing

Rationale: Interrupting tuberculosis (TB) transmission requires an improved understanding of how and when the causative organism, Mycobacterium tuberculosis (Mtb), is aerosolized. Although cough is commonly assumed to be the dominant source of Mtb aerosols, recent evidence of cough-independent Mtb release implies the contribution of alternative mechanisms. Objectives: To compare the aerosolization of Mtb bacilli and total particulate matter from patients with TB during three separate respiratory maneuvers: tidal breathing (TiBr), FVC, and cough. Methods: Bioaerosol sampling and Mtb enumeration by live-cell, fluorescence microscopy were combined with real-time measurement of CO₂ concentration and total particle counts from 38 patients with GeneXpert-positive TB before treatment initiation. Measurements and Main Results: For all maneuvers, the proportions of particles detected across five size categories were similar, with most particles falling between 0.5-5 μm. Although total particle counts were 4.8-fold greater in cough samples than either TiBr or FVC, all three maneuvers returned similar rates of positivity for Mtb. No correlation was observed between total particle production and Mtb count. Instead, for total Mtb counts, the variability between individuals was greater than the variability between sampling maneuvers. Finally, when modelled using 24-hour breath and cough frequencies, our data indicate that TiBr might contribute more than 90% of the daily aerosolized Mtb among symptomatic patients with TB. Conclusions: Assuming the number of viable Mtb organisms released offers a reliable proxy of patient infectiousness, our observations imply that TiBr and interindividual variability in Mtb release might be significant contributors to TB transmission among active cases.

Role of Curcumin as a Potential Immunomodulator to Adjunct Tuberculosis Treatment in Indonesia

This study aimed to highlight and focus on curcumin’s role in enhancing the body defense mechanism against tuberculosis (TB) infection, using a narrative review. This review was identified by four search engines: PubMed, Science Direct, Research Gate, and Google Scholar. We found that as an immunomodulator, curcumin reduces the production of specific cytokines by inhibiting the transcription factor. In the same mechanism, curcumin also activates the host macrophages, dendritic maturation, and modulation of the antigen-presenting cell process. Curcumin also increases apoptosis as a defence mechanism against TB infection. Curcumin also increases B-cell proliferation and downregulates oxidative stress on B-cells. As results, curcumin is a potential immunomodulator that complements M. TB treatment, especially in Indonesia. It can be stated that curcumin is proven to be a promising strategy in complementing TB prevention also treatment.

Application of Droplet Digital PCR to Detection of Mycobacterium tuberculosis and Mycobacterium leprae Infections: A Narrative Review

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (MTB) infection, which has seriously endangered human health for many years. With the emergence of multidrug-resistant and extensively drug-resistant MTB, the prevention and treatment of TB has become a pressing need. Early diagnosis, drug resistance monitoring, and control of disease transmission are critical aspects in the prevention and treatment of TB. However, the currently available diagnostic technologies and drug sensitivity tests are time consuming, and thus, it is difficult to achieve the goal of early diagnosis and detection drug sensitivity, which results in limited control of disease transmission. The development of molecular testing technology has gradually achieved the vision of rapid and accurate diagnosis of TB. Droplet digital PCR (ddPCR) is an excellent nucleic acid quantification method with high sensitivity and no need for a calibration curve. Herein, we review the application of ddPCR in TB diagnosis and drug resistance detection and transmission monitoring.

Rapid detection of airborne protein from Mycobacterium tuberculosis using a biosensor detection system

The developed biosensor detection system can complete the detection of air samples by collecting exhaled breath condensate, greatly reducing the time to diagnose tuberculosis.

