Tuberculosis (TB) remains one of the world’s deadliest communicable diseases. In 2013, an estimated 9.0 million people developed TB and 1.5 million died from the disease [1] . An estimated 1.1 million (13%) of the 9 million people who developed TB in 2013 were HIV-positive. The African Region accounts for about four out of every five HIV-positive TB cases and TB deaths among people who are HIV positive and the majority of victim live in sub Saharan Africa, which accounts seventy percent (70%) [1] [2] . Some Africa countries have reported continuing rises in tuberculosis case rates despite declining HIV prevalence, while others show stable or declining tuberculosis incidence among HIV-negative individuals [3] .

Tuberculosis has been recognized as a major public health problem for more than five decades in Ethiopia. Ethiopia is one of the 22 high burden countries (HBCs) and TB remains one of the leading causes of mortality. According to the 2014 WHO report, the prevalence and incidence of all forms of TB are 211 and 224 per 100,000 of the population, respectively. About 13% of all new TB cases are also HIV co-infected. Moreover, Ethiopia is one of the high TB/HIV and multidrug resistant TB (MDR TB) burden countries. Among TB patients with known HIV status, about 11% were HIV co-infected. [1] [4]

Despite increased deliverance of antiretroviral therapy (ART), morbidity and mortality from TB are still predominant among PLHIV. Among 33.2 million individuals acquiring human immune deficiency virus (HIV), one-third of them are concomitantly infected with Mycobacterium tuberculosis [5] .

The TB/HIV co-infection results derangement of quality of life, poor physical health than HIV infected individuals and has a greater risk of common mental disorders [6] [7] .

Moreover, the management of a TB and HIV co-infected individual is challenging because of frequent oral drug intake which can cause different problem [8] , increased drug adverse effects [9] , drug and drug interaction [10] and the immune reconstitution inflammatory syndrome (IRIS) [11] .

The risk of tuberculosis among PLHIV is 20 times higher than HIV negative people [2] [12] [13] , and baseline CD4+ lymphocyte count, history of injectable drug use, antiretroviral therapy, body mass index, anemia, and educational status were some of the contributing factors for TB in HIV patients [14] [15] .

Many efforts have been made to integrate TB diagnosis and treatment with HIV care in order to prevent, diagnose and manage TB among HIV infected individuals, though TB still occur in HIV patients who are on HAART receiving individuals [1] [16] . Therefore; there should be early screening and detection of TB in PLHIV as TB can occur in any course of HIV treatment [17] [18] .

Furthermore, adequate understanding of the specific situation through follow-up research should be done to provide baseline finding to program designing for respective organization. Therefore, this study aimed to determine the incidence and predictors of TB among PLHIV registered at Arba Minch General Hospital.

Since the introduction of HIV infection in the world, TB is one of common opportunistic infection and Persons co-infected with TB and HIV were 21 - 34 times more likely to develop active TB disease than persons without HIV [20] .

In this study, cumulative incidence and overall incidence rate of TB were 21.4% and 5.36 per 100 PY respectively.

This study used cumulative incidence of TB as outcome variable. Thus, cumulative incidence of Tuberculosis (21.4%) reported in this study was lower than study done in former capital of Tanzania, Dares Salaam (27.1%) and study done in North west Ethiopia (Debre Markos hospital) (44%) [21] . But, the finding was higher than studies done in Spain and Brazil which were 7.7% [22] , and 4.62% [23] respectively. Higher incidence rate could be explained by the fact that unlike these two countries, Ethiopia is one of the high TB burden countries in the world [24] besides advanced economic development compared to Ethiopia might improve HIV chronic care and reduce occurrence of TB. Lower cumulative incidence might due to improved TB/HIV chronic care and introduction of new regimen which effectively prevent occurrence of TB among HIV. Overall cumulative density reported in this study was lower than studies done in many other Sub Sahara African countries including, Ethiopia with reported incidence rate ranging from 5.4 to 11 per 100 PY [25] - [28] . Lower incidence rate could be explained by improved TB/HIV Care and new introduction of regimen which effectively prevent occurrence of TB among HIV.

In multivariable analysis; Family size, History of Cigarettes smoking, WHO Baseline clinical stage and hemoglobin level were important predictors of incidence of Tuberculosis among HIV infected patients.

This study could establish association between TB and number of people in the household. Thus, an individual who live in the family size of 3 - 4 was two times at risk of developing Tuberculosis than an individual who live in family with <2 children. It is consistent with Studies, which have shown that risk of TB was associated with the number of people living together in the household (overcrowding) [29] - [31] , but inconsistent with study done in Addis Ababa [32] . This might be related to high proportions of married persons in the study population resulted in high number of family size in the house hold which might resulted overcrowding which exposed HIV infected patients to Tuberculosis.

