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The Infectious Disease Tuberculosis (TB)



Introduction

In this assignment, Tuberculosis (TB) is reviewed. The infectious disease is caused by a bacterium known as Mycobacterium tubercuslosis that mostly affects the lungs (World Health Organization, 2015). The bacterium is transmitted from one person to another through droplets that originate from the throat or lungs of those who have the disease. Healthy people infected by the bacterium do not exhibit symptoms due to active immune system that guards against the disease. Ten percent of those who have latent TB develop active TB at some point in their lives (U.S. Department of Health and Human Services, 2010). Even though many people think that developed countries, such as the United States, do not have cases of TB, this assumption might not be true because the disease still remains a major killer in the world. Nearly one-third of the world’s population or 2 billion people are thought to be suffering from the disease (U.S. Department of Health and Human Services, 2010).

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TB rates vary depending on age, ethnicity, race, as well as country of origin (U.S. Department of Health and Human Services, 2010). For instance, in the United States, TB affects minorities disproportionately; thus, it is not uncommon for foreign-born individuals to suffer from the disease compared to those who are born in the country.

Diagnosis of Tuberculosis

Robert Koch recognized Mycobacterium tuberculosis as the microorganism that causes tuberculosis, and this development led to the identification of methods for staining specimens suspected to contain the microorganism (Dorman, 2012). The technique was critical in the development of tuberculosis diagnostics. Unfortunately, both the development and the implementation of the diagnostics did not keep pace with technology that was introduced in the medical field. Likewise, the diagnostic techniques could not effectively support the identification of drug-resistant tuberculosis, particularly at the time when Human Immunodeficiency Virus (HIV) was becoming pandemic.

Lack of tools as well as weak systems that were used in laboratory diagnosis of active TB led to the following underdiagnosis that was accompanied by morbidity. It also resulted into mortality and continued transmission. In contrast, overdiagnosis contributed to needless treatments. It also led to delayed diagnosis, which played a role in the development of drug resistance (Dorman, 2012). Apart from inadequate diagnostic tools, there is also the problem of access that remains a major challenge. Nevertheless, remarkable progresses have been made in TB diagnostic technologies in the previous years, and there is still a chance for making meaningful developments in tuberculosis clinical care and control.

There is a number of tests that can be used in diagnosing TB apart from the various tests that help in finding out whether an individual is infected with the TB bacteria and whether the bacteria responds to treatments or not. One of the methods used in everyday diagnostic of active TB is the acid fast staining of the specimen. Usually, specimens are suspected to have the mycobacterium is subjected to this method of diagnosis. Sputum is smeared and stained before being examined using a microscope to detect TB. In Acid Fast Bacteria (AFB) testing, sputum is smeared onto a slide followed by the addition of Ziehl-Neelsen stain. The assay is specific for Mycobacterium tuberculosis.

However, the sensitivity of the test varies, and its usefulness has been questioned in patients whose pulmonary activity formation is compromised, or those with reduced sputum bacillary load such as HIV-coinfected patients or children (Parsons et al., 2011). Sputum smear is disadvantageous because of its low sensitivity. The sensitivity of the method depends on staff training. Therefore, the sensitivity of the method is estimated to be 70 percent, but it can be as low as 35 percent sensitive in cases where there is HIV and TB co-infection (Parsons et al., 2011). The problem of infection is confounded by the fact that there are no adequate quality assurance tools in most of the resource-restrained hospitals.

In turn, this increases workload during the process of diagnosis. Notably, smear microscopy cannot be used to test drug susceptibility (Dorman, 2014). The reason for this is the fact that it can only detect 50 percent of patients infected with the TB bacteria. The method is also not very sensitive in cases where the patient being tested also happens to have HIV/AIDS since such patients possess high mortality resulting from smear-negative TB.

Culture of Mycobacterium tuberculosis that is made from clinical specimens is usually more sensitive than smear microscopy. Important media that used to make culture include Lowenstein-Jensen or other commercial types. For a long time, the use of culture media to isolate the bacterium was a must for physical drug-susceptibility testing. However, culture testing has the disadvantage of taking a long time (10 days to one month) before producing the results (Dorman, 2014). Apparently, the bacterium has a long doubling time.

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The current culture methods demand numerous techniques that require biosafety knowledge and tools to prevent infection of laboratory personnel. Noncommercial and drug susceptibility testing methods, which have been assessed, include microscopically observed drug susceptibility (MODS) as well as the nitrate reductase assay (NRA) method. These methods are usually used to provide temporary solution in countries that lack modern testing tools. Using solid media to test for multidrug-resistant TB (MDR-TB) and extensively drug resistant TB (XDR-TB), it takes six or more weeks to produce results (Parsons et al, 2011).

Systematic reviews as well as meta-analyses of how conventional drug susceptibility test methods and molecular line probe assays (LPA) compare have shown that LPAs are often very sensitive and specific. Before clinical specimens are cultured, they undergo pretreatment that includes digestion, homogenization, decontamination, as well as concentration. The procedure helps to remove faster growing contaminants such as other bacteria and fungi. The efficacy of such procedures depends on how long an agent has been exposed to a reagent used, how efficient the centrifuge is, the toxicity of the reagent used, and the effect of heat buildup during centrifugation (Parsons et al., 2011).

Decontamination methods such as N-acetyl-L-cysteine (NALC)-NaOH can be very effective. For instance, in this method, up to 33 percent of the mycobacterium are killed. NALC-NaOH is currently one of the methods used in diagnostic laboratories. However, there are other methods that can also be applied in the laboratories. The method is widely used because it is PH sensitive as opposed to most of the other methods. There is also the sodium dodecyl (lauryl) sulfate (SDS)-NaOH method (Parsons et al., 2011).