Rapid and Sensitive Detection of Mycobacterium tuberculosis by an Enhanced Nanobiosensor

Tuberculosis (TB) mostly spreads from person to person through Mycobacterium tuberculosis (MTB). However, the majority of conventional detection methods for MTB cannot satisfy the requirements for actual TB detection. As one of the most promising powerful platforms, a silicon nanowire field-effect transistor (SiNW-FET) biosensor shows good prospect in TB detection. In this study, an enhanced SiNW-FET biosensor was developed for the rapid and sensitive detection of MTB. The surface functional parameters of the biosensor were explored and optimized. The SiNW-FET biosensor has good sensitivity with a detection limit of 0.01 fg/mL toward protein. The current change value shows a linear upward trend with the increase in protein concentration in the range of 1 fg/mL to 100 μg/mL. One whole test cycle can be accomplished within only 30 s. More importantly, a good distinction was realized in the sputum without pretreatment between normal people and TB patients, which greatly shortened the TB detection time (only 2-5 min, considering the dilution of sputum). Compared with other methods, the SiNW-FET biosensor can detect MTB with a remarkably broad dynamic linear range in a shorter time.

Ultra-low Dose Aerosol Infection of Mice with Mycobacterium tuberculosis More Closely Models Human Tuberculosis

Tuberculosis (TB) is a heterogeneous disease manifesting in a subset of individuals infected with aerosolized Mycobacterium tuberculosis (Mtb). Unlike human TB, murine infection results in uniformly high lung bacterial burdens and poorly organized granulomas. To develop a TB model that more closely resembles human disease, we infected mice with an ultra-low dose (ULD) of between 1-3 founding bacteria, reflecting a physiologic inoculum. ULD-infected mice exhibited highly heterogeneous bacterial burdens, well-circumscribed granulomas that shared features with human granulomas, and prolonged Mtb containment with unilateral pulmonary infection in some mice. We identified blood RNA signatures in mice infected with an ULD or a conventional Mtb dose (50-100 CFU) that correlated with lung bacterial burdens and predicted Mtb infection outcomes across species, including risk of progression to active TB in humans. Overall, these findings highlight the potential of the murine TB model and show that ULD infection recapitulates key features of human TB.

Bacterial and host determinants of cough aerosol culture positivity in patients with drug-resistant versus drug-susceptible tuberculosis

A burgeoning epidemic of drug-resistant tuberculosis (TB) threatens to derail global control efforts. Although the mechanisms remain poorly clarified, drug-resistant strains are widely believed to be less infectious than drug-susceptible strains. Consequently, we hypothesized that lower proportions of patients with drug-resistant TB would have culturable Mycobacterium tuberculosis from respirable, cough-generated aerosols compared to patients with drug-susceptible TB, and that multiple factors, including mycobacterial genomic variation, would predict culturable cough aerosol production. We enumerated the colony forming units in aerosols (≤10 µm) from 452 patients with TB (227 with drug resistance), compared clinical characteristics, and performed mycobacterial whole-genome sequencing, dormancy phenotyping and drug-susceptibility analyses on M. tuberculosis from sputum. After considering treatment duration, we found that almost half of the patients with drug-resistant TB were cough aerosol culture-positive. Surprisingly, neither mycobacterial genomic variants, lineage, nor dormancy status predicted cough aerosol culture positivity. However, mycobacterial sputum bacillary load and clinical characteristics, including a lower symptom score and stronger cough, were strongly predictive, thereby supporting targeted transmission-limiting interventions. Effective treatment largely abrogated cough aerosol culture positivity; however, this was not always rapid. These data question current paradigms, inform public health strategies and suggest the need to redirect TB transmission-associated research efforts toward host-pathogen interactions.

Exhaled Mycobacterium tuberculosis output and detection of subclinical disease by face-mask sampling: prospective observational studies

BACKGROUND

Tuberculosis remains a global health challenge, with early diagnosis key to its reduction. Face-mask sampling detects exhaled Mycobacterium tuberculosis. We aimed to investigate bacillary output from patients with pulmonary tuberculosis and to assess the potential of face-mask sampling as a diagnostic method in active case-finding.

METHODS

We did a 24-h longitudinal study in patients from three hospitals in Pretoria, South Africa, with microbiologically confirmed pulmonary tuberculosis. Patients underwent 1 h of face-mask sampling eight times over a 24-h period, with contemporaneous sputum sampling. M tuberculosis was detected by quantitative PCR. We also did an active case-finding pilot study in inhabitants of an informal settlement near Pretoria. We enrolled individuals with symptoms of tuberculosis on the WHO screening questionnaire. Participants provided sputum and face-mask samples that were tested with the molecular assay Xpert MTB/RIF Ultra. Sputum-negative and face-mask-positive individuals were followed up prospectively for 20 weeks by bronchoscopy, PET-CT, and further sputum analysis to validate the diagnosis.

