According to the global tuberculosis report, during 2017, 10 million new cases were reported, with an estimated mortality of 1.3 million, with TB being the main cause of death from an infectious disease caused by a single etiological agent and the ninth highest cause of death from all causes ¹. Although the disease can affect people of any age or social condition, it is maintained and perpetuated, via transmission, in the poorest, socially excluded communities, where people generally have higher rates of immune-debilitating comorbidities and access barriers to health services ^2,3.

The population deprived of liberty (PDL) represents one of the most vulnerable population groups for the transmission and development of the disease. Reporting up to 2,213 cases per 100,000 PDL in prisons in Peru and, together with other countries such as El Salvador, these populations have reached between 25-50 times the incidence with respect to the general population ^4-6. In Colombia, during 2017, 985 cases of tuberculosis (all forms) in PDL were notified to the TB Surveillance System, with an incidence of 800 cases per 100,000 PDL. 92% of these cases were TBp ⁷.

In a prison study in Tolima, Colombia, a high prevalence of TBp was demonstrated in PDL (1.5%; 17/1,129; 95% CI: 0.8-2.2%) likewise, in Latin American countries such as Chile, Brazil, Bolivia, Ecuador and Paraguay have a higher prevalence of TBp in PDL than in the general population ⁸. The high transmission of TBp in prisons is explained by the combination of various social factors, such as barriers to access to health services (OR: 7.38; 95% CI: 2.3-23.4) ⁹, low level of education (OR: 10.7; 95% CI: 7.6- 13.6) ¹⁰, drug abuse (OR: 4.6; 95% CI: 1.7-12.4, p: 0.006) ¹¹, alcohol (OR: 11.5; 95 CI %: 2.0-67.0) ⁹, and long sentences; environmental such as the high rates of overcrowding 88.2%; OR: 9.8; 95% CI: 3.1-31.6, p <0.001) ¹²; biological, related to immunosuppression such as HIV / AIDS (OR: 3.1; 95% CI: 1.02-9.40) ^13,14, malnutrition (body mass index less than 18.5 kg/m²) (OR: 2.1; 95% CI: 1.3-3.0) ¹² and depression. Likewise, in prisons in Colombia, overcrowding has been reported as the main risk factor for developing TBp ^11,15,16.

Some authors note that prisons are a constant source of dissemination of the etiological agent Mycobacterium tuberculosis to the non-prison population; it is estimated that around 6% of cases originate from prison contacts ⁸. To reduce the vulnerability of PDL to TBp, the WHO urges TB control programs to implement, in prisons, strategies to capture, diagnose and treat the population with active TB in a timely manner ¹⁷. The limitations of access to prisons, by the TB control programs, and the high turnover rate of the PDL, limit the success in recruiting, diagnosing, treating and monitoring these patients ^15,18-20. The understanding of the dynamics of TB transmission in prisons is achieved through constant evaluation of the burden of the disease and the presence of risk factors. This research aimed to determine the prevalence of TBp, and identify risk factors in PDL of a prison in Cali, Colombia 2013-2014.

Between January 1, 2013 and December 31, 2014, the Health Department of the Villahermosa prison in Cali evaluated 3,900 respiratory symptoms in the 11 prison yards and reported 98 incident cases of TBp to the municipal program of TB control in Cali (Figure 1).

Figure 1

The cumulative incidence during the study period was 1,685 cases of TBp per 100,000 PDL, rising from 447 cases of TBp per 100,000 PDL in 2013 to 1,238 cases of TBp per 100,000 PDL in 2014. Regarding the proportion of respiratory symptoms in individuals in which TBp had been diagnosed, this was 2.5% (98/3,900) in both years of the study, and 1.7% (26/1,566) and 3.1% (72/2,334) for 2013 and 2014 respectively. The temporal behavior of incident cases showed an increase of almost double in 2014 compared to 2013. The months with the highest number of new cases were June with 12 cases, and May and November with 9 (Figure 2).

