A cross-sectional study was conducted between February 2019 and December 2020 in Addis Ababa City, Ethiopia. Addis Ababa is the capital City of Ethiopia. Presently, the size of the its population is estimated to be 3,384,569, with an annual growth rate of 3.8% (11). The City is inhabited by diversified Ethiopian ethnic groups, and only 1% of the population of the City are foreigners. The City is fastest growing City in Africa (12) and constitutes 30% urban population of Ethiopia (11). It has the highest rural-urban migration that accounts for 40% of its population growth. Subsequently, there is an increase in the number of homeless individuals in the City. In order to support the number of homeless individuals, the City Administration established temporary shelters for homeless individuals while this study was being undertaken. Six temporary shelters were established in six sub cities including in Arada, Yeka, Bole, Akaki-Kality, Chirkos and Addis Ketema. These temporary shelters were used for the recruitment of the study participants.

According to the European Typology of Homelessness and Housing Exclusion (ETHOS) (13), homeless are not a separate species of people, but they are by-products of the society on the margins of which they live. These people have no home or shelter to reside in and instead reside on the corners of streets, in parks, or in public places, if not provided a residence by the governmental or non-governmental organizations (14). Homeless individuals who registered for shelter accommodation in Addis Ababa City during the study period, had a history of having been homeless for at least 1 month prior to the study period (15), age 18 years and older, and gave their written informed consent were included in the study.

These homeless individuals were screened for PTB using the WHO guideline TB symptom screening standard document (16) between February 2019 and December 2020 by trained health professionals. The symptoms include cough ≥ 2 weeks, fever ≥ 2 weeks, night sweats ≥ 2 weeks, appetite loss ≥ 2 weeks, chest pain ≥ 2 weeks and weight loss ≥ 2 weeks. Each participant completed a questionnaire with the help of trained health professionals. The questionnaire included demographic data (age, gender, total duration of homelessness, previous residence, educational background, and marital status), TB risk behaviors (cigarette smoking, alcohol consumption, chewing khat [a plant contain amphetamine-like stimulants that has legally been used for centuries in East Africa and the Southern Arabian Peninsula. Fresh leaves of this plant contain more than 40 types of alkaloid compounds, of which cathinone and cathine are known stimulants. The stimulants cause excitement, loss of appetite and immune modulation on the users (17), drug abuse, HIV status, and malnutrition] and TB specific information (history and symptoms of TB, imprisonment, history of contact with chronically coughing individuals and history of contact with TB patients) (18). All symptoms were recorded as reported by the participants and assessed by another qualified health professional.

Presumptive TB cases: patients with cough ≥2 weeks, fever ≥ 2 weeks, night sweats, hemoptysis or weight loss (19). Pulmonary tuberculosis (PTB): a participant with pulmonary TB confirmed by Xpert, smear microscopy or clinically diagnosed according to the national (19) and WHO (20) TB guidelines. Bacteriologically confirmed TB case: a patient from whom at least one sputum was positive for M. tuberculosis by GeneXpert, smear microscopy or culture (19, 20). Clinically diagnosed TB case: a participant who did not meet the criteria for a bacteriologically confirmed case, but was diagnosed with TB by an experienced clinician and received a full course of TB treatment (19, 20).

A total of 5,600 homeless individuals were screened for PTB symptoms using WHO TB symptoms screening guidelines (21). Of these, 641 were screening positive and provided sputum samples for bacteriological analysis. The participants were properly advised by trained health worker on how to produce a good sputum sample. Two sputum samples were collected from each participant (21). The first sample was collected on the spot and sent to the health facilities for Gene-Xpert MTB/RIF assay [a fully automated molecular diagnostic test for TB that simultaneously detects MTBC and resistance to rifampin (RIF) in < 2 h] (22), while the second sample was collected the next day in the early morning (morning sputum) and transported to the Aklilu Lemma Institute of Pathobiology (ALIPB) TB Laboratory, Addis Ababa University in a cold box and stored at 2–8°C until processed for mycobacteria isolation as previously described (23).

Sputum samples were digested and decontaminated by the modified Petroff method (24). The digested sputum samples were inoculated onto solid Lowenstein Jensen (LJ) medium. Bacterial growth was checked for contamination and fast growers in the first week. Contaminated cultures were recorded as contaminated. The cultures were observed on weekly basis and if there was no growth at the end of 8 weeks, the result was considered negative (25). The sputum samples with growth of M. tuberculosis were confirmed based on microscopic examination of acid-fast bacilli in a culture smear (26).

The weight and height of each study participant were measured by trained health professionals in order to estimate body mass index (BMI) of the study participants. A digital scale was used to measure the weight of each study participant, and weight was measured to the nearest 0.1 kg, while height was measured with the vertical measuring rod to the nearest 0.1 cm (27, 28).