FINDINGS

Between Sept 22, 2015, and Dec 3, 2015, 78 patients with pulmonary tuberculosis were screened for the longitudinal study, of whom 24 completed the study (20 had HIV co-infection). M tuberculosis was detected in 166 (86%) of 192 face-mask samples and 38 (21%) of 184 assessable sputum samples obtained over a 24-h period. Exhaled M tuberculosis output showed no diurnal pattern and did not associate with cough frequency, sputum bacillary content, or chest radiographic disease severity. On May 16, 2018, 45 individuals were screened for the prospective active case-finding pilot study, of whom 20 had tuberculosis symptoms and were willing to take part. Eight participants were diagnosed prospectively with pulmonary tuberculosis, of whom six were exclusively face-mask positive at screening. Four of these participants (three of whom were HIV-positive) had normal findings on chest radiography but had treatment-responsive early tuberculosis-compatible lesions on PET-CT scans, with Xpert-positive sputum samples after 6 weeks.

INTERPRETATION

Face-mask sampling offers a highly efficient and non-invasive method for detecting exhaled M tuberculosis, informing the presence of active infection both with greater consistency and at an earlier disease stage than with sputum samples. The approach shows potential for diagnosis and screening, particularly in difficult-to-reach communities.

FUNDING

Wellcome Trust, CARA (Council for At-Risk Academics), University of Leicester, the UK Medical Research Council, and the National Institute for Health Research. VIDEO ABSTRACT.

A fieldable electrostatic air sampler enabling tuberculosis detection in bioaerosols

Tuberculosis (TB) infects about 25% of the world population and claims more human lives than any other infectious disease. TB is spread by inhalation of aerosols containing viable Mycobacterium tuberculosis expectorated or exhaled by patients with active pulmonary disease. Air-sampling technology could play an important role in TB control by enabling the detection of airborne M. tuberculosis, but tools that are easy to use and scalable in TB hotspots are lacking. We developed an electrostatic air sampler termed the TB Hotspot DetectOR (THOR) and investigated its performance in laboratory aerosol experiments and in a prison hotspot of TB transmission. We show that THOR collects aerosols carrying microspheres, Bacillus globigii spores and M. bovis BCG, concentrating these microparticles onto a collector piece designed for subsequent detection analysis. The unit was also successfully operated in the complex setting of a prison hotspot, enabling detection of a molecular signature for M. tuberculosis in the cough of inmates. Future deployment of this device may lead to a measurable impact on TB case-finding by screening individuals through the aerosols they generate.

Contact tracing strategies in household and congregate environments to identify cases of tuberculosis in low- and moderate-incidence populations

BACKGROUND

Tuberculosis is an infectious bacterial disease that is spread via respiratory droplets from infected individuals to susceptible contacts. To eliminate this disease from low- and medium-incidence settings, people who are most likely to be infected (contacts) must be identified. Recently, study authors have examined alternate approaches to contact tracing methods that demonstrate improved detection and prioritization of contacts. The comparative benefit of these methods has not been established.

OBJECTIVES

To assess the effectiveness of novel methods of contact tracing versus current standard of care to identify latent and active cases in low- to moderate-incidence settings.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, LILACS, Web of Science, and CINAHL up to 15 July 2019. We also searched for clinical trials and examined reference lists and conference proceedings.

SELECTION CRITERIA

Randomized controlled trials (RCTs) and cluster-RCTs of contact tracing strategies that included alternate approaches (other than standard practice).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed identified articles for eligibility and quality using prespecified criteria.

MAIN RESULTS

No trials met the inclusion criteria of this review. Several study authors described an alternate method for examining contacts and performing social network analysis but did not compare this with the current contact tracing approach.

