Institutional control measures for tuberculosis in the era of multiple drug resistance. ACCP/ATS Consensus Conference. American College of Chest Physicians and the American Thoracic Society

Cytochrome bc1-aa3 oxidase supercomplex as emerging and potential drug target against tuberculosis

The cytochrome bc1-aa3 supercomplex plays an essential role in the cellular respiratory system of Mycobacterium Tuberculosis. It transfers electrons from menaquinol to cytochrome aa3 (Complex IV) via cytochrome bc1 (Complex III), which reduces the oxygen. The electron transfer from a variety of donors into oxygen through the respiratory electron transport chain is essential to pump protons across the membrane creating an electrochemical transmembrane gradient (proton motive force, PMF) that regulates the synthesis of ATP via the oxidative phosphorylation process. Cytochrome bc1-aa3 supercomplex in M. tuberculosis is, therefore, a major drug target for antibiotic action. In recent years, several respiratory chain components have been targeted for developing new candidate drugs, illustrating the therapeutic potential of obstructing energy conversion of M. tuberculosis. The recently available cryo-EM structure of mycobacterial cytochrome bc1-aa3 supercomplex with open and closed conformations has opened new avenues for understanding its structure and function for developing more effective, new therapeutics against pulmonary tuberculosis. In this review, we discuss the role and function of several components, subunits, and drug targeting elements of the supercomplex cytochrome bc1-aa3, and its potential inhibitors in detail.

The path of anti-tuberculosis drugs: from blood to lesions to mycobacterial cells

For the successful treatment of pulmonary tuberculosis, drugs need to penetrate complex lung lesions and permeate the mycobacterial cell wall in order to reach their intracellular targets. However, most currently used anti-tuberculosis drugs were introduced into clinical use without considering the pharmacokinetic and pharmacodynamic properties that influence drug distribution, and this has contributed to the long duration and limited success of current therapies. In this Progress article, I describe new methods to quantify and image drug distribution in infected lung tissue and in mycobacterial cells, and I explore how this technology could be used to design optimized multidrug regimens.

Intervals before tuberculosis diagnosis and isolation at a regional hospital in Taiwan

Background/Purpose

Nosocomial tuberculosis (TB) infection is still a problem in many Taiwanese hospitals. The objectives of this study were to explore the intervals before TB diagnosis and isolation at a regional hospital in Taiwan, and to provide useful knowledge to hospitals for the purpose of TB infection control.

Methods

From 2002 to 2005, we included a total of 343 patients with culture-positive pulmonary TB in a regional hospital in Southern Taiwan for this study. Their medical records were reviewed, and the time intervals between patient-hospital contact points and isolation were recorded.

Results

Of 343 culture-positive pulmonary TB patients, the majority were male, over 40 years old, and unemployed. The mean interval between the first admission and isolation was 20.5 days (median, 2.0 days). The mean intervals between the first admission from outpatient clinics, emergency department and hospitalization and suspected TB were < 1 day, 6.07 days and 25.53 days, respectively. The mean accumulated exposure time was 0.35 days, 0.61 days and 10.09 days in outpatient clinics, the emergency department and hospitalization, respectively; 75.5% of patients had their diagnosis confirmed at the chest department of the department of internal medicine.

Conclusion

Delayed diagnosis was most likely in the case of hospitalized patients and least likely in outpatient clinics. Delayed diagnosis in hospitalized patients also contributed more severely to TB exposure time than others. Enhancing the quality, speed and ability of specialists and physicians to diagnose TB, especially in emergency departments and in hospitalized patients, is essential.

Role of ventilation in airborne transmission of infectious agents in the built environment - a multidisciplinary systematic review

There have been few recent studies demonstrating a definitive association between the transmission of airborne infections and the ventilation of buildings. The severe acute respiratory syndrome (SARS) epidemic in 2003 and current concerns about the risk of an avian influenza (H5N1) pandemic, have made a review of this area timely. We searched the major literature databases between 1960 and 2005, and then screened titles and abstracts, and finally selected 40 original studies based on a set of criteria. We established a review panel comprising medical and engineering experts in the fields of microbiology, medicine, epidemiology, indoor air quality, building ventilation, etc. Most panel members had experience with research into the 2003 SARS epidemic. The panel systematically assessed 40 original studies through both individual assessment and a 2-day face-to-face consensus meeting. Ten of 40 studies reviewed were considered to be conclusive with regard to the association between building ventilation and the transmission of airborne infection. There is strong and sufficient evidence to demonstrate the association between ventilation, air movements in buildings and the transmission/spread of infectious diseases such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS. There is insufficient data to specify and quantify the minimum ventilation requirements in hospitals, schools, offices, homes and isolation rooms in relation to spread of infectious diseases via the airborne route. PRACTICAL IMPLICATION: The strong and sufficient evidence of the association between ventilation, the control of airflow direction in buildings, and the transmission and spread of infectious diseases supports the use of negatively pressurized isolation rooms for patients with these diseases in hospitals, in addition to the use of other engineering control methods. However, the lack of sufficient data on the specification and quantification of the minimum ventilation requirements in hospitals, schools and offices in relation to the spread of airborne infectious diseases, suggest the existence of a knowledge gap. Our study reveals a strong need for a multidisciplinary study in investigating disease outbreaks, and the impact of indoor air environments on the spread of airborne infectious diseases.