The HIV status of study participants was determined through the provision of pre-test counseling by trained health professionals. Briefly, a whole blood sample was collected by finger prick. The presence of antibodies against HIV-1 and HIV-2 was determined by using HIV antibody colloidal gold (1 + 2) rapid diagnostic kits (KHB, Shanghi Kehua Bio-engineering Co Ltd, China) as a screening test, followed by HIV12 STAT -PAK^® (Chembio Diagnostics, USA), when the KBH result was reactive. When the STAT-PAK^® result was discordant with KBH, a third test, Unigold TM HIV (Trinity Biotech, Ireland), was also used as a tiebreaker to determine the test result following the manufacturer's instructions. Finally, post-test counseling was provided to all participants (29).

The questionnaire was prepared in English and translated into the local language (Amharic) and then back-translated into English by an expert fluent in both languages to maintain consistency. The questionnaire was pretested among 30 (5%) randomly selected homeless individuals before the actual data collection. The project supervisor and principal investigator strictly followed the data collection process day to day. Reagents and culture media were checked for sterility and performance characteristics in each batch of newly prepared reagent lots.

The data captured in the questionnaires were pooled, error-checked, cleaned, and entered into Microsoft Excel version 2013 for storage. Later the data were transferred to SPSS version 26 statistical software and analyzed. Descriptive statistics were used to summarize socio-demographic, behavioral, environmental factors and the morbidity history of the patients. BMI was used to assess nutritional status. BMI was calculated as = weight (in kilograms)/height (in meters). A BMI value of < 18.5 kg/m² was considered underweight (27). Cross-tabulation was performed between the potential risk factors and prevalence of PTB for the determination of chi-square and p-values. Binomial and multinomial logistic regression analyses were performed to identify potential risk factors associated with PTB. In the multivariable logistic regression analysis, adjusted Odds Ratio (AOR) and 95% confidence interval (CI) were determined. P-value < 0.05 was considered statistically significant.

Ethical clearance prior to data collection was obtained from the Addis Ababa University, College of Natural and Computational Sciences Institutional Review Board (IRB) and Addis Ababa City Administration Health Bureau. Then, an official permission letter was obtained from Addis Ababa City Administration, Labor and Social Affairs Bureau. Written informed consent was obtained from all study participants after providing adequate information on the possible benefits and risks of the study in the local language (Amharic). Those participants who tested positive for TB and/or HIV infection were connected to health facilities in temporary shelters for treatment and follow-up. It is noteworthy that the decision to decline screening did not affect shelter access. Patient disease status was kept confidential through the use of anonymous personal identifiers.

The sociodemographic characteristics of the study participants is presented in Table 1. Majority of the participants (80.3%) were male and their mean ± SD age was 27.8 ± 9.5 years. Significant proportion of the participants addicted to smoking (82.1%) and alcohol (78.0%). Addictions to khat and drug were observed only in 1.1% and 1.0% (31/2,980) culture positive PTB cases.

GeneXpert and LJ culture were performed for 641 sputa samples of which 59 sputa were positive for PTB in both tests. The prevalence of bacteriological confirmed PTB in homeless individuals was 1.1% (59/5,600) or 10.54 per 1,000 population. The highest (1.53%) prevalence of PTB was recorded in Yeka subcity, while the lowest (0.39%) was in Bole sub city (Figure 1). Co-infection with HIV was observed in 32.2% (19/59) of bacteriologically confirmed TB cases (Table 1). The 582 homeless individuals with symptoms suggestive of TB who were bacteriologically negative were treated with antibiotics for pneumonia for 2 weeks and all were recovered.

All variables significantly associated with the prevalence of bacteriological confirmed PTB in the binary logistic regression analysis remained significant in the multivariable logistic regression analysis except alcohol consumption and drug abuse. Accordingly, being homeless for more than 5 years [AOR = 3.99, 95% CI: 1.31, 11.59], BMI < 18.5 [AOR = 3.20, 95% CI : 1.68, 6.18], smoking cigarette[AOR = 5.71, 95% CI: 1.29, 25.28], living or sleeping in a restricted area with more than five individuals [AOR = 7.82 , 95% CI: 1.02, 60.16], close contact with chronically coughers [AOR = 3.53, 95% CI: 1.14, 10.91], history of imprisonment (AOR = 2.26, 95% CI: 1.08,5.89) and HIV infection [AOR = 2.34 , 95% CI: 1.17, 4.71] were significantly associated with the prevalence of PTB (P < 0.05) (Table 2).

A chest X-ray was not performed for screening participants with suspected TB; this may have underestimated the true prevalence of PTB. Extrapulomnary tuberculosis was not included in the study due to time and logistic limitations.