AUTHORS' CONCLUSIONS

This Cochrane Review highlights the lack of research in support of the current contact tracing method and the need for RCTs to compare new methods such as social network analysis to improve contact tracing processes.

Immunological mechanisms of human resistance to persistent Mycobacterium tuberculosis infection

Mycobacterium tuberculosis is a leading cause of mortality worldwide and establishes a long-lived latent infection in a substantial proportion of the human population. Multiple lines of evidence suggest that some individuals are resistant to latent M. tuberculosis infection despite long-term and intense exposure, and we term these individuals 'resisters'. In this Review, we discuss the epidemiological and genetic data that support the existence of resisters and propose criteria to optimally define and characterize the resister phenotype. We review recent insights into the immune mechanisms of M. tuberculosis clearance, including responses mediated by macrophages, T cells and B cells. Understanding the cellular mechanisms that underlie resistance to M. tuberculosis infection may reveal immune correlates of protection that could be utilized for improved diagnostics, vaccine development and novel host-directed therapeutic strategies.

Risk factors for active tuberculosis in 938 QuantiFERON-positive schoolchildren in Mongolia: a community-based cross-sectional study

BACKGROUND

There is controversy regarding the relative influence of 'exogenous' versus 'endogenous' factors on the risk of progression from latent tuberculosis infection to active tuberculosis (TB) disease in children.

METHODS

We conducted a cross-sectional analysis to identify risk factors for active tuberculosis in QuantiFERON®-TB Gold (QFT-G)-positive children aged 6-13 years attending 18 schools in Ulaanbaatar, Mongolia. Children underwent clinical and radiological screening for active tuberculosis, and data relating to potential risk factors for disease progression were collected by questionnaire and determination of serum 25-hydroxyvitamin D (25[OH]D) concentrations. Risk ratios were calculated using generalized estimating equations with adjustment for potential confounders.

RESULTS

129/938 (13.8%) QFT-positive children were diagnosed with active tuberculosis. Risk of active tuberculosis was independently associated with household exposure to pulmonary TB (adjusted risk ratio [aRR] 2.40, 95% CI 1.74 to 3.30, P < 0.001), month of sampling (adjusted risk ratio [aRR] for March-May vs. June-November 3.31, 95% CI 1.63 to 6.74, P < 0.001; aRR for December-February vs. June-November 2.53, 95% CI 1.23 to 5.19, P = 0.01) and active smoking by the child (aRR 5.23, 95% CI 2.70 to 10.12, P < 0.001). No statistically significant independent association was seen for age, sex, socio-economic factors, presence of a Bacillus Calmette-Guérin (BCG) scar, tobacco exposure or vitamin D status.

CONCLUSIONS

Household exposure to active TB, winter or spring season and active smoking were independently associated with risk of active tuberculosis in QFT-positive children. Our findings highlight the potentially high yield of screening child household contacts of infectious index cases for active tuberculosis in low- and middle-income countries.

Detection of Mycobacterium tuberculosis RNA in bioaerosols from pulmonary tuberculosis patients

BACKGROUND

Bioaerosols from pulmonary tuberculosis (PTB) patients are a quantitative predictor of transmission. Current methods involve sophisticated instruments and time-consuming techniques to assess viable TB bacteria in bioaerosols. We tested the feasibility of detecting Mycobacterium tuberculosis (Mtb) specific RNA from bioaerosols retained on TB patients' masks.

METHODS

Adult PTB patients (n=33) were recruited at diagnosis before GeneXpert confirmation between April-2017 to February-2019 from private TB clinics in Mumbai. Face mask worn for 1 or 3h or N95 mask containing a cellulose acetate membrane worn for 5min by the patients were tested for the presence of Mtb RNA by quantitative PCR and bacterial load was estimated.

RESULTS

Quantitative PCR targeting rpoB, sigA,16S and fgd1 and sequencing of rpoB confirmed the presence of Mtb specific RNA in mask samples including masks of two patients with unproductive sputum. Membrane samples had seven-fold higher RNA and bacterial load that correlated to bacterial load estimated by sputum GeneXpert.