Risco de infecção pelo Mycobacterium tuberculosis entre alunos da Faculdade de Medicina da Universidade Federal do Rio de Janeiro

INTRODUÇÃO: Até o momento raros estudos prospectivos na América Latina demonstraram que estudantes de Medicina estão sob mais alto risco de apresentar conversão tuberculínica do que a população em geral (1,3%). OBJETIVO: Descrever a incidência acumulada de conversão tuberculínica e o risco relativo para tuberculose infecção entre estudante de Medicina. MÉTODO: Em 1.998, uma coorte prospectiva foi iniciada entre estudantes da Faculdade de Medicina da Universidade Federal do Rio de Janeiro, negativos ao teste tuberculínico (<10 mm) realizado em dois tempos no ano anterior. Esses estudantes foram re-testados no ano seguinte ao primeiro teste. Os estudantes têm dois níveis de treinamento: períodos básicos (sem contato com pacientes) e períodos profissionais (com contato com pacientes). Foi usado um questionário padronizado para avaliação das características sócio-demográficas, vacinação pelo BCG (remota e recente) e exposição potencial ao Mycobacterium tuberculosis. Completaram o estudo 72% dos estudantes (414/575). RESULTADOS: Dos 414 participantes do estudo, 16 (3,9%, IC 95% 1,06% a 12,1%) apresentaram conversão tuberculínica, ou seja, a incidência acumulada de conversão foi de 3,9%. Osalunos dos períodos profissionais apresentaram um risco quatro vezes maior de infecção pelo Mycobacterium tuberculosis quando comparados com os dos períodos básicos. CONCLUSÃO: É alta a taxa de conversão tuberculínica entre alunos da Faculdade de Medicina da Universidade Federal do Rio de Janeiro.

Risk of tuberculosis among healthcare workers: can tuberculosis be considered as an occupational disease?

This study aimed to determine the incidence of tuberculosis among hospital employees in four major urban institutions, which employ nearly 90% of all hospital workers caring for adult patients in a city of 2.5 million inhabitants. It also had the objective of finding out whether this incidence changes according to the in-hospital setting, i.e. the departments, and thus, whether tuberculosis can be considered to pose an occupational risk. The study population consisted of all healthcare workers of the four hospitals between 1986 and 1998. From these, those who developed tuberculosis within this period were determined and were considered as the case group. All the remaining employees constituted the control group. Fifty-nine healthcare workers were found to have developed the disease. The annual incidence was found to range between 0.016 and 0.139%. Tuberculosis was seen 3 times more frequently among the hospital employees than the general population. The workers in departments of chest diseases were found to have a higher risk than those of other departments (OR: 6.37, CI: 3.69-11.00). Similarly, the nurses were also at a higher risk than the doctors (OR: 2.63, CI: 1.12-6.36). These findings suggest that tuberculosis can be considered as an occupational disease.

Tuberculosis and tuberculin quality: best intentions, misleading results

OBJECTIVE

To compare the performance of three purified protein derivative (PPD) formulations: Tubersol (Connaught); RT23, Statens Serum Institut (SSI); and RT23, Mexico, tested in Mexican populations at low and high risk for tuberculosis (TB).

DESIGN

A double-blinded clinical trial.

SETTING

A university hospital in Mexico City.

PARTICIPANTS

The low-risk population was first or second-year medical students with no patient contact; the high-risk population was healthcare workers at a university hospital.

METHODS

Each of the study subjects received the three different PPD preparations. Risk factors for TB, including age, gender, occupation, bacille Calmette-Guérin (BCG) status, and TB exposure, were recorded. A 0.1-mL aliquot of each preparation was injected in the left and right forearms of volunteers using the Mantoux technique. Blind readings were done 48 to 72 hours later. Sensitivity and specificity were calculated at 10 mm of induration using Tubersol as the reference standard. The SSI tested the potency of the different PPD preparations in previously sensitized guinea pigs.

