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.