CONCLUSION

The study demonstrates that patient masks can be used to sample bioaerosols for detection of viable Mtb. The findings have translational value in the diagnosis of TB and monitoring Mtb variations between and within patients useful for assessing infectiousness and treatment response.

Host Determinants of Infectiousness in Smear-Positive Patients With Pulmonary Tuberculosis

Background

Epidemiologic data suggests that only a minority of tuberculosis (TB) patients are infectious. Cough aerosol sampling is a novel quantitative method to measure TB infectiousness.

Methods

We analyzed data from three studies conducted in Uganda and Brazil over a 13-year period. We included sputum acid fast bacilli (AFB) and culture positive pulmonary TB patients and used a cough aerosol sampling system (CASS) to measure the number of colony-forming units (CFU) of Mycobacterium tuberculosis in cough-generated aerosols as a measure for infectiousness. Aerosol data was categorized as: aerosol negative (CFU = 0) and aerosol positive (CFU > 0). Logistic regression models were built to identify factors associated with aerosol positivity.

Results

M. tuberculosis was isolated by culture from cough aerosols in 100/233 (43%) TB patients. In an unadjusted analysis, aerosol positivity was associated with fewer days of antituberculous therapy before CASS sampling (p = .0001), higher sputum AFB smear grade (p = .01), shorter days to positivity in liquid culture media (p = .02), and larger sputum volume (p = .03). In an adjusted analysis, only fewer days of TB treatment (OR 1.47 per 1 day of therapy, 95% CI 1.16-1.89; p = .001) was associated with aerosol positivity.

Conclusion

Cough generated aerosols containing viable M. tuberculosis, the infectious moiety in TB, are detected in a minority of TB patients and rapidly become non-culturable after initiation of antituberculous treatment. Mechanistic studies are needed to further elucidate these findings.

Transmission of drug-resistant tuberculosis in HIV-endemic settings

The emergence and expansion of the multidrug-resistant tuberculosis epidemic is a threat to the global control of tuberculosis. Multidrug-resistant tuberculosis is the result of the selection of resistance-conferring mutations during inadequate antituberculosis treatment. However, HIV has a profound effect on the natural history of tuberculosis, manifesting in an increased rate of disease progression, leading to increased transmission and amplification of multidrug-resistant tuberculosis. Interventions specific to HIV-endemic areas are urgently needed to block tuberculosis transmission. These interventions should include a combination of rapid molecular diagnostics and improved chemotherapy to shorten the duration of infectiousness, implementation of infection control measures, and active screening of multidrug-resistant tuberculosis contacts, with prophylactic regimens for individuals without evidence of disease. Development and improvement of the efficacy of interventions will require a greater understanding of the factors affecting the transmission of multidrug-resistant tuberculosis in HIV-endemic settings, including population-based molecular epidemiology studies. In this Series article, we review what we know about the transmission of multidrug-resistant tuberculosis in settings with high burdens of HIV and define the research priorities required to develop more effective interventions, to diminish ongoing transmission and the amplification of drug resistance.

Multiple exposures, reinfection and risk of progression to active tuberculosis

A recent study reported on a tuberculosis (TB) outbreak in a largely Inuit village. Among newly infected individuals, exposure to additional active cases was associated with an increasing probability of developing active disease within a year. Using binomial risk models, we evaluated two potential mechanisms by which multiple infections during the first year following initial infection could account for increasing disease risk with increasing exposures. In the reinfection model, each infectious contact confers an independent risk of an infection, and infections contribute independently to active disease. In the threshold model, disease risk follows a sigmoidal function with small numbers of infectious contacts conferring a low risk of active disease and large numbers of contacts conferring a high risk. To determine the dynamic impact of reinfection during the early phase of infection, we performed simulations from a modified Reed-Frost model of TB dynamics following spread from an initial number of cases. We parametrized this model with the maximum-likelihood estimates from the reinfection and threshold models in addition to the observed distribution of exposures among new infections. We find that both models can plausibly account for the observed increase in disease risk with increasing infectious contacts, but the threshold model confers a better fit than a nested model without a threshold (p = 0.04). Our simulations indicate that multiple exposures to infectious individuals during this critical time period can lead to dramatic increases in outbreak size. In order to decrease TB burden in high-prevalence settings, it may be necessary to implement measures aimed at preventing repeated exposures, in addition to preventing primary infection.

