Tuberculosis (TB) is a significant infectious disease that mainly affects the respiratory system (Ortblad et al., 2015). It is chiefly caused by Mycobacterium tuberculosis bacteria that are transmitted from one person to another through droplets generated via sneezes and coughs (Nardell, 2015). In the lungs, the mycobacteria induce a rapid inflammatory process with the formation of granuloma and eventually caseous necrosis of lung tissue and lymph nodes (Prats et al., 2016).
Latent tuberculosis is a type of TB in which an individual is infected with TB-causing mycobacteria, but the organisms remain inactive and do not cause clinically significant symptoms (Getahun et al., 2015). This form of tuberculosis is not contagious (Koul, 2016). The infection is kept under control because the individual has a competent immune system (Cliff et al., 2015). The body of the individual is able to maintain a consistent immune response to the stimulation resulting from mycobacterial antigens without the production of overt clinical symptoms (Bukhary et al., 2018). Latent TB, however, has the potential of becoming active TB and therefore treatment of latent tuberculosis is necessary in order to prevent the spread of the disease (Menzies et al., 2018).
Epidemiology of latent tuberculosis
According to the World Health Organization’s Global Tuberculosis report of 2018, there are about 1.7 billion individuals with latent tuberculosis infection globally. This figure has been constant since 2014, representing a global burden of 23% with a 95% uncertainty interval (Houben & Dodd, 2016). Africa, Western Pacific, and South East Asia regions experienced the highest prevalence of latent tuberculosis, accounting for eighty percent of the global burden (Houben & Dodd, 2016). The prevalence of new infections stood at 0.8% of the global population at 95% uncertainty interval (Houben & Dodd, 2016). This population was at risk of tuberculosis disease.
In a population-based sample study with 1369 volunteers carried out in Saudi Arabia to find out the prevalence of latent tuberculosis, the estimate of infection was found to be 9.3% when utilizing the tuberculin skin test and 9.1% using Quantiferon TB Gold (Balkhy et al., 2017). The conclusion was that the results were similar (p=0.872) (Balkhy et al., 2017).
A study conducted to evaluate the determinants and distribution of TB in Saudi Arabia between 2005 and 2012 indicates that there was an overall decrease in the incidence of TB from 15.8 per 100,000 in 2005 to 13.16 per 100,000 in 2012 (Almutairi et al., 2018). During the period, the incidence rates were higher for males (Almutairi et al., 2018). The incidence rates for non-residents were double those of residents for the period, and Mecca accounted for the greatest regional incidence rate at 25.13 per 100,000 (Almutairi et al., 2018).
Risk factors of latent TB
The main risk factor for latent TB infection is close contact with individuals with an active infection (Zumla et al., 2016). Other risk factors include HIV infection, low body weight, leukemia, diabetes mellitus, Hodgkin’s disease, silicosis, vitamin D deficiency, head and neck cancers, and immunosuppressive treatment such as corticosteroids and anti-rejection medication (Deziel & Razonable, 2018).
Individuals from Yemen and Indonesia are more likely to get latent TB infection in Mecca (Almutairi et al., 2018). Most of the new cases occur in people aged less than 15 years (Almutairi et al., 2018). The incidence of TB is highest in employed non-residents followed by employed Saudi residents (Almutairi et al., 2018).
Diagnosis of latent TB
The World Health Organization (2018) recommends that testing for latent Tb infection is conducted using tuberculin skin test or interferon-gamma release assay. These tests are coupled with chest radiography in order to rule out active tuberculosis disease (World Health Organization, 2018).
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Balkhy, H., El Beltagy, K., El-Saed, A., Aljasir, B., Althaqafi, A., & Alothman, A. et al. (2017). Prevalence of latent mycobacterium tuberculosis infection (LTBI) in Saudi Arabia; population-based survey. International Journal of Infectious Diseases, 60, 11-16. Web.
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Prats, C., Vilaplana, C., Valls, J., Marzo, E., Cardona, P., & López, D. (2016). Local inflammation, dissemination and coalescence of lesions are key for the progression toward active tuberculosis: The bubble model. Frontiers in Microbiology, 7. Web.
World Health Organization. (2018). Global tuberculosis report 2018 (pp. 105-138). Geneva: World Health Organization.
Zumla, A., Saeed, A., Alotaibi, B., Yezli, S., Dar, O., & Bieh, K. et al. (2016). Tuberculosis and mass gatherings—opportunities for defining burden, transmission risk, and the optimal surveillance, prevention, and control measures at the annual Hajj pilgrimage. International Journal of Infectious Diseases, 47, 86-91. Web.