Smear positive pulmonary tuberculosis and its risk factors among tuberculosis suspect in South East Ethiopia; a hospital based cross-sectional study

Tuberculosis (TB) is still one of the infectious diseases known by its significant cause of morbidity and mortality affecting millions of people worldwide. Although it is a global epidemic, TB predominantly affects developing countries, where 98% of worldwide TB death occurs [1, 2]. Resource poor countries share the global burden with highest rates, with an estimated 55% of global case in Asia and 31% in Africa [2–5]. According to the WHO Global TB Report, Ethiopia ranks seventh among the world’s 22 high-burden TB countries. The estimated incidence rate was 261 cases per 100,000 population and 29 thousand deaths in 2010, with an estimated prevalence rate of 394 cases per 100,000 populations [2].

Studies have shown that human immunodeficiency virus (HIV)/AIDS, diabetes, cancer, malnutrition, alcoholism, smoking cigarette, active TB contact, extreme poverty, homelessness, and being in prison were among the commonly identified risk factors associated with tuberculosis in most developing countries including Ethiopia [6–9].

In Ethiopia, a study conducted in Metehara sugar factory hospital showed 14.2% prevalence of smear positive pulmonary tuberculosis [10]. Another study on smear positive TB conducted in Agaro health centre showed a prevalence of 10.9% [11]. However, the rate of pulmonary TB (PTB) and its associated risk factors in the study area were not known. Therefore, the purpose of this study was to determine the prevalence of smear positive PTB and its associated risk factors among PTB suspected patients attending Bale Goba and Robe Hospitals.

A cross-sectional study was conducted in Bale Goba and Robe Hospitals of Bale zone, which are 444 km and 432 km away from the capital city, Addis Ababa, respectively towards the South East part of Ethiopia. The study was conducted from February 01 to May 25, 2012. Sample size was calculated using single population proportion formula [n = (Z α/₂) ² P (1-P) /d²], where, n = sample size, Zα/₂ = statistic for the level of confidence at 95%, which is 1.96, P = expected prevalence which was set 50% to yield maximum sample size, and d = precision which is 5%. Including 10% non response rate the sample size became 420. However, 391 of them participated with none response rate of 93.1.”

Pretested questionnaire was used to collect information on socio-demographic characteristics and other associated risk factors. Data collectors were also trained for one day on the instrument of data collection and how to collect the sputum specimen and also supervised by the investigators during the entire data collection.

Three consecutive sputum samples, i.e. spot-morning-spot were collected from each of the PTB suspected cases. Experienced laboratory technologists performed the laboratory test following the standard procedure of Ziehl-Neelsen staining technique recommended by WHO [12, 13]. The completeness of the questionnaire was checked and the examination sputum samples were performed both in the hospital's laboratory and Madawalabu University Biomedical Laboratory for quality control. Provider initiative counseling and testing (PIHCT) for HIV is being practiced for all TB suspects hence, HIV results were collected from hospital records with patient card numbers.

The data from questionnaires and laboratory results were analyzed using statistical software (SPSS package version 16). The results were summarized using descriptive statistics including frequencies and mean. Difference of proportion was evaluated using Chi-square test and p < 0.05 was considered as significant. A binary and multiple logistic regression analysis were used and odds ratio was calculated to determine the strength of association between variables and lifetime exposure to TB infection.

The study was approved by Research Ethics and Review Committee of Madawalabu University. In addition, official permission was obtained from the administration offices of Goba and Robe Hospitals. Furthermore, the objective of the study was explained to the participants and written consent was obtained before specimen collection. All participants who were affected by the disease were treated in the hospital accordingly.