Cough in pulmonary tuberculosis: Existing knowledge and general insights

Cough is a prominent symptom of pulmonary tuberculosis (TB), one of the oldest and most prevalent infectious diseases. Coughing probably has a pivotal role in transmission of the causative organism Mycobacterium tuberculosis. Despite this, little research to date has addressed this subject. Current knowledge of the mechanisms of cough in TB and how exactly coughing patterns predict infectiousness is scant, but this is changing. This overview summarises the existing evidence for the infectiousness of cough in TB, clinical correlates, and possible causes of cough in TB. Potential unique characteristics of cough in the disease are discussed, as is treatment and the subjective awareness of coughing in the disease.

Cough-aerosol cultures of Mycobacterium tuberculosis in the prediction of outcomes after exposure. A household contact study in Brazil

Background

Mycobacterium tuberculosis cultures of cough-generated aerosols from patients with pulmonary tuberculosis (TB) are a quantitative method to measure infectiousness and to predict secondary outcomes in exposed contacts. However, their reproducibility has not been established.

Objective

To evaluate the predictive value of colony-forming units (CFU) of M. tuberculosis in cough aerosols on secondary infection and disease in household contacts in Brazil.

Methods

Adult sputum smear+ and culture+ pulmonary TB cases underwent a standard evaluation and were categorized according to aerosol CFU. We evaluated household contacts for infection at baseline and at 8 weeks with TST and IGRA, and secondary disease.

Results

We enrolled 48 index TB cases; 40% had negative aerosols, 27% low aerosols (<10 CFU) and 33% high aerosols (≥10 CFU). Of their 230 contacts, the proportion with a TST ≥10 mm at 8 weeks was 59%, 65% and 75%, respectively (p = 0.34). Contacts of high aerosol cases had greater IGRA readouts (median 4.6 IU/mL, IQR 0.02–10) when compared to those with low (0.8, 0.2–10) or no aerosol (0.1, 0–3.7; p = 0.08). IGRA readouts in TST converters of high aerosol cases (median 20 IU/mL, IQR 10–24) were larger than those from aerosol-negative (0.13, 0.04–3; p = o.o2). 8/9 (89%) culture+ secondary TB cases occurred in contacts of aerosol+ cases.

Conclusion

Aerosol CFU predicts quantitatively IGRA readouts among household contacts of smear positive TB cases. Our results strengthen the argument of using cough aerosols to guide targeted preventive treatment strategies, a necessary component of current TB elimination projections.

Mycobacterium tuberculosis Reporter Strains as Tools for Drug Discovery and Development

Reporter strains have proven to be powerful tools to study Mycobacterium tuberculosis (Mtb) physiology. Transcriptional and translational reporter strains are engineered by fusing a readout gene, encoding a fluorescent, luminescent or enzymatic protein, downstream of a promoter or in-frame with a gene of interest. When the reporter is expressed, it generates a signal that acts as a synthetic phenotype, enabling the study of physiologies that might have otherwise been hidden. This review will discuss approaches for generating reporter strains in Mtb and how they can be used as tools for high-throughput genetic and small molecule screening and as biomarkers for examining Mtb responses to drug or immune stresses during animal infections. Fluorescent reporter strains have an added benefit in that they can be used for single-cell studies both in vitro and in vivo, thus enabling the study of mechanisms underlying phenotypic heterogeneity. Recent examples of the use of Mtb reporter strains will be presented with a focus on how they can be used as tools for drug discovery and development. © 2018 IUBMB Life, 70(9):818-825, 2018.