Figure 2

Demographic and clinical information from 196 PDL records (98 incident cases and 98 controls) was analyzed. The median age was 29.8 years (IQR: 23.0-33.5), the predominant race was mestizo [mixed] at 55.0% (108/196) and the most frequently reported marital status was single at 57% (112/196). 75% (129/196) of the participants reported having completed basic secondary education and only the two lowest socio-economic strata were reported, of which 71% (138/196) belonged to Class 2. With regard to insurance, 99% (194/196) had a subsidized regime and 71% (123/196) declared that they worked in the construction sector.

When comparing cases and controls through bivariate analysis of their demographic characteristics, it was found that age (OR: 0.96; 95% CI: 0.92-0.99, p: 0.02), and socioeconomic level (OR: 0.51; 95% CI: 0.27-0.96, p: 0.03), were significant at p: <0.05 (Table 1).

Table 1

Characteristics	Description	Cases (n= 98)	Controls (n= 98)	OR	IC LI-LS	p
Age	years	28.0(22-33)	28.5 (25-37)	0.96	0.92-0.99	0.02
Ethnicity	Mixed	49	59	1.51	0.82-2.77	0.15
	Afrocolombian	49	39
Marital status	Partner	46	38	1.39	0.79-2.56	0.24
	No partner	52	60
Socioeconomic status	Class 1	35	22	0.51	0.27-0.96	0.03
	Class 2	62	76
Occupation	Construction	57	66	0.81	0.39-1.64	0.53
	Other occupation	21	30
Level of education	Primary	18	25	1.06	0.50-2.29	0.85
	Secondary	56	73
Type of health insurance	Subsidized	97	97	1.00	0.01-79.29	1.00
	Contibutes	1	1

Regarding the clinical characteristics, the bivariate analysis showed a statistically significant association between TBp, with malnutrition (OR: 17.53 95% CI: 4.06-76.78, p: 0.01), and HIV infection (OR: 8.93; 95% CI: 1.07-74.18 p: 0.04) being statistically significant (Table 2).

Table 2

Characteristics	Description	cases (n=98)	controls (n=98)	OR	IC LI-lS	p
Malnutrition (BMI <18.5)	Yes	24	2	1.75	4.06-76.78	0.01*
	No	65	95
HIV	Yes	7	1	8.93	1.07-74.18	0.04*
	No	76	97
Diabetes	Yes	2	3	0.78	0.12-4.79	0.79
	No	81	95
Pneumonia	Yes	1	2	0.58	0.05-6.57	0.66
	No	82	96
Hypertension	Yes	2	5	0.45	0.08-2.43	0.36
	No	81	93
Asthma	Yes	3	9	0.37	0.09-1.41	0.14
	No	80	89
Scabies	Yes	3	2	1.79	0.29-11.03	0.52
	No	80	96
Syphilis	Yes	1	1	1.18	0.07-19.20	0.9
	No	82	97
Gastritis	Yes	2	7	0.32	0.06-1.58	0.16
	No	81	91
Drug dependent	Yes	61	61	1	0.56-1.78	1.0
	No	37	37

According to the findings of the multivariate logistic regression, and after adjusting for the other demographic and clinical characteristics and habits of consumption of psychoactive substances and alcohol (Drug Dependence), the presence of TBp in this population of PDL in Cali is explained by their state of malnutrition and their HIV status, which reveals that subjects with TBp had 16.7 (95% CI: 3.7-74.1 p: 0.000) and 8.95 (95% CI: 1.02-77.86, p: 0.04) times more chance of acquiring this infectious disease (Table 3).

Table 3

Characteristics	Description	Cases (n=98)	Controls (n=98)	OR Adjusted	IC 95%	p
Malnutrition	Yes	24	2	16.76	3.7-74.5	0.000
	No	65	95
HIV	Yes	7	1	8.95	1.0-77.9	0.040
	No	76	97

This is the first study to evaluate the frequency and determinants associated with the presence of TBp in PDL incarcerated in the Villahermosa prison in the city of Cali, Colombia. Demographic, clinical and alcohol and psychoactive substance use (drug dependence) information was analyzed from 98 incident cases and 98 controls between 2013 and 2014.