This study tries to provide insights into the prevalence of smear positive PTB among tuberculosis suspected patients attending Bale Robe and Goba hospitals, as well as outline some possible risk factors. The results showed 9.2% prevalence of smear positive PTB. This shows that TB is still one of the major public health concerns in the study area and in Ethiopia as well. Similar studies conducted in Rwanda reported (17.3%) [5], and in Nigeria (14.7%) [14] which was significantly higher compared to the findings in this study. This may be due to the community based program launched several years ago using home to home community health workers, who are capable of creating awareness better than the previous strategies in Ethiopia. The result in this study was in line with similar study conducted in hospitals and health centers of Ethiopia; Agaro Teaching Health Center, (10.9%) [11], Jimma University Specialized Hospital, (8.5%) [15], and in Jimma Seka (10.6%) [16]. However, the finding of the present study showed lower prevalence than similar study conducted in Tigray (17.7%) [17], in Addis Ababa (21.3%) [18], and in Eastern Ethiopia 14.2% [10]. This could be associated to differences in awareness level of the patients leading to passive detection in those who had sign and symptoms of the disease.

This study also indicated that the prevalence of smear positive PTB was significantly higher in HIV positive patients than HIV-negative. Out of the total 36 smear positive pulmonary tuberculosis 44.4% were HIV positive. Similarly, a number of studies conducted in different parts of the world and some other African countries showed the prevalence rate of co-infection ranges from 8% in Congo to 82% in Swaziland [3, 5, 19]. In Ethiopia, based on the WHO report in 2012 the rate of co-infection was (41%) [2]. As it is well established the strong association between HIV and TB is attributed to the overlapping of the age group that both infections are affecting and the immunological deprivation that HIV results in.

As far as sex is concerned, similar studies conducted in Ethiopia and other countries like Rwanda, and Myanmar, reported that smear positive PTB is more common among men than women [2, 5, 15, 20–22]. In the present study, the prevalence of smear positive tuberculosis was not statistically significant between sexes, though a relatively higher prevalence was reported among men 55.6%, and women 44.4%. Similar to previous studies conducted in Ethiopia and other countries [5, 15, 20, 21], smear positive PTB affects mostly adults in the economically productive age groups; around two-thirds of cases were estimated to occur among people aged 15–59 years.

Urban dwellers were found to be more associated with smear positive TB in this study. The prevalence of smear positive PTB was 72.2% among urban dwellers compared to 27.8% among the rural dwellers. This finding is consistent with similar studies conducted in India (69.2%) and Ethiopia (52.7%) [9, 23]. This might be due to the fact that urban set up is characterized by overcrowding and suffocation which is an important risk for respiratory disease including tuberculosis.

The role of active smoking in the development of TB is well known [2, 6], the same is true in this study in which active smoking was significantly associated with smear positive TB with (p = 0. 021). A history of active TB patient contact and HIV- sero status was also among the risk factors that showed significant association with smear positive TB (P < 0.005). This is consistent with WHO report and studies conducted in different parts of the world [2, 6, 24].

Some of the limitations of this study include direct smear microscope alone may underestimate the prevalence of PTB in the study population. Other techniques like culture and molecular assays could best estimate the prevalence of PTB among the study subjects. However, due to financial constraints, we were unable to perform these advanced tests. Selection bias may also arise from convenience sampling.

In conclusion, the prevalence of smear positive PTB among tuberculosis suspect was high (9.2%) in Bale Goba and Robe hospitals. Smear positive PTB was more frequently reported among urban residence, age > 36 years, male sex, and unemployed individuals. Risk factors like HIV sero-status, active TB patient contact, and cigarette smoking were significant to acquire smear positive TB. Hence, we recommend strict PTB screening of HIV patients, and health education to avoid smoking. It would be better to expand health education to household contacts of smear positive PTB patients on how to protect them from TB infection. Finally, we would also like to recommend longitudinal studies with more advanced laboratory techniques.

BT* and ND conceptualized and designed the study. BT and YK assisted in designing the study design. BT*, ND and YK analyzed and interpreted the data, drafted the manuscript and critically reviewed the manuscript. BT assisted in drafting and critically reviewing the manuscript. All the authors’ read and approved the manuscript.