Detection of Mycobacterium tuberculosis bacilli in bio-aerosols from untreated TB patients

Background: Tuberculosis (TB) is predominantly an airborne disease. However, quantitative and qualitative analysis of bio-aerosols containing the aetiological agent, Mycobacterium tuberculosis (Mtb), has proven very challenging. Our objective is to sample bio-aerosols from newly diagnosed TB patients for detection and enumeration of Mtb bacilli. Methods: We monitored each of 35 newly diagnosed, GeneXpert sputum-positive, TB patients during 1 hour confinement in a custom-built Respiratory Aerosol Sampling Chamber (RASC). The RASC (a small clean-room of 1.4m ) incorporates aerodynamic particle size detection, viable and non-viable sampling devices, real-time CO 2 monitoring, and cough sound-recording. Microbiological culture and droplet digital polymerase chain reaction (ddPCR) were used to detect Mtb in each of the bio-aerosol collection devices. Results:  Mtb was detected in 27/35 (77.1%) of aerosol samples; 15/35 (42.8%) samples were positive by mycobacterial culture and 25/27 (92.96%) were positive by ddPCR. Culturability of collected bacilli was not predicted by radiographic evidence of pulmonary cavitation, sputum smear positivity. A correlation was found between cough rate and culturable bioaerosol.  Mtb was detected on all viable cascade impactor stages with a peak at aerosol sizes 2.0-3.5μm. This suggests a median of 0.09 CFU/litre of exhaled air (IQR: 0.07 to 0.3 CFU/l) for the aerosol culture positives and an estimated median concentration of 4.5x10 CFU/ml (IQR: 2.9x10 -5.6x10 ) of exhaled particulate bio-aerosol. Conclusions:  Mtb was identified in bio-aerosols exhaled by the majority of untreated TB patients using the RASC. Molecular detection was more sensitive than mycobacterial culture on solid media, suggesting that further studies are required to determine whether this reflects a significant proportion of differentially detectable bacilli in these samples.

Risk factors for infectiousness of patients with tuberculosis: a systematic review and meta-analysis

We performed a systematic review and meta-analyses of studies assessing tuberculosis (TB) patient-related risk factors for transmission of Mycobacterium tuberculosis infection. Meta-analyses were conducted for sputum smear-positivity, lung cavitation and HIV seropositivity of index patients with both crude and adjusted odds ratios (AORs) pooled using random effect models. Thirty-seven studies were included in the review. We found that demographic characteristics such as age and sex were not significant risk factors, while behaviours such as smoking and alcohol intake were associated with infectiousness although inconsistently. Treatment delay of >28 days was a significant predictor of greater infectiousness. Contacts of sputum smear-positive index patients were found to be more likely to be infected than contacts of sputum smear-negative patients, with a pooled AOR of 2.15 (95% confidence interval (CI) 1.47-3.17, I 2 = 38%). Similarly, contacts of patients with the cavitary disease were around twice as likely to be infected as contacts of patients without cavitation (pooled AOR 1.9, 95% CI 1.26-2.84, I 2 = 63%). In contrast, HIV seropositive patients were associated with few contact infections than HIV seronegative patients (AOR 0.45, 95% CI 0.26-0.80, I 2 = 52%). In conclusion, behavioural and clinical characteristics of TB patients can be used to identify highly infectious patients for targeted interventions.

Designing and Evaluating Interventions to Halt the Transmission of Tuberculosis

To reduce the incidence of tuberculosis, it is insufficient to simply understand the dynamics of tuberculosis transmission. Rather, we must design and rigorously evaluate interventions to halt transmission, prioritizing those interventions most likely to achieve population-level impact. Synergy in reducing tuberculosis transmission may be attainable by combining interventions that shrink the reservoir of latent Mycobacterium tuberculosis infection (preventive therapy), shorten the time between disease onset and treatment initiation (case finding and diagnosis), and prevent transmission in key settings, such as the built environment (infection control). In evaluating efficacy and estimating population-level impact, cluster-randomized trials and mechanistic models play particularly prominent roles. Historical and contemporary evidence suggests that effective public health interventions can halt tuberculosis transmission, but an evidence-based approach based on knowledge of local epidemiology is necessary for success. We provide a roadmap for designing, evaluating, and modeling interventions to interrupt the process of transmission that fuels a diverse array of tuberculosis epidemics worldwide.