RESULTS

The low-risk population had a prevalence of positive PPD of 26%. In the low-risk population, RT23 prepared in Mexico, compared to the 5 TU of Tubersol, had a sensitivity of 51%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 86%. The RT23 prepared at the SSI had a sensitivity of 69%, a specificity of 99%, a positive predictive value of 95%, and a negative predictive value of 90%. In the high-risk population, the prevalence of positive PPD was 57%. The RT23 prepared in Mexico had a sensitivity of 33%, a specificity of 100%, and a positive predictive value of 53%; the RT23 prepared at the SSI had a sensitivity of 91%, a specificity of 98%, a positive predictive value of 98%, and a negative predictive value of 89%. RT23 used in Mexico had a potency of only 23% of that of the control. There was no statistical association among those with a positive PPD, irrespective of previous BCG vaccination (relative risk, 0.97; 95% confidence interval, 0.76-1.3;P=.78).

CONCLUSIONS

Healthcare workers had twice the prevalence of positive PPD compared to medical students. RT23 prepared in Mexico had a low sensitivity in both populations compared to 5 TU of Tubersol and RT23 prepared at the SSI. Previous BCG vaccination did not correlate with a positive PPD. Low potency of the RT23 preparation in Mexico was confirmed in guinea pigs. Best intentions in a TB program are not enough if they are not followed by high-quality control.

Treatment and prevention of multidrug-resistant tuberculosis

Multidrug-resistant tuberculosis (MDRTB), which is defined as combined resistance to isoniazid and rifampicin, is a 'man-made' disease that is caused by improper treatment, inadequate drug supplies or poor patient supervision. Patients with MDRTB face chronic disability and death, and represent an infectious hazard for the community. Cure rates of 96% have been achieved but require prompt recognition of the disease, rapid accurate susceptibility results, and early administration of an individualised re-treatment regimen. Such regimens are usually based on a quinolone and an injectable agent (i.e. an aminoglycoside or capreomycin) supplemented by other 'second-line' drugs. This therapy is prolonged (e.g. 24 months), expensive, and has multiple adverse effects. Prevention of MDRTB is therefore of paramount importance. The World Health Organization (WHO) has recommended a multifaceted programme, known by the acronym DOTS (directly observed therapy, short-course), that promotes effective treatment of drug-susceptible TB as the prime method of limiting drug resistance. DOTS was part of a successful MDRTB control programme in New York City, which also included treatment of prevalent MDRTB cases, streamlined laboratory testing, effective infection control procedures and wider application of screening and preventive therapy (although the optimal chemotherapy for MDRTB infection remains undefined). Industrialised countries have the resources to treat patients with MDRTB and to mount these extensive control programmes. Unfortunately, MDRTB is also prevalent in Asia, South America and the former Soviet Union. First world countries have a vested interest, as well as a moral responsibility, to assist in controlling MDRTB in these 'hot spots'.

Tuberculosis. Part I

Tuberculosis has been a disease of human beings for thousands of years. In recent times it has waxed to become the feared White Plague of the eighteenth and nineteenth centuries and waned under the impact of effective chemotherapy until its elimination seemed possible by the early twenty-first century. The resurgence of tuberculosis in the past 10 to 15 years, caused by unanticipated events such as the appearance of the human immunodeficiency virus and deteriorating social conditions, also brought with it the problem of multiple drug resistance. Control measures such as tuberculin skin testing, perhaps somewhat forgotten when tuberculosis seemed to be a disease of the past, again became first-line defenses against spread of the disease. Environmental controls must be well understood and used effectively. Diagnosis of tuberculosis requires knowledge of the strengths and shortcomings of the various diagnostic methods and experience in their use. Practitioners are cautioned to remember that no diagnostic method, by itself, can be relied on to confirm or rule out tuberculosis. Well-tested diagnostic methods of chest radiograph, tuberculin skin testing, smear, and culture have been recently supplemented by rapid diagnostic tests based on amplification of bacterial RNA and DNA. More invasive diagnostic methods are sometimes required to diagnose extrapulmonary disease. Two-drug up to seven-drug therapy may be indicated for a case of tuberculosis, depending on evidence of the presence of multiple drug resistance. Duration of treatment can range from 6 to 12 months, also depending on identification of drug-sensitive or drug-resistant organisms. Failure of compliance can be a significant problem in patients who are homeless, or drug abusers, or who for various reasons cannot or will not complete a course of therapy. Directly observed therapy is strongly recommended for these patients, and for assistance in its administration the physician must cooperate with the local or state health department. The health department also must be notified whenever a case of tuberculosis is identified.