Prevalence rates of TB in prisons usually exceed the rates in the general population substantially and in average it can reach up to 55 times higher than national prevalence [5]. In agreement to this, in the current study, the point prevalence of smear positive TB in Hadiya Zone Prison was 349.2 per 100,000 populations which was 3.3 times higher than the TB in the general population [3]. However, the prevalence in Hossana was lower than the report from Eastern Ethiopian prisons and North Gondar Zone Prison which was 1913/100,000 and 1482.3/100,000 respectively [8, 9]. The difference could be attributed to the difference in sample size and/or population size and study design as the Eastern Ethiopian study conducted in three prisons which contain 2300 including those TB patients who are on TB treatment already and culture was employed to detect M. tuberculosis apart from microscopy. On the other hand, study in Gondar was conducted in a prison containing 1754 prisoners using a light emitting diode (LED) fluorescence microscopy while the present study was conducted in a prison comprising only 859 inmates using compound light microscopy.
Studies from Zambia, Botswana, Russia, Georgia and Thailand showed much higher prevalences [6, 11, 16, 17] On the other hand, lower prevalences were reported from prisons of some Asian and European countries, 259/100,000 in Taiwan, 341/100,000 in Turkey and 215/100,000 in France [18–20]. The relatively lower prevalence in these countries could be due to a good TB control strategy and low TB incidence in the general population as well as in the prisons.
An interesting finding of this study is that smear positive PTB in prisoners from rural areas particularly in farmers was higher than those from urban areas. One possible explanation could be their frequent contact with cattle and more consumption of unpasteurized milk [21]. This is in contrast to the finding of the study in Eastern Ethiopia which showed prisoners from urban areas have higher risk of acquiring PTB than those from rural areas [8]. The study linked the higher risk with relatively high rate of associated HIV infection in urban areas as HIV is the leading modulator of TB infection [22]. Nevertheless, other studies in Tajikistan and different parts of Ethiopia indicated the higher proportion of pulmonary tuberculosis cases in rural prisoners without statistically significant association [23–25].
The current study also identified that all the PTB cases were males. This might be due to small sample size of the female prisoners which may preclude the actual effect of sex, thus making risk comparison inaccurate. However, the male prisoners may be at greater risk of acquiring the infection and become source of transmission, as there is a high overcrowding and poor housing condition compared to their female counterparts. This argument is corroborated by studies carried out among Zambian [6], Malawian [26] and US [27] prisons that documented higher TB prevalence among males than females. Congruent to this observation there were also studies that report male as being a risk factor for TB among Thai [28] and Spanish [29] prisons.
Young adults, who were in the age range between 15–35 years, were found to have higher PTB cases. Although it did not show any level of significant association, a high rate of HIV infection could be one of the possible explanations to the high TB prevalence in this age group. This association was consistently reported among the prison and general population in Africa [30–32]. Likewise, prison studies from high and low TB burden countries documented a high TB prevalence among young adults [6, 26–28].
Prisoners who had no visit from family are significantly at higher risk of acquiring PTB. This could be related to psychosocial support they lack as during stress the adaptive immune system is suppressed due to continually high levels of stress hormones. As a result, the body is less able to produce antibodies and more susceptible to infections [33].
In this study, the length of stay in the prison was not significantly associated with PTB, despite the majority of study participants stayed for the short duration. It was similar to that of Eastern Ethiopian prison and Zambian prison study [6, 8], whereas, Ivory Coast [12] and Cameroon [2] studies indicated a short staying as the risk factor for TB. On the contrary, Spain [29] and Georgian [11] studies reported a longer staying as the risk factor. Although it did not show any level of association in current study, frequent imprisonment could put an individual to repeated exposure of TB infection. This has also been documented usually among individuals who commit crime repeatedly, such as homeless and street gangs that are likely to be deprived of living conditions and health care, thus have greater risk of acquiring TB [27]. Similarly, studies carried out in Spain [29] and Cameroon [7] identified re-imprisonment as the risk factor for TB.
Factors relating to living and crowding conditions did not show any level of significance and hence were not considered as explanatory variables for PTB prevalence in this study, though they are known to favour dissemination of TB. This finding was similar with that of a Zambian study [6]; where there is no differences related to living conditions such as overcrowding, poor dietary conditions and large number of prisoners per cell. In contrary, a case-control study in Russia [10] mentioned prison factors like high ratio of prisoners per available bed, not having own bed clothes, and little time out-doors as independent risk factors. Cross-sectional nature of the study could be one of the possible reasons for not observing the significance level of these factors.
The current study showed that all of the TB positive inmates developed TB symptoms after they joined the prison. Even though there wasn’t any significant association between the symptoms and TB positivity in this study, there are a number of studies that showed significant associations. A Brazilian prison study reported a range of symptoms that had significant association with TB [34]. Similarly, a Georgian study mentioned loss of appetite as an independent risk factor [11]. In Thailand prisons study, weight loss made significant independent contribution to a diagnosis of smear-positive TB [28]. This in conjunction with long cough duration shows an extended lag time before patients get diagnosed and treated rendering the smear positive prisoners to transmit the infection to many others. This could be intensified by the nature of the cells shared by the inmates.
The cells in the study area were poorly ventilated having a single window some of them even not opened throughout the day and accommodate more than one hundred prisoners (the mean number of inmates per cell was 160) who mix all day long with detainees from other cells in enclosed spaces. The lengthy stay of the inmates in the prison could have been rendering the prison to serve as a reservoir of TB transmission. The time left to stay in the prison for most of the TB positive inmates was more than a year which could further enhance transmission of TB.).
The limitations of the study are that it didn’t include prisoners who had a difficulty of getting productive sputum and adequate amount. Similarly, over and under reporting about the risks of PTB by the study participants is highly anticipated in this study. This may have influenced on the value of parameter estimators, such as odds ratio, P value and confidence interval; it may have also underestimated or overestimated the prediction of risk factors for PTB. Furthermore, the small sample size of PTB patients could have similar influence on the analysis.