Detection of Mycobacterium tuberculosis bacilli in bio-aerosols from untreated TB patients

Background: Tuberculosis (TB) is predominantly an airborne disease. However, quantitative and qualitative analysis of bio-aerosols containing the aetiological agent, Mycobacterium tuberculosis (Mtb), has proven very challenging. Our objective is to sample bio-aerosols from newly diagnosed TB patients for detection and enumeration of Mtb bacilli. Methods: We monitored each of 35 newly diagnosed, GeneXpert sputum-positive, TB patients during 1 hour confinement in a custom-built Respiratory Aerosol Sampling Chamber (RASC). The RASC (a small clean-room of 1.4m ) incorporates aerodynamic particle size detection, viable and non-viable sampling devices, real-time CO 2 monitoring, and cough sound-recording. Microbiological culture and droplet digital polymerase chain reaction (ddPCR) were used to detect Mtb in each of the bio-aerosol collection devices. Results:  Mtb was detected in 27/35 (77.1%) of aerosol samples; 15/35 (42.8%) samples were positive by mycobacterial culture and 25/27 (92.96%) were positive by ddPCR. Culturability of collected bacilli was not predicted by radiographic evidence of pulmonary cavitation, sputum smear positivity, or cough rate. Mtb was detected on all viable cascade impactor stages with a peak at aerosol sizes 2.0-3.5μm. This suggests a median of 0.09 CFU/litre of exhaled air (IQR: 0.07 to 0.3 CFU/l) for the aerosol culture positives and an estimated median concentration of 4.5x10 CFU/ml (IQR: 2.9x10 -5.6x10 ) of exhaled particulate bio-aerosol. Conclusions:  Mtb was identified in bio-aerosols exhaled by the majority of untreated TB patients using the RASC. Molecular detection was more sensitive than mycobacterial culture on solid media, suggesting that further studies are required to determine whether this reflects a significant proportion of differentially detectable  bacilli in these samples.

Drivers of Tuberculosis Transmission

Measuring tuberculosis transmission is exceedingly difficult, given the remarkable variability in the timing of clinical disease after Mycobacterium tuberculosis infection; incident disease can result from either a recent (ie, weeks to months) or a remote (ie, several years to decades) infection event. Although we cannot identify with certainty the timing and location of tuberculosis transmission for individuals, approaches for estimating the individual probability of recent transmission and for estimating the fraction of tuberculosis cases due to recent transmission in populations have been developed. Data used to estimate the probable burden of recent transmission include tuberculosis case notifications in young children and trends in tuberculin skin test and interferon γ-release assays. More recently, M. tuberculosis whole-genome sequencing has been used to estimate population levels of recent transmission, identify the distribution of specific strains within communities, and decipher chains of transmission among culture-positive tuberculosis cases. The factors that drive the transmission of tuberculosis in communities depend on the burden of prevalent tuberculosis; the ways in which individuals live, work, and interact (eg, congregate settings); and the capacity of healthcare and public health systems to identify and effectively treat individuals with infectious forms of tuberculosis. Here we provide an overview of these factors, describe tools for measurement of ongoing transmission, and highlight knowledge gaps that must be addressed.

Tuberculosis in Enclosed Populations

Transmission of tuberculosis (TB) is most effective in close contact indoor environments in various congregate settings including health care facilities, homeless shelters, correctional facilities, long-term care facilities, as well as community settings such as homes, schools, workplaces, and various modes of transportation. Outbreaks are fueled by numerous factors including the HIV epidemic, ease of global travel, unstable socio-economic and/or political situations, and lapses in response to potentially infectious patients. Organized approaches to TB control include an appropriate index of suspicion, identification and isolation of contagious patients in appropriate facilities, use of environmental controls, and personal protective equipment in accordance to national and international published guidelines. These all require tailoring to the various settings where TB is encountered using a determination of risk. Concerted efforts at the local, regional, national, and international levels at identifying patients with active disease, enforcing completion of treatment, and testing and fully treating patients with latent TB infection are paramount in reducing TB burden and continued transmission.