During the study period, the prevalence of TBp in PDL in the Villahermosa prison was 1.68%: 0.44% (2013) and 1.23% (2014), while the positivity of TBp in respiratory symptomatic patients was 67.0% and 1.7 and 3.1% respectively. Other studies in PDL in Colombia confirm the high frequency of TBp positivity in this vulnerable population. In 2013, it was reported that 16.2% (1,129/6,961) of the total PDL in 10 prisons in the department of Tolima, were respiratory symptoms, while the prevalence of TBp was 1.5% (17/1129) in this population ⁸.

The prevalence reported in prisons in other countries such as Brazil and Peru, can reach 12.9% (36/279) and 79.5% (245/308) respectively ^21,22. With respect to reports from prisons in Africa, Nigeria reports a prevalence of 54.2% (91/168) ²³ and in Ethiopia the prevalence ranges from 4.9% (765/15,495) and 19.4% (24/124) ²⁴, with incidences of 211 per 100,000 inhabitants, this being more than double that reported in the general population ²⁵. In Zambia, the prevalence is up to 18 times higher (6.4) ²⁶. The above data are within the estimate given by the WHO, of up to 100 times higher prevalence in prisons compared to the general population ²⁷.

The main findings regarding the risk factors for developing TBp in PDL at the Villahermosa prison were malnutrition and HIV infection, as described in the literature. Scientific research shows a greater susceptibility of the host to TB in patients with compromised immune system, including HIV infection and malnutrition states ^28-30. In our study, the state of malnutrition was evaluated through the BMI considering scores equal to or less than 18.5 kg/m² as low nutritional status.

Other studies carried out in prisons in Latin American countries reported BMI lower than 18.5 kg/m² in patients with TBp (OR: 12.7; 95% CI: 9.6-15.7) ³¹ and two cross-sectional studies in prisons, Central de Mbuji-Mayi, Democratic Republic of Congo (BMI <18.5 kg / m2, OR: 2.1; 95% CI: 1.3- 3.0 PAF: 35.6%), and Tajikistan (BMI <18.5 kg / m2, OR: 5.79; 95% CI: 3.07-10.91), indicate that PDLs, being in a state of malnutrition, are more likely to develop TBp ^12,32.

Regarding our finding that HIV is a risk factor for developing TB in the PDL of the Villahermosa Prison, this is in line with reports from prisons in the North of Gondar, northwestern Ethiopia, Southeastern Iran and cities such as Bucaramanga and Medellín in Colombia, where HIV prevalence was significantly associated with TBp among prisoners (AOR: 7.26; 95% CI: 1.10-33.30; p: 0.024), (OR: 2.4; 95% CI. 1.1-5.0, p: 0.25), and 4.2% respectively, confirming that HIV infection presents a great opportunity to pass from infection to TB disease ^11,33,34.

The main weaknesses of this research are that the variables regarding habits and behavior recognized as risk factors were self-reported by the subjects, meaning that there may be underreporting or information bias due to socially accepted responses. Additionally, malnutrition was only measured with the BMI and not with other methods, such as the measurement of the thickness of the skinfolds (with gauges), underwater weighing, bioelectrical impedance, dual X-ray absorptiometry (DXA) and isotope dilution, as outlined by the Center for Disease Control and Prevention (CDC). These methods are not always available, as they are highly expensive and also require highly qualified personnel ³¹. Given that the dynamics and conditions of prisons may vary in each prison institution, these data only represent the Villahermosa prison and penitentiary for the period analyzed.

The dynamics of TBp transmission is determined not only by the health conditions of the individuals, but also by the characteristics of the environment where they interact as social beings. In prisons, the risk factors for developing TBp are magnified by the extreme conditions of overcrowding, high rates of consumption of psychoactive substances, violence, and limitations in access to health services. The control of TBp in Villahermosa must be approached from the perspective of health determinants, improving the environmental and nutritional conditions of the PDL and their access to health services, evaluating the presence of physical, environmental and psychosocial risk factors at the time of admission to the prison. It is also important to ensure timely diagnosis and treatment and comprehensiveness in the provision of health services.

The concentration and perpetuation of TBp in prisons acts as a focus for other geographic areas of the cities. TB control programs must, therefore, carry out indicator analysis in prisons independently of the general population in order to implement prevention and control strategies focused on risk management.