Using centrifugation during sputum processing may require a biological safety cabinet (BSC) with safety cups as well as aerosol rotors. These equipments can be expensive, and their maintenance cost may be challenging. Nonetheless, simpler processing methods have been developed. One of the modified methods is the Kudoh method where sputum specimens are exposed to 4 percent sodium hydroxide and then allowed to settle for approximately 15 minutes before the sediment is inoculated onto solid Ogawa medium. The other approach is where 4 ml of 0.124 percent of chlorhexidine gluconate is added to sputum specimen, and then incubated for between 18 to 20 hours (Parsons et al., 2011).

There is also the direct detection of TB in patient specimens. For instance, direct nucleic acid amplification (NAA) testing. This method significantly reduces the period of laboratory diagnosis by two to four weeks (Parsons et al., 2011). Many laboratories have included the method in their routine laboratory analysis, particularly in high income countries. There are various assays that offer the capability for detecting multi drug testing TB in patient specimens. The assays use either polymerase chain reaction or loop-mediated isothermal amplification (Parsons et al., 2011).

The newest addition in this category has been the isothermal nucleic acid amplification, which suites diagnosis in resource-constrained countries. Bacteriophages that infect and replicate in M. bacterium have also been suggested for use in clinical settings where they can be used to diagnose the presence of viable bacterial cells. The development of phage-based tests was based on providing rapid and low-cost diagnosis in poor countries (Parsons et al., 2011). Rapid identification of cultured Mycobacterium tuberculosis includes nucleic acid hybridization techniques, lateral flow assays, line probe assays, and DNA sequencing (Parsons et al., 2011).

DNA/RNA probes can identify the mycobacterium in contaminated liquid cultures because of their near 100 percent sensitivity and specificity, particularly if the bacterial populations reach 105 (Parsons et al., 2011). Lateral flow immunochromatographic assays have been used in rapid identification of multidrug resistant TB. The assays detect the presence of a specific multidrug resistant TB-protein in culture isolates. The detection limit has been approximated at 105 colony forming units per milliliter (Parsons et al., 2011). The bacterial colonies have to be grown on solid or liquid culture before testing. In real-time PCR, hybridization with fluorescence-labeled molecular beacons or probes is used during amplification. Melting profiles then follow in detecting mutations that occur due to resistance. Real-time PCR is advantageous because the reaction occurs in a closed system thereby minimizing the possibility of contamination (Parsons et al., 2011).

Quality assurance practices have to be adhered to in TB diagnostics. For instance, to enhance quality of acid fast bacterium smear in microscopy testing, each country should provide the necessary support through a functioning external quality assessment (EQA). Such programs should promote blinded rechecking of sputum smears, site supervision, as well as external competency testing. Limited opportunity for tuberculosis culture and drug susceptibility test external quality assessment has been noted in countries that lack resources. To overcome the problem, performance indicators have recently been implemented to enhance internal quality assessment in a number of hospitals. Some of the indicators that have been found to be vital include data collection, monitoring, determination of the percentage of specimens that are being contaminated, FB positive smears, and turnaround time for smears (Parsons et al., 2011).

In molecular testing, quality assurance should focus on registering and measuring the performance of reagents, routine checking of temperature of instruments, maintenance, and calibration of equipment used. External quality assessment can be done using non-infectious DNA panels (Parsons et al., 2011). Tuberculosis is treated through administration of appropriate antibiotics. There are first line and second line drugs. First line drugs include rifampin, ethambutol, isoniazid, Second line drugs include amikacin, capreomycin, ciprofloxacin, ethionamide, kanamycin, levofloxacin, and ofloxacin (Parsons et al., 2011).

Providing quality tuberculosis laboratory services still face challenges even though numerous opportunities are abound as well in resource-starved countries. Many countries do not have development and implementation policies or strategic plans, which are crucial when working with donors and partners. The plans or policies are important because they define objectives, help in setting standards and decision making, particularly on resource allocation and personnel management to ensure sustainable laboratory services. However, there is a chance for the ministry of health to support clinical laboratory services by instituting policies that set minimal laboratory standards and manage laboratory network to ensure vital services reach different populations wherever they live (Parsons et al., 2011).

It is also important to improve technical resources, particularly in countries that have weak networks. Such a strategy would help to optimize resources from all sectors. For instance, there is the need for collaboration between national academic institutions and research laboratories both from public and private sectors. Likewise, there is the need to create links with international laboratory networks. However, the nature as well as scope of such partnerships has to be established from the onset so that each party knows its roles and responsibilities (Parsons et al., 2011).

There is also the opportunity to establish and manage the flow of information through a laboratory information management system for data on samples, instruments, results, as well as quality indicators (Parsons et al., 2011). In addition, such a system could be used for accounting and accreditation purposes. Laboratory managers need to be thoughtful in their needs and priorities when implementing laboratory management systems. In addition, there is an opportunity for the systems to direct the completion of laboratory tests at various diagnostic levels, and initiate therapy. This will require a close cooperation between clinicians, laboratory workers, and the community (Parsons et al., 2011).

Conclusion

TB is a global problem because of the increasing number of people who are getting infected and the difficulty in diagnosing and treating it. Lack of better treatment strategies has led to the development of multidrug resistant and extensively drug resistant strains that are now posing more challenges. Along with that, the problem of HIV-coinfection is worsening the already existing issue. It is evident that TB future research should focus on relatively cheaper alternative methods, through which the disease can be diagnosed. Diagnosing it can also be enhanced through quality assurance practices both from internal and from external sources. There is an opportunity for clinicians, laboratory workers and the community to work together. In addition, closer collaboration between laboratories, local and international research institutions will help in developing efficient diagnostic systems that can work well in resource-starved nations.

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