ETIOLOGY AND EPIDEMIOLOGY
The etiologic spectrum is changing all the time since CP was first described in 1669 by Lower[1]. The causes of CP vary by region. Although idiopathic or post-viral infection may be the leading cause of CP in developed countries, tubercle bacilli are still the leading cause of CP worldwide, especially in developing countries like Africa and a certain area in Asia. Besides, cardiac surgery, mediastinal radiation therapy, HIV and some connective tissue disorders such as systemic lupus erythematosus (SLE) and rheumatoid arthritis are also associated with CP[2-4]. TB was instigated by Mycobacterium tuberculosis (MTBC), including M. tuberculosis (Mtb), M. africanum, M. bovis, M.bovis Bacillus Calmette-Guerin (BCG) vaccine strain, M. canetti, M. caprae, M. pinnipedii, M. microti, and M. mungi, which infect animals as well as humans. Of these entire members of the MTBC, the M. tuberculosis, first identified in 1882 by Robert Koch, is the most infamous member, and the main reason causing TB in humans[5].
TBP is a form of TB, which is estimated to occur in 1% to 2% of instances of pulmonary tuberculosis[6]. TBCP is one of the most severe sequelae of TBP, occurring in 30% to 60% of patients, despite prompt anti-TB treatment and the use of corticosteroids[7]. Therefore, the epidemiology of TB reflects the epidemiology of TBCP to a certain extent.
It is worth mentioning that TB, one of the oldest recorded human afflictions, is still one of the biggest killers among infectious diseases, despite the extensive use of a live attenuated vaccine and several antibiotics. TB can be preserved for thousands of years in hard tissues like the bone of patients with bone TB who died more than 4000 years ago, which indicates that TB was appeared throughout the world up to then[8]. The first global estimation led by the World Health Organization (WHO) in the early 1990s reckoned that there were about 8 million incident TB cases in 1990 with 2.6 to 2.9 million deaths[9]. About 8 million new cases in 1997 and 10.4 million in 2016[10]. The WHO’s End TB Strategy[11] have defined ambitious targets for 2035, including a 95% reduction in the absolute number of TB deaths and a 90% reduction in TB incidence by 2035, compared with 2015.
The targets are far away, and we still have a long way to go. The emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB makes the management of TB more difficult. MDR-TB is caused by MTBC, resistant to at least isoniazid and rifampin[12]. XDR-TB is a complicated form of MDR-TB with additional resistance to at least one kind of second-line injectable antimicrobial drug and a fluoroquinolone. It is said that approximately half a million new cases of MDR-TB challenge global health in 2017[10], especially in India, China, and the Russian Federation[13], with the highest-burden amongst women of reproductive age (15 to 45 years). In women of this age, tuberculosis is the leading cause of death from an infectious agent and a common non-obstetric cause of maternal mortality[14].
The epidemic of human immune-deficiency virus (HIV) is another barrier affecting TB-control. Despite tremendous progress in the use of antiretroviral drugs for the treatment of HIV, there were still 940000 deaths and 1.8 million new infections in the world in 2017. The number of new HIV infections is increasing in about 50 countries. The total number of people living with HIV in South Africa still ranks first in the world (over 7 million), and the proportion of infected people has increased year by year, the infection rate has reached 12.57%[15]. As is known to all, HIV and TB have a synergistic interaction. What’s more, HIV causes an atypical presentation of TB with less pulmonary involvement but more extrapulmonary symptoms. It is said that TB often occurs at an earlier stage in the course of HIV infection. Pulmonary TB is the prevalent form of TB, while the count of CD4+ T lymphocytes cell is high. However, extrapulmonary TB (EPTB) becomes more prevalent, while HIV infection progresses to Acquired Immune Deficiency Syndrome (AIDS)[16].
Another risk factor for TB that maybe forget is diabetes mellitus (DM), especially during the second half of the 20th, with the advent of widely available treatment for both TB and DM. However, the association between these two diseases has reappeared due to the global epidemic of type 2 DM (T2DM)[17]. According to the report published in 2017, about 415 million people live with diabetes worldwide, and an estimated 193 million people have undiagnosed diabetes. T2DM accounts for more than 90% of patients. The incidence and prevalence of DM continue to rise globally due to obesity, physical inactivity, and energy-dense diets. Besides, a meta-analysis produced evidence that smoking is a risk factor for TB infection and TB disease[13,18].
TB is no longer a disease only caused by poverty, and the mind to end TB through reducing poverty should change. Deborah Wallace[19] argued that debt such as housing conditions, working conditions, malnutrition, and ventilation could affect TB incidence and mortality, as well as Major social upheaval including war, mass evictions, land-grabbing, slavery, refugee-creation and denial of essential services. The Global Fund to Fight AIDS, TB, and Malaria suspended grants to North Korea, one of the highest rates of TB in the world, for both TB and malaria control programs on June 30, 2018. North Korea’s public health system will be tested more and more in the coming years. The reasons may range from failure of the North Koreans to adhere to the Fund’s standards for record-keeping to applying pressure on the North Korean regime for its nuclear endeavors. In Brazil, the election of a right-wing president, Jair Bolsonaro, who encourages land-grabbing by loggers and Big Agriculture, signals significant changes in Brazilian economic and political structure. Women’s rights and the rights of marginalized populations are not guaranteed, which will destroy the system of TB control in Brazil in myriad ways. In New York, the discriminatory policy persists, such as routine denial of parole to black prisoners and routine denial of essential municipal services to poor neighborhoods, which will be detrimental to the control of TB. In Africa, feeling insecure, most working people have to work long hours for low wages under unsafe conditions, they even have no protection by culture or regulation, and then, obesity, diabetes, HIV, TB, unsafe sex, drug abuse, and violence will blossom. Therefore, we can’t regard TB as only a medical problem, but it should be considered as a political and economic issue, which was driven by national interests. So not only developing nations, developed nations are not spared from this menace. When the civil war first gripped Syria in 2011, the country had a population roughly equivalent to New York state. In the eight years since the conflict has displaced more than half of its people. Liberia is within the 30 countries with the highest TB burden, probably as a consequence of the long civil war[20]. A study suggested that by 2030, two-thirds of the world’s wealth will be in the hands of 1% of the world’s population. The economic and political imbalance may play an unfavorable role in the management of TB. So, it is expected that the epidemic of TBCP will go on for many years.