Others predictors associated with incidence of tuberculosis was history of cigarette smoking, thus cigarette smoker were 3 times at higher risk of developing TB than non-smokers. The finding was consistent with study done in Taiwan [33] and not consistent with study done in northwest Ethiopia and Burkina that cigarette smoking had no effect on occurrence of TB among HIV infected patients [13] [31] . This might due to person who smoke cigarette was exposed for low immunity and this would increase the risk of developing Tuberculosis among HIV infected patients. Furthermore cigarette smoking was associated with other substance abuse which can increase the risk of unprotected sexual intercourse and compromisation of immunity, resulting in occurrence of TB.

Baseline WHO clinical staging was strong predictor for Incidence of Tuberculosis; accordingly HIV patients with clinical stage III and IV were 20 and 22 times more likely develop tuberculosis than an individual who was started follow up on the first WHO clinical stage. The finding was supported by different study done in Ethiopia [12] [13] [32] [34] , the similarity might be due to starting ART in advanced stage will reduce immunity and expose an individual for TB. It also suggests that HIV patients who had WHO stage III or IV might be immune- compromised and predisposed to TB.

In addition, patients having a hemoglobin level of <10 mg/dl have 2.5 times higher risk of developing TB than those patients having hemoglobin level 10.0 mg/dl, the finding was similar to other study findings in south west Ethiopia [34] and case control study done in Addis Ababa [32] . This shows that patients having higher hemoglobin level were less likely to develop TB than those with low level of hemoglobin. TB and hemoglobin level might be indirectly associated with advanced stage of HIV disease. When HIV positive patients have chronic disease and high viral load, it resulted in immune-suppression and suppression of red blood production in bone marrow. This is also consistent with the previous findings that predict the occurrence of TB which implied that advance disease condition in HIV patients may predict occurrence of Tuberculosis after ART initiation.

Other factors like; Age in group, addiction, sex of respondent, CD4 count, ART intervention, type of initial regimen and past history of TB treatment were significant predictors of incidence of tuberculosis among HIV infected patients in bivariable analysis, but the effect of this socio demographic and clinical characteristics were diluted in multivariable analysis.

Analysis of the past history of TB after adjustment, that it was a TB risk factor among PLWHAs, which is in agreement with a number of previous studies [15] [29] [34] , But this was not the case in the study done in Arba Minch Hospital (our study), which reported that the past history of TB was not independent predictor of incidence of TB.

Many studies have used the patients’ CD4 cell counts to assess association between CD4 Count and TB incidence and found that a lower CD4 cell count was associated with a higher risk of TB infection [13] [31] [35] . These studies are not consistent with our findings where the median CD4 cell count was not significant predictors of TB among HIV infected patients, though it had significant effect on occurrence of Tuberculosis in bivariable analysis.

The main limitation of our study was the retrospective nature of the cohort. The study individuals whose charts were lost not included in the study, which could undermine the result if the charts excluded were related to incidence of TB.

Cumulative and overall incidence rate of tuberculosis were found to be 21.4% and 5.36 per 100 PY respectively, which one was the highest. Family size, history of cigarettes smoking, heamoglobin level and WHO baseline clinical stage were important predictors of incidence of tuberculosis among HIV infected patients.

Finding that smoking is important predictors for TB in Ethiopia has obvious TB control implication which requires high attention focused on fighting against cigarette smoking in HIV infected populations.

The health institutions particularly work on lifestyle modification specifically on halting cigarette smoking habit through counseling. Early initiation of HAART as current guideline should get emphasis and behavioral education that discourages addiction is important to reduce the risk of TB infection. Furthermore, concomitant infections and risk factors for anemia among HIV patients should get managed and prevented.

The authors are very grateful to Arba Minch General Hospital, for its administrative and technical assistance. Data collectors, supervisors and Arba Minch University deserves especial acknowledgement for data abstraction, care full supervision and provide ethical clearance to conduct this research work respectively.

The authors declare that there is no competing interest

¹MD was the primary researcher, conceived the study, designed, participated in data collection and quality assurances, conducted data analysis, drafted and finalized the manuscript for publication. ²AT was assisted in data collection and analysis and reviewed the initial and final drafts of the manuscript

Mulugeta Dalbo,Alemu Tamiso, (2016) Incidence and Predictors of Tuberculosis among HIV/AIDS Infected Patients: A Five-Year Retrospective Follow-Up Study. Advances in Infectious Diseases,06,70-81. doi: 10.4236/aid.2016.62010

AGH: Arba Minch General Hospital; AIDS: Acquired Immuno Deficiency Syndrome; ART: Active Antiretroviral Therapy; AZT: Zidovudine; EFV: Efavirenz; HAART: Highly Active Antiretroviral Therapy; IRIS: Immune Reconstitution Inflammatory Syndrome; NVP: Nevirapine; OIs: Opportunistic Infections; PY: Person Years; SPSS: Statistical Package for Social Science; TB: Tuberculosis; 3TC: Lamuvudine; WHO: World Health Organization.